springboot统一接口返回数据的实现

一，没有异常的情况，正常返回数据

希望接口统一返回的数据格式如下：

{
  "status": 0,
  "msg": "成功",
  "data": null
}

和接口数据对应的bean

/**
 * 统一返回结果的实体
 * @param <T>
 */
public class Result<T> implements Serializable {

  private static final long serialVersionUID = 1L;

  /**
   * 错误码
   */
  private int status;

  /**
   * 提示消息
   */
  private String msg;

  /**
   * 返回的数据体
   */
  private T data;

  public int getStatus() {
    return status;
  }

  public void setStatus(int status) {
    this.status = status;
  }

  public String getMsg() {
    return msg;
  }

  public void setMsg(String msg) {
    this.msg = msg;
  }

  public T getData() {
    return data;
  }

  public void setData(T data) {
    this.data = data;
  }
}

操作Result实体的工具类

/**
 * 生成result的工具类，避免重复代码
 */
public class ResultUtils {

  /**
   * 成功时生成result的方法,有返回数据
   */
  public static <T> Result<T> success(T t){
    Result<T> result = new Result<>();
    result.setStatus(ResultEnum.SUCCESS.getCode());
    result.setMsg(ResultEnum.SUCCESS.getMsg());
    result.setData(t);
    return result;
  }

  /**
   * 成功时生成result的方法,无返回数据
   */
  public static <T> Result<T> success(){
    return success(null);
  }

  /**
   * 失败时生成result的方法
   */
  public static <T> Result<T> error(int status, String msg){
    Result<T> result = new Result<>();
    result.setStatus(status);
    result.setMsg(msg);
    return result;
  }
}

封装错误码和错误消息的枚举类

/**
 * 所有返回结果的枚举
 */
public enum ResultEnum {

  UNKNOWN_ERROR(-1, "未知错误"),
  SUCCESS(0, "成功"),
  BASIC_INFO_ID_IS_EMPTY(600, "基本信息中BasicInfoId为空"),
  BASIC_INFO_ADD_TO_DATABASE_FAILURE(601, "向数据库添加基本信息失败"),
  DETAILS_DATA_BASIC_INFO_ID_IS_EMPTY(602, "测试数据中BasicInfoId为空"),
  DETAILS_DATA_ADD_TO_DATABASE_FAILURE(603, "向数据库添加测试数据失败");

  ResultEnum(int code, String msg) {
    this.code = code;
    this.msg = msg;
  }

  private int code;

  private String msg;

  public int getCode() {
    return code;
  }

  public void setCode(int code) {
    this.code = code;
  }

  public String getMsg() {
    return msg;
  }

  public void setMsg(String msg) {
    this.msg = msg;
  }

  @Override
  public String toString() {
    return "ResultEnum{" +
        "code=" + code +
        ", msg='" + msg + '\'' +
        '}';
  }
}

统一封装返回结果的切面

之所以需要这个切面，是为了避免每个Controller方法中都要调用ResultUtils.success()。有了这个切面，Controller可以和原来一样正常返回对象，字符串，void，在切面里面将结果封装成Result实体，而不需要每个Controller方法都返回Result实体。

/**
 * 统一处理返回结果的切面，避免每个controller方法里面都要调用ResultUtils.success()这句话
 * 统一在这个切面里面调用
 */
@ControllerAdvice
public class MyResponseAdvice implements ResponseBodyAdvice<Object> {

  @Autowired
  private ObjectMapper objectMapper;

  /**
   * Whether this component supports the given controller method return type
   * and the selected {@code HttpMessageConverter} type.
   *
   * @param returnType  the return type
   * @param converterType the selected converter type
   * @return {@code true} if {@link #beforeBodyWrite} should be invoked;
   * {@code false} otherwise
   */
  @Override
  public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
    return true;
  }

  /**
   * Invoked after an {@code HttpMessageConverter} is selected and just before
   * its write method is invoked.
   *
   * @param body         the body to be written
   * @param returnType      the return type of the controller method
   * @param selectedContentType  the content type selected through content negotiation
   * @param selectedConverterType the converter type selected to write to the response
   * @param request        the current request
   * @param response       the current response
   * @return the body that was passed in or a modified (possibly new) instance
   */
  @Override
  public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {
    if(body instanceof Result){ //发生异常之后，异常处理器里面返回的已经是Result了
      return body;
    }else if(body instanceof String){ //String属于特殊情况，需要单独处理，否则会报错
      try {
        return objectMapper.writeValueAsString(ResultUtils.success(body));
      } catch (JsonProcessingException e) {
        e.printStackTrace();
        return ResultUtils.error(ResultEnum.UNKNOWN_ERROR.getCode(), e.getMessage());
      }
    }
    return ResultUtils.success(body);
  }
}

二，有异常的情况下

service层为了自动回滚事务，会抛出一些自定义的RuntimeException。默认情况下，只有RuntimeException才会回滚事务。如果Controller里面直接处理service层抛出的异常，则Controller里面到处都是try catch块，代码会很难看。将异常集中在一个地方处理会好很多。

springboot中是通过@ControllerAdvice和@ExceptionHandler来完成统一异常处理的。这2个注解只能处理Controller和拦截器中抛出的异常，其他地方抛出的异常（比如Filter中抛出的异常），无法捕获。其他地方抛出的异常会转到/error的Controller方法来处理，默认是BasicErrorController来处理，为了能处理其他地方抛出的异常，我们会自定义ErrorController。

