logback源码阅读-Appender

天下之事常成于困约，而败于奢靡。这篇文章主要讲述logback源码阅读-Appender相关的知识，希望能为你提供帮助。
前面我们看到最终logger输出是委托给了appender 如果没有配置appender是不会输出的
示例配置

< ?xml version="1.0" encoding="UTF-8"?> < configuration> < property name="CHARSET" value="https://www.songbingjia.com/android/UTF-8"/> < !--为了防止进程退出时，内存中的数据丢失，请加上此选项--> < shutdownHook class="ch.qos.logback.core.hook.DelayingShutdownHook"/> < appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender"> < Encoder> < pattern> < pattern> |%p|%d{yyyy-MM-dd HH:mm:ss.SSS}|%t|%logger{10}:%line%n%m%n%n< /pattern> < /pattern> < charset> ${CHARSET}< /charset> < /Encoder> < /appender> < appender name="ASYNC_STDOUT" class="ch.qos.logback.classic.AsyncAppender"> < filter class="ch.qos.logback.classic.filter.ThresholdFilter"> < level> info< /level> < /filter> < appender-ref ref="STDOUT"/> < !--最终异步委托给consoleAppender--> < includeCallerData> true< /includeCallerData> < /appender> < !--给root关联appender 默认我们所有logger都没有appender 前面看到是递归网上找父类输出都是父类统一输出--> < root level="info"> < appender-ref ref="ASYNC_STDOUT"/> < /root> < /configuration>

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默认的appender实现我们可以根据需求选择以下默认的实现如果没有合适的需要扩展再参考下面的相关类扩展

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下面我们举例看其中一个如果我们有定制化需求可以参考实现定制
AsyncAppender 类图

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我们需要自定义appender只需要继承UnsynchronizedAppenderBase就行了
startch.qos.logback.core.AsyncAppenderBase#start
调用时机在解析标签处分别调用start 和end

private AsyncAppenderBase< E> .Worker worker = new AsyncAppenderBase.Worker();

/** * 启动worker */ public void start() { //防止重复启用 if (!this.isStarted()) { //AsyncAppenderBase.AppenderAttachableImpl的数量如果美而有保存 if (this.appenderCount == 0) { this.addError("No attached appenders found."); } else if (this.queueSize < 1) { this.addError("Invalid queue size [" + this.queueSize + "]"); } else { //初始化一个线程安全的数组阻塞队列 ququeSize默认为256 this.blockingQueue = new ArrayBlockingQueue(this.queueSize); if (this.discardingThreshold == -1) { this.discardingThreshold = this.queueSize / 5; }this.addInfo("Setting discardingThreshold to " + this.discardingThreshold); this.worker.setDaemon(true); this.worker.setName("AsyncAppender-Worker-" + this.getName()); //重写了父类的start 所以保证不破坏父类逻辑所以调用父类start super.start(); //< 1> 启动一个worker AsyncAppenderBase< E> .Worker worker = new AsyncAppenderBase.Worker(); 内部类消费队列数据委托给当前类的 AppenderAttachableImpl< E> aai = new AppenderAttachableImpl(); this.worker.start(); //这里是调用线程的start } } }

start调用点在解析完append end标签之后后面会讲
ch.qos.logback.core.joran.action.AppenderAction#end

public void end(InterpretationContext ec, String name) { if (!this.inError) { //如果实现了LifeCycle 接口则调用start方法 if (this.appender instanceof LifeCycle) { this.appender.start(); }Object o = ec.peekObject(); if (o != this.appender) { this.addWarn("The object at the of the stack is not the appender named [" + this.appender.getName() + "] pushed earlier."); } else { ec.popObject(); }} }

