/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements. See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You under the Apache license, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License. You may obtain a copy of the License at
    *
    *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the license for the specific language governing permissions and
   * limitations under the license.
   */
  package org.apache.logging.log4j.core.lookup;
  
  import java.util.ArrayList;
  import java.util.Enumeration;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  import java.util.Objects;
  import java.util.Properties;
  
  import org.apache.logging.log4j.core.LogEvent;
  import org.apache.logging.log4j.core.config.Configuration;
  import org.apache.logging.log4j.core.config.ConfigurationAware;
  import org.apache.logging.log4j.status.StatusLogger;
  import org.apache.logging.log4j.util.Strings;
  
  /**
   * Substitutes variables within a string by values.
   * <p>
   * This class takes a piece of text and substitutes all the variables within it.
   * The default definition of a variable is <code>${variableName}</code>.
   * The prefix and suffix can be changed via constructors and set methods.
   * </p>
   * <p>
   * Variable values are typically resolved from a map, but could also be resolved
   * from system properties, or by supplying a custom variable resolver.
   * </p>
   * <p>
   * The simplest example is to use this class to replace Java System properties. For example:
   * </p>
   * <pre>
   * StrSubstitutor.replaceSystemProperties(
   *      "You are running with java.version = ${java.version} and os.name = ${os.name}.");
   * </pre>
   * <p>
   * Typical usage of this class follows the following pattern: First an instance is created
   * and initialized with the map that contains the values for the available variables.
   * If a prefix and/or suffix for variables should be used other than the default ones,
   * the appropriate settings can be performed. After that the <code>replace()</code>
   * method can be called passing in the source text for interpolation. In the returned
   * text all variable references (as long as their values are known) will be resolved.
   * The following example demonstrates this:
   * </p>
   * <pre>
   * Map valuesMap = HashMap();
   * valuesMap.put(&quot;animal&quot;, &quot;quick brown fox&quot;);
   * valuesMap.put(&quot;target&quot;, &quot;lazy dog&quot;);
   * String templateString = &quot;The ${animal} jumped over the ${target}.&quot;;
   * StrSubstitutor sub = new StrSubstitutor(valuesMap);
   * String resolvedString = sub.replace(templateString);
   * </pre>
   * <p>yielding:</p>
   * <pre>
   *      The quick brown fox jumped over the lazy dog.
   * </pre>
   * <p>
   * Also, this class allows to set a default value for unresolved variables.
   * The default value for a variable can be appended to the variable name after the variable
   * default value delimiter. The default value of the variable default value delimiter is ':-',
   * as in bash and other *nix shells, as those are arguably where the default ${} delimiter set originated.
   * The variable default value delimiter can be manually set by calling {@link #setValueDelimiterMatcher(StrMatcher)},
   * {@link #setValueDelimiter(char)} or {@link #setValueDelimiter(String)}.
   * The following shows an example with variable default value settings:
   * </p>
   * <pre>
   * Map valuesMap = HashMap();
   * valuesMap.put(&quot;animal&quot;, &quot;quick brown fox&quot;);
   * valuesMap.put(&quot;target&quot;, &quot;lazy dog&quot;);
   * String templateString = &quot;The ${animal} jumped over the ${target}. ${undefined.number:-1234567890}.&quot;;
   * StrSubstitutor sub = new StrSubstitutor(valuesMap);
   * String resolvedString = sub.replace(templateString);
   * </pre>
   * <p>yielding:</p>
   * <pre>
   *      The quick brown fox jumped over the lazy dog. 1234567890.
   * </pre>
   * <p>
   * In addition to this usage pattern there are some static convenience methods that
   * cover the most common use cases. These methods can be used without the need of
   * manually creating an instance. However if multiple replace operations are to be
   * performed, creating and reusing an instance of this class will be more efficient.
   * </p>
  * <p>
  * Variable replacement works in a recursive way. Thus, if a variable value contains
  * a variable then that variable will also be replaced. Cyclic replacements are
  * detected and will cause an exception to be thrown.
  * </p>
  * <p>
  * Sometimes the interpolation's result must contain a variable prefix. As an example
  * take the following source text:
  * </p>
  * <pre>
  *   The variable ${${name}} must be used.
  * </pre>
  * <p>
  * Here only the variable's name referred to in the text should be replaced resulting
  * in the text (assuming that the value of the <code>name</code> variable is <code>x</code>):
  * </p>
  * <pre>
  *   The variable ${x} must be used.
  * </pre>
  * <p>
  * To achieve this effect there are two possibilities: Either set a different prefix
  * and suffix for variables which do not conflict with the result text you want to
  * produce. The other possibility is to use the escape character, by default '$'.
  * If this character is placed before a variable reference, this reference is ignored
  * and won't be replaced. For example:
  * </p>
  * <pre>
  *   The variable $${${name}} must be used.
  * </pre>
  * <p>
  * In some complex scenarios you might even want to perform substitution in the
  * names of variables, for instance
  * </p>
  * <pre>
  * ${jre-${java.specification.version}}
  * </pre>
  * <p>
  * <code>StrSubstitutor</code> supports this recursive substitution in variable
  * names, but it has to be enabled explicitly by setting the
  * {@link #setEnableSubstitutionInVariables(boolean) enableSubstitutionInVariables}
  * property to <b>true</b>.
  * </p>
  */
 public class StrSubstitutor implements ConfigurationAware {
 
     /**
      * Constant for the default escape character.
      */
     public static final char DEFAULT_ESCAPE = '$';
 
     /**
      * Constant for the default variable prefix.
      */
     public static final StrMatcher DEFAULT_PREFIX = StrMatcher.stringMatcher(DEFAULT_ESCAPE + "{");
 
     /**
      * Constant for the default variable suffix.
      */
     public static final StrMatcher DEFAULT_SUFFIX = StrMatcher.stringMatcher("}");
 
     /**
      * Constant for the default value delimiter of a variable.
      */
     public static final String DEFAULT_VALUE_DELIMITER_STRING = ":-";
     public static final StrMatcher DEFAULT_VALUE_DELIMITER = StrMatcher.stringMatcher(DEFAULT_VALUE_DELIMITER_STRING);
 
     public static final String ESCAPE_DELIMITER_STRING = ":\\-";
     public static final StrMatcher DEFAULT_VALUE_ESCAPE_DELIMITER = StrMatcher.stringMatcher(ESCAPE_DELIMITER_STRING);
 
     private static final int BUF_SIZE = 256;
 
     /**
      * Stores the escape character.
      */
     private char escapeChar;
 
     /**
      * Stores the variable prefix.
      */
     private StrMatcher prefixMatcher;
 
