为什么会有统⼀数据返回？

其实统一数据返回是运用了AOP（对某一类事情的集中处理）的思维。

1.⽅便前端程序员更好的接收和解析后端数据接⼝返回的数据。

2.降低前端程序员和后端程序员的沟通成本，因为所有接⼝都是固定的返回格式。

3.有利于项⽬统⼀数据的维护和修改。

4.有利于后端技术部⻔的统⼀规范的标准制定。

代码实现 

假如我们要统一返回Result 对象

import lombok.Data;

@Data
public class Result<T> {

    private String s = "我是Result的s属性";
    private Integer num = 2008;
    private T data;

    public static <T> Result success(T data) {
        Result result = new Result<>();
        result.setData(data);
        return result;
    }
}

使用TextController进行测试

import com.wh.advice.model.Result;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

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


@RestController
public class TextController {

    @RequestMapping("/text1")
    public Integer text1() {
        return 100;
    }

    @RequestMapping(value = "/text2", produces = "application/json")
    public String text2() {
        return "text";
    }

    @RequestMapping("/text3")
    public Result<List<Integer>> text3() {
        List<Integer> list = new ArrayList();
        list.add(1);
        list.add(2);
        list.add(3);
        return Result.success(list);
    }
}

注意：

produces = "application/json"->表示将生产json格式的数据 

 统⼀的数据返回格式的实现

1. 添加类注解@ControllerAdvice，实现接口ResponseBodyAdvice
2. 重写responseAdvice方法
3. 重写beforeBodyWriter方法

代码： 

import com.wh.advice.model.Result;
import org.springframework.core.MethodParameter;
import org.springframework.http.MediaType;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;

@ControllerAdvice
public class ResponseAdvice implements ResponseBodyAdvice {


    @Override
    public boolean supports(MethodParameter returnType, Class converterType) {
        return true;
    }

    @Override
    public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType, Class selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {
        return Result.success(body);
    }
}

1.supports⽅法: 判断是否要执⾏beforeBodyWrite⽅法. true为执⾏, false不执⾏. 通过该⽅法可以

选择哪些类或哪些⽅法的response要进⾏处理, 其他的不进⾏处理.

2.beforeBodyWrite⽅法: 对response⽅法进⾏具体操作处理 。

1.测试http://127.0.0.1:8080/text1

 添加统⼀数据返回格式之前:

添加统⼀数据返回格式之后:

 2.我们继续测http://127.0.0.1:8080/text2

 多测试⼏种不同的返回结果, 发现只有返回结果为String类型时才有这种错误发⽣

解决问题：

我们要注入ObjectMapper

@Autowired
private ObjectMapper objectMapper;

对 beforeBodyWrite⽅法进行修改： 

 @SneakyThrows
    @Override
    public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType, Class selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {
        if (body instanceof String) {
            return objectMapper.writeValueAsString(Result.success(body));
        }
        return Result.success(body);
    }

 3.如果⼀些⽅法返回的结果已经是Result类型了, 那就直接返回Result类型的结果即可

完整代码：

import com.fasterxml.jackson.databind.ObjectMapper;
import com.wh.advice.model.Result;
import lombok.SneakyThrows;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.MethodParameter;
import org.springframework.http.MediaType;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;

@ControllerAdvice
public class ResponseAdvice implements ResponseBodyAdvice {
    @Autowired
    private ObjectMapper objectMapper;

    @Override
    public boolean supports(MethodParameter returnType, Class converterType) {
        return true;
    }

    @SneakyThrows
    @Override
    public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType, Class selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {
        if (body instanceof Result) {
            return body;
        }
        if (body instanceof String) {
            return objectMapper.writeValueAsString(Result.success(body));
        }
        return Result.success(body);
    }
}

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