Java tutorial
/* * Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.util.logging; /** * {@code Handler} that buffers requests in a circular buffer in memory. * <p> * Normally this {@code Handler} simply stores incoming {@code LogRecords} * into its memory buffer and discards earlier records. This buffering * is very cheap and avoids formatting costs. On certain trigger * conditions, the {@code MemoryHandler} will push out its current buffer * contents to a target {@code Handler}, which will typically publish * them to the outside world. * <p> * There are three main models for triggering a push of the buffer: * <ul> * <li> * An incoming {@code LogRecord} has a type that is greater than * a pre-defined level, the {@code pushLevel}. </li> * <li> * An external class calls the {@code push} method explicitly. </li> * <li> * A subclass overrides the {@code log} method and scans each incoming * {@code LogRecord} and calls {@code push} if a record matches some * desired criteria. </li> * </ul> * <p> * <b>Configuration:</b> * By default each {@code MemoryHandler} is initialized using the following * {@code LogManager} configuration properties where {@code <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. * If no default value is defined then a RuntimeException is thrown. * <ul> * <li> <handler-name>.level * specifies the level for the {@code Handler} * (defaults to {@code Level.ALL}). </li> * <li> <handler-name>.filter * specifies the name of a {@code Filter} class to use * (defaults to no {@code Filter}). </li> * <li> <handler-name>.size * defines the buffer size (defaults to 1000). </li> * <li> <handler-name>.push * defines the {@code pushLevel} (defaults to {@code level.SEVERE}). </li> * <li> <handler-name>.target * specifies the name of the target {@code Handler } class. * (no default). </li> * </ul> * <p> * For example, the properties for {@code MemoryHandler} would be: * <ul> * <li> java.util.logging.MemoryHandler.level=INFO </li> * <li> java.util.logging.MemoryHandler.formatter=java.util.logging.SimpleFormatter </li> * </ul> * <p> * For a custom handler, e.g. com.foo.MyHandler, the properties would be: * <ul> * <li> com.foo.MyHandler.level=INFO </li> * <li> com.foo.MyHandler.formatter=java.util.logging.SimpleFormatter </li> * </ul> * * @since 1.4 */ public class MemoryHandler extends Handler { private final static int DEFAULT_SIZE = 1000; private volatile Level pushLevel; private int size; private Handler target; private LogRecord buffer[]; int start, count; /** * Create a {@code MemoryHandler} and configure it based on * {@code LogManager} configuration properties. */ public MemoryHandler() { // configure with specific defaults for MemoryHandler super(Level.ALL, new SimpleFormatter(), null); LogManager manager = LogManager.getLogManager(); String cname = getClass().getName(); pushLevel = manager.getLevelProperty(cname + ".push", Level.SEVERE); size = manager.getIntProperty(cname + ".size", DEFAULT_SIZE); if (size <= 0) { size = DEFAULT_SIZE; } String targetName = manager.getProperty(cname + ".target"); if (targetName == null) { throw new RuntimeException("The handler " + cname + " does not specify a target"); } Class<?> clz; try { clz = ClassLoader.getSystemClassLoader().loadClass(targetName); @SuppressWarnings("deprecation") Object o = clz.newInstance(); target = (Handler) o; } catch (ClassNotFoundException | InstantiationException | IllegalAccessException e) { throw new RuntimeException("MemoryHandler can't load handler target \"" + targetName + "\"", e); } init(); } // Initialize. Size is a count of LogRecords. private void init() { buffer = new LogRecord[size]; start = 0; count = 0; } /** * Create a {@code MemoryHandler}. * <p> * The {@code MemoryHandler} is configured based on {@code LogManager} * properties (or their default values) except that the given {@code pushLevel} * argument and buffer size argument are used. * * @param target the Handler to which to publish output. * @param size the number of log records to buffer (must be greater than zero) * @param pushLevel message level to push on * * @throws IllegalArgumentException if {@code size is <= 0} */ public MemoryHandler(Handler target, int size, Level pushLevel) { // configure with specific defaults for MemoryHandler super(Level.ALL, new SimpleFormatter(), null); if (target == null || pushLevel == null) { throw new NullPointerException(); } if (size <= 0) { throw new IllegalArgumentException(); } this.target = target; this.pushLevel = pushLevel; this.size = size; init(); } /** * Store a {@code LogRecord} in an internal buffer. * <p> * If there is a {@code Filter}, its {@code isLoggable} * method is called to check if the given log record is loggable. * If not we return. Otherwise the given record is copied into * an internal circular buffer. Then the record's level property is * compared with the {@code pushLevel}. If the given level is * greater than or equal to the {@code pushLevel} then {@code push} * is called to write all buffered records to the target output * {@code Handler}. * * @param record description of the log event. A null record is * silently ignored and is not published */ @Override public synchronized void publish(LogRecord record) { if (!isLoggable(record)) { return; } int ix = (start + count) % buffer.length; buffer[ix] = record; if (count < buffer.length) { count++; } else { start++; start %= buffer.length; } if (record.getLevel().intValue() >= pushLevel.intValue()) { push(); } } /** * Push any buffered output to the target {@code Handler}. * <p> * The buffer is then cleared. */ public synchronized void push() { for (int i = 0; i < count; i++) { int ix = (start + i) % buffer.length; LogRecord record = buffer[ix]; target.publish(record); } // Empty the buffer. start = 0; count = 0; } /** * Causes a flush on the target {@code Handler}. * <p> * Note that the current contents of the {@code MemoryHandler} * buffer are <b>not</b> written out. That requires a "push". */ @Override public void flush() { target.flush(); } /** * Close the {@code Handler} and free all associated resources. * This will also close the target {@code Handler}. * * @exception SecurityException if a security manager exists and if * the caller does not have {@code LoggingPermission("control")}. */ @Override public void close() throws SecurityException { target.close(); setLevel(Level.OFF); } /** * Set the {@code pushLevel}. After a {@code LogRecord} is copied * into our internal buffer, if its level is greater than or equal to * the {@code pushLevel}, then {@code push} will be called. * * @param newLevel the new value of the {@code pushLevel} * @exception SecurityException if a security manager exists and if * the caller does not have {@code LoggingPermission("control")}. */ public synchronized void setPushLevel(Level newLevel) throws SecurityException { if (newLevel == null) { throw new NullPointerException(); } checkPermission(); pushLevel = newLevel; } /** * Get the {@code pushLevel}. * * @return the value of the {@code pushLevel} */ public Level getPushLevel() { return pushLevel; } /** * Check if this {@code Handler} would actually log a given * {@code LogRecord} into its internal buffer. * <p> * This method checks if the {@code LogRecord} has an appropriate level and * whether it satisfies any {@code Filter}. However it does <b>not</b> * check whether the {@code LogRecord} would result in a "push" of the * buffer contents. It will return false if the {@code LogRecord} is null. * * @param record a {@code LogRecord} (may be null). * @return true if the {@code LogRecord} would be logged. * */ @Override public boolean isLoggable(LogRecord record) { return super.isLoggable(record); } }