SpringMVC-请求参数注入-基本类型参数注入源码探讨

前言

这篇文章分享SringMVC处理请求流程中的一个环节，注入请求参数值，请求参数注入是DispatcherServlet接收并处理请求的流程其中的一个环节，最后选取最基础的参数解析器RequestParamMethodArgumentResolver，了解注入其如何注入基本类型，如int、String等。

Spring Version：5.0.6.RELEASE
Spring MVC Version：5.0.6.RELEASE

Demo项目

搭建一个demo项目，控制器使用@Controller注解，并使用@RequestMapping映射请求路径对应的方法。

pom.xml

<properties>
    <project.build.sourceEncoding>UTF-8project.build.sourceEncoding>
    <maven.compiler.source>1.7maven.compiler.source>
    <maven.compiler.target>1.7maven.compiler.target>
    <spring.version>5.0.6.RELEASEspring.version>
properties>
<dependencies>
    <dependency>
        <groupId>junitgroupId>
        <artifactId>junitartifactId>
        <version>4.11version>
        <scope>testscope>
    dependency>

    
    <dependency>
        <groupId>org.springframeworkgroupId>
        <artifactId>spring-coreartifactId>
        <version>${spring.version}version>
    dependency>
    <dependency>
        <groupId>org.springframeworkgroupId>
        <artifactId>spring-beansartifactId>
        <version>${spring.version}version>
    dependency>
    <dependency>
        <groupId>org.springframeworkgroupId>
        <artifactId>spring-contextartifactId>
        <version>${spring.version}version>
    dependency>
    <dependency>
        <groupId>org.springframeworkgroupId>
        <artifactId>spring-webmvcartifactId>
        <version>${spring.version}version>
    dependency>
    <dependency>
        <groupId>org.springframeworkgroupId>
        <artifactId>spring-webartifactId>
        <version>${spring.version}version>
    dependency>
    <dependency>
        <groupId>org.springframeworkgroupId>
        <artifactId>spring-context-supportartifactId>
        <version>${spring.version}version>
        <exclusions>
            <exclusion>
                <groupId>commons-logginggroupId>
                <artifactId>commons-loggingartifactId>
            exclusion>
        exclusions>
    dependency>
    

    <dependency>
        <groupId>javax.servletgroupId>
        <artifactId>javax.servlet-apiartifactId>
        <version>3.0.1version>
        <scope>providedscope>
    dependency>

    <dependency>
        <groupId>commons-fileuploadgroupId>
        <artifactId>commons-fileuploadartifactId>
        <version>1.3version>
    dependency>

dependencies>

Spring容器配置文件springContext.xml

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:p="http://www.springframework.org/schema/p"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:task="http://www.springframework.org/schema/task"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-4.0.xsd 
    http://www.springframework.org/schema/tx
    http://www.springframework.org/schema/tx/spring-tx-4.0.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-4.0.xsd
    http://www.springframework.org/schema/aop
    http://www.springframework.org/schema/aop/spring-aop-4.0.xsd
    http://www.springframework.org/schema/task
    http://www.springframework.org/schema/task/spring-task-3.1.xsd">

    <context:annotation-config/>

beans>

SpringMVC容器配置文件springServlet.xml

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-4.0.xsd
    http://www.springframework.org/schema/mvc
    http://www.springframework.org/schema/mvc/spring-mvc-4.0.xsd">


    <context:component-scan base-package="cn.wzx.controller">
    context:component-scan>

    <mvc:annotation-driven>
        <mvc:argument-resolvers>
        mvc:argument-resolvers>
        <mvc:message-converters register-defaults="true">
            <bean id="stringHttpMessageConverter"
                  class="org.springframework.http.converter.StringHttpMessageConverter">
                <property name="supportedMediaTypes">
                    <list>
                        <value>text/html;charset=UTF-8value>
                    list>
                property>
            bean>
            <bean id="formHttpMessageConverter"
                  class="org.springframework.http.converter.FormHttpMessageConverter"/>
            <bean id="byteArrayMessageConverter"
                  class="org.springframework.http.converter.ByteArrayHttpMessageConverter"/>
            <bean id="bufferedImageHttpMessageConverter"
                  class="org.springframework.http.converter.BufferedImageHttpMessageConverter"/>
        mvc:message-converters>
    mvc:annotation-driven>

