com.ibm.websphere.logging.hpel

Class LogRecordContext

  • java.lang.Object
    • com.ibm.websphere.logging.hpel.LogRecordContext


  • public class LogRecordContext
    extends java.lang.Object
    Provides a means to add key-value pairs to log and trace records.

    There are two ways to add key-value pairs to the LogRecordContext. The one you should use depends on whether the value is fixed, or variable.

    Fixed value extensions

    When you want to add an extension with a fixed value use the addExtension method. As an example, the following code uses addExtension to register an extension.

     
     Logger myLogger = Logger.getLogger("myLogger");
     LogRecordContext.addExtension("someName", "someValue");
     // This message will have the someName=someValue extension added to it
     logger.info("some message");
     LogRecordContext.removeExtension("someName");
     // This message will not have the extension added to it
     logger.info("some other message");
     
     

    Variable value extensions

    When you want to add an extension with a callback method to compute the extension value use the registerExtension method. As an example, the following code uses registerExtension to add an extension that provides the ThreadId of the current thread.

    
     import com.ibm.websphere.logging.hpel.LogRecordContext;
     
     public class ThreadIdExtension {
     
            // a strong reference to the LogRecordContext.Extension to make
            // sure it is not garbage collected
            private final static LogRecordContext.Extension extension = new LogRecordContext.Extension() {
                    public String getValue() {
                            return Long.toString(Thread.currentThread().getId());
                    }
            };
            
            public static void init() {
                    LogRecordContext.registerExtension("ThreadId", extension);
            }
            
            public static void destroy() {
                    LogRecordContext.unregisterExtension("ThreadId");
            }
            
     }
     
     

    Using the extensions

    Log handlers can use the key-value pairs in log and trace output by calling the getExtensions(Map) method. The getExtensions method first calls the getValue method for each LogRecordContext.Extension, adding the resultant key-value pairs to the Map. getExtensions then copies the fixed key-value pairs into the Map. An example log handler could be written as follows:

     import java.io.PrintWriter;
     import java.util.HashMap;
     import java.util.Map;
     import java.util.logging.Handler;
     import java.util.logging.LogRecord;
     
     import com.ibm.websphere.logging.hpel.LogRecordContext;
     
     public class MyHandler extends Handler {
     
            private PrintWriter printWriter;
            
            MyHandler(PrintWriter printWriter) {
                    this.printWriter = printWriter; 
            }
            
            public void close() { printWriter.close(); }
            public void flush() { printWriter.flush(); }
            
            public void publish(LogRecord record) {
                    Map context = new HashMap();
                    
                    // get the extension keys/values
                    LogRecordContext.getExtensions(context);
                    
                    String threadId = context.get("ThreadId");
                    printWriter.println("[" + threadId + "] " + record.getMessage());
            }
     
     }
     
    Note that the HPEL handlers call LogRecordContext.getExtensions and store the resultant key-value pairs in the log and trace data repositories. This information can then be accessed via the com.ibm.websphere.logging.hpel.reader.RepositoryLogRecord getExtensions method. Extension information can also be used for filtering log and trace records via the LogViewer command line tool's -includeExtensions option.
    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class and Description
      static interface  LogRecordContext.Extension
      Call back interface to retrieve current extension value.
    • Constructor Summary

      Constructors 
      Constructor and Description
      LogRecordContext() 
    • Method Summary

      Methods 
      Modifier and Type Method and Description
      static void addExtension(java.lang.String extensionName, java.lang.String extensionValue)
      Adds an extension key/value to the context.
      static void getExtensions(java.util.Map<java.lang.String,java.lang.String> map)
      Retrieves values for all registered context extensions.
      static void registerExtension(java.lang.String key, LogRecordContext.Extension extension)
      Registers new context extension.
      static boolean removeExtension(java.lang.String extensionName)
      Removes an extension key/value from the context
      static boolean unregisterExtension(java.lang.String key)
      Removes context extension registration.
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    • Constructor Detail

      • LogRecordContext

        public LogRecordContext()
    • Method Detail

      • addExtension

        public static void addExtension(java.lang.String extensionName,
                        java.lang.String extensionValue)
        Adds an extension key/value to the context.
        Parameters:
        extensionName - String extensionName key name for the new extension
        extensionValue - String extensionValue key value for the new extension
        Throws:
        java.lang.IllegalArgumentException - if parameter extensionName or extensionValue are null
      • removeExtension

        public static boolean removeExtension(java.lang.String extensionName)
        Removes an extension key/value from the context
        Parameters:
        extensionName - String extensionName associated with the registered extension.
        Throws:
        java.lang.IllegalArgumentException - if parameter extensionName is null.
      • registerExtension

        public static void registerExtension(java.lang.String key,
                             LogRecordContext.Extension extension)
        Registers new context extension. To avoid memory leaks Extensions are stored as weak references. It means that caller need to keep strong reference (a static field for example) to keep that extension in the registration map.
        Parameters:
        key - String key to associate with the registered extension
        extension - LogRecordContext.Extension implementation returning extension runtime values
        Throws:
        java.lang.IllegalArgumentException - if parameter key or extension are null; or if key already has extension associated with it.
      • unregisterExtension

        public static boolean unregisterExtension(java.lang.String key)
        Removes context extension registration.
        Parameters:
        key - String key associated with the registered extension.
        Returns:
        true if key had extension associated with it.
        Throws:
        java.lang.IllegalArgumentException - if parameter key is null.
      • getExtensions

        public static void getExtensions(java.util.Map<java.lang.String,java.lang.String> map)
                                  throws java.lang.IllegalArgumentException
        Retrieves values for all registered context extensions.
        Parameters:
        map - Map instance to populate with key-value pairs of the context extensions.
        Throws:
        java.lang.IllegalArgumentException - if parameter map is null
IBM WebSphere Application ServerTM
Release 9.0