和钉钉请假一个道理，一层一层（层层处理）同意。
订单处理也类似，优惠券（满减、固定减）、物流、库存、支付。等等

实现方式一

  1. package com.example.demo.designMode;
  3. /**
  4.  * 责任链
  5.  * 请假决策-》 组长批准 -》 部门经理批准 -》副经理批准
  6.  */
  7. public abstract class Approver {
  9.     public  Approver approver; //下一个节点
  11.     public Approver setApprover(Approver approver){
  12.         this.approver = approver;
  13.         return this;
  14.     }
  16.     /**
  17.      * 处理方法
  18.      * @param day 请假天数
  19.      * @return
  20.      */
  21.     public abstract Boolean checkOut(Integer day);
  22. }
  24. /**
  25.  * 组长
  26.  */
  27. class GroupApprover extends Approver{
  29.     @Override
  30.     public Boolean checkOut(Integer day) {
  31.         if(day <2){
  32.             System.out.println("组长通过请假！");
  33.             return true;
  34.         }else{
  35.             System.out.println("组长通过请假！");
  36.             return approver.checkOut(day);
  37.         }
  38.     }
  39. }
  41. /**
  42.  * 部门经理
  43.  */
  44. class DepartmentApprover  extends Approver{
  46.     @Override
  47.     public Boolean checkOut(Integer day) {
  48.         if(day <5){
  49.             System.out.println("部门经理通过请假！");
  50.             return true;
  51.         }else{
  52.             System.out.println("部门经理通过请假！");
  53.             return approver.checkOut(day);
  54.         }
  55.     }
  56. }
  59. /**
  60.  * 副经理
  61.  */
  62. class VicePresidentApprover extends Approver{
  64.     @Override
  65.     public Boolean checkOut(Integer day) {
  66.         if(day <10){
  67.             System.out.println("副经理通过请假！");
  68.             return true;
  69.         }else{
  70.             System.out.println("请假不通过，天数太长！");
  71.             return false;
  72.         }
  73.     }
  74. }

测试： 

  1. package com.example.demo.designMode;
  3. public class Test {
  4.     public static void main(String[] args) {
  5.         Approver approver = new GroupApprover()
  6.                 .setApprover(new DepartmentApprover()
  7.                         .setApprover(new VicePresidentApprover()));
  8.         System.out.println(approver.checkOut(9));
  9.     }
  10. }

实现方式二

  1. package com.example.demo.designMode;
  3. import java.util.function.Function;
  4. import java.util.function.Predicate;
  6. /**
  7.  * 责任链2
  8.  * 请假决策-》 组长批准 -》 部门经理批准 -》副经理批准
  9.  */
  10. public abstract class Approver2 {
  12.     public Approver2 nextHandler; //下一个节点
  13.     public Predicate<Integer> predicate; //验证进入下个节点的方法
  15.     public Approver2 setApprover2(Approver2 nextHandler){
  16.         this.nextHandler = nextHandler;
  17.         return this;
  18.     }
  20.     public final Boolean handleMessage(Integer day){
  21.         if(predicate.test(day)){
  22.            return checkOut(day);
  23.         }else{
  24.             if (this.nextHandler != null) {
  25.                 System.out.println("事情太严重，需报告上一级");
  26.                 return this.nextHandler.handleMessage(day);
  27.             } else {
  28.                 System.out.println("我就是boss，没有上头");
  29.                 return false;
  30.             }
  31.         }
  32.     }
  35.     /**
  36.      * 处理方法
  37.      * @param day 请假天数
  38.      * @return
  39.      */
  40.     public abstract Boolean checkOut(Integer day);
  41. }
  43. /**
  44.  * 组长
  45.  */
  46. class GroupApprover2 extends Approver2{
  48.     {
  49.         predicate = i ->i<2;
  50.     }
  52.     @Override
  53.     public Boolean checkOut(Integer day) {
  54.         System.out.println("组长通过请假！");
  55.         return true;
  56.     }
  57. }
  59. /**
  60.  * 部门经理
  61.  */
  62. class DepartmentApprover2  extends Approver2{
  64.     {
  65.         predicate = i ->i<5;
  66.     }
  68.     @Override
  69.     public Boolean checkOut(Integer day) {
  70.         System.out.println("组长通过请假！");
  71.         return true;
  72.     }
  73. }
  76. /**
  77.  * 副经理
  78.  */
  79. class VicePresidentApprover2 extends Approver2{
  81.     {
  82.         predicate = i ->i<10;
  83.     }
  85.     @Override
  86.     public Boolean checkOut(Integer day) {
  87.         System.out.println("副经理通过请假！");
  88.         return true;
  89.     }
  90. }

测试

  1. package com.example.demo.designMode;
  3. public class Test {
  4.     public static void main(String[] args) {
  5.         Approver2 approver2 = new GroupApprover2()
  6.                 .setApprover2(new DepartmentApprover2()
  7.                         .setApprover2(new VicePresidentApprover2()));
  8.         System.out.println(approver2.handleMessage(9));
  9.     }
  10. }

