* Normally this Handler simply stores incoming LogRecords * into its memory buffer and discards earlier records. This buffering * is very cheap and avoids formatting costs. On certain trigger * conditions, the MemoryHandler will push out its current buffer * contents to a target Handler, which will typically publish * them to the outside world. *
* There are three main models for triggering a push of the buffer: *
* Configuration: * By default each MemoryHandler 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. * If no default value is defined then a RuntimeException is thrown. *
* For example, the properties for {@code MemoryHandler} would be: *
* For a custom handler, e.g. com.foo.MyHandler, the properties would be: *
* @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; // Private method to configure a MemoryHandler from LogManager // properties and/or default values as specified in the class // javadoc. private void configure() { 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; } setLevel(manager.getLevelProperty(cname +".level", Level.ALL)); setFilter(manager.getFilterProperty(cname +".filter", null)); setFormatter(manager.getFormatterProperty(cname +".formatter", new SimpleFormatter())); } /** * Create a MemoryHandler and configure it based on * LogManager configuration properties. */ public MemoryHandler() { doWithControlPermission(this::configure); LogManager manager = LogManager.getLogManager(); String handlerName = getClass().getName(); String targetName = manager.getProperty(handlerName+".target"); if (targetName == null) { throw new RuntimeException("The handler " + handlerName + " does not specify a target"); } Class clz; try { clz = ClassLoader.getSystemClassLoader().loadClass(targetName); target = (Handler) clz.newInstance(); } 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 MemoryHandler. *
* The MemoryHandler is configured based on LogManager * properties (or their default values) except that the given 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) { if (target == null || pushLevel == null) { throw new NullPointerException(); } if (size <= 0) { throw new IllegalArgumentException(); } doWithControlPermission(this::configure); this.target = target; this.pushLevel = pushLevel; this.size = size; init(); } /** * Store a LogRecord in an internal buffer. *
* If there is a Filter, its 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 pushLevel. If the given level is * greater than or equal to the pushLevel then push * is called to write all buffered records to the target output * 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 Handler. *
* 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 Handler. *
* Note that the current contents of the MemoryHandler * buffer are not written out. That requires a "push". */ @Override public void flush() { target.flush(); } /** * Close the Handler and free all associated resources. * This will also close the target Handler. * * @exception SecurityException if a security manager exists and if * the caller does not have LoggingPermission("control"). */ @Override public void close() throws SecurityException { target.close(); setLevel(Level.OFF); } /** * Set the pushLevel. After a LogRecord is copied * into our internal buffer, if its level is greater than or equal to * the pushLevel, then push will be called. * * @param newLevel the new value of the pushLevel * @exception SecurityException if a security manager exists and if * the caller does not have LoggingPermission("control"). */ public synchronized void setPushLevel(Level newLevel) throws SecurityException { if (newLevel == null) { throw new NullPointerException(); } checkPermission(); pushLevel = newLevel; } /** * Get the pushLevel. * * @return the value of the pushLevel */ public Level getPushLevel() { return pushLevel; } /** * Check if this Handler would actually log a given * LogRecord into its internal buffer. *
* This method checks if the LogRecord has an appropriate level and * whether it satisfies any Filter. However it does not * check whether the LogRecord would result in a "push" of the * buffer contents. It will return false if the LogRecord is null. *
* @param record a LogRecord * @return true if the LogRecord would be logged. * */ @Override public boolean isLoggable(LogRecord record) { return super.isLoggable(record); } }