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应用中的异常，有两件事要考虑，怎么处理这个异常，怎么把异常可读性高地返回给前端用户

1.怎么把异常可读性高的返回给前端用户或API的消费者

自定义错误代码和错误内容

2.怎么处理异常

比如遇到某个异常时需要发邮件通知IT团队

@ControllerAdvice 是 Spring Framework 提供的一个注解，用于定义全局的异常处理、数据绑定和模型属性的增强。

它的主要作用是集中管理控制器的全局逻辑，例如异常处理，而不需要在每个控制器中重复编写相同的代码。  

主要功能

全局异常处理：通过 @ExceptionHandler 注解 捕获并处理控制器中抛出的异常。

全局数据绑定：通过 @InitBinder 注解对请求参数进行预处理。

全局模型属性：通过 @ModelAttribute 注解为所有控制器提供公共的模型数据

3.自定义错误代码和内容，并且使用@ControllerAdvice统一处理异常

3.1 自定义错误码，可以把Demo换成projectname

public enum ExceptionCode {IN_VALID_REQUEST("Demo0001", ""),BAD_REQUEST("Demo400", "Bad Request"),NOT_FOUND("Demo404", "Resource Not Found"),INTERNAL_SERVER_ERROR("Demo500", "Internal Server Error");private final String code;private final String message;ExceptionCode(String code, String message) {this.code = code;this.message = message;}public String getCode() {return code;}public String getMessage() {return message;}
}

3.2 自定义异常InvalidationException

public class InvalidationRequestException extends RuntimeException {public InvalidationRequestException(String message) {super(message);}public InvalidationRequestException(String message, Throwable cause) {super(message, cause);}
}

3.3 自定义ExceptionAdvice，统一处理exception

当controller中抛出InvalidationRequestException时，就会被@ControllerAdvice 中的 @ExceptionHandler handleInvalidationException()方法捕获并处理该异常

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;import java.util.HashMap;
import java.util.Map;@ControllerAdvice
public class GlobalExceptionHandler {private static final Logger logger = LoggerFactory.getLogger(GlobalExceptionHandler.class);@ExceptionHandler(InvalidationRequestException.class)@ResponseBodypublic ResponseEntity<Map<String, String>> handleInvalidationException(InvalidationRequestException ex) {logger.warn("InvalidationRequestException: {}", ex.getMessage());//其它异常处理逻辑，比如发邮件，打电话通知IT团队//返回给UI或API消费者Map<String, String> response = new HashMap<>();response.put("code", ExceptionCode.IN_VALIDATED_REQUEST.getCode());response.put("detail",ex.getMessage());return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(response);}@ExceptionHandler(Exception.class)public ResponseEntity<String> handleGenericException(Exception ex) {return new ResponseEntity<>("An error occurred: " + ex.getMessage(), HttpStatus.INTERNAL_SERVER_ERROR);}
}

3.4 controller， 抛出InvalidationException异常

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;@RestController
public class DemoController {@GetMapping("/validate")public String validateParameter(@RequestParam String input) {if (input == null || input.trim().isEmpty()) {throw new InvalidationRequestException("Input parameter is invalid or empty");}return "Input is valid: " + input;}
}

3.5 测试

启动应用，访问 http://localhost:8082/validate?input

校验失败时，返回http状态码是400，body如下

{"code": "Demo0001","detail": "Input parameter is invalid or empty"}

==========================================

1.异常直接抛出

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;@RestController
public class DemoController {@GetMapping("/throwException")public String throwException() {throw new RuntimeException("This is a runtime exception!");}
}

启动应用，访问 http://localhost:8082/throwException

会获得一个状态码为500的异常 An error occurred: This is a runtime exception!

思考：这个异常对用户或者call API的消费者来说，可读性太低，不能明确的知道是什么错误

2.自定义状态码和错误信息，返回给前端用户或者API 消费者可读性高的异常

自定义错误码，可以把Demo换成projectname

public enum ExceptionCode {IN_VALIDATED_REQUEST("Demo0001", ""),BAD_REQUEST("Demo400", "Bad Request"),NOT_FOUND("Demo404", "Resource Not Found"),INTERNAL_SERVER_ERROR("Demo500", "Internal Server Error");private final String code;private final String message;ExceptionCode(String code, String message) {this.code = code;this.message = message;}public String getCode() {return code;}public String getMessage() {return message;}
}

controller抛出异常

import com.example.demo_async.exception.ExceptionCode;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;import java.util.HashMap;
import java.util.Map;@RestController
public class DemoController {@GetMapping("/testErrorCode")public ResponseEntity<Map<String, String>> testErrorCode() {Map<String, String> response = new HashMap<>();response.put("code", ExceptionCode.BAD_REQUEST.getCode());response.put("detail", ExceptionCode.BAD_REQUEST.getMessage());return new ResponseEntity<>(response, HttpStatus.BAD_REQUEST);}
}

返回http status  400， body 如下

{"code": "Demo400","detail": "Bad Request"}

思考：如果有很多个controller方法都会抛出这个异常，就需要在每个方法里写一遍异常处理的逻辑，会产生大量的重复代码，怎么解决呢？