Item exception handling in SSM

One 、 Exception handler  

 

  reflection 1：

  reflection 2：

  Actually ,spring It has helped us solve the problem of handling exceptions early , No, we'll write it again AOP Code. , But we should follow spring Write in the format of handling exceptions

Simulate that the front end sends a request to access resources , Received an exception message （ At this time, there is no exception handler on the back end ）：

  After the front-end accesses the resource path of the added function , The information received is as follows ：（ At this time, the front end is confused , I TM Access is to add functions , this tm What's going back ~）

Therefore, we need to do exception handling at the back end （ Here are other exceptions , There is no need to create a class like system exceptions and business exceptions , Used to encapsulate prompt user information into attributes ）：

After the backend handles the exception, the client accesses and adds functional resources again , What information will you receive ：

  Therefore, the client is also B Said , I didn't receive any data , What's the matter with me ,

Therefore, after the exception is handled by our backend , You can return some data to front-end users , Then the user will know , Oh, the back end is abnormal ~

  The information received by the front-end user is as follows ：

Two 、 How to deal with different kinds of exceptions in the project

Different types of abnormal forms in the project ：

  So how to deal with the above three types of exceptions ：

The code demo is shown below ：

First step ： First, the system exception class 、 Write the business exception class ：（ In the actual development, there are only system exceptions in the business , Then write a system exception class , Here are three cases （ System exception 、 Business exceptions 、 Other exceptions are written ）, In the actual development, the exception class is written according to the exception , Then you can process it through the exception handler and return the prompt message to the user ）

System exception class ：

package com.itheima.exception;

/**
 *   Business exception class 
 *
 *   notes ： Inherit RuntimeException The purpose of the runtime exception class is to stop manually throwing up when an exception occurs at runtime , Automatically help us throw up 
 *
 */
public class SystemException extends RuntimeException{

    private Integer code;    //  Add one code Number attributes , To mark what kind of exception appears in the future 

    /**
     *   It's best to write out the construction methods 
     */

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

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

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

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

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

    /**
     *  getter and setter Method 
     */
    public Integer getCode() {
        return code;
    }

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

Business exception class ：

package com.itheima.exception;

/**
 *   System exception class 
 *
 *   notes ： Inherit RuntimeException The purpose of the runtime exception class is to stop manually throwing up when an exception occurs at runtime , Automatically help us throw up 
 *
 */
public class BusinessException extends RuntimeException{

    private Integer code;    //  Add one code Number attributes , Use the status code to mark what kind of exception appears in the future 

    /**
     *   It's best to write out the construction methods 
     */


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

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

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

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

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

    /**
     *  getter and setter Method 
     */
    public Integer getCode() {
        return code;
    }

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

The second step ： Suppose the business side passes id There is a system exception when querying the function （ for instance ： Server down ）：

Then capture the system exceptions , Encapsulate the information you want to return to the front-end user into the attributes of the system exception class （ By construction method ）, Then it returns the front-end user information through the exception handler

Be careful 1： Suppose that both system exceptions and business exceptions appear in a function of the business layer , So what kind of exception is caught first , The exception handler will get the exception information , And return the prompt data to the user （ Here are the system exceptions captured first , Because the system is abnormal, it ranks first ）

package com.itheima.service.impl;

import com.itheima.controller.Code;
import com.itheima.dao.BookDao;
import com.itheima.domain.Book;
import com.itheima.exception.BusinessException;
import com.itheima.exception.SystemException;
import com.itheima.service.BookService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;


@Service
public class BookServiceImpl implements BookService {

    /**
     *   Inject dao The data layer depends on  : private BookDao bookDao;
     *       Then wait spring The container gets to the business layer of management BookServiceImpl After the object , And because there is a dependency between the business layer and the data layer 
     *       Through the dependency relationship, you can call the function of adding, deleting, modifying and querying the data layer 
     */

    @Autowired //  Automatic assembly （ Dealing with dependencies ） annotation 
    private BookDao bookDao;

    //  increase 
    public boolean save(Book book) {

        //  Call the added functions of the data layer 
        bookDao.save(book);
        return true;
    }

    //  Delete 
    public boolean delete(Integer id) {

        //  Call the deletion function of the data layer 
        bookDao.delete(id);
        return true;
    }

    //  Change 
    public boolean update(Book book) {

        //  Call the modification function of the data layer 
        bookDao.update(book);
        return true;
    }

    //  adopt id Inquire about 
    public Book getById(Integer id) {

        /**
         *   The simulation assumes that this place appears   System exception （ for instance ： The server went down after the program ran here ）
         *
         *       We use it  1/0 To simulate the ： Server down 
         *
         */
        try {
            int i =1/0; //  The simulation system is abnormal 
        } catch (Exception e){    //  After catching the system exception , Encapsulate the information you want to return to the front end into 
                                   //  In the attribute of the system exception class （ By construction method ）
            throw new SystemException(" Server access timeout ~",e, Code.SYSTEM_ERR);
            //  Encapsulate the information you want to return to the front end into SystemException Object properties 
            // Code.SYSTEM_ERR : System abnormal status code identification  50001
        }
        
