Springboot 之 HandlerMethodReturnValueHandler 运用

简介

现在项目中大部分采用前后端分离的架构，采用这种架构的项目，在返回数据时，几乎都是采用返回 json 格式的数据。而 spring 中返回 json 格式的数据一般采用 @RestController 或者 @ResponseBody 注解。代码样例

@ResponseBody
@RequestMapping("/reqBody")
public ResultInfo<Map<String, Object>> reqBody(){
		ResultInfo<Map<String, Object>> resultInfo = new ResultInfo<>();
		resultInfo.setCode(200);
		resultInfo.setMessage("success");

		Map<String, Object> map = new HashMap<>();
		map.put("userId", 100);
		map.put("tenantId", 1001);
		map.put("userName", "bug弄潮儿");
		resultInfo.setBody(map);

		return resultInfo;
	}

今天定义一个注解读返回的 json 进行加密，来运用 HandlerMethodReturnValueHandler

pom.xml 文件引入依赖

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>com.olive</groupId>
	<artifactId>springmvc-response-body</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

	<name>springmvc-response-body</name>
	<url>http://maven.apache.org</url>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.5.14</version>
		<relativePath /> <!-- lookup parent from repository -->
	</parent>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<maven.compiler.source>8</maven.compiler.source>
		<maven.compiler.target>8</maven.compiler.target>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>org.projectlombok</groupId>
			<artifactId>lombok</artifactId>
		</dependency>
		<dependency>
		    <groupId>org.springframework.boot</groupId>
		    <artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		<dependency>
			<groupId>com.alibaba.fastjson2</groupId>
			<artifactId>fastjson2</artifactId>
			<version>2.0.14</version>
		</dependency>

	</dependencies>
</project>

定义加密注解

package com.olive.annotation;

import java.lang.annotation.*;

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Encrypted {

    boolean value() default true;
}

Encrypted 注解，该注解是一个标识注解；如果打上该注解标识加密

统一返回定义

主要包含 code、message 和 body 属性定义

package com.olive.dto;

import lombok.Data;

import java.io.Serializable;

@Data
public class ResultInfo<T> implements Serializable {

    public  int code;

    public String message;

    private T body;

    private boolean encrypt;

}

自定义 ResponseBodyHandler

该类实现 HandlerMethodReturnValueHandler 类，主要对 @RestController 或者 @ResponseBody 注解进行解析

package com.olive.config;

import com.alibaba.fastjson2.JSON;
import com.olive.annotation.Encrypted;
import com.olive.dto.ResultInfo;
import org.springframework.core.MethodParameter;
import org.springframework.core.annotation.AnnotatedElementUtils;
import org.springframework.util.Base64Utils;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.method.support.ModelAndViewContainer;

import java.nio.charset.StandardCharsets;

public class ResponseBodyHandler implements HandlerMethodReturnValueHandler {

    protected final HandlerMethodReturnValueHandler handlerMethodReturnValueHandler;

    public ResponseBodyHandler(HandlerMethodReturnValueHandler handlerMethodReturnValueHandler){
        this.handlerMethodReturnValueHandler = handlerMethodReturnValueHandler;
    }

    @Override
    public boolean supportsReturnType(MethodParameter returnType) {
        //如果被@ResponseBody注解修饰的 返回true
        return (AnnotatedElementUtils.hasAnnotation(returnType.getContainingClass(), ResponseBody.class) || returnType.hasMethodAnnotation(ResponseBody.class))
                && returnType.hasMethodAnnotation(Encrypted.class);
    }

    @Override
    public void handleReturnValue(Object returnValue,
                                  MethodParameter returnType,
                                  ModelAndViewContainer mavContainer,
                                  NativeWebRequest webRequest) throws Exception {
        if(returnValue instanceof ResultInfo){
            ResultInfo<?> resultInfo = (ResultInfo<?>)returnValue;
            ResultInfo<String> newResultInfo = new ResultInfo<>();
            newResultInfo.setCode(resultInfo.getCode());
            newResultInfo.setMessage(resultInfo.getMessage());
            newResultInfo.setEncrypt(true);
            newResultInfo.setBody(Base64Utils.encodeToString(JSON.toJSONString(resultInfo.getBody()).getBytes(StandardCharsets.UTF_8)));
            //ResponseBody注解执行器
            handlerMethodReturnValueHandler.handleReturnValue(newResultInfo,
                    returnType, mavContainer, webRequest);
        }else{
            handlerMethodReturnValueHandler.handleReturnValue(returnValue,
                    returnType, mavContainer,  webRequest);
        }
    }
}

注册 ResponseBodyHandler 到 controller 返回值处理器里，即添加自己的返回值处理器

package com.olive.config;

import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;
import org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor;

import java.util.ArrayList;
import java.util.List;

@Configuration
public class WebConfig implements InitializingBean {

    @Autowired
    private RequestMappingHandlerAdapter adapter;

    @Override
    public void afterPropertiesSet() throws Exception {
        List<HandlerMethodReturnValueHandler> unmodifiableList = adapter.getReturnValueHandlers();
        List<HandlerMethodReturnValueHandler> list = new ArrayList<>(unmodifiableList.size());
        for (HandlerMethodReturnValueHandler returnValueHandler : unmodifiableList) {
            if (returnValueHandler instanceof RequestResponseBodyMethodProcessor) {
                //将RequestResponseBodyMethodProcessor 实际返回值替换为自定义的，实际执行为RequestResponseBodyMethodProcessor
                //重要
                HandlerMethodReturnValueHandler handler = new ResponseBodyHandler(returnValueHandler);
                list.add(handler);
            } else {
                list.add(returnValueHandler);
            }
        }
        adapter.setReturnValueHandlers(list);
    }
}

测试

编写 Springboot 启动引导类

package com.olive;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

/**
 * https://cloud.tencent.com/developer/article/1616704
 *
 * @author 2230
 *
 */
@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class);
    }

}

编写测试 Controller

package com.olive.controller;

import java.util.HashMap;
import java.util.Map;

import com.olive.annotation.Encrypted;
import com.olive.dto.ResultInfo;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class TestController {

	@Encrypted
	@RequestMapping("/reqBody")
	public ResultInfo<Map<String, Object>> reqBody(){
		ResultInfo<Map<String, Object>> resultInfo = new ResultInfo<>();
		resultInfo.setCode(200);
		resultInfo.setMessage("success");

		Map<String, Object> map = new HashMap<>();
		map.put("userId", 100);
		map.put("tenantId", 1001);
		map.put("userName", "bug弄潮儿");
		resultInfo.setBody(map);

		return resultInfo;
	}

}

通过 HandlerMethodReturnValueHandler 可以对返回的数据进行进一步的封装，减少在业务代码中进行重复的返回值处理。例如，文章中的对返回数据进行统一加密。