< 1>

class Worker extends Thread { Worker() { }public void run() { AsyncAppenderBase< E> parent = AsyncAppenderBase.this; AppenderAttachableImpl aai = parent.aai; //判断主类对象是否started while (parent.isStarted()) { try { //循环消费 E e = parent.blockingQueue.take(); //< 3> 这里是委托给前面 < appender-ref ref="STDOUT"/> 配置最终还是Console 这里我们可以配置的appender 上面用例配置的STDOUT aai.appendLoopOnAppenders(e); } catch (InterruptedException var5) { break; } } AsyncAppenderBase.this.addInfo("Worker thread will flush remaining events before exiting. "); //以下是当started关闭不接受消息但是还是要消费完 Iterator i$ = parent.blockingQueue.iterator(); while (i$.hasNext()) { E ex = i$.next(); aai.appendLoopOnAppenders(ex); parent.blockingQueue.remove(ex); } //相关委托的appender started也标识为false aai.detachAndStopAllAppenders(); } }

可以看到aynycAppender最终没有做实际的事情最终还是委托给了 AppenderAttachableImpl 对应上面配置内部封装的就是ConsoleAppender
AppenderAttachableImpl < 3> appendLoopOnAppendersch.qos.logback.core.spi.AppenderAttachableImpl#appendLoopOnAppenders

public int appendLoopOnAppenders(E e) { int size = 0; //获得容器内的所有appender Appender< E> [] appenderArray = (Appender[])this.appenderList.asTypedArray(); int len = appenderArray.length; for(int i = 0; i < len; ++i) { //< 4> 逐个调用doAppend appenderArray[i].doAppend(e); ++size; }return size; }

UnsynchronizedAppenderBase < 4> doAppendch.qos.logback.core.spi.AppenderAttachableImpl#appendLoopOnAppenders
->
ch.qos.logback.core.UnsynchronizedAppenderBase#doAppend

private ThreadLocal< Boolean> guard = new ThreadLocal(); public void doAppend(E eventObject) { //防止一个线程同时进入多个吧。。。 if (!Boolean.TRUE.equals(this.guard.get())) { try { this.guard.set(Boolean.TRUE); //必须为started状态 if (this.started) { //appender的过滤器参考ThresholdFilter 实现可以对消息搜集做过滤 if (this.getFilterChainDecision(eventObject) == FilterReply.DENY) { return; } //< 5> 模板模式化由子类实现 this.append(eventObject); return; }if (this.statusRepeatCount++ < 3) { this.addStatus(new WarnStatus("Attempted to append to non started appender [" + this.name + "].", this)); } } catch (Exception var6) { if (this.exceptionCount++ < 3) { this.addError("Appender [" + this.name + "] failed to append.", var6); }return; } finally { this.guard.set(Boolean.FALSE); }} }protected abstract void append(E var1);

OutputStreamAppender < 5> appendch.qos.logback.core.spi.AppenderAttachableImpl#appendLoopOnAppenders
->
ch.qos.logback.core.UnsynchronizedAppenderBase#doAppend
->
ch.qos.logback.core.OutputStreamAppender#append

protected void append(E eventObject) { if (this.isStarted()) { this.subAppend(eventObject); } }

ch.qos.logback.core.OutputStreamAppender#subAppend

protected void subAppend(E event) { if (this.isStarted()) { try { if (event instanceof DeferredProcessingAware) { ((DeferredProcessingAware)event).prepareForDeferredProcessing(); }
//encoder具体查看https://www.cnblogs.com/LQBlog/p/12164918.html#autoid-2-0-0 byte[] byteArray = this.encoder.encode(event); this.writeBytes(byteArray); } catch (IOException var3) { this.started = false; this.addStatus(new ErrorStatus("IO failure in appender", this, var3)); }} }

private void writeBytes(byte[] byteArray) throws IOException { if (byteArray != null & & byteArray.length != 0) { this.lock.lock(); try { //System.out进行输出 this.outputStream.write(byteArray); if (this.immediateFlush) { this.outputStream.flush(); } } finally { this.lock.unlock(); }} }

总结1.Logger必须和appender关联才可以产生作用
【logback源码阅读-Appender】2.我们可以为Appender配置Filter做定制的过滤