        /**
         *   Here the simulation hypothesis appears   Business exceptions 
         */

        if (id==2){
            throw new BusinessException(" Please don't challenge my patience with your technology ~",Code.BUSINESS_ERR);
            // Code.BUSINESS_ERR :  Business exception status code identification  60001
        }

        //  Call the data layer to pass id Query function 
        Book books = bookDao.getById(id);
        return books;
    }

    //  Query all 
    public List<Book> getAll() {

        //  Call all functions of the data layer 
        List<Book> list = bookDao.getAll();
        return list;
    }
}

The third step ： The system or business or other exception processing is carried out through the exception handler and encapsulated into the system exception class / The data returned to the customer in the business exception class attribute , Return to the user ：

details ： In real development , We can actually write these three exception handlers directly , Then, if there is a system exception in the project , Then it is directly handled by the system exception handler and returned to the user information , If it is the other two , It can also be directly caught by the other two exception handlers and then handle exceptions

package com.itheima.controller;

import com.itheima.exception.BusinessException;
import com.itheima.exception.SystemException;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.RestControllerAdvice;

/**
 *  spring Handling exceptions  （ Exception handler class ）
 */

// @ControllerAdvice //  This is a common style annotation for handling exceptions  （ As long as the access path is not REST Use this annotation for style ）
@RestControllerAdvice   //  This is a REST Style annotation for handling exceptions  （ tell spring This is an annotation of a class that handles exceptions ）
//  notes 1： This @RestControllerAdvice Annotations need to be SpringMvcConfig Class @ComponentScan({"com.itheima.controller"}) annotation 
//  Scan to ,（SpringMvcConfig The scanning annotation of the class just reaches controller It's a bag , So you can scan , So if you change to another bag , Remember to sweep ）

public class ProjectExceptionAdvice {

    /**
     *   notes ：  System exception handler 
     *
     * @return:  Return to the front-end information 
     */

    @ExceptionHandler(SystemException.class)    //  The function of this annotation ：  Whether the interception is a system exception , If yes, call the following methods to handle exceptions 
    public Result doSystemException(SystemException sy){
            // (SystemException sy)： hold SystemException Object passed （ Because when the business layer simulated the system exception just now , Encapsulate the information returned to the front end into sy Object attribute ）
        /**
         *   After getting the system exception, you need to do the following steps ：
         *  1、 Log 
         *  2、 Send it to O & M , Developer 
         *  3、 Appease the customer （ There is an exception when the customer accesses resources , We must say something nice to users ）
         */

        return new Result(null,sy.getCode(), sy.getMessage());
        //  Encapsulate into sy The system exception status code information in the system exception class attribute is returned to the user 
    }

    /**
     *   notes ：  Business exception handler   （ It is the same as the system exception handler ）
     *
     * @return:  Return to the front-end information 
     */

    @ExceptionHandler(BusinessException.class)   //   Whether the interception is a business exception , If yes, call the following methods to handle exceptions 
    public Result doBusinessException(BusinessException bs){


        return new Result(null,bs.getCode(),bs.getMessage());
    }

    /**
     *   notes ：  Other exception handlers  （ It can be understood as all exceptions except business exceptions and system exceptions ）
     */

    @ExceptionHandler(Exception.class)    //   Whether the interception is other exception , If yes, call the following methods to handle exceptions 
    public Result doException(){

        return new Result(null,0," Something is abnormal, iron ~");
    }
}

Suppose the client accesses the system abnormally id When querying the function ：

repair ：Code class ： Dedicated to storing success / Failure identifier

package com.itheima.controller;


/**
 *       Analyze the role of this class ：
 *            Mark the status code （ such as 1： It means success ,2： It means failure ） Class ,（ Result Inside  ）
 *
 *            Be careful ： These status codes are not fixed , It is a kind of state information that the front-end programmer and the back-end programmer discuss and stipulate in the actual development ,
 *            Through these negotiated status codes , You can know whether you get the data 
 *
 */
public class Code {

    /**
     *   The status code mark of the success of calling the function of adding, deleting, modifying and checking 
     *
     *   notes ： the reason being that static Statically decorated , So you can directly use the class name Code Call property name 
     *  public modification ： On behalf of the public （ in other words , Under any package, just pass the class name .  Can be accessed in any way Code Attribute value under class ）
     *
     */
    public static final Integer SAVE_OK = 20011;
    public static final Integer DELETE_OK = 20021;
    public static final Integer UPDATE_OK = 20031;
    public static final Integer SELECT_OK = 20041;

    /**
     *   The status code mark of the failure to call the function of adding, deleting, modifying and querying 
     */
    public static final Integer SAVE_ERR = 20010;
    public static final Integer DELETE_ERR = 20020;
    public static final Integer UPDATE_ERR = 20030;
    public static final Integer SELECT_ERR = 20040;


    /**
     *   System exception  &  The business is exceptionally successful / Failure status code mark 
     */
    public static final Integer SYSTEM_ERR =50001; //  The system abnormal status code appears 
    public static final Integer BUSINESS_ERR =60001;   //  Business exception status code appears 


}