StreamHandler (Java SE 15 & JDK 15)
Description: declaration: module: java.logging, package: java.util.logging, class: StreamHandler
Keywords: java.util.logging.StreamHandler class

Module java.logging
Package java.util.logging

# Class StreamHandler

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

Direct Known Subclasses:
  `ConsoleHandler`, `FileHandler`, `SocketHandler`

    public class StreamHandler
    extends Handler

Stream based logging `Handler`.

This is primarily intended as a base class or support class to be used in implementing other logging `Handlers`.

`LogRecords` are published to a given `java.io.OutputStream`.

Configuration: By default each `StreamHandler` is initialized using the following `LogManager` configuration properties where `<handler-name>` refers to the fully-qualified class name of the handler. If properties are not defined (or have invalid values) then the specified default values are used.

- <handler-name>.level specifies the default level for the `Handler` (defaults to `Level.INFO`).
- <handler-name>.filter specifies the name of a `Filter` class to use (defaults to no `Filter`).
- <handler-name>.formatter specifies the name of a `Formatter` class to use (defaults to `java.util.logging.SimpleFormatter`).
- <handler-name>.encoding the name of the character set encoding to use (defaults to the default platform encoding).

For example, the properties for `StreamHandler` would be:

- java.util.logging.StreamHandler.level=INFO
- java.util.logging.StreamHandler.formatter=java.util.logging.SimpleFormatter

For a custom handler, e.g. com.foo.MyHandler, the properties would be:

- com.foo.MyHandler.level=INFO
- com.foo.MyHandler.formatter=java.util.logging.SimpleFormatter

Since:
  1.4

- ## Constructor Summary

  Constructors
  Constructor | Description
  --- | ---
  `StreamHandler()` | Create a `StreamHandler`, with no current output stream.
  `StreamHandler​(OutputStream out, Formatter formatter)` | Create a `StreamHandler` with a given `Formatter` and output stream.

- ## Method Summary

  Modifier and Type | Method | Description
  --- | --- | ---
  `void` | `close()` | Close the current output stream.
  `void` | `flush()` | Flush any buffered messages.
  `boolean` | `isLoggable​(LogRecord record)` | Check if this `Handler` would actually log a given `LogRecord`.
  `void` | `publish​(LogRecord record)` | Format and publish a `LogRecord`.
  `void` | `setEncoding​(String encoding)` | Set (or change) the character encoding used by this `Handler`.
  `protected void` | `setOutputStream​(OutputStream out)` | Change the output stream.

  ### Methods declared in class java.util.logging.Handler

  `getEncoding, getErrorManager, getFilter, getFormatter, getLevel, reportError, setErrorManager, setFilter, setFormatter, setLevel`

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

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

- ## Constructor Details

  - ### StreamHandler

    public StreamHandler()
    Create a `StreamHandler`, with no current output stream.

  - ### StreamHandler

    public StreamHandler​(OutputStream out, Formatter formatter)
    Create a `StreamHandler` with a given `Formatter` and output stream.
    Parameters:
      `out` - the target output stream
      `formatter` - Formatter to be used to format output

- ## Method Details

  - ### setOutputStream

    protected void setOutputStream​(OutputStream out) throws SecurityException
    Change the output stream.

    If there is a current output stream then the `Formatter`'s tail string is written and the stream is flushed and closed. Then the output stream is replaced with the new output stream.

    Parameters:
      `out` - New output stream. May not be null.
    Throws:
      `SecurityException` - if a security manager exists and if the caller does not have `LoggingPermission("control")`.

  - ### setEncoding

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

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

    Overrides:
      `setEncoding` in class `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.

  - ### publish

    public void publish​(LogRecord record)
    Format and publish a `LogRecord`.

    The `StreamHandler` first checks if there is an `OutputStream` and if the given `LogRecord` has at least the required log level. If not it silently returns. If so, it calls any associated `Filter` to check if the record should be published. If so, it calls its `Formatter` to format the record and then writes the result to the current output stream.

    If this is the first `LogRecord` to be written to a given `OutputStream`, the `Formatter`'s "head" string is written to the stream before the `LogRecord` is written.

    Specified by:
      `publish` in class `Handler`
    Parameters:
      `record` - description of the log event. A null record is silently ignored and is not published

  - ### 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 will also return false if no output stream has been assigned yet or the LogRecord is null.

    Overrides:
      `isLoggable` in class `Handler`
    Parameters:
      `record` - a `LogRecord` (may be null).
    Returns:
      true if the `LogRecord` would be logged.

  - ### flush

    public void flush()
    Flush any buffered messages.
    Specified by:
      `flush` in class `Handler`

  - ### close

    public void close() throws SecurityException
    Close the current output stream.

    The `Formatter`'s "tail" string is written to the stream before it is closed. In addition, if the `Formatter`'s "head" string has not yet been written to the stream, it will be written before the "tail" string.

    Specified by:
      `close` in class `Handler`
    Throws:
      `SecurityException` - if a security manager exists and if the caller does not have LoggingPermission("control").