     /**
      * Stores the variable suffix.
      */
     private StrMatcher suffixMatcher;
 
     /**
      * Stores the default variable value delimiter
      */
     private String valueDelimiterString;
     private StrMatcher valueDelimiterMatcher;
 
     /**
      * Escape string to avoid matching the value delimiter matcher;
      */
     private StrMatcher valueEscapeDelimiterMatcher;
 
     /**
      * Variable resolution is delegated to an implementer of VariableResolver.
      */
     private StrLookup variableResolver;
 
     /**
      * The flag whether substitution in variable names is enabled.
      */
     private boolean enableSubstitutionInVariables = true;
 
     /**
      * The currently active Configuration for use by ConfigurationAware StrLookup implementations.
      */
     private Configuration configuration;
 
     private boolean recursiveEvaluationAllowed;
 
     //-----------------------------------------------------------------------
     /**
      * Creates a new instance with defaults for variable prefix and suffix
      * and the escaping character.
      */
     public StrSubstitutor() {
         this(null, DEFAULT_PREFIX, DEFAULT_SUFFIX, DEFAULT_ESCAPE);
     }
 
     /**
      * Creates a new instance and initializes it. Uses defaults for variable
      * prefix and suffix and the escaping character.
      *
      * @param valueMap  the map with the variables' values, may be null
      */
     public StrSubstitutor(final Map<String, String> valueMap) {
         this(new MapLookup(valueMap), DEFAULT_PREFIX, DEFAULT_SUFFIX, DEFAULT_ESCAPE);
     }
 
     /**
      * Creates a new instance and initializes it. Uses a default escaping character.
      *
      * @param valueMap  the map with the variables' values, may be null
      * @param prefix  the prefix for variables, not null
      * @param suffix  the suffix for variables, not null
      * @throws IllegalArgumentException if the prefix or suffix is null
      */
     public StrSubstitutor(final Map<String, String> valueMap, final String prefix, final String suffix) {
         this(new MapLookup(valueMap), prefix, suffix, DEFAULT_ESCAPE);
     }
 
     /**
      * Creates a new instance and initializes it.
      *
      * @param valueMap  the map with the variables' values, may be null
      * @param prefix  the prefix for variables, not null
      * @param suffix  the suffix for variables, not null
      * @param escape  the escape character
      * @throws IllegalArgumentException if the prefix or suffix is null
      */
     public StrSubstitutor(final Map<String, String> valueMap, final String prefix, final String suffix,
                           final char escape) {
         this(new MapLookup(valueMap), prefix, suffix, escape);
     }
 
     /**
      * Creates a new instance and initializes it.
      *
      * @param valueMap  the map with the variables' values, may be null
      * @param prefix  the prefix for variables, not null
      * @param suffix  the suffix for variables, not null
      * @param escape  the escape character
      * @param valueDelimiter  the variable default value delimiter, may be null
      * @throws IllegalArgumentException if the prefix or suffix is null
      */
     public StrSubstitutor(final Map<String, String> valueMap, final String prefix, final String suffix,
                               final char escape, final String valueDelimiter) {
         this(new MapLookup(valueMap), prefix, suffix, escape, valueDelimiter);
     }
 
     /**
      * Creates a new instance and initializes it. Uses defaults for variable
      * prefix and suffix and the escaping character.
      *
      * @param properties  the map with the variables' values, may be null
      */
     public StrSubstitutor(final Properties properties) {
         this(toTypeSafeMap(properties));
     }
 
     /**
      * Creates a new instance and initializes it.
      *
      * @param variableResolver  the variable resolver, may be null
      */
     public StrSubstitutor(final StrLookup variableResolver) {
         this(variableResolver, DEFAULT_PREFIX, DEFAULT_SUFFIX, DEFAULT_ESCAPE);
     }
 
     /**
      * Creates a new instance and initializes it.
      *
      * @param variableResolver  the variable resolver, may be null
      * @param prefix  the prefix for variables, not null
      * @param suffix  the suffix for variables, not null
      * @param escape  the escape character
      * @throws IllegalArgumentException if the prefix or suffix is null
      */
     public StrSubstitutor(final StrLookup variableResolver, final String prefix, final String suffix,
                           final char escape) {
         this.setVariableResolver(variableResolver);
         this.setVariablePrefix(prefix);
         this.setVariableSuffix(suffix);
         this.setEscapeChar(escape);
     }
 
     /**
      * Creates a new instance and initializes it.
      *
      * @param variableResolver  the variable resolver, may be null
      * @param prefix  the prefix for variables, not null
      * @param suffix  the suffix for variables, not null
      * @param escape  the escape character
      * @param valueDelimiter  the variable default value delimiter string, may be null
      * @throws IllegalArgumentException if the prefix or suffix is null
      */
     public StrSubstitutor(final StrLookup variableResolver, final String prefix, final String suffix, final char escape, final String valueDelimiter) {
         this.setVariableResolver(variableResolver);
         this.setVariablePrefix(prefix);
         this.setVariableSuffix(suffix);
         this.setEscapeChar(escape);
         this.setValueDelimiter(valueDelimiter);
     }
 
     /**
      * Creates a new instance and initializes it.
      *
      * @param variableResolver  the variable resolver, may be null
      * @param prefixMatcher  the prefix for variables, not null
      * @param suffixMatcher  the suffix for variables, not null
      * @param escape  the escape character
      * @throws IllegalArgumentException if the prefix or suffix is null
      */
     public StrSubstitutor(final StrLookup variableResolver, final StrMatcher prefixMatcher,
                           final StrMatcher suffixMatcher,
                           final char escape) {
         this(variableResolver, prefixMatcher, suffixMatcher, escape, DEFAULT_VALUE_DELIMITER,
                 DEFAULT_VALUE_ESCAPE_DELIMITER);
         this.valueDelimiterString = DEFAULT_VALUE_DELIMITER_STRING;
     }
 
     /**
      * Creates a new instance and initializes it.
      *
      * @param variableResolver  the variable resolver, may be null
      * @param prefixMatcher  the prefix for variables, not null
      * @param suffixMatcher  the suffix for variables, not null
      * @param escape  the escape character
      * @param valueDelimiterMatcher  the variable default value delimiter matcher, may be null
      * @throws IllegalArgumentException if the prefix or suffix is null
      */
     public StrSubstitutor(final StrLookup variableResolver, final StrMatcher prefixMatcher,
             final StrMatcher suffixMatcher, final char escape, final StrMatcher valueDelimiterMatcher) {
         this.setVariableResolver(variableResolver);
         this.setVariablePrefixMatcher(prefixMatcher);
         this.setVariableSuffixMatcher(suffixMatcher);
         this.setEscapeChar(escape);
         this.setValueDelimiterMatcher(valueDelimiterMatcher);
     }
 
