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## 后台异常处理
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在开发过程中，不可避免的是需要处理各种异常，异常处理方法随处可见，所以代码中就会出现大量的`try {...} catch {...} finally {...}` 代码块，不仅会造成大量的冗余代码，而且还影响代码的可读性，所以对异常统一处理非常有必要。为此，我们定义了一个统一的异常类`YamiShopBindException` 与异常管理类 `DefaultExceptionHandlerConfig`。
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我们先来看下 `YamiShopBindException`的代码
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```java
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@Getter
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public class YamiShopBindException extends RuntimeException{
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/**
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*
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*/
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private static final long serialVersionUID = -4137688758944857209L;
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/**
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* http状态码
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*/
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private String code;
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private Object object;
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private ServerResponseEntity<?> serverResponseEntity;
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public YamiShopBindException(ResponseEnum responseEnum) {
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super(responseEnum.getMsg());
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this.code = responseEnum.value();
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}
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/**
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* @param responseEnum
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*/
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public YamiShopBindException(ResponseEnum responseEnum, String msg) {
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super(msg);
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this.code = responseEnum.value();
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}
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public YamiShopBindException(ServerResponseEntity<?> serverResponseEntity) {
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this.serverResponseEntity = serverResponseEntity;
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}
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public YamiShopBindException(String msg) {
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super(msg);
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this.code = ResponseEnum.SHOW_FAIL.value();
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}
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public YamiShopBindException(String msg, Object object) {
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super(msg);
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this.code = ResponseEnum.SHOW_FAIL.value();
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this.object = object;
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}
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}
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```
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`ResponseEnum`为我们自定义的返回状态码的枚举类，定义为一个枚举类，更直观处理异常返回的状态码及异常内容，以后每增加一种异常情况，只需增加一个枚举实例即可，不用每一种异常都定义一个异常类。
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```java
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public enum ResponseEnum {
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/**
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* ok
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*/
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OK("00000", "ok"),
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SHOW_FAIL("A00001", ""),
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/**
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* 用于直接显示提示用户的错误，内容由输入内容决定
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*/
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/**
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* 用于直接显示提示系统的成功，内容由输入内容决定
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*/
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SHOW_SUCCESS("A00002", ""),
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/**
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* 未授权
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*/
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UNAUTHORIZED("A00004", "Unauthorized"),
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/**
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* 服务器出了点小差
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*/
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EXCEPTION("A00005", "服务器出了点小差"),
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/**
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* 方法参数没有校验，内容由输入内容决定
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*/
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METHOD_ARGUMENT_NOT_VALID("A00014", "方法参数没有校验");
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private final String code;
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private final String msg;
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public String value() {
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return code;
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}
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public String getMsg() {
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return msg;
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}
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ResponseEnum(String code, String msg) {
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this.code = code;
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this.msg = msg;
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}
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@Override
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public String toString() {
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return "ResponseEnum{" + "code='" + code + '\'' + ", msg='" + msg + '\'' + "} " + super.toString();
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}
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}
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```
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再来看看 `DefaultExceptionHandlerConfig`类
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```java
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@Slf4j
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@RestController
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@RestControllerAdvice
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public class DefaultExceptionHandlerConfig {
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@ExceptionHandler({ MethodArgumentNotValidException.class, BindException.class })
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public ResponseEntity<ServerResponseEntity<List<String>>> methodArgumentNotValidExceptionHandler(Exception e) {
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log.error("methodArgumentNotValidExceptionHandler", e);
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List<FieldError> fieldErrors = null;
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if (e instanceof MethodArgumentNotValidException) {
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fieldErrors = ((MethodArgumentNotValidException) e).getBindingResult().getFieldErrors();
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}
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if (e instanceof BindException) {
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fieldErrors = ((BindException) e).getBindingResult().getFieldErrors();
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}
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if (fieldErrors == null) {
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return ResponseEntity.status(HttpStatus.OK)
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.body(ServerResponseEntity.fail(ResponseEnum.METHOD_ARGUMENT_NOT_VALID));
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}
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List<String> defaultMessages = new ArrayList<>(fieldErrors.size());
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for (FieldError fieldError : fieldErrors) {
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defaultMessages.add(fieldError.getField() + ":" + fieldError.getDefaultMessage());
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}
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return ResponseEntity.status(HttpStatus.OK)
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.body(ServerResponseEntity.fail(ResponseEnum.METHOD_ARGUMENT_NOT_VALID, defaultMessages));
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}
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@ExceptionHandler(YamiShopBindException.class)
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public ResponseEntity<ServerResponseEntity<?>> unauthorizedExceptionHandler(YamiShopBindException e){
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log.error("mall4jExceptionHandler", e);
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ServerResponseEntity<?> serverResponseEntity = e.getServerResponseEntity();
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if (serverResponseEntity!=null) {
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return ResponseEntity.status(HttpStatus.OK).body(serverResponseEntity);
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}
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// 失败返回消息 状态码固定为直接显示消息的状态码
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return ResponseEntity.status(HttpStatus.OK).body(ServerResponseEntity.fail(e.getCode(),e.getMessage()));
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}
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@ExceptionHandler(Exception.class)
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public ResponseEntity<ServerResponseEntity<Object>> exceptionHandler(Exception e){
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log.error("exceptionHandler", e);
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return ResponseEntity.status(HttpStatus.OK).body(ServerResponseEntity.fail(ResponseEnum.EXCEPTION));
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}
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}
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```
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## 前台异常处理
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前端请求与相应做了封装，请求响应的内容会被拦截器所拦截，当后台返回给前台特定的状态码，前台将显示不同报错信息。请求响应非常常见，我们查看在`src\utils\httpRequest.js`里面的其中一段代码
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```javascript
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http.interceptors.response.use(response => {
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return response
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}, error => {
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switch (error.response.status) {
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case 400:
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Message.error(error.response.data)
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break
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case 401:
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clearLoginInfo()
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router.push({ name: 'login' })
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break
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case 405:
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Message.error('http请求方式有误')
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break
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case 500:
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Message.error('服务器出了点小差，请稍后再试')
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break
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case 501:
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Message.error('服务器不支持当前请求所需要的某个功能')
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break
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}
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return Promise.reject(error)
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})
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```
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这里将会统一拦截返回的状态码如`400`，进行错误提示。
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## RESTful 风格
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我们的上述代码使用http状态码对请求进行统一响应，其中最大的
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RESTful架构，就是目前最流行的一种互联网软件架构。它结构清晰、符合标准、易于理解、扩展方便，所以正得到越来越多网站的采用。
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[RESTful概述](https://blog.igevin.info/posts/restful-architecture-in-general/)
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