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| <div class="section"><h2>Lookups<a name="Lookups"></a></h2> |
| <p> |
| Lookups provide a way to add values to the Log4j configuration at arbitrary places. They are |
| a particular type of Plugin that implements the |
| <a href="../log4j2-core/apidocs/org/apache/logging/log4j/core/lookup/StrLookup.html">StrLookup</a> interface. |
| Information on how to use Lookups in configuration files can be found in the |
| <a href="./configuration.html#PropertySubstitution">Property Substitution</a> section of the |
| <a href="./configuration.html">Configuration</a> page. |
| </p> |
| <a name="ContextMapLookup"></a> |
| <div class="section"><h3>ContextMapLookup<a name="ContextMapLookup"></a></h3> |
| <p> |
| The ContextMapLookup allows applications to store data in the Log4j ThreadContext Map and |
| then retrieve the values in the Log4j configuration. In the example below, the application |
| would store the current user's login id in the ThreadContext Map with the key "loginId". During |
| initial configuration processing the first '$' will be removed. The PatternLayout supports |
| interpolation with Lookups and will then resolve the variable for each event. Note that |
| the pattern "%X{loginId}" would achieve the same result. |
| </p> |
| <div class="source"><pre class="prettyprint"> <File name="Application" fileName="application.log"> |
| <PatternLayout> |
| <pattern>%d %p %C{1.} [%t] $${ctx:loginId} %m%n</pattern> |
| </PatternLayout> |
| </File></pre></div> |
| </div> |
| <a name="DateLookup"></a> |
| <div class="section"><h3>DateLookup<a name="DateLookup"></a></h3> |
| <p> |
| The DateLookup is somewhat unusual from the other lookups as it doesn't use the key to locate an item. |
| Instead, the key can be used to specify a date format string that is valid for |
| <a class="externalLink" href="http://docs.oracle.com/javase/6/docs/api/java/text/SimpleDateFormat.html">SimpleDateFormat</a>. |
| The current date, or the date associated with the current log event will be formatted as specified. |
| </p> |
| <div class="source"><pre class="prettyprint"> <RollingFile name="Rolling-${map:type}" fileName="${filename}" |
| filePattern="target/rolling1/test1-$${date:MM-dd-yyyy}.%i.log.gz"> |
| <PatternLayout> |
| <pattern>%d %p %C{1.} [%t] %m%n</pattern> |
| </PatternLayout> |
| <SizeBasedTriggeringPolicy size="500" /> |
| </RollingFile></pre></div> |
| </div> |
| <a name="EnvironmentLookup"></a> |
| <div class="section"><h3>EnvironmentLookup<a name="EnvironmentLookup"></a></h3> |
| <p> |
| The EnvironmentLookup allows systems to configure environment variables, either in global files |
| such as /etc/profile or in the startup scripts for applications, and then retrieve those variables |
| from within the logging configuration. The example below includes the name of the currently logged |
| in user in the application log. |
| </p> |
| <div class="source"><pre class="prettyprint"> <File name="Application" fileName="application.log"> |
| <PatternLayout> |
| <pattern>%d %p %C{1.} [%t] $${env:USER} %m%n</pattern> |
| </PatternLayout> |
| </File></pre></div> |
| </div> |
| <a name="MapLookup"></a> |
| <div class="section"><h3>MapLookup<a name="MapLookup"></a></h3> |
| <p> |
| The MapLookup serves two purposes. |
| </p><ol style="list-style-type: decimal"> |
| <li>Provide the base for Properties declared in the configuration file.</li> |
| <li>Retrieve values from MapMessages in LogEvents.</li> |
| </ol> |
| The first item simply means that the MapLookup is used to substitute properties that are defined |
| in the configuration file. These variables are specified without a prefix - e.g. <tt>${name}</tt>. |
| The second usage allows a value from the current |
| <a href="../log4j2-api/apidocs/org/apache/logging/log4j/message/MapMessage.html">MapMessage</a>, |
| if one is part of the current log event, to be substituted. In the example below the RoutingAppender will |
| use a different RollingFileAppender for each unique value of the key named "type" in the MapMessage. Note |
| that when used this way a value for "type" should be declared in the properties declaration to provide |
| a default value in case the message is not a MapMessage or the MapMessage does not contain the key. See the |
| <a href="./configuration.html#PropertySubstitution">Property Substitution</a> section of the |
| <a href="./configuration.html">Configuration</a> page for information on how to set the default values. |
| |
| <div class="source"><pre class="prettyprint"> <Routing name="Routing"> |
| <Routes pattern="$${map:type}"> |
| <Route> |
| <RollingFile name="Rolling-${map:type}" fileName="${filename}" |
| filePattern="target/rolling1/test1-${map:type}.%i.log.gz"> |
| <PatternLayout> |
| <pattern>%d %p %C{1.} [%t] %m%n</pattern> |
| </PatternLayout> |
| <SizeBasedTriggeringPolicy size="500" /> |
| </RollingFile> |
| </Route> |
| </Routes> |
| </Routing> |
| </pre></div> |
| </div> |
| <a name="StructuredDataLookup"></a> |
| <div class="section"><h3>StructuredDataLookup<a name="StructuredDataLookup"></a></h3> |
| <p> |
| The StructuredDataLookup is very similar to the MapLookup in that it will retrieve values from |
| StructuredDataMessages. In addition to the Map values it will also return the name portion of the |
| id (not including the enterprise number) and the type field. The main difference between the |
| example below and the example for MapMessage is that the "type" is an attribute of the |
| <a href="../log4j2-api/apidocs/org/apache/logging/log4j/message/StructuredDataMessage.html">StructuredDataMessage</a> |
| while "type" would have to be an item in the Map in a MapMessage. |
| </p> |
| <div class="source"><pre class="prettyprint"> <Routing name="Routing"> |
| <Routes pattern="$${sd:type}"> |
| <Route> |
| <RollingFile name="Rolling-${sd:type}" fileName="${filename}" |
| filePattern="target/rolling1/test1-${sd:type}.%i.log.gz"> |
| <PatternLayout> |
| <pattern>%d %p %C{1.} [%t] %m%n</pattern> |
| </PatternLayout> |
| <SizeBasedTriggeringPolicy size="500" /> |
| </RollingFile> |
| </Route> |
| </Routes> |
| </Routing> |
| </pre></div> |
| </div> |
| <a name="SystemPropertiesLookup"></a> |
| <div class="section"><h3>SystemPropertiesLookup<a name="SystemPropertiesLookup"></a></h3> |
| <p> |
| As it is quite common to define values inside and outside the application by using System Properties, |
| it is only natural that they should be accessible via a Lookup. As system properties are often |
| defined outside the application it would be quite common to see something like: |
| </p> |
| <div class="source"><pre class="prettyprint"> <appenders> |
| <File name="ApplicationLog" fileName="${sys:logPath}/app.log"/> |
| </appenders></pre></div> |
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