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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}
* @return true if the {@code LogRecord} would be logged.
*
*/
@Override
public boolean isLoggable(LogRecord record) {
return super.isLoggable(record);
}
}