[译]ava 设计模式之职责链

(文章翻译自Java Design Pattern: Chain of Responsibility)

职责链模式的主要设计思想是为了构建一连串的处理单元,如果阈值满足的话那么这个单元就来处理这个请求。自从这个链构建以后，如果一个单元不满足，那么就会尝试调用下一个，以此类推。每一个请求会沿着这个链被处理。

职责链模式类图

职责链Java 代码

package designpatterns.cor;
 
abstract class Chain {
    public static int One = 1;
    public static int Two = 2;
    public static int Three = 3;
    protected int Threshold;
 
    protected Chain next;
 
    public void setNext(Chain chain) {
        next = chain;
    }
 
    public void message(String msg, int priority) {
        //if the priority is less than Threshold it is handled
    	if (priority <= Threshold) {
            writeMessage(msg);
        }
 
        if (next != null) {
            next.message(msg, priority);
        }
    }
 
    abstract protected void writeMessage(String msg);
}
 
class A extends Chain {
    public A(int threshold) { 
        this.Threshold = threshold;
    }
 
    protected void writeMessage(String msg) {
        System.out.println("A: " + msg);
    }
}
 
 
class B extends Chain {
    public B(int threshold) { 
        this.Threshold = threshold;
    }
 
    protected void writeMessage(String msg) {
        System.out.println("B: " + msg);
    }
}
 
class C extends Chain {
    public C(int threshold) { 
        this.Threshold = threshold;
    }
 
    protected void writeMessage(String msg) {
        System.out.println("C: " + msg);
    }
}
 
 
public class ChainOfResponsibilityExample {
 
    private static Chain createChain() {
        // Build the chain of responsibility
 
    	Chain chain1 = new A(Chain.Three);
 
    	Chain chain2 = new B(Chain.Two);
    	chain1.setNext(chain2);
 
        Chain chain3 = new C(Chain.One);        
        chain2.setNext(chain3);
 
        return chain1;
    }
 
    public static void main(String[] args) {
 
    	Chain chain = createChain();
 
        chain.message("level 3", Chain.Three);
 
        chain.message("level 2", Chain.Two);
 
        chain.message("level 1", Chain.One);
    }
 
}

在这个例子中，Level1穿过了这个链中的每一个处理单元。

A: level 3
A: level 2
B: level 2
A: level 1
B: level 1
C: level 1