本篇内容主要讲解“SpringMVC中的HandlerMethodArgumentResolver接口实现自定义参数类型解析”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“SpringMVC中的HandlerMethodArgumentResolver接口实现自定义参数类型解析”吧!
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HandlerMethodArgumentResolver 接口看起来很陌生，实际上在SpringMVC中很多地方我们都会直接或者间接的接触到
例如:
@RequestParam 解析 RequestParamMethodArgumentResolver (基础类型的默认解析器)
@PathVariable 解析 PathVariableMethodArgumentResolver
@RequestBody 解析 RequestResponseBodyMethodProcessor
@CookieValue 解析 ServletCookieValueMethodArgumentResolver ...
通过查看SpringMVC的源码， 可以看到以下代码片段，这就是SpringMVC初始化时，默认的所有HandlerMethodArgumentResolver实现
// org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter private ListgetDefaultArgumentResolvers() { 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()); } // Catch-all resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true)); resolvers.add(new ServletModelAttributeMethodProcessor(true)); return resolvers; }
HandlerMethodArgumentResolver 接口就两个方法，一个用来判断是否支持参数类型，一个是解析的具体实现
public interface HandlerMethodArgumentResolver {
// 返回是否支持该参数
boolean supportsParameter(MethodParameter parameter);
// 返回解析后的参数值
@Nullable
Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception;
}这个接口主要的使用场景就是来实现自定义的参数注入。例如在很多前后端分离的项目中，我们不会去使用Session，而是自己维护一个token来实现状态管理，
这种时候，如果需要取得用户数据，正常操作，我们可能需要手动去取得token，然后去查询用户数据
例如以下这个例子，我们从Header中取得token数据，然后从redis中查询到用户标识，接着从数据库查询到用户基本信息
@PostMapping("get-user-info")
public UserInfo getUserInfo(@RequestHeader String token) {
// 伪代码
Long userId = redisClient.get(token);
UserInfo useInfo = userDao.getById(userId);
return userInfo;
}这样写没什么问题，不过在实际的项目中，我们可能很多地方都需要用到用户的一些基本信息，每次都这样去手动编码去取，就显得得很繁琐了
我们使用HandlerMethodArgumentResolver接口来实现
// 1. 实现HandlerMethodArgumentResolver接口
public class UserInfoArgumentResolver implements HandlerMethodArgumentResolver{
private final RedisClient redisClient;
private final UserDao userDao;
public UserInfoArgumentResolver(RedisClient redisClient, UserDao userDao) {
this.redisClient = redisClient;
this.userDao = userDao;
}
@Override
public boolean supportsParameter(MethodParameter parameter) {
return UserInfo.class.isAssignableFrom(parameter.getParameterType());
}
@Override
public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
HttpServletRequest nativeRequest = (HttpServletRequest) webRequest.getNativeRequest();
String token = nativeRequest.getHeader("token");
Long userId = redisClient.get(token);
UserInfo useInfo = userDao.getById(userId);
return userInfo;
}
}
// 2. 添加到配置中
@Configuration
@EnableWebMvc
public class FastMvcConfiguration implements WebMvcConfigurer {
@Autowrite
UserDao userDao;
@Autowrite
RedisClient redisClient;
@Override
public void addArgumentResolvers(List resolvers) {
resolvers.add(new UserInfoArgumentResolver(redisClient, userDao));
}
}
// 3. 在Controller中使用
@RestController
public class UserInfoController {
@PostMapping("get-user-info")
public UserInfo getUserInfo(UserInfo userInfo) {
return userInfo;
}
@PostMapping("say-hello")
public String sayHello(UserInfo userInfo) {
return "hello " + userInfo.getNickName();
}
} 添加了 UserInfoArgumentResolver 解释器以后，当我们需要使用UserInfo时，只需要使用指定的类型就可以取得，不需要做其他任何操作
到此，相信大家对“SpringMVC中的HandlerMethodArgumentResolver接口实现自定义参数类型解析”有了更深的了解，不妨来实际操作一番吧！这里是创新互联网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！
