4 Filtering WebLogic Server Log Messages

When WebLogic Server message catalogs and the NonCatalogLogger generate messages, they distribute their messages to a java.util.logging.Logger object. The Logger object publishes the messages to any message handler that has subscribed to the Logger.

WebLogic Server instantiates Logger and Handler objects in three distinct contexts. See Figure 4-1 for more details:

• In client JVMs that use WebLogic logging services. This client Logger object publishes messages that are sent from client applications running in the client JVM.

  The following handlers subscribe to the Logger object in a client JVM:

  • ConsoleHandler, which prints messages from the client JVM to the client's standard out.

    If you use the -Dweblogic.log.StdoutSeverityLevel Java startup option for the client JVM, WebLogic logging services create a filter for this handler that limits the messages that the handler writes to standard out. See Writing Messages from a Client Application in Adding WebLogic Logging Services to Applications Deployed on Oracle WebLogic Server 12.1.3.

  • FileStreamHandler, which writes messages from the client JVM to the client's log file.

• In each instance of WebLogic Server. This server Logger object publishes messages that are sent from subsystems and applications that run on a server instance.

  The following handlers subscribe to the server Logger object:

  • ConsoleHandler, which makes messages available to the server's standard out.

  • FileStreamHandler, which writes messages to the server log file.

  • An internal handler, which broadcasts messages to the domain log and JMX clients, and publishes messages to the Administration Server.

• The Administration Server maintains a domain Logger object in addition to a server Logger object. The domain Logger object receives messages from each Managed Server's Logger object.

  The following handler subscribes to the domain Logger object:

  • FileStreamHandler, which writes messages to the domain log file.

Figure 4-1 WebLogic Logging Services Contexts

Description of "Figure 4-1 WebLogic Logging Services Contexts"

When WebLogic Server message catalogs and the NonCatalogLogger generate messages, they convert the message severity to a weblogic.logging.WLLevel object. A WLLevel object can specify any of the following values, from lowest to highest impact:

Trace, Debug, Info, Notice, Warning, Error, Critical, Alert, Emergency

By default, a Logger object publishes messages of all levels. To set the lowest-level message that a Logger object publishes, you use a simple Logger.setLevel API. When a Logger object receives an incoming message, it checks the message level with the level set by the setLevel API. If the message level is below the Logger level, it returns immediately. If the message level is above the Logger level, the Logger allocates a WLLogRecord object to describe the message.

For example, if you set a Logger object level to Warning, the Logger object publishes only Warning, Error, Critical, Alert, or Emergency messages.

To provide more control over the messages that a Logger object publishes, you can also create and set a filter. A filter is a class that compares data in the WLLogRecord object with a set of criteria. The Logger object publishes only the WLLogRecord objects that satisfy the filter criteria. For example, a filter can configure a Logger to publish only messages from the JDBC subsystem. To create a filter, you instantiate a java.util.logging.Filter object and use the Logger.setFilter API to set it for a Logger object.

Instead of (or in addition to) setting the level and a filter for the messages that a Logger object publishes, you can set the level and filters on individual message handlers.

For example, you can specify that a Logger publishes messages that are of the Warning level or higher. Then you can do the following for each handler:

• For the ConsoleHandler, set a level and filter that selects only Alert messages from the JDBC, JMS, and EJB subsystems. This causes standard out to display only Alert messages from the JDBC, JMS, and EJB subsystems.

• For the FileStreamHandler, set no additional level or filter criteria. Because the Logger object has been configured to publish only messages of the Warning level or higher, the log file will contain all messages from all subsystems that are of Warning severity level or higher.

• Publish all messages of Warning severity level or higher to the domain-wide message log on the Administration Server.

The WebLogic Server Administration Console and WLST provide a way to set the severity level for a Handler object through standard MBean commands. To set the Severity level for a Logger object, you can use the Logger API. You can also set the Severity level for a Logger via the Administrator Console, WLST, or the command line; see Specifying Severity Level for Loggers. To configure Logger and Handler severity level for WLS clients (such as EJB and Web Service clients), you must use the Java Logging API.

