MapFilter

The MapFilter allows filtering against data elements that are in the Mapped Diagnostic Context (MDC).

Parameter Name	Type	Description
Operator	LogString	If the operator is AND then all the key/value pairs must match; any other value is implicitly an OR and a match by any one of the key/value pairs will be considered to be a match. The default value is OR.
AcceptOnMatch	LogString	Action to take when the filter matches. May be true or false. The default value is false.
MDC key	LogString	Any name other than Operator or AcceptOnMatch is considered a key to the MDC along with the value to match on. Keys may only be specified once; duplicate keys will replace earlier ones.

In this configuration, the MapFilter can be used to filter based on system inserted values such as IP address and/or Username. In this example, we assume that the program has inserted appropriate values for user.ip and user.name into the MDC. In this case, when both the IP address is 127.0.0.1 and the Username is test, the entry will not be logged.

<?xml version="1.0" encoding="UTF-8"?>
<log4j:configuration xmlns:log4j="http://logging.apache.org/">
    <appender name="SIMPLE" class="log4cxx.FileAppender">
        <layout class="log4cxx.SimpleLayout">
            <param  name="File"
                    value="logs/app.log"
            />
            <param  name="Append"
                    value="true"
            />
        </layout>
 
        <filter class="log4cxx.MapFilter">
            <param  name="user.ip"
                    value="127.0.0.1"
            />
            <param  name="user.name"
                    value="test"
            />
            <param  name="Operator"
                    value="AND"
            />
            <param  name="AcceptOnMatch"
                    value="false"
            />
        </filter>
    </appender>
 
    <root>
        <priority       value="all"     />
        <appender-ref   ref="SIMPLE"    />
    </root>
</log4j:configuration>

If we wanted to exclude multiple IP addresses from the log, we need to define a separate filter for each one as we don’t support wildcards. Since the default AcceptOnMatch value is false, we can simplify to a single line per filter. In the configuration below we would skip logs for IP addresses matching 192.168.0.5 - 7.

<?xml version="1.0" encoding="UTF-8"?>
<log4j:configuration xmlns:log4j="http://logging.apache.org/">
    <appender name="SIMPLE" class="log4cxx.FileAppender">
        <layout class="log4cxx.SimpleLayout">
            <param  name="File"
                    value="logs/app.log"
            />
            <param  name="Append"
                    value="true"
            />
        </layout>
 
        <filter class="MapFilter">
            <param  name="user.ip" 
                    value="192.168.0.5"
            />
        </filter>
        <filter class="MapFilter">
            <param  name="user.ip"
                    value="192.168.0.6"
            />
        </filter>
        <filter class="MapFilter">
            <param  name="user.ip"
                    value="192.168.0.7"
            />
        </filter>
    </appender>
 
    <root>
        <priority       value="all"     />
        <appender-ref   ref="SIMPLE"    />
    </root>
</log4j:configuration>

In the case where we only want to log entries from a particular set of IP addresses (not recommended as this could be a security vulnerability), we need to have a final DenyAllFilter to catch the fall through. In this configuration, we would only log entries from 192.168.0.251 and 192.168.0.252.

<?xml version="1.0" encoding="UTF-8"?>
<log4j:configuration xmlns:log4j="http://logging.apache.org/">
    <appender name="SIMPLE" class="log4cxx.FileAppender">
        <layout class="log4cxx.SimpleLayout">
            <param  name="File"
                    value="logs/app.log"
            />
            <param  name="Append"
                    value="true"
            />
        </layout>
 
        <filter class="MapFilter">
            <param  name="user.ip"
                    value="192.168.0.251"
            />
            <param  name="AcceptOnMatch"
                    value="true"
            />
        </filter>
        <filter class="MapFilter">
            <param  name="user.ip"
                    value="192.168.0.252"
            />
            <param  name="AcceptOnMatch"
                    value="true"
            />
        </filter>
        <filter class="DenyAllFilter" />
    </appender>
 
    <root>
        <priority       value="all"     />
        <appender-ref   ref="SIMPLE"    />
    </root>
</log4j:configuration>