从头开始写项目（Q）：通过扩展Convertor玩到ResponseBodyAdvice

要求：RestFul风格：统一返回对象格式，统一异常对象处理。

类似于一个Controller返回一个Object，然后统一封装成我们自定义的对象AppResponse。

我一开始的思路如下图：

结果老大对拓展类型转换器产生浓厚的兴趣（典型的自己给自己挖坑）。

直接上用法，再解释原理。

第一步，依赖，我直接贴全部了：

	
		2.0.5.RELEASE
		6.0.8.Final
		5.1.0
		1.1.0
		5.0.4.RELEASE
		2.9.4
		3.0.1
		6.0.6
		5.2.13.Final
		2.7.8
		1.2.3
		3.0
		1.8.8
		1.2.2
	
	
		
			org.springframework
			spring-context
			${org.springframework.version}
			runtime
		
		
			org.springframework
			spring-webmvc
			${org.springframework.version}
		

		
			com.fasterxml.jackson.core
			jackson-core
			${jackson.version}
		
		
			com.fasterxml.jackson.core
			jackson-databind
			${jackson.version}
		
		
			javax.servlet
			javax.servlet-api
			${servlet.version}
			provided
		
		
			org.springframework.data
			spring-data-jpa
			${spring.data.jpa.version}
		
		
			mysql
			mysql-connector-java
			${mysql.connector.version}
		
		
			org.hibernate
			hibernate-core
			${hibernate.version}
		
		
			org.hibernate
			hibernate-entitymanager
			${hibernate.version}
		
		
			org.hibernate
			hibernate-ehcache
			${hibernate.version}
		
		
			org.hibernate
			hibernate-validator
			${hibernate.validator.version}
		
		
		
			com.zaxxer
			HikariCP
			${HikariCP.version}
		
		
			ch.qos.logback
			logback-classic
			${logback.version}
		
		
			org.junit.jupiter
			junit-jupiter-api
			${junit.jupiter.version}
			test
		

		
			org.junit.platform
			junit-platform-runner
			${junit.platform.version}
			test
		
		
			org.junit.jupiter
			junit-jupiter-engine
			${junit.jupiter.version}
		

		
			org.apache.commons
			commons-lang3
			${common.lang3.version}
		
		
			org.aspectj
			aspectjweaver
			${aspectjweaver.version}
		

        org.apache.shiro
        shiro-core
        ${shiro.core.version}
    
	
	
		demo
		
			
				org.apache.maven.plugins
				maven-compiler-plugin
				3.1
				
					1.8
					1.8
				
			
		
	

第二步：创建你自定义的类型转换器：

import java.io.IOException;
import java.lang.reflect.Type;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.HttpOutputMessage;
import org.springframework.http.converter.HttpMessageNotWritableException;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.lang.Nullable;
import org.springframework.stereotype.Component;

import com.kushou.demo.common.AppResponse;
import com.kushou.demo.common.ExceptionInfo;

@Component
public class AppResponseMappingJackson2HttpMessageConverter extends MappingJackson2HttpMessageConverter {
	private static final Logger LOGGER = LoggerFactory.getLogger(AppResponseMappingJackson2HttpMessageConverter.class);

	@Override
	protected void writeInternal(Object object, @Nullable Type type, HttpOutputMessage outputMessage)
			throws IOException, HttpMessageNotWritableException {

		// 做数据处理
		if (object == null) {
			//继续原有的方法
			super.writeInternal(object, type, outputMessage);
		}
		AppResponse appResponse = new AppResponse<>();
		appResponse.setData(object);
		appResponse.setStatus(1);
		ExceptionInfo exceptionInfo = new ExceptionInfo();
		appResponse.setExceptionInfo(exceptionInfo);
		//继续原有的方法
		super.writeInternal(appResponse, type, outputMessage);
	}

}

第三步：把你自定义的类型转换器添加到springMVC的配置文件中：

ok，然后写一个简单的controller测试一下：

@RequestMapping(value = "/getAllUser.action", method = { RequestMethod.GET, RequestMethod.POST })
	public Paging getAllUser(HttpServletRequest request) {
		// 分页
		List users;
		int count;
		users = userService.getAllUser();
		count = userService.getAllUserCount();
		LOGGER.info("获取所有用户信息成功");
		if (users == null) {
			return null;
		}
		Paging paging = new Paging<>();
		paging.setData(users);
		paging.setTotal(count);
		return paging;
	}

我这里用的是@RestController，如果Class上标注的是@Controller注意添加@ResponseBody。

看一下结果：

{
	"status": 1,
	"data": {
		"total": 5,
		"data": [{
			"id": 1,
			"username": "loren",
			"password": "123456",
			"phone": null
		}, {
			"id": 2,
			"username": "loren2",
			"password": "e10adc3949ba59abbe56e057f20f883e",
			"phone": null
		}, {
			"id": 3,
			"username": "loren3",
			"password": "25f9e794323b453885f5181f1b624d0b",
			"phone": null
		}, {
			"id": 4,
			"username": "loren4",
			"password": "e10adc3949ba59abbe56e057f20f883e",
			"phone": null
		}],
		"empty": false
	},
	"exceptionInfo": {
		"code": null,
		"message": null
	}
}

似乎完成了返回对象的包装，然而这样做其实有一个问题，那就是如果我的controller返回值是null，就会有问题。看过源码的就会知道这个问题，不过等下再解释，先解决问题。

其实再spring源码RequestResponseBodyMethodProcessor的handleReturnValue这个方法里有这么一句话：

// Try even with null return value. ResponseBodyAdvice could get involved.

你可以用ResponseBodyAdvice来处理controller方法返回值为null的情况。而这个ResponseBodyAdvice方法更加简单。

第一步：自定义一个advice实现ResponseBodyAdvice：

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.core.MethodParameter;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.lang.Nullable;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;


@ControllerAdvice
public class MyResponseBodyAdvice implements ResponseBodyAdvice