     /**
      * Creates a new instance and initializes it.
      *
      * @param variableResolver  the variable resolver, may be null
      * @param prefixMatcher  the prefix for variables, not null
      * @param suffixMatcher  the suffix for variables, not null
      * @param escape  the escape character
      * @param valueDelimiterMatcher  the variable default value delimiter matcher, may be null
      * @param valueEscapeMatcher the matcher to escape defaulting, may be null.
      * @throws IllegalArgumentException if the prefix or suffix is null
      */
     public StrSubstitutor(final StrLookup variableResolver, final StrMatcher prefixMatcher,
                           final StrMatcher suffixMatcher, final char escape, final StrMatcher valueDelimiterMatcher,
                           final StrMatcher valueEscapeMatcher) {
         this.setVariableResolver(variableResolver);
         this.setVariablePrefixMatcher(prefixMatcher);
         this.setVariableSuffixMatcher(suffixMatcher);
         this.setEscapeChar(escape);
         this.setValueDelimiterMatcher(valueDelimiterMatcher);
         valueEscapeDelimiterMatcher = valueEscapeMatcher;
     }
 
     StrSubstitutor(final StrSubstitutor other) {
         Objects.requireNonNull(other, "other");
         this.setVariableResolver(other.getVariableResolver());
         this.setVariablePrefixMatcher(other.getVariablePrefixMatcher());
         this.setVariableSuffixMatcher(other.getVariableSuffixMatcher());
         this.setEscapeChar(other.getEscapeChar());
         this.setValueDelimiterMatcher(other.valueDelimiterMatcher);
         this.valueEscapeDelimiterMatcher = other.valueEscapeDelimiterMatcher;
         this.configuration = other.configuration;
         this.recursiveEvaluationAllowed = other.isRecursiveEvaluationAllowed();
         this.enableSubstitutionInVariables = other.isEnableSubstitutionInVariables();
         this.valueDelimiterString = other.valueDelimiterString;
     }
 
     //-----------------------------------------------------------------------
     /**
      * Replaces all the occurrences of variables in the given source object with
      * their matching values from the map.
      *
      * @param source  the source text containing the variables to substitute, null returns null
      * @param valueMap  the map with the values, may be null
      * @return the result of the replace operation
      */
     public static String replace(final Object source, final Map<String, String> valueMap) {
         return new StrSubstitutor(valueMap).replace(source);
     }
 
     /**
      * Replaces all the occurrences of variables in the given source object with
      * their matching values from the map. This method allows to specify a
      * custom variable prefix and suffix
      *
      * @param source  the source text containing the variables to substitute, null returns null
      * @param valueMap  the map with the values, may be null
      * @param prefix  the prefix of variables, not null
      * @param suffix  the suffix of variables, not null
      * @return the result of the replace operation
      * @throws IllegalArgumentException if the prefix or suffix is null
      */
     public static String replace(final Object source, final Map<String, String> valueMap, final String prefix,
                                  final String suffix) {
         return new StrSubstitutor(valueMap, prefix, suffix).replace(source);
     }
 
     /**
      * Replaces all the occurrences of variables in the given source object with their matching
      * values from the properties.
      *
      * @param source the source text containing the variables to substitute, null returns null
      * @param valueProperties the properties with values, may be null
      * @return the result of the replace operation
      */
     public static String replace(final Object source, final Properties valueProperties) {
         if (valueProperties == null) {
             return source.toString();
         }
         final Map<String, String> valueMap = new HashMap<>();
         final Enumeration<?> propNames = valueProperties.propertyNames();
         while (propNames.hasMoreElements()) {
             final String propName = (String) propNames.nextElement();
             final String propValue = valueProperties.getProperty(propName);
             valueMap.put(propName, propValue);
         }
         return StrSubstitutor.replace(source, valueMap);
     }
 
     private static Map<String, String> toTypeSafeMap(final Properties properties) {
         final Map<String, String> map = new HashMap<>(properties.size());
         for (final String name : properties.stringPropertyNames()) {
             map.put(name, properties.getProperty(name));
         }
         return map;
     }
 
     private static String handleFailedReplacement(String input, Throwable throwable) {
         StatusLogger.getLogger().error("Replacement failed on {}", input, throwable);
         return input;
     }
 
     //-----------------------------------------------------------------------
     /**
      * Replaces all the occurrences of variables with their matching values
      * from the resolver using the given source string as a template.
      *
      * @param source  the string to replace in, null returns null
      * @return the result of the replace operation
      */
     public String replace(final String source) {
         return replace(null, source);
     }
     //-----------------------------------------------------------------------
     /**
      * Replaces all the occurrences of variables with their matching values
      * from the resolver using the given source string as a template.
      *
      * @param event The current LogEvent if there is one.
      * @param source  the string to replace in, null returns null
      * @return the result of the replace operation
      */
     public String replace(final LogEvent event, final String source) {
         if (source == null) {
             return null;
         }
         final StringBuilder buf = new StringBuilder(source);
         try {
             if (!substitute(event, buf, 0, source.length())) {
                 return source;
             }
         } catch (Throwable t) {
             return handleFailedReplacement(source, t);
         }
         return buf.toString();
     }
 
     /**
      * Replaces all the occurrences of variables with their matching values
      * from the resolver using the given source string as a template.
      * <p>
      * Only the specified portion of the string will be processed.
      * The rest of the string is not processed, and is not returned.
      * </p>
      *
      * @param source  the string to replace in, null returns null
      * @param offset  the start offset within the array, must be valid
      * @param length  the length within the array to be processed, must be valid
      * @return the result of the replace operation
      */
     public String replace(final String source, final int offset, final int length) {
         return replace(null, source, offset, length);
     }
 
     /**
      * Replaces all the occurrences of variables with their matching values
      * from the resolver using the given source string as a template.
      * <p>
      * Only the specified portion of the string will be processed.
      * The rest of the string is not processed, and is not returned.
      * </p>
      *
      * @param event the current LogEvent, if one exists.
      * @param source  the string to replace in, null returns null
      * @param offset  the start offset within the array, must be valid
      * @param length  the length within the array to be processed, must be valid
      * @return the result of the replace operation
      */
     public String replace(final LogEvent event, final String source, final int offset, final int length) {
         if (source == null) {
             return null;
         }
         final StringBuilder buf = new StringBuilder(length).append(source, offset, length);
         try {
             if (!substitute(event, buf, 0, length)) {
                 return source.substring(offset, offset + length);
             }
         } catch (Throwable t) {
             return handleFailedReplacement(source, t);
         }
         return buf.toString();
     }
 
