文章目录

  • 一、前言
  • 二、类型转换器Converter
    • 1、自定义类型转换器
  • 三、参数解析器
    • 1、自定义分页参数解析器
    • 2、自定义注解参数解析器

一、前言

Spring MVC源码分析相关文章已出:

  1. Spring MVC <Form>表单中支持REST风格DELETE、PUT类型方法的方式和原理
  2. Spring MVC请求执行流程
  3. Spring MVC如何将请求映射到Controller
  4. 使用FastJsonHttpMessageConverter解析@RequestBody参数
  5. Spring MVC多种请求入参处理方式都在这了

更多Spring系列源码分析文章见SpringBoot专栏:

  • 精通Spring Boot

二、类型转换器Converter

Spring官方文档

Spring 3.0 引入了一个 core.convert,并提供通用类型转换系统的包。系统定义了一个 SPI 来实现类型转换逻辑,并定义一个 API 来在运行时执行类型转换。

这套类型转换系统的顶层接口为:Converter

@FunctionalInterfacepublic interface Converter<S, T> {/** * Convert the source object of type {@code S} to target type {@code T}. * @param source the source object to convert, which must be an instance of {@code S} (never {@code null}) * @return the converted object, which must be an instance of {@code T} (potentially {@code null}) * @throws IllegalArgumentException if the source cannot be converted to the desired target type */@NullableT convert(S source);}

Converter的作用是将类型 S 转换为 T,在参数解析器中使用该接口的实现类 将前端请求参数 转换成 控制器方法(Controller#Method) 需要的参数类型。

此外,还有ConverterFactory(将类型S 转换为 R及其子类型)、ConversionService(用来在运行时执行类型转换);

Spring 提供的所有支持的类型转换器实现类都在 org.springframework.core.convert.support 包下,大多数转换器的convert()方法都很简单,感兴趣可以自己看一下源码。

比如:

  1. StringToCollectionConverter将String转换为集合;例如:ids -> 1,2,3 能够用 List 接收;
  2. StringToBooleanConverter将String转换为Boolean,例如:enable -> no 能够用 Boolean 接收;

1、自定义类型转换器

要实现的效果:

  • 请求中传递JavaModel数据,多个属性之间以英文逗号,分隔;
    比如:POST请求 http://127.0.0.1:38888/person/other" />

    三、参数解析器

    Spring中参数解析器的最上层接口为HandlerMethodArgumentResolver,其中有两个方法:

    • supportsParameter() 判断当前参数解析器是否支持解析的方法参数;
    • resolveArgument() 从请求数据中解析出当前方法参数对应的参数值。
    public interface HandlerMethodArgumentResolver {/** * Whether the given {@linkplain MethodParameter method parameter} is * supported by this resolver. */boolean supportsParameter(MethodParameter parameter);/** * Resolves a method parameter into an argument value from a given request. * A {@link ModelAndViewContainer} provides access to the model for the * request. A {@link WebDataBinderFactory} provides a way to create * a {@link WebDataBinder} instance when needed for data binding and * type conversion purposes. */@NullableObject resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception;}

    1、自定义分页参数解析器

    前端请求传递两个分页参数 pageNum、pageSize,后端用一个IPage模型接收;

    参数解析器策略要支持的是 IPage.class,核心是 HandlerMethodArgumentResolver 的两个方法实现。

    这里基于spring-data-common 包下的PageableHandlerMethodArgumentResolver 做一个扩展。

    1> maven依赖:

    <dependency>    <groupId>org.springframework.data</groupId>    <artifactId>spring-data-commons</artifactId></dependency>