    <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver"
          p:defaultEncoding="utf-8"/>

    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/views/"/>
        <property name="suffix" value=".jsp"/>
        <property name="order" value="2"/>
    bean>


    <mvc:default-servlet-handler/>
    

beans>

web.xml文件

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         metadata-complete="true" version="3.0" id="WebApp_1464923168398">
    <display-name>Archetype Created Web Applicationdisplay-name>

    <context-param id="ParamValue_1466561753096">
        <param-name>contextConfigLocationparam-name>
        <param-value>
            classpath*:conf/springContext.xml
        param-value>
    context-param>

    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListenerlistener-class>
    listener>
    <listener>
        <listener-class>org.springframework.web.context.request.RequestContextListenerlistener-class>
    listener>

    <filter id="characterEncodingFilter">
        <filter-name>characterEncodingFilterfilter-name>
        <filter-class>org.springframework.web.filter.CharacterEncodingFilterfilter-class>
        <init-param>
            <param-name>encodingparam-name>
            <param-value>utf-8param-value>
        init-param>
        <init-param>
            <param-name>forceEncodingparam-name>
            <param-value>trueparam-value>
        init-param>
    filter>

    <filter-mapping>
        <filter-name>characterEncodingFilterfilter-name>
        <url-pattern>/*url-pattern>
    filter-mapping>

    <servlet>
        <servlet-name>SpringMVCServletservlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServletservlet-class>
        <init-param>
            <param-name>contextConfigLocationparam-name>
            <param-value>classpath:conf/springServlet.xmlparam-value>
        init-param>
        <init-param>
            <param-name>throwExceptionIfNoHandlerFoundparam-name>
            <param-value>trueparam-value>
        init-param>
        <load-on-startup>1load-on-startup>
    servlet>
    <servlet-mapping>
        <servlet-name>SpringMVCServletservlet-name>
        <url-pattern>/url-pattern>
    servlet-mapping>

    <welcome-file-list>
        <welcome-file>loginwelcome-file>
    welcome-file-list>

web-app>

项目目录结构

Person.class

package cn.wzx.model;

/**
 * @author wzx
 * @time 2018/8/11
 */
public class Person {
    private String name;

    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

TestController.class

package cn.wzx.controller;

import cn.wzx.model.Person;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

/**
 * @author wzx
 * @time 2018/8/4
 */
@Controller
@RequestMapping("/test")
public class TestController {

    @RequestMapping("/index")
    public String test(String name, Person person) {
        return "index";
    }
}

至此，项目搭建完毕，下面开始钻进源码。

DispatcherServlet

DispatcherServlet类是整个Spring MVC前端接收请求的核心，外部容器将http请求封装成HttpServletRequest实例和HttpServletResponse实例后调用doDispatch()方法，开始处理请求。

DispatcherServlet#doDispatch()时序图

以上是doDispatch()时序图，简要列举doDispatch()方法重要步骤，可以看出，SpringMVC的分层做得很好，再看看doDispatch()方法源码。

DispatcherServlet#doDispatch()

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    HttpServletRequest processedRequest = request;
    HandlerExecutionChain mappedHandler = null;
    boolean multipartRequestParsed = false;

    WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

    try {
        ModelAndView mv = null;
        Exception dispatchException = null;

        try {
            //处理上传文件请求
            processedRequest = checkMultipart(request);
            multipartRequestParsed = (processedRequest != request);

            // Determine handler for the current request.
            //根据请求创建处理器执行链,其包括处理器和一系列拦截器
            mappedHandler = getHandler(processedRequest);
            if (mappedHandler == null) {
                noHandlerFound(processedRequest, response);
                return;
            }

