关于SpringMVC在Controller层方法的参数解析详解

使用版本：

spring-boot: 2.1.6.RELEASE

sping: 5.1.8.RELEASE

java: openjdk 11.0.13

自定义参数解析器

为了能够实现自定义参数解析器，只需要实现 HandlerMethodArgumentResolver 并将添加到 WebMvcConfigurer#addArgumentResolvers 即可。

实现效果

下面以添加一个获取请求头的 client-type 参数为例进行是实现。定义注解 @ClientTypeMark 以及enum ClientType ，用于注入header中的值。

@Target({ElementType.PARAMETER})

@Retention(RetentionPolicy.RUNTIME)

@Documented

public @interface ClientTypeMark {

}

public enum ClientType {

WEB,

MOBILE,

UNKNOWN

;

}

最终实现的效果为在Controller的方法中，可以按照如下实现使用。

@RestController

@RequestMapping("/client")

public class ClientTypeEndpoint {

@GetMapping("/cur")

public ClientType getCurClientType(@ClientTypeMark ClientType clientType) {

return clientType;

}

}

实现和配置

按照如下方法实现 HandlerMethodArgumentResolver ，用于解析header中的 client-type 并转化为 ClientType 。

package io.github.donespeak.springbootsamples.web.common;

import org.apache.commons.lang3.StringUtils;

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;

public class CurClientTypeMethodArgumentResolver implements HandlerMethodArgumentResolver {

private final String[] CLIENT_TYPE_HEADER_NAMES = {"client-type", "CLIENT-TYPE", "Client-Type"};

// 选择要被注入的参数：判断参数是否符合解析的条件

@Override

public boolean supportsParameter(MethodParameter param) {

return param.hasParameterAnnotation(ClientTypeMark.class)

&& ClientType.class.isAssignableFrom(param.getParameterType());

}

// 返回值将被注入到被选中参数中

@Override

public Object resolveArgument(MethodParameter methodParameter, ModelAndViewContainer modelAndViewContainer,

NativeWebRequest nativeWebRequest, WebDataBinderFactory webDataBinderFactory) throws Exception {

String clientType = null;

for (String clientTypeHeader: CLIENT_TYPE_HEADER_NAMES) {

clientType = nativeWebRequest.getHeader(clientTypeHeader);

if (StringUtils.isNotBlank(clientType)) {

break;

}

}

try {

return StringUtils.isBlank(clientType) ? ClientType.UNKNOWN : ClientType.valueOf(clientType.toUpperCase());

} catch (Exception e) {

return ClientType.UNKNOWN;
       }
   }
}

为了使得配置能够生效，可以按照如下的方法添加解析器。

@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
   @Override
   public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {

// 解析@CurUserId注解的参数

argumentResolvers.add(new CurClientTypeMethodArgumentResolver());

}

}

至此，自定义参数解析器的工作就完成了。

Spring提供解析器

当你完成上面的自定 * 析器的时候，大体就能知道Spring在Controller层的其他参数解析都是怎么实现的了。

如下是Spring Mvc默认的一些参数解析器。

package org.springframework.web.servlet.mvc.method.annotation;

public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter

implements BeanFactoryAware, InitializingBean {

...

/**

* Return the list of argument resolvers to use including built-in resolvers

* and custom resolvers provided via {@link #setCustomArgumentResolvers}.

*/

private List<HandlerMethodArgumentResolver> getDefaultArgumentResolvers() {

List<HandlerMethodArgumentResolver> resolvers = new ArrayList<>();

// Annotation-based argument resolution

// 解析：@RequestParam(required = false)

resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), false));

// 解析：@RequestParam Map

resolvers.add(new RequestParamMapMethodArgumentResolver());

// 解析：@PathVariable

resolvers.add(new PathVariableMethodArgumentResolver());

// 解析：@PathVariable Map

resolvers.add(new PathVariableMapMethodArgumentResolver());

// 解析：@MatrixVariable

resolvers.add(new MatrixVariableMethodArgumentResolver());

// 解析：@MatrixVariable Map

resolvers.add(new MatrixVariableMapMethodArgumentResolver());

// 解析：@ModelAttribute(required = false)

resolvers.add(new ServletModelAttributeMethodProcessor(false));

// 解析：@RequestBody

resolvers.add(new RequestResponseBodyMethodProcessor(getMessageConverters(), this.requestResponseBodyAdvice));

// 解析：@RequestPart

resolvers.add(new RequestPartMethodArgumentResolver(getMessageConverters(), this.requestResponseBodyAdvice));

// 解析：@RequestHeader

resolvers.add(new RequestHeaderMethodArgumentResolver(getBeanFactory()));