    2> 自定义参数解析器PageHandlerMethodArgumentResolver

    package com.saint.config;import com.saint.model.IPage;import org.springframework.core.MethodParameter;import org.springframework.data.domain.PageRequest;import org.springframework.data.domain.Pageable;import org.springframework.data.web.PageableHandlerMethodArgumentResolver;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;/** * 自定义分页参数解析器 * * @author Saint */public class PageHandlerMethodArgumentResolver implements HandlerMethodArgumentResolver {    private static final int DEFAULT_PAGE = 0;    private static final int DEFAULT_SIZE = 10;    private static final String DEFAULT_PAGE_PARAM = "pageNum";    private static final String DEFAULT_SIZE_PARAM = "pageSize";    /**     * 组合 `spring-data-commons` 包下的PageableHandlerMethodArgumentResolver,实现分页参数解析功能     */    private final PageableHandlerMethodArgumentResolver pageableArgumentResolver;    public PageHandlerMethodArgumentResolver() {        PageableHandlerMethodArgumentResolver resolver = new PageableHandlerMethodArgumentResolver();        resolver.setFallbackPageable(PageRequest.of(DEFAULT_PAGE, DEFAULT_SIZE));        resolver.setSizeParameterName(DEFAULT_SIZE_PARAM);        resolver.setPageParameterName(DEFAULT_PAGE_PARAM);        resolver.setOneIndexedParameters(true);        this.pageableArgumentResolver = resolver;    }    @Override    public boolean supportsParameter(MethodParameter parameter) {        return IPage.class.equals(parameter.getParameterType());    }    @Override    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {        Pageable pageable =                pageableArgumentResolver.resolveArgument(                        parameter, mavContainer, webRequest, binderFactory);        return new IPage(pageable.getPageNumber() + 1, pageable.getPageSize());    }}

    3> 将自定义的参数解析器添加到Spring MVC 的参数解析器集合中:

    @Configurationpublic class WebMvcConfig {    @Bean    public WebMvcConfigurer webMvcConfigurer() {        return new WebMvcConfigurer() {            @Override            public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {                resolvers.add(new PageHandlerMethodArgumentResolver());            }        };    }}

    4> Controller方法:

    /** * http://localhost:38888/page?pageNum=9&pageSize=20 */@GetMapping("/page")public String page(IPage page) {    return page.toString();}

    5> 效果:

    • GET /xxx?pageNum=1&pageSize=10请求的分页参数被解析成了IPage对象

    2、自定义注解参数解析器

    自定义一个注解用于标注某个JavaModel,JavaModel中的信息是根据请求中的某些数据间接得到。

    1> 自定义的注解@UserParam:

    @Target(ElementType.PARAMETER)@Retention(RetentionPolicy.RUNTIME)public @interface UserParam {}

    2> 自定义的JavaModel:

    @Data@NoArgsConstructor@AllArgsConstructorpublic class UserInfo {    private String userCode;    private String userName;    private String address;}

    3> 自定义的参数解析器:

    package com.saint.config;import com.saint.annotation.UserParam;import com.saint.model.UserInfo;import com.saint.service.UserInfoService;import org.springframework.beans.factory.annotation.Autowired;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;import javax.servlet.http.HttpServletRequest;/** * @author Saint */public class UserInfoArgumentResolver implements HandlerMethodArgumentResolver {    @Autowired    private UserInfoService userInfoService;    @Override    public boolean supportsParameter(MethodParameter methodParameter) {        return methodParameter.getParameterType() == UserInfo.class                && methodParameter.hasParameterAnnotation(UserParam.class);    }    @Override    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {        HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);        String token = request.getHeader("token");        UserInfo userInfo = userInfoService.getUserInfoByToken(token);        return userInfo;    }}

    4> UserInfoService:

    package com.saint.service;import com.saint.model.UserInfo;import org.springframework.stereotype.Service;/** * @author Saint */@Servicepublic class UserInfoService {    public UserInfo getUserInfoByToken(String token) {        // todo 调用用户中心返回用户的信息        UserInfo user = new UserInfo("code01", "saint", "你心里 " + token);        return user;    }}

    5> 将自定义的参数解析器添加到Spring MVC 的参数解析器集合中:

    • 一定要先将自定义的参数解析器实例化一个Bean到Spring容器中,否则其中无法调用其他SpringBean。
    package com.saint.config;import com.saint.model.Person;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;import org.springframework.core.convert.converter.Converter;import org.springframework.format.FormatterRegistry;import org.springframework.util.StringUtils;import org.springframework.web.method.support.HandlerMethodArgumentResolver;import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;import java.util.List;/** * @author Saint */@Configurationpublic class WebMvcConfig {    @Bean    public UserInfoArgumentResolver getUserInfoArgumentResolver() {        return new UserInfoArgumentResolver();    }    @Bean    public WebMvcConfigurer webMvcConfigurer() {        return new WebMvcConfigurer() {            @Override            public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {                resolvers.add(getUserInfoArgumentResolver());            }        };    }}

    6> 效果: