spring boot 2 全局统一返回RESTful风格数据、统一异常处理

全局统一返回RESTful风格数据，主要是实现ResponseBodyAdvice接口的方法，对返回值在输出之前进行修改。
使用注解@RestControllerAdvice拦截异常并统一处理。

开发环境：
IntelliJ IDEA 2019.2.2
jdk1.8
Spring Boot 2.2.2

1、创建一个SpringBoot项目，pom.xml引用的依赖包如下

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.62</version>
        </dependency>

2、定义一个返回类

package com.example.response.entity;

import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;

import java.io.Serializable;

@Data
@NoArgsConstructor
@ToString
public class ResponseData<T> implements Serializable {
    /**
     * 状态码：0-成功，1-失败
     * */
    private int code;

    /**
     * 错误消息，如果成功可为空或SUCCESS
     * */
    private String msg;

    /**
     * 返回结果数据
     * */
    private T data;

    public static ResponseData success() {
        return success(null);
    }

    public static ResponseData success(Object data) {
        ResponseData result = new ResponseData();
        result.setCode(0);
        result.setMsg("SUCCESS");
        result.setData(data);
        return result;
    }

    public static ResponseData fail(String msg) {
        return fail(msg,null);
    }

    public static ResponseData fail(String msg, Object data) {
        ResponseData result = new ResponseData();
        result.setCode(1);
        result.setMsg(msg);
        result.setData(data);
        return result;
    }
}

3、统一拦截接口返回数据

新建一个类GlobalResponseHandler，用注解@RestControllerAdvice，并且实现ResponseBodyAdvice接口的方法，其中方法supports可以判断哪些需要拦截，方法beforeBodyWrite可以对返回值在输出之前进行修改，从而实现返回统一的接口数据。

package com.example.response.config;

import com.alibaba.fastjson.JSON;
import com.example.response.entity.ResponseData;
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.web.bind.annotation.RestControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;

/**
 * 实现ResponseBodyAdvice接口，可以对返回值在输出之前进行修改
 */
@RestControllerAdvice
public class GlobalResponseHandler implements ResponseBodyAdvice<Object> {

    //判断支持的类型
    @Override
    public boolean supports(MethodParameter methodParameter, Class<? extends HttpMessageConverter<?>> aClass) {
        // 检查注解是否存在，存在则忽略拦截
        if (methodParameter.getDeclaringClass().isAnnotationPresent(IgnorReponseAdvice.class)) {
            return false;
        }
        if (methodParameter.getMethod().isAnnotationPresent(IgnorReponseAdvice.class)) {
            return false;
        }
        return true;
    }

    @Override
    public Object beforeBodyWrite(Object o, MethodParameter methodParameter, MediaType mediaType, Class<? extends HttpMessageConverter<?>> aClass, ServerHttpRequest serverHttpRequest, ServerHttpResponse serverHttpResponse) {
        // 判断为null构建ResponseData对象进行返回
        if (o == null) {
            return ResponseData.success();
        }
        // 判断是ResponseData子类或其本身就返回Object o本身，因为有可能是接口返回时创建了ResponseData,这里避免再次封装
        if (o instanceof ResponseData) {
            return (ResponseData<Object>) o;
        }
        // String特殊处理，否则会抛异常
        if (o instanceof String) {
            return JSON.toJSON(ResponseData.success(o)).toString();
        }
        return ResponseData.success(o);
    }
}

新建自定义注解IgnorReponseAdvice

package com.example.response.config;

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

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

4、统一异常处理

package com.example.response.exception;
import com.example.response.entity.ResponseData;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.RestControllerAdvice;

@RestControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(Exception.class)
    public ResponseData exceptionHandler(Exception e) {
        e.printStackTrace();
        return ResponseData.fail("服务器异常：" + e.getMessage());
    }
}

5、新建一个测试用的实体类

package com.example.response.entity;

import lombok.Data;

@Data
public class User {
    private Long userId;
    private String userName;
    public User(Long userId, String userName){
        this.userId = userId;
        this.userName = userName;
    }
}

6、新建一个测试用的控制器类

package com.example.response.controller;

import com.example.response.config.IgnorReponseAdvice;
import com.example.response.entity.ResponseData;
import com.example.response.entity.User;
import org.springframework.web.bind.annotation.*;

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

@RestController
public class DemoController {
    @GetMapping("user")
    public User user() {
        User u = new User(100L, "u1");
        return u;
    }

    @GetMapping("userList")
    public List<User> userList(){
        List<User> list = new ArrayList<User>();
        list.add(new User(100L, "u1"));
        list.add(new User(200L, "u2"));
        return list;
    }

    @GetMapping("test1")
    public String test1(){
        return "test1";
    }

    @GetMapping("test2")
    public ResponseData test2(){
        return ResponseData.success("test2");
    }

    @IgnorReponseAdvice
    @GetMapping("test3")
    public String test3() {
        return "test3";
    }

    @GetMapping("test4")
    public String test4() {
        Integer x = 1 / 0;
        return x.toString();
    }

    @GetMapping("test5")
    public String test5() throws Exception {
        throw new Exception("自定义异常信息");
    }
}

7、用Postman测试

(1)请求http://localhost:8080/user，返回

{
    "code": 0,
    "msg": "SUCCESS",
    "data": {
        "userId": 100,
        "userName": "u1"
    }
}

(2)请求http://localhost:8080/userList，返回

{
    "code": 0,
    "msg": "SUCCESS",
    "data": [
        {
            "userId": 100,
            "userName": "u1"
        },
        {
            "userId": 200,
            "userName": "u2"
        }
    ]
}

(3)请求http://localhost:8080/tes1，返回

{"msg":"SUCCESS","code":0,"data":"test1"}

(4)请求http://localhost:8080/test2，返回

{
    "code": 0,
    "msg": "SUCCESS",
    "data": "test2"
}

(5)请求http://localhost:8080/test3，返回

test3

(6)请求http://localhost:8080/test4，返回

{
    "code": 1,
    "msg": "服务器异常：/ by zero",
    "data": null
}

(7)请求http://localhost:8080/test5，返回

{
    "code": 1,
    "msg": "服务器异常：自定义异常信息",
    "data": null
}

参考文章：
https://blog.csdn.net/lrt890424/article/details/83624761
https://www.cnblogs.com/Purgeyao/p/11599810.html