            // Determine handler adapter for the current request.
            //根据处理器创建处理器适配器，其调用处理器处理请求
            HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

            // Process last-modified header, if supported by the handler.
            String method = request.getMethod();
            boolean isGet = "GET".equals(method);
            if (isGet || "HEAD".equals(method)) {
                long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                if (logger.isDebugEnabled()) {
                    logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
                }
                if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                    return;
                }
            }
            //执行拦截器的preHandle方法,如果返回false,终止请求处理
            if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                return;
            }

            // Actually invoke the handler.
            //处理器适配器调用处理器处理请求
            mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

            if (asyncManager.isConcurrentHandlingStarted()) {
                return;
            }

            applyDefaultViewName(processedRequest, mv);
            //执行拦截器postHandle()方法
            mappedHandler.applyPostHandle(processedRequest, response, mv);
        }
        catch (Exception ex) {
            dispatchException = ex;
        }
        catch (Throwable err) {
            // As of 4.3, we're processing Errors thrown from handler methods as well,
            // making them available for @ExceptionHandler methods and other scenarios.
            dispatchException = new NestedServletException("Handler dispatch failed", err);
        }
        //处理执行结果,渲染视图
        processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
    }
    catch (Exception ex) {
        triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
    }
    catch (Throwable err) {
        triggerAfterCompletion(processedRequest, response, mappedHandler,
                new NestedServletException("Handler processing failed", err));
    }
    finally {
        if (asyncManager.isConcurrentHandlingStarted()) {
            // Instead of postHandle and afterCompletion
            if (mappedHandler != null) {
                mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
            }
        }
        else {
            // Clean up any resources used by a multipart request.
            if (multipartRequestParsed) {
                cleanupMultipart(processedRequest);
            }
        }
    }
}

可以看出，DispatcherServlet作为前端控制器，其调用不同层级的组件实现不同功能，步骤主要：
1.判断是否是上传文件请求，如果是，作处理上传文件相关处理；
2.根据请求生成处理器执行链，其包括处理器和一系列拦截器，demo项目用的@RequestMapping注解方法，所以处理器是HandlerMethod类实例；
3.根据处理创建处理器适配器实例，此demo中创建的是RequestMappingHandlerAdapter实例；
4.执行拦截器applyPreHandle()方法，如果返回false，终止请求执行；
5.处理器适配器调用处理器处理请求；
6.执行拦截器postHandle()方法；
7.处理执行结果，渲染视图；
此处重点是RequestMappingHandlerAdapter如何调用处理器去处理请求；

RequestMappingHandlerAdapter

RequestMappingHandlerAdapter类结构

其父类AbstractHandlerMethodAdapter定义了抽象方法handleInternal()，由其子类RequestMappingHandlerAdapter实现处理请求逻辑，父类handle()直接调用handleInternal()。

handleInternal()执行的时序图：

RequestMappingHandlerAdapter#handleInternal()

@Override
protected ModelAndView handleInternal(HttpServletRequest request,
        HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

    ModelAndView mav;
    checkRequest(request);

    // Execute invokeHandlerMethod in synchronized block if required.
    if (this.synchronizeOnSession) {
        HttpSession session = request.getSession(false);
        if (session != null) {
            Object mutex = WebUtils.getSessionMutex(session);
            synchronized (mutex) {
                mav = invokeHandlerMethod(request, response, handlerMethod);
            }
        }
        else {
            // No HttpSession available -> no mutex necessary
            mav = invokeHandlerMethod(request, response, handlerMethod);
        }
    }
    else {
        // No synchronization on session demanded at all...
        mav = invokeHandlerMethod(request, response, handlerMethod);
    }

    if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
        if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
            applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
        }
        else {
            prepareResponse(response);
        }
    }

    return mav;
}

以上重点关注invokeHandlerMethod(request, response, handlerMethod);方法，再看invokeHandlerMethod()。

