* This is primarily intended as a base class or support class to * be used in implementing other logging {@code Handlers}. *
* {@code LogRecords} are published to a given {@code java.io.OutputStream}. *
* Configuration:
* By default each {@code StreamHandler} is initialized using the following
* {@code LogManager} configuration properties where {@code
* For example, the properties for {@code StreamHandler} would be:
*
* For a custom handler, e.g. com.foo.MyHandler, the properties would be:
*
* If there is a current output stream then the {@code Formatter}'s
* tail string is written and the stream is flushed and closed.
* Then the output stream is replaced with the new output stream.
*
* @param out New output stream. May not be null.
*/
protected synchronized void setOutputStream(OutputStream out) {
if (out == null) {
throw new NullPointerException();
}
flushAndClose();
output = out;
doneHeader = false;
String encoding = getEncoding();
if (encoding == null) {
writer = new OutputStreamWriter(output);
} else {
try {
writer = new OutputStreamWriter(output, encoding);
} catch (UnsupportedEncodingException ex) {
// This shouldn't happen. The setEncoding method
// should have validated that the encoding is OK.
throw new Error("Unexpected exception " + ex);
}
}
}
/**
* Set (or change) the character encoding used by this {@code Handler}.
*
* The encoding should be set before any {@code LogRecords} are written
* to the {@code Handler}.
*
* @param encoding The name of a supported character encoding.
* May be null, to indicate the default platform encoding.
* @throws UnsupportedEncodingException if the named encoding is
* not supported.
*/
@Override
public synchronized void setEncoding(String encoding)
throws java.io.UnsupportedEncodingException {
super.setEncoding(encoding);
if (output == null) {
return;
}
// Replace the current writer with a writer for the new encoding.
flush();
if (encoding == null) {
writer = new OutputStreamWriter(output);
} else {
writer = new OutputStreamWriter(output, encoding);
}
}
/**
* Format and publish a {@code LogRecord}.
*
* The {@code StreamHandler} first checks if there is an {@code OutputStream}
* and if the given {@code LogRecord} has at least the required log level.
* If not it silently returns. If so, it calls any associated
* {@code Filter} to check if the record should be published. If so,
* it calls its {@code Formatter} to format the record and then writes
* the result to the current output stream.
*
* If this is the first {@code LogRecord} to be written to a given
* {@code OutputStream}, the {@code Formatter}'s "head" string is
* written to the stream before the {@code LogRecord} is written.
*
* @implSpec This method avoids acquiring locks during {@code LogRecord}
* formatting, but {@code this} instance is synchronized when writing to the
* output stream. To avoid deadlock risk, subclasses must not hold locks
* while calling {@code super.publish()}. Specifically, subclasses must
* not define the overridden {@code publish()} method to be
* {@code synchronized} if they call {@code super.publish()}.
*
* @param record description of the log event. A null record is
* silently ignored and is not published
*/
@Override
public void publish(LogRecord record) {
if (!isLoggable(record)) {
return;
}
// Read once for consistency (whether in or outside the locked region
// is not important).
Formatter formatter = getFormatter();
// JDK-8349206: To avoid deadlock risk, it is essential that the handler
// is not locked while formatting the log record. Methods such as
// reportError() and isLoggable() are defined to be thread safe, so we
// can restrict locking to just writing the message.
String msg;
try {
msg = formatter.format(record);
} catch (Exception ex) {
// We don't want to throw an exception here, but we
// report the exception to any registered ErrorManager.
reportError(null, ex, ErrorManager.FORMAT_FAILURE);
return;
}
try {
synchronized (this) {
// Re-check writer between isLoggable() and here.
Writer writer = this.writer;
if (writer != null) {
if (!doneHeader) {
writer.write(formatter.getHead(this));
doneHeader = true;
}
writer.write(msg);
synchronousPostWriteHook();
}
}
} catch (Exception ex) {
// We don't want to throw an exception here, but we
// report the exception to any registered ErrorManager.
reportError(null, ex, ErrorManager.WRITE_FAILURE);
}
}
/**
* Overridden by other handlers in this package to facilitate synchronous
* post-write behaviour. If other handlers need similar functionality, it
* might be feasible to make this method protected (see JDK-8349206), but
* please find a better name if you do ;).
*/
void synchronousPostWriteHook() {
// Empty by default. We could do:
// assert Thread.holdsLock(this);
// but this is already covered by unit tests.
}
/**
* Check if this {@code Handler} would actually log a given {@code LogRecord}.
*
* This method checks if the {@code LogRecord} has an appropriate level and
* whether it satisfies any {@code Filter}. It will also return false if
* no output stream has been assigned yet or the 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) {
if (writer == null || record == null) {
return false;
}
return super.isLoggable(record);
}
/**
* Flush any buffered messages.
*/
@Override
public synchronized void flush() {
Writer writer = this.writer;
if (writer != null) {
try {
writer.flush();
} catch (Exception ex) {
// We don't want to throw an exception here, but we
// report the exception to any registered ErrorManager.
reportError(null, ex, ErrorManager.FLUSH_FAILURE);
}
}
}
// Called synchronously with "this" handler instance locked.
private void flushAndClose() {
Writer writer = this.writer;
if (writer != null) {
Formatter formatter = getFormatter();
try {
if (!doneHeader) {
writer.write(formatter.getHead(this));
doneHeader = true;
}
writer.write(formatter.getTail(this));
writer.flush();
writer.close();
} catch (Exception ex) {
// We don't want to throw an exception here, but we
// report the exception to any registered ErrorManager.
reportError(null, ex, ErrorManager.CLOSE_FAILURE);
}
output = null;
this.writer = null;
}
}
/**
* Close the current output stream.
*
* The {@code Formatter}'s "tail" string is written to the stream before it
* is closed. In addition, if the {@code Formatter}'s "head" string has not
* yet been written to the stream, it will be written before the
* "tail" string.
*/
@Override
public synchronized void close() {
flushAndClose();
}
}
*
*
*
*
*
*
* @since 1.4
*/
public class StreamHandler extends Handler {
private OutputStream output;
private boolean doneHeader;
private volatile Writer writer;
/**
* Create a {@code StreamHandler}, with no current output stream.
*/
public StreamHandler() {
// configure with specific defaults for StreamHandler
super(Level.INFO, new SimpleFormatter(), null);
}
/**
* Create a {@code StreamHandler} with a given {@code Formatter}
* and output stream.
*
* @param out the target output stream
* @param formatter Formatter to be used to format output
*/
public StreamHandler(OutputStream out, Formatter formatter) {
// configure with default level but use specified formatter
super(Level.INFO, null, Objects.requireNonNull(formatter));
setOutputStream(out);
}
/**
* @see Handler#Handler(Level, Formatter, Formatter)
*/
StreamHandler(Level defaultLevel,
Formatter defaultFormatter,
Formatter specifiedFormatter) {
super(defaultLevel, defaultFormatter, specifiedFormatter);
}
/**
* Change the output stream.
*