行为模式：Chain Of Responsibility（职责链）-优快云博客

本文通过实现Java中的日志系统，演示了如何使用链式责任模式来处理不同级别的日志消息，包括控制日志输出的目标、级别及处理顺序。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

import java.util.*;
 
abstract class Logger 
{
    public static int ERR = 3;
    public static int NOTICE = 5;
    public static int DEBUG = 7;
    protected int mask;
 
    // The next element in the chain of responsibility
    protected Logger next;
    public Logger setNext( Logger l)
    {
        next = l;
        return this;
    }
 
    public final void message( String msg, int priority )
    {
        if ( priority <= mask ) 
        {
            writeMessage( msg );
            if ( next != null )
            {
                next.message( msg, priority );
            }
        }
    }
 
    protected abstract void writeMessage( String msg );
 
}
 
class StdoutLogger extends Logger 
{
 
    public StdoutLogger( int mask ) { this.mask = mask; }
 
    protected void writeMessage( String msg )
    {
        System.out.println( "Writting to stdout: " + msg );
    }
}
 
 
class EmailLogger extends Logger 
{
 
    public EmailLogger( int mask ) { this.mask = mask; }
 
    protected void writeMessage( String msg )
    {
        System.out.println( "Sending via email: " + msg );
    }
}
 
class StderrLogger extends Logger 
{
 
    public StderrLogger( int mask ) { this.mask = mask; }
 
    protected void writeMessage( String msg )
    {
        System.out.println( "Sending to stderr: " + msg );
    }
}
 
public class ChainOfResponsibilityExample
{
    public static void main( String[] args )
    {
        // Build the chain of responsibility
        Logger l = new StdoutLogger( Logger.DEBUG).setNext(
                            new EmailLogger( Logger.NOTICE ).setNext(
                            new StderrLogger( Logger.ERR ) ) );
 
        // Handled by StdoutLogger
        l.message( "Entering function y.", Logger.DEBUG );
 
        // Handled by StdoutLogger and EmailLogger
        l.message( "Step1 completed.", Logger.NOTICE );
 
        // Handled by all three loggers
        l.message( "An error has occurred.", Logger.ERR );
    }
}