统一的异常处理类，处理Controller和拦截器抛出的异常

/**
 * 统一的异常处理类
 */
@ControllerAdvice
public class MyExceptionHandler {

  /**
   * 转发到/error，表示由BasicErrorController处理，
   * BasicErrorController是由springboot自动装配到容器中的
   */
  /*@ExceptionHandler(BasicInfoException.class)
  public String handleException(Exception ex, HttpServletRequest request){
    request.setAttribute("javax.servlet.error.status_code", 401);
    request.setAttribute("exMsg", ex.getMessage());
    return "forward:/error";
  }*/

  /**
   * 处理基本信息相关的异常
   */
  @ExceptionHandler(BasicInfoException.class)
  @ResponseBody
  public Result handleBasicInfoException(BasicInfoException ex){
    return ResultUtils.error(ex.getCode(), ex.getMessage());
  }

  /**
   * 处理测试数据相关的异常
   */
  @ExceptionHandler(DetailsDataException.class)
  @ResponseBody
  public Result handleDetailsDataException(DetailsDataException ex){
    return ResultUtils.error(ex.getCode(), ex.getMessage());
  }

  /**
   * 处理未知异常
   */
  @ExceptionHandler(Exception.class)
  @ResponseBody
  public Result handleUnKnowException(Exception ex){
    return ResultUtils.error(ResultEnum.UNKNOWN_ERROR.getCode(), ex.getMessage());
  }

}

自定义的异常类示例

public class BasicInfoException extends RuntimeException {

  private int code;

  public BasicInfoException(int code, String msg){
    super(msg);
    this.code = code;
  }

  public int getCode() {
    return code;
  }
}

处理其他地方抛出的异常（不是Controller和拦截器抛出的异常）,自定义ErrorController

/**
 * 自定义ErrorController，处理其他地方抛出的异常（不是Controller和拦截器抛出的异常）
 */
@Controller
public class MyBasicErrorController extends AbstractErrorController {

  private Logger logger = LoggerFactory.getLogger(this.getClass());

  /**
   * 可以通过@Value获取到
   */
  @Value("${server.error.path}")
  private String myPath;

  private final ErrorProperties errorProperties;

  private ErrorAttributes mErrorAttributes;

  public MyBasicErrorController(ErrorAttributes errorAttributes, ServerProperties serverProperties) {
    super(errorAttributes);
    this.errorProperties = serverProperties.getError();
    this.mErrorAttributes = errorAttributes;
  }

  //@RequestMapping(value = "/error")
  @RequestMapping("${server.error.path}") //从properties文件中获取
  @ResponseBody
  public Result<Object> error(HttpServletRequest request) throws Throwable {
    logger.debug("myPath = " + myPath);

    //发生错误之后直接将异常抛出去，异常会到统一异常处理器中处理
    WebRequest webRequest = new ServletWebRequest(request);
    Throwable throwable = this.mErrorAttributes.getError(webRequest).getCause();
    throw throwable;
    /*UserException ex;
    if(throwable instanceof UserException){
      ex = (UserException) throwable;
      throw ex;
    }else{
      throw throwable;
    }*/
    /*HttpStatus status = getStatus(request);
    if (status == HttpStatus.NO_CONTENT) {
      return ResultUtils.error(status.value(), status.name());
    }
    Map<String, Object> body = getErrorAttributes(request, isIncludeStackTrace(request, MediaType.ALL));
    return ResultUtils.error((Integer) body.get("status"), (String)body.get("message"));*/
  }

  /**
   * Determine if the stacktrace attribute should be included.
   * @param request the source request
   * @param produces the media type produced (or {@code MediaType.ALL})
   * @return if the stacktrace attribute should be included
   */
  private boolean isIncludeStackTrace(HttpServletRequest request, MediaType produces) {
    ErrorProperties.IncludeStacktrace include = getErrorProperties().getIncludeStacktrace();
    if (include == ErrorProperties.IncludeStacktrace.ALWAYS) {
      return true;
    }
    if (include == ErrorProperties.IncludeStacktrace.ON_TRACE_PARAM) {
      return getTraceParameter(request);
    }
    return false;
  }

  /**
   * Provide access to the error properties.
   * @return the error properties
   */
  private ErrorProperties getErrorProperties() {
    return this.errorProperties;
  }

  /**
   * Returns the path of the error page.
   *
   * @return the error path
   */
  @Override
  public String getErrorPath() {
    return this.errorProperties.getPath();
  }
}

自定义ErrorController中错误处理的方法中，也可以直接将异常抛出，这样异常就会交给统一异常处理器进行处理。

 //@RequestMapping(value = "/error")
  @RequestMapping("${server.error.path}") //从properties文件中获取
  @ResponseBody
  public Result<Object> error(HttpServletRequest request) throws Throwable {
    logger.debug("myPath = " + myPath);

    //发生错误之后直接将异常抛出去，异常会到统一异常处理器中处理
    WebRequest webRequest = new ServletWebRequest(request);
    Throwable throwable = this.mErrorAttributes.getError(webRequest).getCause();
    UserException ex;
    if(throwable instanceof UserException){
      ex = (UserException) throwable;
      throw ex;
    }else{
      throw throwable;
    }
    /*HttpStatus status = getStatus(request);
    if (status == HttpStatus.NO_CONTENT) {
      return ResultUtils.error(status.value(), status.name());
    }
    Map<String, Object> body = getErrorAttributes(request, isIncludeStackTrace(request, MediaType.ALL));
    return ResultUtils.error((Integer) body.get("status"), (String)body.get("message"));*/
  }

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