HandlerMethodArgumentResolver-自定参数解析器

1. 前置

理解Springmvc自带的一些实现,我们可以根据业务进行接口重写

- ServletRequestMethodArgumentResolver和ServletResponseMethodArgumentResolver处理了自动绑定HttpServletRequest和HttpServletResponse
- RequestParamMapMethodArgumentResolver处理了@RequestParam
- RequestHeaderMapMethodArgumentResolver处理了@RequestHeader
- PathVariableMapMethodArgumentResolver处理了@PathVariable
- ModelAttributeMethodProcessor处理了@ModelAttribute
RequestResponseBodyMethodProcessor处理了@RequestBody

2. 方法分析

自定义解析器需要实现HandlerMethodArgumentResolver接口,HandlerMethodArgumentResolver接口包含两个接口:

package org.springframework.web.method.support;

import org.springframework.core.MethodParameter;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;


public interface HandlerMethodArgumentResolver {

	boolean supportsParameter(MethodParameter parameter);
	Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception;

}

2.1 接口说明:

supportsParameter:用于判定是否需要处理该参数分解,返回true为需要,并会去调用下面的方法resolveArgument
resolveArgument:真正用于处理参数分解的方法,返回的Object就是controller方法上的形参对象。

3. 使用方法

3.1 自定义注解

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * 登录用户信息
 */
@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
public @interface LoginUser {

}

3.2 自定义参数解析器,实现HandlerMethodArgumentResolver接口

package io.renren.modules.app.resolver;

import io.renren.modules.app.annotation.LoginUser;
import io.renren.modules.app.entity.UserEntity;
import io.renren.modules.app.interceptor.AuthorizationInterceptor;
import io.renren.modules.app.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.MethodParameter;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.context.request.RequestAttributes;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.ModelAndViewContainer;

/**
 * 有@LoginUser注解的方法参数,注入当前登录用户
 */
@Component
public class LoginUserHandlerMethodArgumentResolver implements HandlerMethodArgumentResolver {
    @Autowired
    private UserService userService;

    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        return parameter.getParameterType().isAssignableFrom(UserEntity.class) && parameter.hasParameterAnnotation(LoginUser.class);
    }

    @Override
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer container,
                                  NativeWebRequest request, WebDataBinderFactory factory) throws Exception {
        //获取用户ID
        Object object = request.getAttribute(AuthorizationInterceptor.USER_KEY, RequestAttributes.SCOPE_REQUEST);
        if(object == null){
            return null;
        }
        //获取用户信息
        UserEntity user = userService.selectById((Long)object);
        return user;
    }
}

3.3 注册自定义参数解析器

Springboot中使用方法:

import java.util.List;

/**
 * MVC配置
 */
@Configuration
public class WebMvcConfig extends WebMvcConfigurerAdapter {
    @Autowired
    private AuthorizationInterceptor authorizationInterceptor;
    @Autowired
    private LoginUserHandlerMethodArgumentResolver loginUserHandlerMethodArgumentResolver;

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(authorizationInterceptor).addPathPatterns("/api/**");
    }

    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
        argumentResolvers.add(loginUserHandlerMethodArgumentResolver);
    }
}

###3.4 Controller使用自定义注解

    @GetMapping("info")
    public UserEntity userInfo(@LoginUser UserEntity user){
        return user;
    }

4. 总结

多读Spring全家桶源码,多了解,多理解,多实践!!!

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