Java设计模式之责任链模式的示例详解

private String login(String username,String passWord) {
    if(username == null || password == null) {
        return "账户或者密码为null";
    }
    User user = queryUserInfo(username, password);
    if(user == null) {
        return "找不到用户";
    }
    if(!Objects.equals(user.getRoleName(), "超管")){
        return "没有权限";
    }
    return "登录成功";

}

private User queryUserInfo(String username,String password){
    if(Objects.equals(username, "土豆") && Objects.equals(password, "666666")) {
        return new User(username,password,"超管");
    }else if(Objects.equals(username, "土豆2号") && Objects.equals(password, "666666")){
        return new User(username,password,"普通员工");
    }
    return null;
}

public abstract class Handler {
    protected Handler next;

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

    public abstract void doHandler(User user);
}

public class ValidatedHandler extends Handler {
    @Override
    public void doHandler(User user) {
        if(user.getUsername() == null || user.getPassword() == null) {
            System.out.println("账户或者密码为null");
        }else{
            this.next.doHandler(user);
        }
    }
}

public class UserHandler extends Handler{
    @Override
    public void doHandler(User user) {
        queryUserInfo(user);
        if(user.getRoleName() == null){
            System.out.println("没有找到用户");
        }else{
            this.next.doHandler(user);
        }
    }
    private static void queryUserInfo(User user){
        if(Objects.equals(user.getUsername(), "土豆") && Objects.equals(user.getPassword(), "666666")) {
            user.setRoleName("超管");
        }else if(Objects.equals(user.getUsername(), "土豆2号") && Objects.equals(user.getPassword(), "666666")){
            user.setRoleName("普通员工");
        }
    }
}

public class AuthHandler extends Handler{
    @Override
    public void doHandler(User user) {
        if(!Objects.equals(user.getRoleName(), "超管")){
            System.out.println("没有权限");
        }
        System.out.println("登入成功");
    }
}

public static void main(String[] args) {
    User user = new User("土豆","666666");
    Handler validatedHandler = new ValidatedHandler();
    Handler userHandler = new UserHandler();
    Handler authHandler = new AuthHandler();
    validatedHandler.setNext(userHandler);
    userHandler.setNext(authHandler);
    validatedHandler.doHandler(user);

}

public abstract class Handler {
    protected Handler next;

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

    public abstract void doHandler(User user);

    public static class Builder {
        private Handler head;
        private Handler tail;

        public Builder addHandler(Handler handler) {
            if(this.head == null){
                this.head = this.tail = handler;
                return this;
            }
            this.tail.setNext(handler);
            this.tail = handler;
            return this;
        }

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

Handler.Builder builder = new Handler.Builder();
builder.addHandler(new ValidatedHandler())
        .addHandler(new UserHandler())
        .addHandler(new AuthHandler());
builder.build().doHandler(user);