一个项目在运行过程中必定会产生异常的，那么异常处理就是必须的。一个结构良好的异常类，对于快速定位产生的bug是非常有利的。
1.异常枚举类

public enum SysExceptionEnum {
/**
* 枚举异常码
*/
INTERNAL_ERROR("501", "系统内部异常"),
ILLEGAL_PARAM("502", "请求参数不合法"),
SQL_ERROR("503", "数据库操作异常,字段不合格或者主键冲突等!"),
;
/**
* 私有枚举构造参数和构造函数
*/
    private String code;
    private String message;

    SysExceptionEnum(String code, String message) {
        this.code = code;
        this.message = message;
    }
    /**
     * 通过code找枚举的方法
     */
    public  static SysExceptionEnum get(Long code){
        for (SysExceptionEnum result : values()){
            if (result.getCode().equals(code)){
                return result;
            }
        }
        return null;
    }
    public String getCode() {
        return code;
    }

    public String getMessage() {
        return message;
    }
}

2.自定义异常
*继承了RuntimeException

public class SystemException extends RuntimeException {

    private String code ;

    private String message;


    public SystemException(String code,String message) {
        super(message);
        this.code = code;
        this.message = message;
    }

    public String getCode() {
        return code;
    }

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

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

到此步其实已经可以使用自定异常了，写个测试类测试

public class Test {
    public static void main(String[] args){
            throw new SystemException(SysExceptionEnum.INTERNAL_ERROR.getCode(), 
                SysExceptionEnum.INTERNAL_ERROR.getMessage());
    }
}

异常测试

4.统一异常抛出类
进一步封装异常抛出

public class LeaseException {

    public static void throwSystemException(SysExceptionEnum sysExceptionEnum) {
        try {
            throw new SystemException(sysExceptionEnum.getCode(), sysExceptionEnum.getMessage());
        }catch (SystemException e){
            e.printStackTrace();
        }
    }
}

5.在Spring项目中配套使用统一异常返回处理

@Controller
@ControllerAdvice
public class BaseController {

    protected <T> ResponseObject<T> success(T dataObject) {
        return new ResponseObject<>(dataObject);
    }

    protected  ResponseObject success(){
        return  new ResponseObject();
    }

    @ExceptionHandler
    public @ResponseBody
    ResponseObject exceptionHandler(HttpServletRequest request, HttpServletResponse httpResponse, Exception ex) {
        ResponseObject responseObject = new ResponseObject() ;
        ex.printStackTrace();
        try {

            if(ex instanceof SystemException) {//自定义异常提示
                SystemException  systemException = (SystemException) ex;
                responseObject.setMessage(systemException.getMessage());
                responseObject.setCode(systemException.getCode());
                return responseObject;
            }else if( ex instanceof DataAccessException){//数据库操作异常
                responseObject.setMessage(SysExceptionEnum.SQL_ERROR.getMessage());
                responseObject.setCode(SysExceptionEnum.SQL_ERROR.getCode());
                return responseObject;
            }else{
                responseObject.setMessage(SysExceptionEnum.INTERNAL_ERROR.getMessage());
                responseObject.setCode(SysExceptionEnum.INTERNAL_ERROR.getCode());
                return responseObject;
            }
        } catch (Exception e) {//其他系统内部异常
            responseObject.setMessage(SysExceptionEnum.INTERNAL_ERROR.getCode());
            responseObject.setCode(SysExceptionEnum.INTERNAL_ERROR.getMessage());
            return responseObject;
        }

    }

}