     //-----------------------------------------------------------------------
     /**
      * Replaces all the occurrences of variables with their matching values
      * from the resolver using the given source array as a template.
      * The array is not altered by this method.
      *
      * @param source  the character array to replace in, not altered, null returns null
      * @return the result of the replace operation
      */
     public String replace(final char[] source) {
         return replace(null, source);
     }
 
     //-----------------------------------------------------------------------
     /**
      * Replaces all the occurrences of variables with their matching values
      * from the resolver using the given source array as a template.
      * The array is not altered by this method.
      *
      * @param event the current LogEvent, if one exists.
      * @param source  the character array to replace in, not altered, null returns null
      * @return the result of the replace operation
      */
     public String replace(final LogEvent event, final char[] source) {
         if (source == null) {
             return null;
         }
         final StringBuilder buf = new StringBuilder(source.length).append(source);
         try {
             substitute(event, buf, 0, source.length);
         } catch (Throwable t) {
             return handleFailedReplacement(new String(source), t);
         }
         return buf.toString();
     }
 
     /**
      * Replaces all the occurrences of variables with their matching values
      * from the resolver using the given source array as a template.
      * The array is not altered by this method.
      * <p>
      * Only the specified portion of the array will be processed.
      * The rest of the array is not processed, and is not returned.
      * </p>
      *
      * @param source  the character array to replace in, not altered, null returns null
      * @param offset  the start offset within the array, must be valid
      * @param length  the length within the array to be processed, must be valid
      * @return the result of the replace operation
      */
     public String replace(final char[] source, final int offset, final int length) {
         return replace(null, source, offset, length);
     }
 
     /**
      * Replaces all the occurrences of variables with their matching values
      * from the resolver using the given source array as a template.
      * The array is not altered by this method.
      * <p>
      * Only the specified portion of the array will be processed.
      * The rest of the array is not processed, and is not returned.
      * </p>
      *
      * @param event the current LogEvent, if one exists.
      * @param source  the character array to replace in, not altered, null returns null
      * @param offset  the start offset within the array, must be valid
      * @param length  the length within the array to be processed, must be valid
      * @return the result of the replace operation
      */
     public String replace(final LogEvent event, final char[] source, final int offset, final int length) {
         if (source == null) {
             return null;
         }
         final StringBuilder buf = new StringBuilder(length).append(source, offset, length);
         try {
             substitute(event, buf, 0, length);
         } catch (Throwable t) {
             return handleFailedReplacement(new String(source, offset, length), t);
         }
         return buf.toString();
     }
 
     //-----------------------------------------------------------------------
     /**
      * Replaces all the occurrences of variables with their matching values
      * from the resolver using the given source buffer as a template.
      * The buffer is not altered by this method.
      *
      * @param source  the buffer to use as a template, not changed, null returns null
      * @return the result of the replace operation
      */
     public String replace(final StringBuffer source) {
         return replace(null, source);
     }
 
     //-----------------------------------------------------------------------
     /**
      * Replaces all the occurrences of variables with their matching values
      * from the resolver using the given source buffer as a template.
      * The buffer is not altered by this method.
      *
      * @param event the current LogEvent, if one exists.
      * @param source  the buffer to use as a template, not changed, null returns null
      * @return the result of the replace operation
      */
     public String replace(final LogEvent event, final StringBuffer source) {
         if (source == null) {
             return null;
         }
         final StringBuilder buf = new StringBuilder(source.length()).append(source);
         try {
             substitute(event, buf, 0, buf.length());
         } catch (Throwable t) {
             return handleFailedReplacement(source.toString(), t);
         }
         return buf.toString();
     }
 
     /**
      * Replaces all the occurrences of variables with their matching values
      * from the resolver using the given source buffer as a template.
      * The buffer is not altered by this method.
      * <p>
      * Only the specified portion of the buffer will be processed.
      * The rest of the buffer is not processed, and is not returned.
      * </p>
      *
      * @param source  the buffer to use as a template, not changed, null returns null
      * @param offset  the start offset within the array, must be valid
      * @param length  the length within the array to be processed, must be valid
      * @return the result of the replace operation
      */
     public String replace(final StringBuffer source, final int offset, final int length) {
         return replace(null, source, offset, length);
     }
 
     /**
      * Replaces all the occurrences of variables with their matching values
      * from the resolver using the given source buffer as a template.
      * The buffer is not altered by this method.
      * <p>
      * Only the specified portion of the buffer will be processed.
      * The rest of the buffer is not processed, and is not returned.
      * </p>
      *
      * @param event the current LogEvent, if one exists.
      * @param source  the buffer to use as a template, not changed, null returns null
      * @param offset  the start offset within the array, must be valid
      * @param length  the length within the array to be processed, must be valid
      * @return the result of the replace operation
      */
     public String replace(final LogEvent event, final StringBuffer source, final int offset, final int length) {
         if (source == null) {
             return null;
         }
         final StringBuilder buf = new StringBuilder(length).append(source, offset, length);
         try {
             substitute(event, buf, 0, length);
         } catch (Throwable t) {
             return handleFailedReplacement(source.substring(offset, offset + length), t);
         }
         return buf.toString();
     }
 
     //-----------------------------------------------------------------------
     /**
      * Replaces all the occurrences of variables with their matching values
      * from the resolver using the given source builder as a template.
      * The builder is not altered by this method.
      *
      * @param source  the builder to use as a template, not changed, null returns null
      * @return the result of the replace operation
      */
     public String replace(final StringBuilder source) {
         return replace(null, source);
     }
 
     //-----------------------------------------------------------------------
     /**
      * Replaces all the occurrences of variables with their matching values
      * from the resolver using the given source builder as a template.
      * The builder is not altered by this method.
      *
      * @param event The LogEvent.
      * @param source  the builder to use as a template, not changed, null returns null.
      * @return the result of the replace operation.
      */
     public String replace(final LogEvent event, final StringBuilder source) {
         if (source == null) {
             return null;
         }
         final StringBuilder buf = new StringBuilder(source.length()).append(source);
         try {
             substitute(event, buf, 0, buf.length());
         } catch (Throwable t) {
             return handleFailedReplacement(source.toString(), t);
         }
         return buf.toString();
     }
     /**
      * Replaces all the occurrences of variables with their matching values
      * from the resolver using the given source builder as a template.
      * The builder is not altered by this method.
      * <p>
      * Only the specified portion of the builder will be processed.
      * The rest of the builder is not processed, and is not returned.
      * </p>
      *
      * @param source  the builder to use as a template, not changed, null returns null
      * @param offset  the start offset within the array, must be valid
      * @param length  the length within the array to be processed, must be valid
      * @return the result of the replace operation
      */
     public String replace(final StringBuilder source, final int offset, final int length) {
         return replace(null, source, offset, length);
     }
 
