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https://issues.apache.org/jira/browse/LOG4J2-3469?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17519396#comment-17519396
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Jody Garnett commented on LOG4J2-3469:
--------------------------------------
Still not sure how to use Arbiters to feed in a log file location...
Based on:
{quote}[SystemPropertyArbiter.isCondition()|https://logging.apache.org/log4j/log4j-2.17.1/log4j-core/apidocs/org/apache/logging/log4j/core/config/arbiters/SystemPropertyArbiter.html#isCondition--]
Returns true if either the property name is defined (it has any value) or the
property value matches the requested value.
{quote}
In the very simple case of a system property:
{code:java}
<Properties>
<Select>
<SystemPropertyArbiter propertyName="GEOSERVER_LOG_LOCATION"
<Property
name="GEOSERVER_LOG_LOCATION">${env:GEOSERVER_LOG_LOCATION}</Property>
</SystemPropertyArbiter>
<DefaultArbiter>
<Property
name="GEOSERVER_LOG_LOCATION">${web:initParam.GEOSERVER_LOG_LOCATION}</Property>
</DefaultArbiter>
</Select>
</Properties>{code}
> Create new builder from existing Appender
> -----------------------------------------
>
> Key: LOG4J2-3469
> URL: https://issues.apache.org/jira/browse/LOG4J2-3469
> Project: Log4j 2
> Issue Type: New Feature
> Components: Configuration, Configurators, Core
> Affects Versions: 2.17.2
> Reporter: Jody Garnett
> Priority: Minor
> Attachments: DEFAULT_LOGGING.xml
>
>
>
> The documentation covers both [Initialize Log4j by Combining Configuration
> File with Programmatic
> Configuration|https://logging.apache.org/log4j/2.x/manual/customconfig.html#Hybrid]
> and [Programmatically Modifying the Current Configuration after
> Initialization|https://logging.apache.org/log4j/2.x/manual/customconfig.html#Programmatically_Modifying_the_Current_Configuration_after_Initialization].
>
> However both these techniques are limited as to what they can accomplish:
> * MyXMLConfiguration.doConfigure() is shown adding an appender, via
> addLogger method
> * A custom configuration super.setup() method is shown using
> config.addLogger() and then ctx.updateLoggers().
> My challenge is to programatically update the configuration to:
> * Override logfile output location, either directly modifying appender, or
> modifying config property used by appender.
> * Optionally Filter out any RollingFileAppender or FileAppender appenders
> * Optionally suppress (filter out) any Console loggers if asked
> I am seeking an api used to pre-process configuration objects if one is
> available.
> In the past when using a fluent / builder API there is an option to
> jump-start a builder with the configuration of an existing object. This
> approach would allow a builder to be loaded with an existing appender;
> revised, and a new appender generated as a replacement.
> {code:java}
> @Override protected void doConfigure() {
> super.doConfigure();
> getProperties().put("GEOSERVER_LOG_LOCATION","geoserver.log");
> Appender appender = getAppenders("geoserverlogfile");
> if( appender instanceof RollingFileAppender){
> RollingFileAppender fileAppender =(RollingFileAppender) appender;
> RollingFileAppender replacement =
> RollingFileAppender.newBuilder(fileAppender)
> .withFileName("${GEOSERVER_LOG_LOCATION}.log")
> .withFilePattern("${GEOSERVER_LOG_LOCATION}-%i.log")
> .build();
>
> getAppenders().remove("geoserverlogfile");
> addAppender(replacement);
> }
> }{code}
> The alternative is verbose and may miss copying new parameters added over
> time.
> Alternatives considered:
> *MyXMLConfiguration.setup()* prior to super.setup(): Unclear how easy/safe it
> is to to modify _rootNode_ structure directly? Is this what is intended by
> the documentation.
> {code:java}
> public void setup() {
> for( Node child : rootNode.getChildren()){
> if ("Properties".equals(child.getName())){
> for( Node property : child.getChildren() ){
> if( property.getAttributes().containsKey("name") &&
>
> property.getAttributes().get("name").equals("GEOSERVER_LOG_LOCATION")) {
> // override value with current GEOSERVER_LOG_LOCATION
> property.setValue("foo.log");
> }
> }
> }
> }
> super.setup();
> }{code}
> *MyXMLConfiguration.doConfigure()* before super.doConfigure(): should be able
> to modify _rootNode_ and make any changes required. Unclear how easy/safe it
> is to to modify node structure directly?
> *MyXMLConfiguration.doConfigure()* after super.doConfigure(): is too late as
> shown above.
> - Can add loggers and appenders
> - Modifications to config.getProperties() are not reflected in appender
> configuration
> - Modifications to existing appenders cannot be accomplished
> {*}MyXMLConfiguration.{*}{*}preConfigure(Node){*} allows xml to be rewritten
> just-in-time:
> {code:java}
> @Overrideprotected void preConfigure(Node node) {
> if( !node.isRoot() && node.getName().equals("Property")){
> if( node.getAttributes().containsKey("name") &&
>
> node.getAttributes().get("name").equals("GEOSERVER_LOG_LOCATION")) {
> // override value with current GEOSERVER_LOG_LOCATION
> node.setValue("foo.log");
> }
> }
> super.preConfigure(node);
> } {code}
> For reference see attached {*}DEFAULT_LOGGING.xml{*}.
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