RequestMappingHandlerAdapter#invokeHandlerMethod()

@Nullable
protected ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

    ServletWebRequest webRequest = new ServletWebRequest(request, response);
    try {
        WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
        ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);

        ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
        if (this.argumentResolvers != null) {
            invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
        }
        if (this.returnValueHandlers != null) {
            invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
        }
        invocableMethod.setDataBinderFactory(binderFactory);
        invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);

        ModelAndViewContainer mavContainer = new ModelAndViewContainer();
        mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
        modelFactory.initModel(webRequest, mavContainer, invocableMethod);
        mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);

        AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
        asyncWebRequest.setTimeout(this.asyncRequestTimeout);

        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
        asyncManager.setTaskExecutor(this.taskExecutor);
        asyncManager.setAsyncWebRequest(asyncWebRequest);
        asyncManager.registerCallableInterceptors(this.callableInterceptors);
        asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);

        if (asyncManager.hasConcurrentResult()) {
            Object result = asyncManager.getConcurrentResult();
            mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
            asyncManager.clearConcurrentResult();
            if (logger.isDebugEnabled()) {
                logger.debug("Found concurrent result value [" + result + "]");
            }
            invocableMethod = invocableMethod.wrapConcurrentResult(result);
        }
        //调用方法处理请求
        invocableMethod.invokeAndHandle(webRequest, mavContainer);
        if (asyncManager.isConcurrentHandlingStarted()) {
            return null;
        }

        return getModelAndView(mavContainer, modelFactory, webRequest);
    }
    finally {
        webRequest.requestCompleted();
    }
}

这里主要是配置参数绑定器，接着创建ServletInvocableHandlerMethod实例，调用其invokeAndHandle()方法。

RequestMappingHandlerAdapter#invokeHandlerMethod()

public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
        Object... providedArgs) throws Exception {
    //调用方法处理请求
    Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
    setResponseStatus(webRequest);

    if (returnValue == null) {
        if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
            mavContainer.setRequestHandled(true);
            return;
        }
    }
    else if (StringUtils.hasText(getResponseStatusReason())) {
        mavContainer.setRequestHandled(true);
        return;
    }

    mavContainer.setRequestHandled(false);
    Assert.state(this.returnValueHandlers != null, "No return value handlers");
    try {
        this.returnValueHandlers.handleReturnValue(
                returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
    }
    catch (Exception ex) {
        if (logger.isTraceEnabled()) {
            logger.trace(getReturnValueHandlingErrorMessage("Error handling return value", returnValue), ex);
        }
        throw ex;
    }
}

再看看invokeForRequest()。

RequestMappingHandlerAdapter#invokeForRequest()

@Nullable
public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
        Object... providedArgs) throws Exception {
    //根据参数解析器设置方法参数值
    Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
    if (logger.isTraceEnabled()) {
        logger.trace("Invoking '" + ClassUtils.getQualifiedMethodName(getMethod(), getBeanType()) +
                "' with arguments " + Arrays.toString(args));
    }
    //通过反射,调用处理器方法
    Object returnValue = doInvoke(args);
    if (logger.isTraceEnabled()) {
        logger.trace("Method [" + ClassUtils.getQualifiedMethodName(getMethod(), getBeanType()) +
                "] returned [" + returnValue + "]");
    }
    return returnValue;
}

