给报错全局异常处理器

1. 员工表给账号字段增加了唯一索引，添加同名账号报错：
   java.sql.SQLIntegrityConstraintViolationException: Duplicate entry 'admin' for key 'idx_username'

2. 添加全局异常处理器，在里面处理具体报错

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;

import java.sql.SQLIntegrityConstraintViolationException;

/**
 * 全局异常处理
 * @ControllerAdvice 表示这是一个关于Controller的通知，拦截类上加了注解RestController，Controller的类
 * @ResponseBody 将结果封装成json格式返回
 * @Slf4j 方便打印日志
 */
@ControllerAdvice(annotations = {RestController.class, Controller.class})
@ResponseBody
@Slf4j
public class GlobalExceptionHandler {

    /**
     * 异常处理方法
     * @ExceptionHandler
     * SQLIntegrityConstraintViolationException.class 要处理的异常类
     * Controller抛的SQLIntegrityConstraintViolationException异常都会在这里处理
     * @return
     */
    @ExceptionHandler(SQLIntegrityConstraintViolationException.class)
    public R<String> exceptionHandler(SQLIntegrityConstraintViolationException ex) {//声明一下异常，框架会把异常信息注进来
        log.error(ex.getMessage());

        if (ex.getMessage().contains("Duplicate entry")) {
            String[] split = ex.getMessage().split(" ");
            String msg = split[2] + "已存在";
            return R.error(msg);
        }

        return R.error("未知错误");
    }
}

3. 效果