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:
- Spring MVC <Form>表单中支持REST风格DELETE、PUT类型方法的方式和原理
- Spring MVC请求执行流程
- Spring MVC如何将请求映射到Controller
- 使用FastJsonHttpMessageConverter解析@RequestBody参数
- 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:
- StringToCollectionConverter将String转换为集合;例如:
ids -> 1,2,3
能够用List
接收; - 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: