The java.util.logging package defines a sophisticated and highly-configurable logging facility that Java applications can use to emit, filter, format, and output warning, diagnostic, tracing and debugging messages. An application generates log messages by calling various methods of a Logger object. The content of a log message (with other pertinant details such as the time and sequence number) is encapsulated in a LogRecord object generated by the Logger. A Handler object represents a destination for LogRecord objects. Concrete subclasses of Handler support destinations such as files and sockets. Most Handler objects have an associated Formatter that converts a LogRecord object into the actual text that is logged. The subclasses SimpleFormatter and XMLFormatter produce simple plain-text log messages and detailed XML logs respectively.

Each log message has an associated severity level. The Level class defines a type-safe enumeration of defined levels. Logger and Handler objects both have an associated Level, and discard any log messages whose severity is less than that specified level. In addition to this level-based filtering, Logger and Handler objects may also have an associated Filter object which may be implemented to filter log messages based on any desired criteria.

Applications that desire complete control over the logs they generate can create a Logger object, along with Handler, Formatter and Filter objects that control the destination, content, and appearance of the log. Simpler applications need only to create a Logger for themselves, and can leave the rest to the LogManager class. LogManager reads a system-wide configuration file (or a configuration class) and automatically directs log messages to a standard destination (or destinations) for the system. In Java 5.0, LoggingMXBean defines an interface for monitoring and management of the logging facility through the javax.management packages (which are beyond the scope of this book).

Interfaces

public interface Filter;
public interface LoggingMXBean;

Classes

public class ErrorManager;
public abstract class Formatter;
   public class SimpleFormatter extends Formatter;
   public class XMLFormatter extends Formatter;
public abstract class Handler;
   public class MemoryHandler extends Handler;
   public class StreamHandler extends Handler;
      public class ConsoleHandler extends StreamHandler;
      public class FileHandler extends StreamHandler;
      public class SocketHandler extends StreamHandler;
public class Level implements Serializable;
public class Logger;
public final class LoggingPermission extends java.security.BasicPermission;
public class LogManager;
public class LogRecord implements Serializable;