Handler (Java SE 21 & JDK 21)
Description: declaration: module: java.logging, package: java.util.logging, class: Handler
Keywords: java.util.logging.Handler class

Module java.logging
Package java.util.logging

# Class Handler

java.lang.Object
java.util.logging.Handler

Direct Known Subclasses:
  `MemoryHandler`, `StreamHandler`

public abstract class Handler extends Object
A `Handler` object takes log messages from a `Logger` and exports them. It might for example, write them to a console or write them to a file, or send them to a network logging service, or forward them to an OS log, or whatever.

A `Handler` can be disabled by doing a `setLevel(Level.OFF)` and can be re-enabled by doing a `setLevel` with an appropriate level.

`Handler` classes typically use `LogManager` properties to set default values for the `Handler`'s `Filter`, `Formatter`, and `Level`. See the specific documentation for each concrete `Handler` class.

Since:
  1.4

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `Handler()`
  Default constructor.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `abstract void`
  `close()`
  Close the `Handler` and free all associated resources.
  `abstract void`
  `flush()`
  Flush any buffered output.
  `String`
  `getEncoding()`
  Return the character encoding for this `Handler`.
  `ErrorManager`
  `getErrorManager()`
  Retrieves the ErrorManager for this Handler.
  `Filter`
  `getFilter()`
  Get the current `Filter` for this `Handler`.
  `Formatter`
  `getFormatter()`
  Return the `Formatter` for this `Handler`.
  `Level`
  `getLevel()`
  Get the log level specifying which messages will be logged by this `Handler`.
  `boolean`
  `isLoggable(LogRecord record)`
  Check if this `Handler` would actually log a given `LogRecord`.
  `abstract void`
  `publish(LogRecord record)`
  Publish a `LogRecord`.
  `protected void`
  `reportError(String msg, Exception ex, int code)`
  Protected convenience method to report an error to this Handler's ErrorManager.
  `void`
  `setEncoding(String encoding)`
  Set the character encoding used by this `Handler`.
  `void`
  `setErrorManager(ErrorManager em)`
  Define an ErrorManager for this Handler.
  `void`
  `setFilter(Filter newFilter)`
  Set a `Filter` to control output on this `Handler`.
  `void`
  `setFormatter(Formatter newFormatter)`
  Set a `Formatter`.
  `void`
  `setLevel(Level newLevel)`
  Set the log level specifying which message levels will be logged by this `Handler`.

  ### Methods declared in class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Constructor Details

  - ### Handler

    protected Handler()
    Default constructor. The resulting `Handler` has a log level of `Level.ALL`, no `Formatter`, and no `Filter`. A default `ErrorManager` instance is installed as the `ErrorManager`.

- ## Method Details

  - ### publish

    public abstract void publish(LogRecord record)
    Publish a `LogRecord`.

    The logging request was made initially to a `Logger` object, which initialized the `LogRecord` and forwarded it here.

    The `Handler` is responsible for formatting the message, when and if necessary. The formatting should include localization.

    Parameters:
      `record` - description of the log event. A null record is silently ignored and is not published

  - ### flush

    public abstract void flush()
    Flush any buffered output.

  - ### close

    public abstract void close() throws SecurityException
    Close the `Handler` and free all associated resources.

    The close method will perform a `flush` and then close the `Handler`. After close has been called this `Handler` should no longer be used. Method calls may either be silently ignored or may throw runtime exceptions.

    Throws:
      `SecurityException` - if a security manager exists and if the caller does not have `LoggingPermission("control")`.

  - ### setFormatter

    public void setFormatter(Formatter newFormatter) throws SecurityException
    Set a `Formatter`. This `Formatter` will be used to format `LogRecords` for this `Handler`.

    Some `Handlers` may not use `Formatters`, in which case the `Formatter` will be remembered, but not used.

    Parameters:
      `newFormatter` - the `Formatter` to use (may not be null)
    Throws:
      `SecurityException` - if a security manager exists and if the caller does not have `LoggingPermission("control")`.

  - ### getFormatter

    public Formatter getFormatter()
    Return the `Formatter` for this `Handler`.
    Returns:
      the `Formatter` (may be null).

  - ### setEncoding

    public void setEncoding(String encoding) throws SecurityException, UnsupportedEncodingException
    Set the character encoding used by this `Handler`.

    The encoding should be set before any `LogRecords` are written to the `Handler`.

    Parameters:
      `encoding` - The name of a supported character encoding. May be null, to indicate the default platform encoding.
    Throws:
      `SecurityException` - if a security manager exists and if the caller does not have `LoggingPermission("control")`.
      `UnsupportedEncodingException` - if the named encoding is not supported.

  - ### getEncoding

    public String getEncoding()
    Return the character encoding for this `Handler`.
    Returns:
      The encoding name. May be null, which indicates the default encoding should be used.

  - ### setFilter

    public void setFilter(Filter newFilter) throws SecurityException
    Set a `Filter` to control output on this `Handler`.

    For each call of `publish` the `Handler` will call this `Filter` (if it is non-null) to check if the `LogRecord` should be published or discarded.

    Parameters:
      `newFilter` - a `Filter` object (may be null)
    Throws:
      `SecurityException` - if a security manager exists and if the caller does not have `LoggingPermission("control")`.

  - ### getFilter

    public Filter getFilter()
    Get the current `Filter` for this `Handler`.
    Returns:
      a `Filter` object (may be null)

  - ### setErrorManager

    public void setErrorManager(ErrorManager em)
    Define an ErrorManager for this Handler.

    The ErrorManager's "error" method will be invoked if any errors occur while using this Handler.

    Parameters:
      `em` - the new ErrorManager
    Throws:
      `SecurityException` - if a security manager exists and if the caller does not have `LoggingPermission("control")`.

  - ### getErrorManager

    public ErrorManager getErrorManager()
    Retrieves the ErrorManager for this Handler.
    Returns:
      the ErrorManager for this Handler
    Throws:
      `SecurityException` - if a security manager exists and if the caller does not have `LoggingPermission("control")`.

  - ### reportError

    protected void reportError(String msg, Exception ex, int code)
    Protected convenience method to report an error to this Handler's ErrorManager. Note that this method retrieves and uses the ErrorManager without doing a security check. It can therefore be used in environments where the caller may be non-privileged.
    Parameters:
      `msg` - a descriptive string (may be null)
      `ex` - an exception (may be null)
      `code` - an error code defined in ErrorManager

  - ### setLevel

    public void setLevel(Level newLevel) throws SecurityException
    Set the log level specifying which message levels will be logged by this `Handler`. Message levels lower than this value will be discarded.

    The intention is to allow developers to turn on voluminous logging, but to limit the messages that are sent to certain `Handlers`.

    Parameters:
      `newLevel` - the new value for the log level
    Throws:
      `SecurityException` - if a security manager exists and if the caller does not have `LoggingPermission("control")`.

  - ### getLevel

    public Level getLevel()
    Get the log level specifying which messages will be logged by this `Handler`. Message levels lower than this level will be discarded.
    Returns:
      the level of messages being logged.

  - ### isLoggable

    public boolean isLoggable(LogRecord record)
    Check if this `Handler` would actually log a given `LogRecord`.

    This method checks if the `LogRecord` has an appropriate `Level` and whether it satisfies any `Filter`. It also may make other `Handler` specific checks that might prevent a handler from logging the `LogRecord`. It will return false if the `LogRecord` is null.

    Parameters:
      `record` - a `LogRecord` (may be null).
    Returns:
      true if the `LogRecord` would be logged.