1. Invokes the one of the following Log4jLoggingHelper methods (See Example 4-3).

   • getLog4jServerLogger if the current context is a server JVM and you want to retrieve the Logger object that a server uses to manage its local server log.

   • getLog4jDomainLogger if the current context is the Administration Server and you want to retrieve the Logger object that manages the domain log.

2. Invokes the logger.getAllAppenders() method.

   Enumeration e = logger.getAllAppenders();
   

   The method returns all the appenders that are registered with the Logger object.

3. Iterates through the list of appenders and gets each appender name.
4. Invokes the app.setThreshold(WLLog4jLevel level) method.

   To set the level of a Log4j Appender object, you must pass a value that is defined in the weblogic.logging.log4j.WLLog4jLevel class. WebLogic Server maps the org.apache.log4j.Level to the appropriate WLLevel. For a list of valid values, see the description of the weblogic.logging.WLLevel class in Java API Reference for Oracle WebLogic Server.

package weblogic.logging.examples;
import java.util.Enumeration;
import org.apache.log4j.AppenderSkeleton;
import org.apache.log4j.Logger;
import org.apache.log4j.spi.Filter;
import org.apache.log4j.spi.LoggingEvent;
import weblogic.logging.LoggerNotAvailableException;
import weblogic.logging.NonCatalogLogger;
import weblogic.logging.Severities;
import weblogic.logging.log4j.AppenderNames;
import weblogic.logging.log4j.Log4jLoggingHelper;
import weblogic.logging.log4j.WLLog4jLevel;
import weblogic.logging.log4j.WLLog4jLogEvent;
/**
 * This class sets a level and filter on a Log4j Appender.
 */
public class Log4jFilterExamplesStartup {
  public static void main(String[] args) {
    try {
      System.out.println("Invoked the log4j filter example startup class");
      Logger logger = Log4jLoggingHelper.getLog4jServerLogger();
      Enumeration e = logger.getAllAppenders();
      while (e.hasMoreElements()) {
        AppenderSkeleton app = (AppenderSkeleton) e.nextElement();
        String name = app.getName();
        if (name == null) continue;
        if (name.equals(AppenderNames.LOG_FILE_APPENDER)) { 
          // Set the threshold level of messages going to the log file to WARNING
          // This will result in NOTICE, INFO, DEBUG, and TRACE messages being
          // suppressed from going to the server log file
          app.setThreshold(WLLog4jLevel.WARN);
          System.out.println("Set WARNING level on the log file appender");
        } else if (name.equals(AppenderNames.STDOUT_APPENDER)) {
          // Set level to INFO on the stdout filter
          app.setThreshold(WLLog4jLevel.INFO);
          // First clear the existing filters on the appender
          app.clearFilters();
          // Add a filter to block INFO messages from the HTTP subsystem
          app.addFilter(new MyFilter());
        } 
      }
      // Now test the filter
      NonCatalogLogger nc = new NonCatalogLogger("MyFilterTest");
      nc.info("INFO messages will not be published to the file but to stdout");
      nc.warning("WARNINFG messages will be published to the file and stdout"); 

    } catch(LoggerNotAvailableException lex) {
      System.err.println("Log4j logger is not available on this server
    }
  }
  /**
   * Deny messages from the HTTP subsystem of level INFO
   */
  private static class MyFilter extends Filter {
    public int decide(LoggingEvent event) {
      if (event instanceof WLLog4jLogEvent) {
        WLLog4jLogEvent wlsEvent = (WLLog4jLogEvent)event;
        if (wlsEvent.getSubsystem().equals("HTTP")
          && wlsEvent.getSeverity() == Severities.INFO) {
        return DENY;
      }
    }
    return ACCEPT;
  }
 }
}