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 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义解析器的时候,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 getDefaultArgumentResolvers() {

        List 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 argumentResolvers = adapter.getArgumentResolvers();

            LinkedList 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;
    }

} 

总结

到此这篇关于SpringMVC在Controller层方法的参数解析的文章就介绍到这了,更多相关SpringMVC在Controller层方法参数内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家!

你可能感兴趣的