關於SpringMVC在Controller層方法的參數解析詳解

使用版本:

spring-boot: 2.1.6.RELEASE

sping: 5.1.8.RELEASE

java: openjdk 11.0.13

自定義參數解析器

為瞭能夠實現自定義參數解析器,隻需要實現 HandlerMethodArgumentResolver 並將添加到 WebMvcConfigurer#addArgumentResolvers 即可。

實現效果

下面以添加一個獲取請求頭的 client-type 參數為例進行是實現。定義註解 @ClientTypeMark 以及enum ClientType ,用於註入header中的值。

@Target({ElementType.PARAMETER})

@Retention(RetentionPolicy.RUNTIME)

@Documented

public @interface ClientTypeMark {

}
public enum ClientType {

    WEB,

    MOBILE,

    UNKNOWN

    ;

}

最終實現的效果為在Controller的方法中,可以按照如下實現使用。

@RestController

@RequestMapping("/client")

public class ClientTypeEndpoint {



    @GetMapping("/cur")

    public ClientType getCurClientType(@ClientTypeMark ClientType clientType) {

        return clientType;

    }

}

實現和配置

按照如下方法實現 HandlerMethodArgumentResolver ,用於解析header中的 client-type 並轉化為 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"};

    // 選擇要被註入的參數:判斷參數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());

    }

    // 返回值將被註入到被選中參數中

    @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;
        }
    }
}

為瞭使得配置能夠生效,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註解的參數

        argumentResolvers.add(new CurClientTypeMethodArgumentResolver());

    }

}

至此,自定義參數解析器的工作就完成瞭。

Spring提供解析器

當你完成上面的自定義解析器的時候,大體就能知道Spring在Controller層的其他參數解析都是怎麼實現的瞭。

如下是Spring Mvc默認的一些參數解析器。

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

調整解析器的順序

在一次使用spring security的開發中,定義的 UserDetials 實現類在實現 UserDetails 的同時還是實現瞭一個 Account 接口,在使用時,希望實現如下的效果。

public void doSomething(@AuthenticationPrincipal Account accout) {}

但因為同時使用瞭,spring-data,spring-data提供的 ProxyingHandlerMethodArgumentResolver 會在 AuthenticationPrincipalArgumentResolver 前面對Account進行註入處理。ProxyingHandlerMethodArgumentResolver 會攔截掉所有非org.springframework中定義的 接口 ,並嘗試賦值。為瞭能夠正常賦值給Account,需要調整兩者的位置。實現如下:

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,如果不做調整,

 * 會因為ProxyingHandlerMethodArgumentResolver在AuthenticationPrincipalArgumentResolver前面,

 * 導致 @AuthenticationPrincipal Account account 無法註入

 */

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

到此這篇關於SpringMVC在Controller層方法的參數解析的文章就介紹到這瞭,更多相關SpringMVC在Controller層方法參數內容請搜索WalkonNet以前的文章或繼續瀏覽下面的相關文章希望大傢以後多多支持WalkonNet!

推薦閱讀: