自定义HandlerMethodArgumentResolver参数解析器和源码分析
在初学springmvc框架时，我就一直有一个疑问，为什么controller方法上竟然可以放这么多的参数，而且都能得到想要的对象，比如HttpServletRequest或HttpServletResponse，各种注解@RequestParam、@RequestHeader、@RequestBody、@PathVariable、@ModelAttribute等。相信很多初学者都曾经感慨过。
这一章就是讲解处理这方面工作的
org.springframework.web.method.support.HandlerMethodArgumentResolver接口。
springmvc自带的一些实现：
ServletRequestMethodArgumentResolver和ServletResponseMethodArgumentResolver处理了自动绑定HttpServletRequest和HttpServletResponseRequestParamMapMethodArgumentResolver处理了@RequestParamRequestHeaderMapMethodArgumentResolver处理了@RequestHeaderPathVariableMapMethodArgumentResolver处理了@PathVariableModelAttributeMethodProcessor处理了@ModelAttributeRequestResponseBodyMethodProcessor处理了@RequestBody- 整体的spring实现为以下：
-
private List<HandlerMethodArgumentResolver> getDefaultArgumentResolvers() { List<HandlerMethodArgumentResolver> resolvers = new ArrayList<HandlerMethodArgumentResolver>(); // Annotation-based argument resolution resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), false)); resolvers.add(new RequestParamMapMethodArgumentResolver()); resolvers.add(new PathVariableMethodArgumentResolver()); resolvers.add(new PathVariableMapMethodArgumentResolver()); resolvers.add(new MatrixVariableMethodArgumentResolver()); resolvers.add(new MatrixVariableMapMethodArgumentResolver()); resolvers.add(new ServletModelAttributeMethodProcessor(false)); resolvers.add(new RequestResponseBodyMethodProcessor(getMessageConverters())); resolvers.add(new RequestPartMethodArgumentResolver(getMessageConverters())); resolvers.add(new RequestHeaderMethodArgumentResolver(getBeanFactory())); resolvers.add(new RequestHeaderMapMethodArgumentResolver()); resolvers.add(new ServletCookieValueMethodArgumentResolver(getBeanFactory())); resolvers.add(new ExpressionValueMethodArgumentResolver(getBeanFactory())); // Type-based argument resolution resolvers.add(new ServletRequestMethodArgumentResolver()); resolvers.add(new ServletResponseMethodArgumentResolver()); resolvers.add(new HttpEntityMethodProcessor(getMessageConverters())); resolvers.add(new RedirectAttributesMethodArgumentResolver()); resolvers.add(new ModelMethodProcessor()); resolvers.add(new MapMethodProcessor()); resolvers.add(new ErrorsMethodArgumentResolver()); resolvers.add(new SessionStatusMethodArgumentResolver()); resolvers.add(new UriComponentsBuilderMethodArgumentResolver()); // Custom arguments if (getCustomArgumentResolvers() != null) { resolvers.addAll(getCustomArgumentResolvers()); } // Catch-all resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true)); resolvers.add(new ServletModelAttributeMethodProcessor(true)); return resolvers; }
我们可以模仿springmvc的源码，实现一些我们自己的实现类，而方便我们的代码开发。
接口说明
package org.springframework.web.method.support;
import org.springframework.core.MethodParameter;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
public interface HandlerMethodArgumentResolver {
//用于判定是否需要处理该参数分解，返回true为需要，并会去调用下面的方法resolveArgument（可通过参数类型或注解等等）。
boolean supportsParameter(MethodParameter parameter);
//真正用于处理参数分解的方法，返回的Object就是controller方法上的形参对象。
Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception;
}
自定义实现
import org.springframework.core.MethodParameter;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.ModelAndViewContainer;
/**
* 用于绑定@CurrentUser的方法参数解析器
*
* @author lism
*/
public class CurrentUserMethodArgumentResolver implements HandlerMethodArgumentResolver {
public CurrentUserMethodArgumentResolver() {
}
@Override
public boolean supportsParameter(MethodParameter parameter) {
if (parameter.getParameterType().isAssignableFrom(UserBean.class) && parameter.hasParameterAnnotation(CurrentUser.class)) {
return true;
}
return false;
}
@Override
public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
CurrentUser currentUserAnnotation = parameter.getParameterAnnotation(CurrentUser.class);
//从Session 获取用户
Object object = webRequest.getAttribute(currentUserAnnotation.value(), NativeWebRequest.SCOPE_SESSION);
//从 accessToken获得用户信息
if (object == null) {
String token = webRequest.getHeader("Authorization");
if (token == null) {
token = webRequest.getParameter("accessToken");
}
//为了测试先写死用户名
//TODO: 取真实用户
return new UserBean(1L,"admin");
}
return object;
}
}
import java.lang.annotation.*;
/**
* <p>绑定当前登录的用户</p>
* <p>不同于@ModelAttribute</p>
*
* @author lism
*/
@Target({ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface CurrentUser {
/**
* 当前用户在request中的名字
*
* @return
*/
String value() default "user";
}
@RestController
@RequestMapping(value = "/test")
public class TestController {
/**
* 根据name查询
*
* @param request
* @return
*/
@RequestMapping(value = "/testCurrentUser", method = RequestMethod.POST, produces = "application/json", consumes = "application/json")
@ResponseBody
public void test(@CurrentUser UserBean userBean, @RequestBody SubjectRequest request) {
String createdBy = userBean.getUsername();
log.info(createdBy);
}
}
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import java.io.Serializable;
@Data
@NoArgsConstructor
@AllArgsConstructor
public class UserBean implements Serializable {
private Long id;
private String username;
}
另外，我需要将他配置到spring context中。
<!--自定义controller接受参数进行解析 --> <mvc:annotation-driven> <mvc:argument-resolvers> <bean class="com.common.util.CurrentUserMethodArgumentResolver" /> </mvc:argument-resolvers> </mvc:annotation-driven>
或者中配置的方式：
<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter"> <property name="synchronizeOnSession" value="true" /> <property name="customArgumentResolvers"> <list> <bean class="com.common.util.CurrentUserMethodArgumentResolver" /> </list> </property> </bean>
spring-boot方式配置
package com.demo;
import java.util.List;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport;
import com.demo.mvc.component.MultiPersonArgumentResolver;
import com.demo.mvc.component.PersonArgumentResolver;
@SpringBootApplication
public class WebMvcConfiguration extends WebMvcConfigurationSupport {
@Override
protected void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
// 注册Person的参数分解器
argumentResolvers.add(new PersonArgumentResolver());
}
}
