Package org.apache.logging.log4j.core.lookup

Interface StrLookup

All Known Implementing Classes:
AbstractConfigurationAwareLookup, AbstractLookup, ContextMapLookup, DateLookup, EnvironmentLookup, EventLookup, Interpolator, JavaLookup, JmxRuntimeInputArgumentsLookup, JndiLookup, Log4jLookup, LowerLookup, MainMapLookup, MapLookup, MarkerLookup, PropertiesLookup, ResourceBundleLookup, StructuredDataLookup, SystemPropertiesLookup, UpperLookup
public interface StrLookup
Lookup a String key to a String value.

This class represents the simplest form of a string to string map. It has a benefit over a map in that it can create the result on demand based on the key.

This class comes complete with various factory methods. If these do not suffice, you can subclass and implement your own matcher.

For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the value on demand from the database

  • Field Details

  • Method Details

    • lookup

      String lookup(String key)
      Looks up a String key to a String value.

      The internal implementation may use any mechanism to return the value. The simplest implementation is to use a Map. However, virtually any implementation is possible.

      For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the value on demand from the database Or, a numeric based implementation could be created that treats the key as an integer, increments the value and return the result as a string - converting 1 to 2, 15 to 16 etc.

      This method always returns a String, regardless of the underlying data, by converting it as necessary. For example: 

       Map<String, Object> map = new HashMap<String, Object>();
 map.put("number", new Integer(2));
 assertEquals("2", StrLookup.mapLookup(map).lookup("number"));
      Parameters:
      key - the key to be looked up, may be null
      Returns:
      the matching value, null if no match

    • lookup

      String lookup(LogEvent event, String key)
      Looks up a String key to a String value possibly using the current LogEvent.

      The internal implementation may use any mechanism to return the value. The simplest implementation is to use a Map. However, virtually any implementation is possible.

      For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the value on demand from the database Or, a numeric based implementation could be created that treats the key as an integer, increments the value and return the result as a string - converting 1 to 2, 15 to 16 etc.

      This method always returns a String, regardless of the underlying data, by converting it as necessary. For example: 

       Map<String, Object> map = new HashMap<String, Object>();
 map.put("number", new Integer(2));
 assertEquals("2", StrLookup.mapLookup(map).lookup("number"));
      Parameters:
      event - The current LogEvent.
      key - the key to be looked up, may be null
      Returns:
      the matching value, null if no match

    • evaluate

      default LookupResult evaluate(String key)
      Same as lookup(String), but provides additional metadata describing the result. Returns null if the key cannot be evaluated, otherwise a LookupResult wrapping the non-null string value.

    • evaluate

      default LookupResult evaluate(LogEvent event, String key)
      Same as lookup(LogEvent, String), but provides additional metadata describing the result. Returns null if the key cannot be evaluated, otherwise a LookupResult wrapping the non-null string value.