logback源码阅读-Appender

Posted 2021-03-17 意犹未尽

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="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>

 

 

 

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

 

 

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

 

 

 我们需要自定义appender只需要继承UnsynchronizedAppenderBase就行了

start

ch.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>appendLoopOnAppenders

ch.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>doAppend

ch.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>append

ch.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

2.我们可以为Appender配置Filter做定制的过滤