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本文主要研究一下logback的StatusListener

StatusListener

ch/qos/logback/core/status/StatusListener.java

/**
 * A StatusListener registered with logback context's {@link StatusManager} will
 * receive notification of every incoming {@link Status status} message.
 * 
 * @author Ceki Gülcü
 */
public interface StatusListener {
    void addStatusEvent(Status status);
}

StatusListener定义了addStatusEvent方法，注册到logback上下文的StatusManager的StatusListener将接收每个传入状态消息

NopStatusListener

ch/qos/logback/core/status/NopStatusListener.java

public class NopStatusListener implements StatusListener {

    public void addStatusEvent(Status status) {
        // nothing to do
    }
}

NopStatusListener实现了StatusListener，它的addStatusEvent是空操作

OnPrintStreamStatusListenerBase

abstract public class OnPrintStreamStatusListenerBase extends ContextAwareBase implements StatusListener, LifeCycle {

    boolean isStarted = false;

    static final long DEFAULT_RETROSPECTIVE = 300;
    long retrospectiveThresold = DEFAULT_RETROSPECTIVE;
    
    /**
     * The prefix to place before each status message
     * @since 1.1.10
     */
    String prefix;
    
    /**
     * The PrintStream used by derived classes
     * @return
     */
    abstract protected PrintStream getPrintStream();

    public void addStatusEvent(Status status) {
        if (!isStarted)
            return;
        print(status);
    }

    private void print(Status status) {
        StringBuilder sb = new StringBuilder();
        if(prefix != null)
            sb.append(prefix);
        
        StatusPrinter.buildStr(sb, "", status);
        getPrintStream().print(sb);
    }

    //......
}            

OnPrintStreamStatusListenerBase声明实现了StatusListener接口，它是一个抽象类，其addStatusEvent方法执行print，而print则先添加prefix，再添加status，最后通过getPrintStream抽象方法获取PrintStream，然后进行print

OnConsoleStatusListener

ch/qos/logback/core/status/OnConsoleStatusListener.java

/**
 * Print all new incoming status messages on the console (System.out).
 *
 * @author Ceki Gülcü
 */
public class OnConsoleStatusListener extends OnPrintStreamStatusListenerBase {
    
    
    @Override
    protected PrintStream getPrintStream() {
        return System.out;
    }

}

OnConsoleStatusListener继承了OnPrintStreamStatusListenerBase，其getPrintStream返回的是System.out

OnErrorConsoleStatusListener

ch/qos/logback/core/status/OnErrorConsoleStatusListener.java

/**
 * Print all new incoming status messages on the error console (System.err).
 *
 * @author Ceki Gülcü
 * @since 1.0.8
 */
public class OnErrorConsoleStatusListener extends OnPrintStreamStatusListenerBase {

    @Override
    protected PrintStream getPrintStream() {
        return System.err;
    }
}

OnErrorConsoleStatusListener继承了OnPrintStreamStatusListenerBase，其getPrintStream返回的是System.err

StatusListenerAsList

ch/qos/logback/core/status/StatusListenerAsList.java

/**
 * Collect all incoming events in a list.
 * 
 * @author Ceki Gülcü
 * 
 */
public class StatusListenerAsList implements StatusListener {

    List<Status> statusList = new ArrayList<Status>();

    public void addStatusEvent(Status status) {
        statusList.add(status);
    }

    public List<Status> getStatusList() {
        return statusList;
    }

}

StatusListenerAsList实现了StatusListener接口，其addStatusEvent将status添加到statusList

小结

logback的StatusListener用于打印logback内部的status信息，它有NopStatusListener实现及OnPrintStreamStatusListenerBase的实现(OnConsoleStatusListener及OnErrorConsoleStatusListener)，即往System.out或者err打印。

doc

• statusListener