     /**
      * Replaces all the occurrences of variables with their matching values
      * from the resolver using the given source builder as a template.
      * The builder is not altered by this method.
      * <p>
      * Only the specified portion of the builder will be processed.
      * The rest of the builder is not processed, and is not returned.
      * </p>
      *
      * @param event the current LogEvent, if one exists.
      * @param source  the builder to use as a template, not changed, null returns null
      * @param offset  the start offset within the array, must be valid
      * @param length  the length within the array to be processed, must be valid
      * @return the result of the replace operation
      */
     public String replace(final LogEvent event, final StringBuilder source, final int offset, final int length) {
         if (source == null) {
             return null;
         }
         final StringBuilder buf = new StringBuilder(length).append(source, offset, length);
         try {
             substitute(event, buf, 0, length);
         } catch (Throwable t) {
             return handleFailedReplacement(source.substring(offset, offset + length), t);
         }
         return buf.toString();
     }
 
     //-----------------------------------------------------------------------
     /**
      * Replaces all the occurrences of variables in the given source object with
      * their matching values from the resolver. The input source object is
      * converted to a string using <code>toString</code> and is not altered.
      *
      * @param source  the source to replace in, null returns null
      * @return the result of the replace operation
      */
     public String replace(final Object source) {
         return replace(null, source);
     }
     //-----------------------------------------------------------------------
     /**
      * Replaces all the occurrences of variables in the given source object with
      * their matching values from the resolver. The input source object is
      * converted to a string using <code>toString</code> and is not altered.
      *
      * @param event the current LogEvent, if one exists.
      * @param source  the source to replace in, null returns null
      * @return the result of the replace operation
      */
     public String replace(final LogEvent event, final Object source) {
         if (source == null) {
             return null;
         }
         String stringValue = String.valueOf(source);
         final StringBuilder buf = new StringBuilder(stringValue.length()).append(stringValue);
         try {
             substitute(event, buf, 0, buf.length());
         } catch (Throwable t) {
             return handleFailedReplacement(stringValue, t);
         }
         return buf.toString();
     }
 
     //-----------------------------------------------------------------------
     /**
      * Replaces all the occurrences of variables within the given source buffer
      * with their matching values from the resolver.
      * The buffer is updated with the result.
      *
      * @param source  the buffer to replace in, updated, null returns zero
      * @return true if altered
      */
     public boolean replaceIn(final StringBuffer source) {
         if (source == null) {
             return false;
         }
         return replaceIn(source, 0, source.length());
     }
 
     /**
      * Replaces all the occurrences of variables within the given source buffer
      * with their matching values from the resolver.
      * The buffer is updated with the result.
      * <p>
      * Only the specified portion of the buffer will be processed.
      * The rest of the buffer is not processed, but it is not deleted.
      * </p>
      *
      * @param source  the buffer to replace in, updated, null returns zero
      * @param offset  the start offset within the array, must be valid
      * @param length  the length within the buffer to be processed, must be valid
      * @return true if altered
      */
     public boolean replaceIn(final StringBuffer source, final int offset, final int length) {
         return replaceIn(null, source, offset, length);
     }
 
     /**
      * Replaces all the occurrences of variables within the given source buffer
      * with their matching values from the resolver.
      * The buffer is updated with the result.
      * <p>
      * Only the specified portion of the buffer will be processed.
      * The rest of the buffer is not processed, but it is not deleted.
      * </p>
      *
      * @param event the current LogEvent, if one exists.
      * @param source  the buffer to replace in, updated, null returns zero
      * @param offset  the start offset within the array, must be valid
      * @param length  the length within the buffer to be processed, must be valid
      * @return true if altered
      */
     public boolean replaceIn(final LogEvent event, final StringBuffer source, final int offset, final int length) {
         if (source == null) {
             return false;
         }
         final StringBuilder buf = new StringBuilder(length).append(source, offset, length);
         try {
             if (!substitute(event, buf, 0, length)) {
                 return false;
             }
         } catch (Throwable t) {
             StatusLogger.getLogger().error("Replacement failed on {}", source, t);
             return false;
         }
         source.replace(offset, offset + length, buf.toString());
         return true;
     }
 
     //-----------------------------------------------------------------------
     /**
      * Replaces all the occurrences of variables within the given source
      * builder with their matching values from the resolver.
      *
      * @param source  the builder to replace in, updated, null returns zero
      * @return true if altered
      */
     public boolean replaceIn(final StringBuilder source) {
         return replaceIn(null, source);
     }
 
     //-----------------------------------------------------------------------
     /**
      * Replaces all the occurrences of variables within the given source
      * builder with their matching values from the resolver.
      *
      * @param event the current LogEvent, if one exists.
      * @param source  the builder to replace in, updated, null returns zero
      * @return true if altered
      */
     public boolean replaceIn(final LogEvent event, final StringBuilder source) {
         if (source == null) {
             return false;
         }
         return substitute(event, source, 0, source.length());
     }
     /**
      * Replaces all the occurrences of variables within the given source
      * builder with their matching values from the resolver.
      * <p>
      * Only the specified portion of the builder will be processed.
      * The rest of the builder is not processed, but it is not deleted.
      * </p>
      *
      * @param source  the builder to replace in, null returns zero
      * @param offset  the start offset within the array, must be valid
      * @param length  the length within the builder to be processed, must be valid
      * @return true if altered
      */
     public boolean replaceIn(final StringBuilder source, final int offset, final int length) {
         return replaceIn(null, source, offset, length);
     }
 
     /**
      * Replaces all the occurrences of variables within the given source
      * builder with their matching values from the resolver.
      * <p>
      * Only the specified portion of the builder will be processed.
      * The rest of the builder is not processed, but it is not deleted.
      * </p>
      *
      * @param event   the current LogEvent, if one is present.
      * @param source  the builder to replace in, null returns zero
      * @param offset  the start offset within the array, must be valid
      * @param length  the length within the builder to be processed, must be valid
      * @return true if altered
      */
     public boolean replaceIn(final LogEvent event, final StringBuilder source, final int offset, final int length) {
         if (source == null) {
             return false;
         }
         return substitute(event, source, offset, length);
     }
 
