【转】Chain of Responsibility模式(职责链)

Java深入到一定程度,就不可避免的碰到设计模式这一概念,了解设计模式,将使自己对java中的接口或抽象类应用有更深的理解.设计模式在java的中型系统中应用广泛,遵循一定的编程模式,才能使自己的代码便于理解,易于交流,Chain of Responsibility(职责链模式)模式便是其中一个.
   Chain of Responsibility(CoR)职责链模式，CoR模式是用一系列类(classes)试图处理一个请求request,这些类之间是一个松散的耦合,唯一共同点是在他们之间传递request. 也就是说，来了一个请求，A类先处理，如果没有处理，就传递到B类处理，如果没有处理，就传递到C类处理，就这样象一个链条(chain)一样传递下去。
   优点: 因为无法预知来自外界（客户端）的请求是属于哪种类型，每个类如果碰到它不能处理的请求只要放弃就可以。
   缺点: 缺点是效率低，因为一个请求的完成可能要遍历到最后才可能完成;扩展性差，因为在CoR中，一定要有一个统一的接口Handler.局限性就在这里.
 
   在此写了10个java类来描述说明Chain of Responsibility设计模式的实现方式；

  1、 Handler.java    请求处理类接口
  2、 HandlerStudent.java  学生请求处理类
  3、 HandlerTeacher.java  老师请求处理类
  4、 HandlerSchoolmaster.java 校长请求处理类
  5、 Request.java    请求类接口
  6、 RequestStudent.java  学生请求类
  7、 RequestTeacher.java  老师请求类
  8、 RequestSchoolmaster.java 校长请求类
  9、 RequestPresident.java  总统请求类
  10、TestCoR.java    带有main方法的测试类



===============   1、 Handler.java
package cor;
public interface Handler {
  public void handleRequest(Request request);
}
===============  1 end



===============   2、 HandlerStudent.java
package cor;
public class HandlerStudent implements Handler {

  //下一个Handler对象
  private Handler nextSuccessor;

  public HandlerStudent(Handler nextSuccessor) {
    this.nextSuccessor = nextSuccessor;
  }

  public void handleRequest(Request request) {
    //处理 StudentRequest
    if(request.getType().equalsIgnoreCase("StudentRequest")){
      System.out.println("HandlerStudent begin to response StudentRequest;");
      request.execute();
    //把请求传递给其它受理者
    }else{
      if(this.nextSuccessor != null){
        nextSuccessor.handleRequest(request);
      }else{
        System.out.println("request[" + request.getType() + "] has not handler to deal!");
      }
    }
  }
}
===============   2 end



===============   3、 HandlerTeacher.java
package cor;
public class HandlerTeacher implements Handler {

  //下一个Handler对象
  private Handler nextSuccessor;

  public HandlerTeacher(Handler nextSuccessor) {
    this.nextSuccessor = nextSuccessor;
  }

  public void handleRequest(Request request) {
    //处理 TeacherRequest
    if(request.getType().equalsIgnoreCase("TeacherRequest")){
      System.out.println("HandlerTeacher begin to response StudentRequest;");
      request.execute();
    //把请求传递给其它受理者
    }else{
      if(this.nextSuccessor != null){
        nextSuccessor.handleRequest(request);
      }else{
        System.out.println("request[" + request.getType() + "] has not handler to deal!");
      }
    }
  }
}
===============   3 end



===============   4、 HandlerSchoolmaster.java
package cor;
public class HandlerSchoolmaster implements Handler {

  //下一个Handler对象
  private Handler nextSuccessor;

  public HandlerSchoolmaster(Handler nextSuccessor) {
    this.nextSuccessor = nextSuccessor;
  }

  public void handleRequest(Request request) {
    //处理 SchoolmasterRequest
    if(request.getType().equalsIgnoreCase("SchoolmasterRequest")){
      System.out.println("HandlerSchoolmaster begin to response StudentRequest;");
      request.execute();
    //把请求传递给其它受理者
    }else{
      if(this.nextSuccessor != null){
        nextSuccessor.handleRequest(request);
      }else{
        System.out.println("request[" + request.getType() + "] has not handler to deal!");
      }
    }
  }
}
===============   4 end



===============   5、 Request.java
package cor;
public interface Request {
  //请求类型
  public String getType();
  //执行任务
  public void execute();
}
===============   5 end



===============   6、 RequestStudent.java
package cor;
public class RequestStudent implements Request {

  public void execute() {
    System.out.println("[RequestStudent] :\t Students request has been accepted!");
  }

  public String getType() {
    return "StudentRequest";
  }
}
===============   6 end



===============   7、 RequestTeacher.java
package cor;
public class RequestTeacher implements Request {

  public void execute() {
    System.out.println("[RequestTeacher] :\t Teachers request has been accepted!");
  }

  public String getType() {
    return "TeacherRequest";
  }
}
===============   7 end



===============   8、 RequestSchoolmaster.java
package cor;
public class RequestSchoolmaster implements Request {

  public void execute() {
    System.out.println("[RequestSchoolmaster] :\t Schoolmasters request has been accepted!");
  }

  public String getType() {
    return "SchoolmasterRequest";
  }
}
===============   8 end



===============   9、 RequestPresident.java
package cor;
public class RequestPresident implements Request {

  public void execute() {
    System.out.println("[RequestPresident] :\t Presidents request has been accepted!");
  }

  public String getType() {
    return "PresidentRequest";
  }
}
===============   9 end



===============   10、 TestCoR.java
package cor;
public class TestCoR {
  public static void main(String[] args) {
    Handler handler = new HandlerStudent(new HandlerTeacher(new HandlerSchoolmaster(null)));
  
    Request studentReq = new RequestStudent();
    Request teacherReq = new RequestTeacher();
    Request schoolmasterReq = new RequestSchoolmaster();
    Request presidentReq = new RequestPresident();
  
    //传入student request
    handler.handleRequest(studentReq);
    System.out.println("-----------");
    //传入teacher request
    handler.handleRequest(teacherReq);
    System.out.println("-----------");
    //传入schoolmaster request
    handler.handleRequest(schoolmasterReq);
    System.out.println("-----------");
    //传入president request
    handler.handleRequest(presidentReq);
    System.out.println("-----------");
  }
}
===============   10 end