SpringBoot自定义参数解析器

一、背景

平常经常用 @RequestParam注解来获取参数，然后想到我能不能写个自己注解获取请求的ip地址呢？就像这样 @IP String ip

二、分析

于是开始分析 @RequestParam是如何实现的。

从@RequestParam注解开始入手,搜索该注解在源码中使用的地方
分别是类RequestParamMethodArgumentResolver和RequestParamMapMethodArgumentResolver

类关系图

RequestParamMethodArgumentResolver

可以看到两个类都最终实现了HandlerMethodArgumentResolver这个接口。

HandlerMethodArgumentResolver结构

里面就两个方法，supportsParameter方法是检测该参数是否支持这个参数解析器，
如果supportsParameter方法返回true，则调用resolveArgument来进行参数解析工作。

三、代码编写

现在就可以写自己的参数解析器了，但是推荐继承AbstractNamedValueMethodArgumentResolver而不是直接实现HandlerMethodArgumentResolver接口。
1.注解@IP

1. /** 

   ---

2. * 获取参数 

   ---

3. * Created by 2YSP on 2019/1/6. 

   ---

4. */ 

   ---

5. @Documented 

   ---

6. @Retention(value = RetentionPolicy.RUNTIME) 

   ---

7. @Target(ElementType.PARAMETER) 

   ---

8. public @interface IP { 

   ---

9.  

   ---

10. String name() default "ip"; 

    ---

11.  

    ---

12. boolean required() default true; 

    ---

13.  

    ---

14. String defaultValue() default "0"; 

    ---

15. } 

    ---

2.参数解析器IPAddressArgumentResolver

1. /** 

   ---

2. * Created by 2YSP on 2019/1/6. 

   ---

3. */ 

   ---

4. public class IPAddressArgumentResolver extends AbstractNamedValueMethodArgumentResolver { 

   ---

5. @Override 

   ---

6. protected NamedValueInfo createNamedValueInfo(MethodParameter parameter) { 

   ---

7. IP annotation = parameter.getParameterAnnotation(IP.class); 

   ---

8. return new IPAddressArgumentResolver.RequestIPNamedValueInfo(annotation); 

   ---

9. } 

   ---

10.  

    ---

11. @Nullable 

    ---

12. @Override 

    ---

13. protected Object resolveName(String name, MethodParameter parameter, NativeWebRequest request) throws Exception { 

    ---

14. HttpServletRequest servletRequest = request.getNativeRequest(HttpServletRequest.class); 

    ---

15. String ip = servletRequest.getRemoteAddr(); 

    ---

16. return ip == null ? "127.0.0.1":ip; 

    ---

17. } 

    ---

18.  

    ---

19. @Override 

    ---

20. public boolean supportsParameter(MethodParameter parameter) { 

    ---

21. return parameter.hasParameterAnnotation(IP.class) && !Map.class.isAssignableFrom(parameter.nestedIfOptional().getNestedParameterType()); 

    ---

22. } 

    ---

23.  

    ---

24. private static class RequestIPNamedValueInfo extends NamedValueInfo{ 

    ---

25.  

    ---

26. private RequestIPNamedValueInfo(IP annotation) { 

    ---

27. super(annotation.name(), annotation.required(), annotation.defaultValue()); 

    ---

28. } 

    ---

29. } 

    ---

30.  

    ---

31. } 

    ---

这三个方法是必须实现的，还有一个可选重写的handleMissingValue。
3.添加配置

1. @Configuration 

   ---

2. @EnableWebMvc 

   ---

3. public class MvcConfig implements WebMvcConfigurer { 

   ---

4.  

   ---

5.  

   ---

6. @Override 

   ---

7. public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) { 

   ---

8. resolvers.add(new IPAddressArgumentResolver()); 

   ---

9. } 

   ---

10. } 

    ---

4.controller

1. @Slf4j 

   ---

2. @RestController 

   ---

3. public class VOTestController { 

   ---

4.  

   ---

5. @GetMapping("vo/test") 

   ---

6. public BaseVo test(@IP String ip){ 

   ---

7.  

   ---

8. log.info("请求的ip地址为:{}",ip); 

   ---

9. BaseVo baseVo = new BaseVo(); 

   ---

10. //设置为Null 

    ---

11. baseVo.setResult(null); 

    ---

12. return baseVo; 

    ---

13. } 

    ---

14. } 

    ---

四、测试总结

启动项目，游览器请求http://localhost/vo/test可以看到日志显示：

2019-01-11 10:30:24.284 [http-nio-80-exec-3] INFO  cn.sp.controller.VOTestController - 请求的ip地址为:0:0:0:0:0:0:0:1

代码已托管到我的github，点击访问，对@RequestParam实现原理感兴趣的童鞋可以自己看看源码。