调用链例子

优雅的管理类的调用链路，符合开闭原则 添加与修改逻辑只需要修改调用链路即可。可以把类的执行顺序用链表或者list存储起来，存储的顺序就是类执行的顺序。

handler

public abstract class Handler<T> {
    protected Handler next;
    public void next(Handler next){ this.next = next;}

    public abstract void doHandler(Member member);

    public static class Builder<T>{
        private Handler<T> head;
        private Handler<T> tail;

        public Builder<T> addHandler(Handler handler){
//            do {
                if (this.head == null) {
                    this.head = this.tail = handler;
                    return this;
                }
                this.tail.next(handler);
                this.tail = handler;
//            }while (false);//真正框架中，如果是双向链表，会判断是否已经到了尾部
            return this;
        }

        public Handler<T> build(){
            return this.head;
        }

    }
}

handler实现类

public class LoginHandler extends Handler {
    public void doHandler(Member member) {
        System.out.println("登录成功！");
        member.setRoleName("管理员");
        if(null != next) {
            next.doHandler(member);
        }
    }
}

实用类

 Handler.Builder builder = new Handler.Builder();

        builder.addHandler(new LoginHandler());
//                .addHandler(new LoginHandler())
//                .addHandler(new AuthHandler());

        builder.build().doHandler(new Member(loginName,loginPass));