SSM integration - exception handler and project exception handling scheme

• Exceptions are inevitable in the process of program development
• The common locations and causes of abnormal phenomena are as follows :
  • Exceptions thrown inside the framework : Caused by non-conforming use
  • Exceptions thrown by the data layer : Due to external server failure ( for example : Server access timeout )
  • Exceptions thrown by the business layer : Due to business logic writing errors ( for example : Traverse business writing operations , Lead to cable bow | Abnormal etc. )
  • Exceptions thrown by the presentation layer : Due to data collection 、 Verification and other rules lead to ( for example : Mismatched data types cause exceptions )
  • Exception thrown by tool class : Because the writing of tool books is not rigorous and robust enough, it leads to ( for example : The connection that needs to be released has not been released for a long time, etc )
     

problem ：

1、 Exceptions occur at all levels , Which layer is the exception handling code written on ？？

All exceptions are thrown to the presentation layer for processing

2、 The presentation layer handles exceptions , Write separately in each method , The amount of code written is huge and the meaning is not strong , How to solve ？？

AOP thought

Exception handler

Centralized 、 Handle exceptions in the project in a unified way

1、 Using annotations @RestControllerAdvice Declare this class as an exception handler class

This annotation comes with @ResponseBody Annotations and @Component annotation , Have corresponding functions

/**
 *  Exception handler 
 */
@RestControllerAdvice
public class ProjectExceptionAdvice {
    @ExceptionHandler(Exception.class)
    public Result doException(Exception ex){
        var msg = " abnormal , Here you are ！";
        System.out.println(msg);
        return new Result(msg,400,ex.getMessage());
    }
}

2、 Using annotations @ExceptionHandler , Above the controller method used to define exception handling

effect : Set the handling scheme of the specified exception , The function is equivalent to the controller method , Terminate the execution of the original controller after an exception occurs , And go to the current method to execute

Such methods can vary according to the exceptions handled , Make multiple methods to deal with the corresponding exceptions respectively .

effect ：

 

Project exception handling scheme

Project exception classification

• Business exceptions (BusinessException)
  • Exceptions caused by standardized user behavior
  • Exceptions caused by nonstandard user behavior operations
• System exception (SystemException)
  • Predictable and unavoidable exceptions during project operation
• Other anomalies (Exception)
  • Unexpected exceptions by programmers

Project exception handling scheme

• Business exceptions (BusinessException)
  • Send the corresponding message to the user , Remind the standard operation
• System exception (SystemException)
  • Send a fixed message to the user , Appease users
  • Send specific messages to O & M personnel , Remind maintenance
  • Log
• Other anomalies (Exception)
  • Send a fixed message to the user , Appease users
  • Send specific messages to programmers , Remind maintenance ( Within the expected range )
  • Log
     

 1、 Custom item system level exception

public class SystemException extends RuntimeException{
    private Integer code;

    public Integer getCode() {
        return code;
    }
    public void setCode(Integer code) {
        this.code = code;
    }
    public SystemException(Integer code) {
        this.code = code;
    }

    public SystemException(String message, Throwable cause) {
        super(message, cause);
    }

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

2、 Custom item business level exception

public class BusinessException extends RuntimeException {
    private Integer code;

    public Integer getCode() {
        return code;
    }

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

    public BusinessException(Integer code) {
        this.code = code;
    }

    public BusinessException(String message, Throwable cause, Integer code) {
        super(message, cause);
        this.code = code;
    }

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

3、 Custom exception code

public class Code {
    ......

    // Unknown error 
    public static final Integer SYSTEM_UNKNOW_ERR=40010;
    // Timeout error 
    public static final Integer SYSTEM_TIMEOUT_ERR=40020;
    public static final Integer PROJECT_VALIDATE_ERR=40020;
    public static final Integer PROJECT_BUSINESS_ERR=40020;
}

4、 Trigger custom exception

 @GetMapping("/{id}")
    public Result findById(@PathVariable int id) {
        if (id < 0) {
            throw new BusinessException(" Do not operate illegally ！", Code.PROJECT_BUSINESS_ERR);
        }
        var data = userService.findById(id);
        boolean flag = false;
        if (data != null) {
            flag = true;
        }
        var code = flag ? Code.GET_OK : Code.GET_ERR;
        var msg = flag ? " Data query successful " : " Data query failed ";
        Result result = new Result(data, code, msg);
        return result;
    }

5、 Intercept and handle exceptions

/**
 *  Exception handler 
 */
@RestControllerAdvice
public class ProjectExceptionAdvice {
    @ExceptionHandler(BusinessException.class)
    public Result doBusinessException(BusinessException ex){
        return new Result(ex.getMessage(),ex.getCode(),ex.getMessage());
    }
    @ExceptionHandler(SystemException.class)
    public Result doSystemException(SystemException ex){
        // Log （ The error stack ）todo
        // Send mail to developers  todo
        // Send SMS to operation and maintenance personnel  todo
        return new Result(ex.getMessage(),ex.getCode(),ex.getMessage());
    }
    @ExceptionHandler(Exception.class)
    public Result doException(Exception ex){
        // Log （ The error stack ）todo
        // Send mail to developers  todo
        // Send SMS to operation and maintenance personnel  todo
        var msg = " The system is busy , Please contact the Administrator ！";
        return new Result(msg,Code.SYSTEM_UNKNOW_ERR,ex.getMessage());
    }
}

6、 Exception handler effect comparison