设计模式——责任链模式

Posted 2020-10-29 boycelee

背景：

想必奖学金大家都不陌生，在学校里奖学金往往分为三种班奖学金、院级奖学金以及校级奖学金，但是我们往往苦于政策修改，不知道自己的奖学金该找谁领，于是乎就询问顺序就是：班级辅导员->学院老师->学校老师，我们最多且只能在一个人那到一份奖学金，这就是职责链。辅导员处领不到就辅导员就会让你问问学院老师，学院老师处领不到就会让你问问学校老师，这互相（推脱）其实就是职责链模式。

责任链模式图:

        public interface IStudent {

            int getType();

            String getRequest();
        }

        public class Student implements IStudent {
           private int type = 0;

           private String request = "";


           public Student(int type, String request) {
              this.type = type;
              this.request = request;
           }

           public int getType() {
              return this.type;
           }

           public String getRequest() {
              return this.request;
           }
        }

        public abstract class Handler {
              public static final Integer CLASS_SCHOLARSHIP = 1;

              public static final Integer COLLEGE_SCHOLARSHIP = 2;

              public static final Integer UNIVERSITY_SCHOLARSHIP = 3;

              //责任处理级别
              private int level = 0;

              //下一位处理者
              private Handler nextHandler;

              public Handler(int level) {
                  this.level = level;
              }

              public void HandleMsg(IStudent student) {
                  if (student.getType() == this.level) {

              }
            }

            public void setNext(Handler handler) {
            this.nextHandler = handler;
          }

             public abstract void response(IStudent student);


        }
        

    public class ClassTeacher extends Handler {
    public ClassTeacher() {
        super(Handler.CLASS_SCHOLARSHIP);
    }

    public void response(IStudent student) {
        System.out.println(student.getRequest());
        System.out.println("班级老师批准！");
    }
}

public class CollegeTeacher extends Handler{
    public CollegeTeacher() {
        super(Handler.COLLEGE_SCHOLARSHIP);
    }

    public void response(IStudent student) {
        System.out.println(student.getRequest());
        System.out.println("学院老师批准！");
    }
}

public class UniversityTeacher extends Handler {
    public UniversityTeacher() {
        super(Handler.UNIVERSITY_SCHOLARSHIP);
    }

    public void response(IStudent student) {
        System.out.println(student.getRequest());
        System.out.println("学校老师批准！");
    }
}

责任链缺点：
（1）性能问题，每个请求都会从链头遍历到链尾
（2）如果责任块过多，会导致debug异常困难

使用场景，在字符类型判断需求中就可以使用该设计模式