// 解析：@RequestHeader Map

resolvers.add(new RequestHeaderMapMethodArgumentResolver());

// 解析：@CookieValue

resolvers.add(new ServletCookieValueMethodArgumentResolver(getBeanFactory()));

// 解析：@Value

resolvers.add(new ExpressionValueMethodArgumentResolver(getBeanFactory()));

// 解析：@SessionAttribute

resolvers.add(new SessionAttributeMethodArgumentResolver());

// 解析：@RequestAttribute

resolvers.add(new RequestAttributeMethodArgumentResolver());

// Type-based argument resolution

// 解析：WebRequest、ServletRequest、MultipartRequest、HttpSession、

//      Principal、Locale、TimeZone、java.time.ZoneId、InputStream

//      java.io.Reader、org.springframework.http.HttpMethod

resolvers.add(new ServletRequestMethodArgumentResolver());

// 解析：ServletResponse、OutputStream、Writer

resolvers.add(new ServletResponseMethodArgumentResolver());

// 解析：@HttpEntity、@RequestEntity

resolvers.add(new HttpEntityMethodProcessor(getMessageConverters(), this.requestResponseBodyAdvice));

// 解析：RedirectAttributes

resolvers.add(new RedirectAttributesMethodArgumentResolver());

// 解析：org.springframework.ui.Model, 值为ModelAndViewContainer#getModel

resolvers.add(new ModelMethodProcessor());

// 解析：Map, 值为ModelAndViewContainer#getModel

resolvers.add(new MapMethodProcessor());

// 解析：org.springframework.validation.Errors

resolvers.add(new ErrorsMethodArgumentResolver());

// 解析：org.springframework.web.bind.support.SessionStatus

resolvers.add(new SessionStatusMethodArgumentResolver());

// 解析：UriComponentsBuilder 或者 ServletUriComponentsBuilder

resolvers.add(new UriComponentsBuilderMethodArgumentResolver());

// Custom arguments

if (getCustomArgumentResolvers() != null) {

resolvers.addAll(getCustomArgumentResolvers());

}

// Catch-all

// 解析：@RequestParam(required = true)

resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true));

// 解析：@ModelAttribute(required = true)

resolvers.add(new ServletModelAttributeMethodProcessor(true));

return resolvers;
   }
   ...

}

一些使用Tricky

调整解析器的顺序

在一次使用spring security的开发中，定义的 UserDetials 实现类在实现 UserDetails 的同时还是实现了一个 Account 接口，在使用时，希望实现如下的效果。

public void doSomething(@AuthenticationPrincipal Account accout) {}

但因为同时使用了，spring-data，spring-data提供的 ProxyingHandlerMethodArgumentResolver 会在 AuthenticationPrincipalArgumentResolver 前面对Account进行注入处理。ProxyingHandlerMethodArgumentResolver 会拦截掉所有非org.springframework中定义的 接口 ，并尝试赋值。为了能够正常赋值给Account，需要调整两者的位置。实现如下：

import java.util.LinkedList;

import java.util.List;

import org.springframework.beans.BeansException;

import org.springframework.beans.factory.config.BeanPostProcessor;

import org.springframework.security.web.method.annotation.AuthenticationPrincipalArgumentResolver;

import org.springframework.stereotype.Component;

import org.springframework.web.method.support.HandlerMethodArgumentResolver;

import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;

/**

* 将 AuthenticationPrincipalArgumentResolver 移到最前面，如果不做调整，

* 会因为ProxyingHandlerMethodArgumentResolver在AuthenticationPrincipalArgumentResolver前面，

* 导致 @AuthenticationPrincipal Account account 无法注入

*/

public class ArgumentResolverBeanPostProcessor implements BeanPostProcessor {

private static final String BEAN_REQUEST_MAPPING_HANDLER_ADAPTER = "requestMappingHandlerAdapter";

@Override

public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {

if (beanName.equals(BEAN_REQUEST_MAPPING_HANDLER_ADAPTER)) {

RequestMappingHandlerAdapter adapter = (RequestMappingHandlerAdapter)bean;

List<HandlerMethodArgumentResolver> argumentResolvers = adapter.getArgumentResolvers();

LinkedList<HandlerMethodArgumentResolver> resolversAdjusted = new LinkedList<>(argumentResolvers);

argumentResolvers.stream().forEach(r -> {

if (AuthenticationPrincipalArgumentResolver.class.isInstance(r)) {

resolversAdjusted.addFirst(r);

} else {

resolversAdjusted.add(r);

}
           });
adapter.setArgumentResolvers(resolversAdjusted);

}
       return bean;
   }

}

来源：https://www.yangguanrong.com/posts/211225-spring-webmvc-argument-resolver/