背景

假如项目中有多条过滤链处理线，那么如何设计一套多处理链的代码呢？ 假如有以下流程

• 买车流程
• 登陆流程

创建 Chain 接口

package com.design.chain;
/**
/**
 * @program: spring-test
 * @ClassName Handler
 * @description: 责任链处理器接口
 *  * 1. 参数校验 2. 用户名密码校验 3. 权限校验
 * @author: sizegang
 * @create: 2022-01-01 00:40
 * @Version 1.0
 **/
public interface Chain {
    void execute(Member member);
    void doExecute(Member member);
}

登陆处理链

会员辅助类

@Data
public class Member {

    private String userName;
    private String passWord;
    private String roleName;
}

登陆链接口

/**
 * @program: spring-test
 * @ClassName LoginChain
 * @description: 登录责任链
 * @author: sizegang
 * @create: 2022-01-01 13:24
 * @Version 1.0
 **/
public interface LoginChain extends Chain {
}

抽象责任链

/**
 * @program: spring-test
 * @ClassName AbstractHandler
 * @description: 抽象责任链处理器
 * * 1. 参数校验 2. 用户名密码校验 3. 权限校验
 * @author: sizegang
 * @create: 2022-01-01 00:41
 * @Version 1.0
 **/
public abstract class AbstractLoginExecutor<T> implements LoginChain {

    protected Chain chain;

    public void next(Chain chain) {
        this.chain = chain;
    }

    // 这里结合模板方法
    @Override
    public void execute(Member member) {
        doExecute(member);
    }
    /**
     * 责任链模式配合建造者模式
     *
     * @param <T>
     */
    public static class Builder<T> {
        private AbstractLoginExecutor<T> head;
        private AbstractLoginExecutor<T> tail;

        public Builder<T> addChain(AbstractLoginExecutor<T> handler) {
            if (this.head == null) {
                this.head = this.tail = handler;
                return this;
            }
            // 设置自身的下一个节点
            this.tail.next(handler);
            // 修改指针指向
            this.tail = handler;
            return this;
        }

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

    }
}

验证责任链

@Slf4j
public class ValidateExecutor extends AbstractLoginExecutor {

    @Override
    public void doExecute(Member member) {
        if(StringUtils.isBlank(member.getUserName()) || StringUtils.isBlank(member.getPassWord())){
            System.out.println("用户名密码为空");
            return;
        }
        System.out.println("用户名密码校验成功，可以往下执行");
        chain.doExecute(member);
    }
}

### 权限责任链 
```java 

/**
 * @program: spring-test
 * @ClassName AuthHandler
 * @description: 权限校验责任链执行器
 * @author: sizegang
 * @Version 1.0
 **/
public class AuthHandler extends AbstractLoginExecutor {

    @Override
    public void doExecute(Member member) {
        if(!"管理员".equals(member.getRoleName())){
            System.out.println("您不是管理员没有操作权限");
            return;
        }
        System.out.println("您是管理员允许操作");
    }
}

登陆责任链

public class LoginExecutor extends AbstractLoginExecutor {

    @Override
    public void doExecute(Member member) {
        System.out.println("登录成功");
        member.setRoleName("管理员");
        chain.doExecute(member);
    }
}

用户登陆服务

public class LoginAssembler {
    /**
     * 会员等六
     * @param member 会员
     */
    public void login(Member member){
        AbstractLoginExecutor.Builder builder = new AbstractLoginExecutor.Builder();
        AbstractLoginExecutor build = builder.addChain(new ValidateExecutor()).addChain(new LoginExecutor()).addChain(new AuthHandler()).build();
        build.execute(member);
    }
}

测试

public class TestLoginChain {
    public static void main(String[] args) {
        LoginAssembler memberService = new LoginAssembler();
        Member member = new Member();
        member.setPassWord("1234");
        member.setUserName("sizegang");
        memberService.login(member);
    }
}

买车流程

买车接口

public interface BuyCarChain extends Chain {
}

抽象买车流程

@Slf4j
public abstract class AbstractBuyCarChain<T> implements BuyCarChain {
    protected Chain chain;

    public void next(Chain chain) {
        this.chain = chain;
    }

    /**
     * 买车处理器
     *
     * @param member
     */
    @Override
    public void execute(Member member) {
        doExecute(member);
    }


    public static class Build<T> {
        private AbstractBuyCarChain head;
        private AbstractBuyCarChain tail;

        public Build<T> addChain(AbstractBuyCarChain chain) {

            if (this.head == null) {
                this.head = this.tail = chain;
                return this;
            }
            this.tail.next(chain);
            this.tail = chain;
            return this;
        }

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

看车责任链

@Slf4j
public class SeeCarHandler  extends AbstractBuyCarChain{
    @Override
    public void doExecute(Member member) {
        System.out.println("会员开始看车");
        if(chain != null){
            chain.doExecute(member);
        }
    }
}

付款责任链

public class PayMoneyHandler extends AbstractBuyCarChain{

    @Override
    public void doExecute(Member member) {
        System.out.println("付款成功");
        if(chain != null){
            chain.doExecute(member);
        }
    }
}

提车责任链

public class PickCarHandler extends AbstractBuyCarChain{
    @Override
    public void doExecute(Member member) {
        System.out.println(String.format("%s 成功提车", member.getUserName()));
    }
}

责任链触发器

public class BuyCarAssembler {
    public void buyCar(Member member ){
        AbstractBuyCarChain.Build builder = new AbstractBuyCarChain.Build<>();
        AbstractBuyCarChain chain = builder.addChain(new SeeCarHandler()).addChain(new PayMoneyHandler()).addChain(new
                PickCarHandler()).build();
        chain.execute(member);
    }
}

测试

public class TestBuyCar {

    public static void main(String[] args) {
        BuyCarAssembler buyCarAssembler = new BuyCarAssembler();
        Member member = new Member();
        member.setUserName("司泽刚");
        member.setRoleName("研发");
        buyCarAssembler.buyCar(member);
    }
}