设计模式（十六）责任链模式(行为型)

abstract class Handler {  
    //维持对下家的引用  
protected Handler successor;  
      
    public void setSuccessor(Handler successor) {  
        this.successor=successor;  
    }  
      
    public abstract void handleRequest(String request);  
}  

class ConcreteHandler extends Handler {  
    public void handleRequest(String request) {  
        if (请求满足条件) {  
            //处理请求  
        }  
        else {  
            this.successor.handleRequest(request);  //转发请求  
        }  
    }  
}

// 全局变量，接口类型  
/**  
 * 使用Java中的interface定义全局变量，可根据具体需要在   
 * 具体的包中使用静态导入相关的全局变量，语法如下：   
 *  import static package01.package02.*;  
 */ 
interface Levels {  
    public static final int LEVEL_01 = 1;  
    public static final int LEVEL_02 = 2;  
    public static final int LEVEL_03 = 3;  
} 

// 抽象请求类  
abstract class AbstractRequest {  
    private String content = null;  
 
    public AbstractRequest(String content) {  
        this.content = content;  
    }  
 
    public String getContent() {  
        return this.content;  
    }  
 
    // 获得请求的级别  
    public abstract int getRequestLevel();  
}

// 具体请求类01  
class Request01 extends AbstractRequest {  
    public Request01(String content) {  
        super(content);  
    }  
 
    @Override 
    public int getRequestLevel() {  
        return Levels.LEVEL_01;  
    }  
}  
 
// 具体请求类02  
class Request02 extends AbstractRequest {  
    public Request02(String content) {  
        super(content);  
    }  
 
    @Override 
    public int getRequestLevel() {  
        return Levels.LEVEL_02;  
    }  
}  
 
// 具体请求类03  
class Request03 extends AbstractRequest {  
    public Request03(String content) {  
        super(content);  
    }  
 
    @Override 
    public int getRequestLevel() {  
        return Levels.LEVEL_03;  
    }  
} 

// 抽象处理者类，  
abstract class AbstractHandler {  
    // 责任链的下一个节点，即处理者  
    private AbstractHandler nextHandler = null;  
 
    // 捕获具体请求并进行处理，或是将请求传递到责任链的下一级别  
    public final void handleRequest(AbstractRequest request) {  
 
        // 若该请求与当前处理者的级别层次相对应，则由自己进行处理  
        if (this.getHandlerLevel() == request.getRequestLevel()) {  
            this.handle(request);  
        } else {  
            // 当前处理者不能胜任，则传递至职责链的下一节点  
            if (this.nextHandler != null) {  
                System.out.println("当前 处理者-0" + this.getHandlerLevel()  
                        + " 不足以处理 请求-0" + request.getRequestLevel());  
                  
                // 这里使用了递归调用  
                this.nextHandler.handleRequest(request);  
            } else {  
                System.out.println("职责链上的所有处理者都不能胜任该请求...");  
            }  
        }  
    }  
 
    // 设置责任链中的下一个处理者  
    public void setNextHandler(AbstractHandler nextHandler) {  
        this.nextHandler = nextHandler;  
    }  
 
    // 获取当前处理者的级别  
    protected abstract int getHandlerLevel();  
 
    // 定义链中每个处理者具体的处理方式  
    protected abstract void handle(AbstractRequest request);  
} 

// 具体处理者-01  
class Handler01 extends AbstractHandler {  
    @Override 
    protected int getHandlerLevel() {  
        return Levels.LEVEL_01;  
    }  
 
    @Override 
    protected void handle(AbstractRequest request) {  
        System.out.println("处理者-01 处理 " + request.getContent() + "\n");  
    }  
}  
 
// 具体处理者-02  
class Handler02 extends AbstractHandler {  
    @Override 
    protected int getHandlerLevel() {  
        return Levels.LEVEL_02;  
    }  
 
    @Override 
    protected void handle(AbstractRequest request) {  
        System.out.println("处理者-02 处理 " + request.getContent()+ "\n");  
    }  
}  
 
// 具体处理者-03  
class Handler03 extends AbstractHandler {  
    @Override 
    protected int getHandlerLevel() {  
        return Levels.LEVEL_03;  
    }  
 
    @Override 
    protected void handle(AbstractRequest request) {  
        System.out.println("处理者-03 处理 " + request.getContent()+ "\n");  
    }  
} 

// 测试类  
public class Client {  
    public static void main(String[] args) {  
        // 创建指责链的所有节点  
        AbstractHandler handler01 = new Handler01();  
        AbstractHandler handler02 = new Handler02();  
        AbstractHandler handler03 = new Handler03();  
 
        // 进行链的组装，即头尾相连，一层套一层  
        handler01.setNextHandler(handler02);  
        handler02.setNextHandler(handler03);  
 
        // 创建请求并提交到指责链中进行处理  
        AbstractRequest request01 = new Request01("请求-01");  
        AbstractRequest request02 = new Request02("请求-02");  
        AbstractRequest request03 = new Request03("请求-03");  
          
        // 每次提交都是从链头开始遍历  
        handler01.handleRequest(request01);  
        handler01.handleRequest(request02);  
        handler01.handleRequest(request03);  
    }  
}