logback OutputStreamAppender高效日志输出源码解析

目录

• 序
• OutputStreamAppender
• start
• stop
• append
• setOutputStream
• 小结

序

本文主要研究一下logback的OutputStreamAppender

OutputStreamAppender

logback-core/src/main/Java/ch/qos/logback/core/OutputStreamAppender.java

public class OutputStreamAppender<E> extends UnsynchronizedAppenderBase<E> {
    /**
     * It is the encoder which is ultimately responsible for writing the event to an
     * {@link OutputStream}.
     */
    protected Encoder<E> encoder;
    /**
     * All synchronization in this class is done via the lock object.
     */
    protected final ReentrantLock streamWriteLock = new ReentrantLock(false);
    /**
     * This is the {@link OutputStream outputStream} where output will be written.
     */
    private OutputStream outputStream;
    boolean immediateFlush = true;
    //......
}

OutputStreamAppender继承了UnsynchronizedAppenderBase，它定义了encoder、streamWriteLock、outputStream、immediateFlush属性

start

/**
     * Checks that requires parameters are set and if everything is in order,
     * activates this appender.
     */
    public void start() {
        int errors = 0;
        if (this.encoder == null) {
            addStatus(new ErrorStatus("No encoder set for the appender named \"" + name + "\".", this));
            errors++;
        }
        if (this.outputStream == null) {
            addStatus(new ErrorStatus("No output stream set for the appender named \"" + name + "\".", this));
            errors++;
        }
        // only error free appenders should be activated
        if (errors == 0) {
            super.start();
        }
编程    }

其start方法主要是校验encoder、outputStream，然后执行super.start()

stop

/**
     * Stop this appender instance. The underlying stream or writer is also closed.
     * 
     * <p>
     * Stopped appenders cannot be reused.
     */
    public void stop() {
        if(!isStarted())
            return;
        streamWriteLock.lock();
        try {
            closeoutputStream();
            super.stop();
        } finally {
            streamWriteLock.unlock();
        }
    }
    protected void closeOutputStream() {
        if (this.outputStream != null) {
            try {
                // before closing we have to output out layout's footer
                encoderClose();
                this.outputStream.close();
                this.outputStream = null;
            } catch (IOException e) {
                addStatus(new ErrorStatus("Could not close output stream for OutputStreamAppender.", this, e));
            }
        }
    }
    void encoderClose() {
        if (encoder != null && this.outputStream != null) {
            try {
                byte[] footer = encoder.footerBytes();
                writeBytes(footer);
            } catch (IOException ioe) {
                this.started = false;
                addhttp://www.devze.comStatus(new ErrorStatus("Failed to write footer for appender named [" + name + "].", this, ioe));
            }
        }
    }

其stop方法主要是加锁然后closeOutputStream，再执行super.stop；closeOutputStream主要是先写入encoder.footerBytes()，再关闭outputStream

append

protected void append(E eventObject) {
        if (!isStarted()) {
            return;
        }
        subAppend(eventObject);
    }
    protected void subAppend(E event) {
        if (!isStarted()) {
            return;
        }
        try {
            // this step avoids LBCLASSIC-139
            if (event instanceof DeferredProcessingAware) {
                ((DeferredProcessingAware) event).prepareForDeferredProcessing();
            }
            writeOut(event);
        } catch (IOException ioe) {
 编程客栈           // as soon as an exception occurs, move to non-started state
            // and add a single ErrorStatus to the SM.
            this.started = false;
            addStatus(new ErrorStatus("IO failure in appender", this, ioe));
        }
    }    
    protected void writeOut(E event) throws IOException {
        byte[] byteArray = this.encoder.encode(event);
        writeBytes(byteArray);
    }
    private void writeBytes(byte[] byteArray) throws IOException {
        if (byteArray == null || byteArray.length == 0)
            return;
        streamWriteLock.lock();
        try {
            writeByteArrayToOutputStreamWithPossibleFlush(byteArray);
        } finally {
            streamWriteLock.unlock();
        }
    }
    /**
     * A simple method to write to an outputStream and flush the stream if immediateFlush is set to true.
     *
     * @since 1.3.9/1.4.9
     */
    protected final void writeByteArrayToOutputStreamWithPossibleFlush(byte[] byteArray) throws IOException {
        this.outputStream.write(byteArray);
        if (immediateFlush) {
            this.outputStream.flush();
        }
    }

append方法主要是执行writeOut操作，如果是DeferredProcessingAware类型，会先执行prepareForDeferredProcessing；writeOut先执行encoder的encode，然后加锁执行outputStream.write(byteAhttp://www.devze.comrray)，如果需要immediateFlush则会执行outputStream.flush()

setOutputStream

public void setOutputStream(OutputStream outputStream) {
        streamWriteLock.lock();
        try {
            // close any previously opened output stream
            closeOutputStream();
            this.outputStream = outputStream;
            if (encoder == null) {
                addwarn("Encoder has not been set. Cannot invoke its init method.");
                return;
            }
            encoderInit();
        } finally {
            streamWriteLock.unlock();
        }
    }
    protected void closeOutputStream() {
        if (this.outputStream != null) {
            try {
                // before closing we have to output out layout'sandroid footer
                encoderClose();
                this.outputStream.close();
                this.outputStream = null;
            } catch (IOException e) {
                addStatus(new ErrorStatus("Could not close output stream for OutputStreamAppender.", this, e));
            }
        }
    }    
    void encoderInit() {
        if (encoder != null && this.outputStream != null) {
            try {
                byte[] header = encoder.headerBytes();
                writeBytes(header);
            } catch (IOException ioe) {
                this.started = false;
                addStatus(
                        new ErrorStatus("Failed to initialize encoder for appender named [" + name + "].", this, ioe));
            }
        }
    }

setOutputStream方法会加锁执行closeOutputStream、给outputStream赋值，再执行encoderInit；closeOutputStream主要是为了清空前面遗留的数据，encoderInit则先写入encoder.headerBytes()

小结

logback的OutputStreamAppender主要是通过非公平的ReentrantLock来写入outputStream。

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