關(guān)于SpringMVC在Controller層方法的參數(shù)解析詳解

更新時(shí)間：2021年12月26日 15:54:26 作者：DoneSpeak

在SpringMVC中,控制器Controller負(fù)責(zé)處理由DispatcherServlet分發(fā)的請(qǐng)求,下面這篇文章主要給大家介紹了關(guān)于SpringMVC在Controller層方法的參數(shù)解析的相關(guān)資料,需要的朋友可以參考下

自定義參數(shù)解析器

為了能夠?qū)崿F(xiàn)自定義參數(shù)解析器，只需要實(shí)現(xiàn) HandlerMethodArgumentResolver 并將添加到 WebMvcConfigurer#addArgumentResolvers 即可。

實(shí)現(xiàn)效果

下面以添加一個(gè)獲取請(qǐng)求頭的 client-type 參數(shù)為例進(jìn)行是實(shí)現(xiàn)。定義注解 @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

    ;

}

最終實(shí)現(xiàn)的效果為在Controller的方法中，可以按照如下實(shí)現(xiàn)使用。

@RestController

@RequestMapping("/client")

public class ClientTypeEndpoint {



    @GetMapping("/cur")

    public ClientType getCurClientType(@ClientTypeMark ClientType clientType) {

        return clientType;

    }

}

實(shí)現(xiàn)和配置

按照如下方法實(shí)現(xiàn) HandlerMethodArgumentResolver ，用于解析header中的 client-type 并轉(zhuǎn)化為 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"};

    // 選擇要被注入的參數(shù)：判斷參數(shù)是否符合解析的條件

    @Override

    public boolean supportsParameter(MethodParameter param) {

        return param.hasParameterAnnotation(ClientTypeMark.class)

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

    }

    // 返回值將被注入到被選中參數(shù)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;
        }
    }
}

為了使得配置能夠生效，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注解的參數(shù)

        argumentResolvers.add(new CurClientTypeMethodArgumentResolver());

    }

}

至此，自定義參數(shù)解析器的工作就完成了。

Spring提供解析器

當(dāng)你完成上面的自定義解析器的時(shí)候，大體就能知道Spring在Controller層的其他參數(shù)解析都是怎么實(shí)現(xiàn)的了。

如下是Spring Mvc默認(rèn)的一些參數(shù)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, 值為ModelAndViewContainer#getModel

        resolvers.add(new ModelMethodProcessor());

        // 解析：Map, 值為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

調(diào)整解析器的順序

在一次使用spring security的開發(fā)中，定義的 UserDetials 實(shí)現(xiàn)類在實(shí)現(xiàn) UserDetails 的同時(shí)還是實(shí)現(xiàn)了一個(gè) Account 接口，在使用時(shí)，希望實(shí)現(xiàn)如下的效果。

public void doSomething(@AuthenticationPrincipal Account accout) {}

但因?yàn)橥瑫r(shí)使用了，spring-data，spring-data提供的 ProxyingHandlerMethodArgumentResolver 會(huì)在 AuthenticationPrincipalArgumentResolver 前面對(duì)Account進(jìn)行注入處理。ProxyingHandlerMethodArgumentResolver 會(huì)攔截掉所有非org.springframework中定義的接口，并嘗試賦值。為了能夠正常賦值給Account，需要調(diào)整兩者的位置。實(shí)現(xiàn)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;

/**

 * 將 AuthenticationPrincipalArgumentResolver 移到最前面，如果不做調(diào)整，

 * 會(huì)因?yàn)镻roxyingHandlerMethodArgumentResolver在AuthenticationPrincipalArgumentResolver前面，

 * 導(dǎo)致 @AuthenticationPrincipal Account account 無(wú)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;
    }

}

總結(jié)

到此這篇關(guān)于SpringMVC在Controller層方法的參數(shù)解析的文章就介紹到這了,更多相關(guān)SpringMVC在Controller層方法參數(shù)內(nèi)容請(qǐng)搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！

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