这里最重要的两个步骤：
1.根据参数解析器设置方法参数值；
2.通过反射,调用处理器方法；
getMethodArgumentValues()如何注入参数值？

RequestMappingHandlerAdapter#getMethodArgumentValues()

private Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
    Object... providedArgs) throws Exception {
//获取方法参数数组
MethodParameter[] parameters = getMethodParameters();
Object[] args = new Object[parameters.length];
for (int i = 0; i < parameters.length; i++) {
    MethodParameter parameter = parameters[i];
    parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
    args[i] = resolveProvidedArgument(parameter, providedArgs);
    if (args[i] != null) {
        continue;
    }
    //判断是否有解析该参数类型的解析器
    if (this.argumentResolvers.supportsParameter(parameter)) {
        try {
            //解析参数值
            args[i] = this.argumentResolvers.resolveArgument(
                    parameter, mavContainer, request, this.dataBinderFactory);
            continue;
        }
        catch (Exception ex) {
            if (logger.isDebugEnabled()) {
                logger.debug(getArgumentResolutionErrorMessage("Failed to resolve", i), ex);
            }
            throw ex;
        }
    }
    if (args[i] == null) {
        throw new IllegalStateException("Could not resolve method parameter at index " +
                parameter.getParameterIndex() + " in " + parameter.getExecutable().toGenericString() +
                ": " + getArgumentResolutionErrorMessage("No suitable resolver for", i));
    }
}
return args;
}

this.argumentResolvers是HandlerMethodArgumentResolverComposite类实例，它是解析器组合，在创建RequestMappingHandlerAdapter类实例的时候，默认添加一些参数解析器，看看RequestMappingHandlerAdapter实例初始化流程。

RequestMappingHandlerAdapter初始化时序图

RequestMappingHandlerAdapter#getDefaultArgumentResolvers()

private List getDefaultArgumentResolvers() {
    List resolvers = new ArrayList<>();

    // 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(), this.requestResponseBodyAdvice));
    resolvers.add(new RequestPartMethodArgumentResolver(getMessageConverters(), this.requestResponseBodyAdvice));
    resolvers.add(new RequestHeaderMethodArgumentResolver(getBeanFactory()));
    resolvers.add(new RequestHeaderMapMethodArgumentResolver());
    resolvers.add(new ServletCookieValueMethodArgumentResolver(getBeanFactory()));
    resolvers.add(new ExpressionValueMethodArgumentResolver(getBeanFactory()));
    resolvers.add(new SessionAttributeMethodArgumentResolver());
    resolvers.add(new RequestAttributeMethodArgumentResolver());

    // Type-based argument resolution
    resolvers.add(new ServletRequestMethodArgumentResolver());
    resolvers.add(new ServletResponseMethodArgumentResolver());
    resolvers.add(new HttpEntityMethodProcessor(getMessageConverters(), this.requestResponseBodyAdvice));
    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());
    }

    // 处理基本类型参数，如int、String等
    resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true));
    resolvers.add(new ServletModelAttributeMethodProcessor(true));

    return resolvers;
}

这里注册了两个RequestParamMethodArgumentResolver类实例，一个是处理@RequestParam注解的参数，另一个处理基本类型参数(通过useDefaultResolution=true标识)。
再看看resolveName()如何解析参数。

RequestParamMethodArgumentResolver#resolveName()

protected Object resolveName(String name, MethodParameter parameter, NativeWebRequest request) throws Exception {
    HttpServletRequest servletRequest = request.getNativeRequest(HttpServletRequest.class);

    if (servletRequest != null) {
        Object mpArg = MultipartResolutionDelegate.resolveMultipartArgument(name, parameter, servletRequest);
        if (mpArg != MultipartResolutionDelegate.UNRESOLVABLE) {
            return mpArg;
        }
    }

    Object arg = null;
    MultipartHttpServletRequest multipartRequest = request.getNativeRequest(MultipartHttpServletRequest.class);
    if (multipartRequest != null) {
        List files = multipartRequest.getFiles(name);
        if (!files.isEmpty()) {
            arg = (files.size() == 1 ? files.get(0) : files);
        }
    }
    if (arg == null) {
        //解析基本类型参数
        String[] paramValues = request.getParameterValues(name);
        if (paramValues != null) {
            arg = (paramValues.length == 1 ? paramValues[0] : paramValues);
        }
    }
    return arg;
}

以上代码不难看出，如果是基本类型参数，直接调用request获取其参数名对应的值。
后续再分析如何设置普通对象的属性，未完待续。