     //-----------------------------------------------------------------------
     /**
      * Internal method that substitutes the variables.
      * <p>
      * Most users of this class do not need to call this method. This method will
      * be called automatically by another (public) method.
      * </p>
      * <p>
      * Writers of subclasses can override this method if they need access to
      * the substitution process at the start or end.
      * </p>
      *
      * @param event The current LogEvent, if there is one.
      * @param buf  the string builder to substitute into, not null
      * @param offset  the start offset within the builder, must be valid
      * @param length  the length within the builder to be processed, must be valid
      * @return true if altered
      */
     protected boolean substitute(final LogEvent event, final StringBuilder buf, final int offset, final int length) {
         return substitute(event, buf, offset, length, null) > 0;
     }
 
     /**
      * Recursive handler for multiple levels of interpolation. This is the main
      * interpolation method, which resolves the values of all variable references
      * contained in the passed in text.
      *
      * @param event The current LogEvent, if there is one.
      * @param buf  the string builder to substitute into, not null
      * @param offset  the start offset within the builder, must be valid
      * @param length  the length within the builder to be processed, must be valid
      * @param priorVariables  the stack keeping track of the replaced variables, may be null
      * @return the length change that occurs, unless priorVariables is null when the int
      *  represents a boolean flag as to whether any change occurred.
      */
     private int substitute(final LogEvent event, final StringBuilder buf, final int offset, final int length,
                            List<String> priorVariables) {
         final StrMatcher prefixMatcher = getVariablePrefixMatcher();
         final StrMatcher suffixMatcher = getVariableSuffixMatcher();
         final char escape = getEscapeChar();
         final StrMatcher valueDelimiterMatcher = getValueDelimiterMatcher();
         final boolean substitutionInVariablesEnabled = isEnableSubstitutionInVariables();
 
         final boolean top = priorVariables == null;
         boolean altered = false;
         int lengthChange = 0;
         char[] chars = getChars(buf);
         int bufEnd = offset + length;
         int pos = offset;
         while (pos < bufEnd) {
             final int startMatchLen = prefixMatcher.isMatch(chars, pos, offset, bufEnd);
             if (startMatchLen == 0) {
                 pos++;
             } else // found variable start marker
             if (pos > offset && chars[pos - 1] == escape) {
                 // escaped
                 buf.deleteCharAt(pos - 1);
                 chars = getChars(buf);
                 lengthChange--;
                 altered = true;
                 bufEnd--;
             } else {
                 // find suffix
                 final int startPos = pos;
                 pos += startMatchLen;
                 int endMatchLen = 0;
                 int nestedVarCount = 0;
                 while (pos < bufEnd) {
                     if (substitutionInVariablesEnabled
                             && (endMatchLen = prefixMatcher.isMatch(chars, pos, offset, bufEnd)) != 0) {
                         // found a nested variable start
                         nestedVarCount++;
                         pos += endMatchLen;
                         continue;
                     }
 
                     endMatchLen = suffixMatcher.isMatch(chars, pos, offset, bufEnd);
                     if (endMatchLen == 0) {
                         pos++;
                     } else {
                         // found variable end marker
                         if (nestedVarCount == 0) {
                             String varNameExpr = new String(chars, startPos + startMatchLen, pos - startPos - startMatchLen);
                             if (substitutionInVariablesEnabled) {
                                 // initialize priorVariables if they're not already set
                                 if (priorVariables == null) {
                                     priorVariables = new ArrayList<>();
                                 }
                                 final StringBuilder bufName = new StringBuilder(varNameExpr);
                                 substitute(event, bufName, 0, bufName.length(), priorVariables);
                                 varNameExpr = bufName.toString();
                             }
                             pos += endMatchLen;
                             final int endPos = pos;
 
                             String varName = varNameExpr;
                             String varDefaultValue = null;
 
                             if (valueDelimiterMatcher != null) {
                                 final char [] varNameExprChars = varNameExpr.toCharArray();
                                 int valueDelimiterMatchLen = 0;
                                 for (int i = 0; i < varNameExprChars.length; i++) {
                                     // if there's any nested variable when nested variable substitution disabled, then stop resolving name and default value.
                                     if (!substitutionInVariablesEnabled
                                             && prefixMatcher.isMatch(varNameExprChars, i, i, varNameExprChars.length) != 0) {
                                         break;
                                     }
                                     if (valueEscapeDelimiterMatcher != null) {
                                         int matchLen = valueEscapeDelimiterMatcher.isMatch(varNameExprChars, i);
                                         if (matchLen != 0) {
                                             String varNamePrefix = varNameExpr.substring(0, i) + Interpolator.PREFIX_SEPARATOR;
                                             varName = varNamePrefix + varNameExpr.substring(i + matchLen - 1);
                                             for (int j = i + matchLen; j < varNameExprChars.length; ++j){
                                                 if ((valueDelimiterMatchLen = valueDelimiterMatcher.isMatch(varNameExprChars, j)) != 0) {
                                                     varName = varNamePrefix + varNameExpr.substring(i + matchLen, j);
                                                     varDefaultValue = varNameExpr.substring(j + valueDelimiterMatchLen);
                                                     break;
                                                 }
                                             }
                                             break;
                                         } else if ((valueDelimiterMatchLen = valueDelimiterMatcher.isMatch(varNameExprChars, i)) != 0) {
                                             varName = varNameExpr.substring(0, i);
                                             varDefaultValue = varNameExpr.substring(i + valueDelimiterMatchLen);
                                             break;
                                         }
                                     } else if ((valueDelimiterMatchLen = valueDelimiterMatcher.isMatch(varNameExprChars, i)) != 0) {
                                         varName = varNameExpr.substring(0, i);
                                         varDefaultValue = varNameExpr.substring(i + valueDelimiterMatchLen);
                                         break;
                                     }
                                 }
                             }
 
                             // on the first call initialize priorVariables
                             if (priorVariables == null) {
                                 priorVariables = new ArrayList<>();
                                 priorVariables.add(new String(chars, offset, length + lengthChange));
                             }
 
                             // handle cyclic substitution
                             boolean isCyclic = isCyclicSubstitution(varName, priorVariables);
 
                             // resolve the variable
                             String varValue = isCyclic ? null : resolveVariable(event, varName, buf, startPos, endPos);
                             if (varValue == null) {
                                 varValue = varDefaultValue;
                             }
                             if (varValue != null) {
                                 // recursive replace
                                 final int varLen = varValue.length();
                                 buf.replace(startPos, endPos, varValue);
                                 altered = true;
                                 int change = isRecursiveEvaluationAllowed()
                                         ? substitute(event, buf, startPos, varLen, priorVariables)
                                         : 0;
                                 change = change + (varLen - (endPos - startPos));
                                 pos += change;
                                 bufEnd += change;
                                 lengthChange += change;
                                 chars = getChars(buf); // in case buffer was altered
                             }
 
                             // remove variable from the cyclic stack
                             if (!isCyclic) {
                                 priorVariables.remove(priorVariables.size() - 1);
                             }
                             break;
                         }
                         nestedVarCount--;
                         pos += endMatchLen;
                     }
                 }
             }
         }
         if (top) {
             return altered ? 1 : 0;
         }
         return lengthChange;
     }
 
     /**
      * Checks if the specified variable is already in the stack (list) of variables, adding the value
      * if it's not already present.
      *
      * @param varName  the variable name to check
      * @param priorVariables  the list of prior variables
      * @return true if this is a cyclic substitution
      */
     private boolean isCyclicSubstitution(final String varName, final List<String> priorVariables) {
         if (!priorVariables.contains(varName)) {
             priorVariables.add(varName);
             return false;
         }
         final StringBuilder buf = new StringBuilder(BUF_SIZE);
         buf.append("Infinite loop in property interpolation of ");
         appendWithSeparators(buf, priorVariables, "->");
         StatusLogger.getLogger().warn(buf);
         return true;
     }
 
     /**
      * Internal method that resolves the value of a variable.
      * <p>
      * Most users of this class do not need to call this method. This method is
      * called automatically by the substitution process.
      * </p>
      * <p>
      * Writers of subclasses can override this method if they need to alter
      * how each substitution occurs. The method is passed the variable's name
      * and must return the corresponding value. This implementation uses the
      * {@link #getVariableResolver()} with the variable's name as the key.
      * </p>
      *
      * @param event The LogEvent, if there is one.
      * @param variableName  the name of the variable, not null
      * @param buf  the buffer where the substitution is occurring, not null
      * @param startPos  the start position of the variable including the prefix, valid
      * @param endPos  the end position of the variable including the suffix, valid
      * @return the variable's value or <b>null</b> if the variable is unknown
      */
     protected String resolveVariable(final LogEvent event, final String variableName, final StringBuilder buf,
                                      final int startPos, final int endPos) {
         final StrLookup resolver = getVariableResolver();
         if (resolver == null) {
             return null;
         }
         try {
             return resolver.lookup(event, variableName);
         } catch (Throwable t) {
             StatusLogger.getLogger().error("Resolver failed to lookup {}", variableName, t);
             return null;
         }
     }
 
     // Escape
     //-----------------------------------------------------------------------
     /**
      * Returns the escape character.
      *
      * @return the character used for escaping variable references
      */
     public char getEscapeChar() {
         return this.escapeChar;
     }
 
     /**
      * Sets the escape character.
      * If this character is placed before a variable reference in the source
      * text, this variable will be ignored.
      *
      * @param escapeCharacter  the escape character (0 for disabling escaping)
      */
     public void setEscapeChar(final char escapeCharacter) {
         this.escapeChar = escapeCharacter;
     }
 
     // Prefix
     //-----------------------------------------------------------------------
     /**
      * Gets the variable prefix matcher currently in use.
      * <p>
      * The variable prefix is the character or characters that identify the
      * start of a variable. This prefix is expressed in terms of a matcher
      * allowing advanced prefix matches.
      * </p>
      *
      * @return the prefix matcher in use
      */
     public StrMatcher getVariablePrefixMatcher() {
         return prefixMatcher;
     }
 
     /**
      * Sets the variable prefix matcher currently in use.
      * <p>
      * The variable prefix is the character or characters that identify the
      * start of a variable. This prefix is expressed in terms of a matcher
      * allowing advanced prefix matches.
      * </p>
      *
      * @param prefixMatcher  the prefix matcher to use, null ignored
      * @return this, to enable chaining
      * @throws IllegalArgumentException if the prefix matcher is null
      */
     public StrSubstitutor setVariablePrefixMatcher(final StrMatcher prefixMatcher) {
         if (prefixMatcher == null) {
             throw new IllegalArgumentException("Variable prefix matcher must not be null!");
         }
         this.prefixMatcher = prefixMatcher;
         return this;
     }
 
     /**
      * Sets the variable prefix to use.
      * <p>
      * The variable prefix is the character or characters that identify the
      * start of a variable. This method allows a single character prefix to
      * be easily set.
      * </p>
      *
      * @param prefix  the prefix character to use
      * @return this, to enable chaining
      */
     public StrSubstitutor setVariablePrefix(final char prefix) {
         return setVariablePrefixMatcher(StrMatcher.charMatcher(prefix));
     }
 
     /**
      * Sets the variable prefix to use.
      * <p>
      * The variable prefix is the character or characters that identify the
      * start of a variable. This method allows a string prefix to be easily set.
      * </p>
      *
      * @param prefix  the prefix for variables, not null
      * @return this, to enable chaining
      * @throws IllegalArgumentException if the prefix is null
      */
     public StrSubstitutor setVariablePrefix(final String prefix) {
        if (prefix == null) {
             throw new IllegalArgumentException("Variable prefix must not be null!");
         }
         return setVariablePrefixMatcher(StrMatcher.stringMatcher(prefix));
     }
 
     // Suffix
     //-----------------------------------------------------------------------
     /**
      * Gets the variable suffix matcher currently in use.
      * <p>
      * The variable suffix is the character or characters that identify the
      * end of a variable. This suffix is expressed in terms of a matcher
      * allowing advanced suffix matches.
      * </p>
      *
      * @return the suffix matcher in use
      */
     public StrMatcher getVariableSuffixMatcher() {
         return suffixMatcher;
     }
 
     /**
      * Sets the variable suffix matcher currently in use.
      * <p>
      * The variable suffix is the character or characters that identify the
      * end of a variable. This suffix is expressed in terms of a matcher
      * allowing advanced suffix matches.
      * </p>
      *
      * @param suffixMatcher  the suffix matcher to use, null ignored
      * @return this, to enable chaining
      * @throws IllegalArgumentException if the suffix matcher is null
      */
     public StrSubstitutor setVariableSuffixMatcher(final StrMatcher suffixMatcher) {
         if (suffixMatcher == null) {
             throw new IllegalArgumentException("Variable suffix matcher must not be null!");
         }
         this.suffixMatcher = suffixMatcher;
         return this;
     }
 
     /**
      * Sets the variable suffix to use.
      * <p>
      * The variable suffix is the character or characters that identify the
      * end of a variable. This method allows a single character suffix to
      * be easily set.
      * </p>
      *
      * @param suffix  the suffix character to use
      * @return this, to enable chaining
      */
     public StrSubstitutor setVariableSuffix(final char suffix) {
         return setVariableSuffixMatcher(StrMatcher.charMatcher(suffix));
     }
 