实现方式三 Springboot版本

  1. package com.example.designmode.designMode2;
  3. import org.springframework.stereotype.Component;
  5. import java.util.function.Predicate;
  7. /**
  8.  * 责任链3
  9.  * 请假决策-》 组长批准 -》 部门经理批准 -》副经理批准
  10.  */
  11. @Component
  12. public abstract class SpringBootApprover {
  14.     public Predicate<Integer> predicate; //验证进入下个节点的方法
  16.     /**
  17.      * 处理方法
  18.      * @param day 请假天数
  19.      * @return
  20.      */
  21.     public abstract Boolean checkOut(Integer day);
  22. }
  1. package com.example.designmode.designMode2;
  3. import org.springframework.core.annotation.Order;
  4. import org.springframework.stereotype.Service;
  6. /**
  7.  * 组长
  8.  */
  9. @Order(1)
  10. @Service
  11. public class GroupApproverImpl extends SpringBootApprover {
  13.     {
  14.         predicate = i ->i<2;
  15.     }
  17.     @Override
  18.     public Boolean checkOut(Integer day) {
  19.         System.out.println("组长通过请假！");
  20.         return true;
  21.     }
  22. }
  1. package com.example.designmode.designMode2;
  3. import org.springframework.core.annotation.Order;
  4. import org.springframework.stereotype.Service;
  6. /**
  7.  * 部门经理
  8.  */
  9. @Order(2)
  10. @Service
  11. public class DepartmentApproverImpl extends SpringBootApprover {
  13.     {
  14.         predicate = i ->i<5;
  15.     }
  17.     @Override
  18.     public Boolean checkOut(Integer day) {
  19.         System.out.println("组长通过请假！");
  20.         return true;
  21.     }
  22. }
  1. package com.example.designmode.designMode2;
  3. import org.springframework.core.annotation.Order;
  4. import org.springframework.stereotype.Service;
  6. /**
  7.  * 副经理
  8.  */
  9. @Order(3)
  10. @Service
  11. public class VicePresidentApproverImpl extends SpringBootApprover {
  13.     {
  14.         predicate = i ->i<10;
  15.     }
  17.     @Override
  18.     public Boolean checkOut(Integer day) {
  19.         System.out.println("副经理通过请假！");
  20.         return true;
  21.     }
  22. }
  1. package com.example.designmode.designMode2;
  3. import org.springframework.stereotype.Component;
  5. import javax.annotation.Resource;
  6. import java.util.List;
  8. /**
  9.  * 增加流程控制方法
  10.  */
  11. @Component
  12. public class XiangHandlerChain {
  14.     @Resource
  15.     private List<SpringBootApprover> approverList;
  17.     //计数器，用来找到下一个节点
  18.     public Integer index = 0;
  20.     public final Boolean handleMessage(Integer day){
  21.         if(approverList.get(index).predicate.test(day)){
  22.             return approverList.get(index).checkOut(day);
  23.         }else{
  24.             index ++;
  25.             if(index<approverList.size()){
  26.                 System.out.println("事情太严重，需报告上一级");
  27.                 return handleMessage(day);
  28.             } else {
  29.                 System.out.println("我就是boss，没有上头");
  30.                 return false;
  31.             }
  32.         }
  33.     }
  34. }

测试

  1. package com.example.designmode;
  3. import com.example.designmode.designMode2.XiangHandlerChain;
  4. import org.junit.jupiter.api.Test;
  5. import org.springframework.boot.test.context.SpringBootTest;
  7. import javax.annotation.Resource;
  9. @SpringBootTest
  10. class DesignmodeApplicationTests {
  12.     @Resource
  13.     XiangHandlerChain xiangHandlerChain;
  15.     @Test
  16.     void contextLoads() {
  17.         xiangHandlerChain.handleMessage(10);
  18.     }
  20. }

实现方式四：Servlet拦截器Filter

  1. package javax.servlet;
  3. import java.io.IOException;
  5. public interface Filter {
  7.     //初始化方法
  8.     public void init(FilterConfig filterConfig) throws ServletException;
  10.     //主方法
  11.     public void doFilter ( ServletRequest request, ServletResponse response, FilterChain chain ) throws IOException, ServletException;
  13.     //销毁
  14.     public void destroy();
  16. }
  1. package javax.servlet;
  3. import java.io.IOException;
  5. public interface FilterChain {
  7.     public void doFilter ( ServletRequest request, ServletResponse response ) throws IOException, ServletException;
  9. }

通常我们实现的过滤器 

  1. package com.xiang.filter;
  3. import javax.servlet.*;
  4. import java.io.IOException;
  6. /**
  7.  *
  8.  */
  9. public class MyFilter implements Filter {
  11.     //初始化
  12.     public void init(FilterConfig filterConfig) throws ServletException {
  13.         System.out.println("初始化");
  14.     }
  16.     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
  17.         request.setCharacterEncoding("utf-8");
  18.         response.setCharacterEncoding("utf-8");
  19.         response.setContentType("text/html;charset=UTF-8");
  21.         chain.doFilter(request,response);
  22.     }
  24.     //销毁
  25.     public void destroy() {
  27.     }
  28. }

下面是模拟Tomcat实现，使用了观察者模式 

private static class TomcatChain implements FilterChain {

    private final List<? extends Filter> additionalFilters;

    private int currentPosition = 0;

    public TomcatChain(List<? extends Filter> additionalFilters) {
        this.additionalFilters = additionalFilters;
    }

    @Override
    public void doFilter(final ServletRequest request, final ServletResponse response)
            throws IOException, ServletException {

        this.currentPosition++;
        Filter nextFilter = this.additionalFilters.get(this.currentPosition - 1);
        nextFilter.doFilter(request, response, this);
    }
}