     /**
      * Sets the variable suffix to use.
      * <p>
      * The variable suffix is the character or characters that identify the
      * end of a variable. This method allows a string suffix to be easily set.
      * </p>
      *
      * @param suffix  the suffix for variables, not null
      * @return this, to enable chaining
      * @throws IllegalArgumentException if the suffix is null
      */
     public StrSubstitutor setVariableSuffix(final String suffix) {
        if (suffix == null) {
             throw new IllegalArgumentException("Variable suffix must not be null!");
         }
         return setVariableSuffixMatcher(StrMatcher.stringMatcher(suffix));
     }
 
     // Variable Default Value Delimiter
     //-----------------------------------------------------------------------
     /**
      * Gets the variable default value delimiter matcher currently in use.
      * <p>
      * The variable default value delimiter is the character or characters that delimit the
      * variable name and the variable default value. This delimiter is expressed in terms of a matcher
      * allowing advanced variable default value delimiter matches.
      * </p>
      * <p>
      * If it returns null, then the variable default value resolution is disabled.
      * </p>
      *
      * @return the variable default value delimiter matcher in use, may be null
      */
     public StrMatcher getValueDelimiterMatcher() {
         return valueDelimiterMatcher;
     }
 
     /**
      * Sets the variable default value delimiter matcher to use.
      * <p>
      * The variable default value delimiter is the character or characters that delimit the
      * variable name and the variable default value. This delimiter is expressed in terms of a matcher
      * allowing advanced variable default value delimiter matches.
      * </p>
      * <p>
      * If the <code>valueDelimiterMatcher</code> is null, then the variable default value resolution
      * becomes disabled.
      * </p>
      *
      * @param valueDelimiterMatcher  variable default value delimiter matcher to use, may be null
      * @return this, to enable chaining
      */
     public StrSubstitutor setValueDelimiterMatcher(final StrMatcher valueDelimiterMatcher) {
         this.valueDelimiterMatcher = valueDelimiterMatcher;
         return this;
     }
 
     /**
      * Sets the variable default value delimiter to use.
      * <p>
      * The variable default value delimiter is the character or characters that delimit the
      * variable name and the variable default value. This method allows a single character
      * variable default value delimiter to be easily set.
      * </p>
      *
      * @param valueDelimiter  the variable default value delimiter character to use
      * @return this, to enable chaining
      */
     public StrSubstitutor setValueDelimiter(final char valueDelimiter) {
         return setValueDelimiterMatcher(StrMatcher.charMatcher(valueDelimiter));
     }
 
     /**
      * Sets the variable default value delimiter to use.
      * <p>
      * The variable default value delimiter is the character or characters that delimit the
      * variable name and the variable default value. This method allows a string
      * variable default value delimiter to be easily set.
      * </p>
      * <p>
      * If the <code>valueDelimiter</code> is null or empty string, then the variable default
      * value resolution becomes disabled.
      * </p>
      *
      * @param valueDelimiter  the variable default value delimiter string to use, may be null or empty
      * @return this, to enable chaining
      */
     public StrSubstitutor setValueDelimiter(final String valueDelimiter) {
         if (Strings.isEmpty(valueDelimiter)) {
             setValueDelimiterMatcher(null);
             return this;
         }
         String escapeValue = valueDelimiter.substring(0, valueDelimiter.length() - 1) + "\\"
                 + valueDelimiter.substring(valueDelimiter.length() - 1);
         valueEscapeDelimiterMatcher = StrMatcher.stringMatcher(escapeValue);
         return setValueDelimiterMatcher(StrMatcher.stringMatcher(valueDelimiter));
     }
 
     // Resolver
     //-----------------------------------------------------------------------
     /**
      * Gets the VariableResolver that is used to lookup variables.
      *
      * @return the VariableResolver
      */
     public StrLookup getVariableResolver() {
         return this.variableResolver;
     }
 
     /**
      * Sets the VariableResolver that is used to lookup variables.
      *
      * @param variableResolver  the VariableResolver
      */
     public void setVariableResolver(final StrLookup variableResolver) {
         if (variableResolver instanceof ConfigurationAware && this.configuration != null) {
             ((ConfigurationAware) variableResolver).setConfiguration(this.configuration);
         }
         this.variableResolver = variableResolver;
     }
 
     // Substitution support in variable names
     //-----------------------------------------------------------------------
     /**
      * Returns a flag whether substitution is done in variable names.
      *
      * @return the substitution in variable names flag
      */
     public boolean isEnableSubstitutionInVariables() {
         return enableSubstitutionInVariables;
     }
 
     /**
      * Sets a flag whether substitution is done in variable names. If set to
      * <b>true</b>, the names of variables can contain other variables which are
      * processed first before the original variable is evaluated, e.g.
      * <code>${jre-${java.version}}</code>. The default value is <b>true</b>.
      *
      * @param enableSubstitutionInVariables the new value of the flag
      */
     public void setEnableSubstitutionInVariables(final boolean enableSubstitutionInVariables) {
         this.enableSubstitutionInVariables = enableSubstitutionInVariables;
     }
 
     boolean isRecursiveEvaluationAllowed() {
         return recursiveEvaluationAllowed;
     }
 
     void setRecursiveEvaluationAllowed(final boolean recursiveEvaluationAllowed) {
         this.recursiveEvaluationAllowed = recursiveEvaluationAllowed;
     }
 
     private char[] getChars(final StringBuilder sb) {
         final char[] chars = new char[sb.length()];
         sb.getChars(0, sb.length(), chars, 0);
         return chars;
     }
 
     /**
      * Appends a iterable placing separators between each value, but
      * not before the first or after the last.
      * Appending a null iterable will have no effect..
      *
      * @param sb StringBuilder that contains the String being constructed.
      * @param iterable  the iterable to append
      * @param separator  the separator to use, null means no separator
      */
     public void appendWithSeparators(final StringBuilder sb, final Iterable<?> iterable, String separator) {
         if (iterable != null) {
             separator = separator == null ? Strings.EMPTY : separator;
             final Iterator<?> it = iterable.iterator();
             while (it.hasNext()) {
                 sb.append(it.next());
                 if (it.hasNext()) {
                     sb.append(separator);
                 }
             }
         }
     }
 
     @Override
     public String toString() {
         return "StrSubstitutor(" + variableResolver.toString() + ')';
     }
 
     @Override
     public void setConfiguration(final Configuration configuration) {
         this.configuration = configuration;
         if (this.variableResolver instanceof ConfigurationAware) {
             ((ConfigurationAware) this.variableResolver).setConfiguration(this.configuration);
         }
     }
 }