Project training 10 - backup of specific databases

   A valuable data collation system should have the function of database backup . Database management software such as Navicat You can simply back up , And you can extract the backup sql The file exists locally . The project has the functions of backup before deleting the user database and regular backup of the user database , This blog first discusses how to back up a database before deleting it .
   The command to back up the database is mysqldump -u user name -p password Database name > route \\ file name , among mysqldump yes MySQL Server Of bin A... In the catalog exe Executable file , When executing the backup statement on the command line, you should first move the working directory to bin Under the table of contents , And the password position is omitted to ensure data security , Enter and execute the command before entering the password . stay Java No more... In code JDBC Execute backup command , have access to Runtime.getRuntime().exec(command); Calls to perform cmd command . I mentioned earlier that when you execute the backup command on the command line, you should go to MySQL Server Of bin Catalog , So in Java In the code, you should also go to this directory and execute the statement . Can be found in mysqldump with bin Directory address , You can also create a new folder in the project directory , take mysqldump.exe Copy in . Before the table of contents cmd /c,cmd /c dir After execution dir Close the command window after the command , If it is not added, the command will not be executed . The specific code is in serviceImpl In file , As shown below ：

    // Back up before deleting ！
    @Override
    public int backupDB(int id) throws IOException {
    
        DB db=dbMapper.findDBById(id);
        String dbName=db.getDBEN();
        System.out.println(dbName);

        String user = "root";
        String password = "xxxxxxxx";

        logger.info(" The system backs up the database to be deleted ");
        //  current time   Date format 
        LocalDate localDate = LocalDate.now();
        //  Backup file name 
        String fileName = dbName+localDate.toString() + ".sql";
        String outFilePath = "D:\\backup\\"+fileName;
        String command="cmd /c D:\\mysql\\mysqldump -u" + user + " -p" + password +" "+ dbName+ " > " +outFilePath;
        Runtime.getRuntime().exec(command);

        System.out.println(" Backup complete ！");

        return 1;
    }

   I encountered many errors when implementing the backup function .

1. mysqldump The command execution environment must be in MySQL Server Of bin Under the table of contents , There has to be cmd /c, And there must be no extra space in the command ,“>” Add the absolute path to the file name after , On the one hand, problems may lead to 0KB The file of .
2. Many online tutorials are biased towards Runtime Object executes the command and stores a Process object , Then, this object is marked with InputStream Input stream format storage BufferedReader In the object , Finally, a file output stream is generated to write the backup contents to the newly created file . This is not only troublesome , And invalid , You'll get one 0KB The file of . Direct the command to “>” Change the file name after to the absolute path + file name , The suffix is .sql, You can get the backup content directly sql file .
3. The resulting backup file lacks table structure and table data . After solving the above two problems , I got a non - 0KB Of sql file , But only the database name information and some comments are available after opening , There is no table structure and data in the database . I tried again and again and found , Just delete the database after executing the backup command , Got sql The file has only comments . There may be a deviation in the execution order of the statements . So I chose to change the logic , A backup button is added to the delete database interface , You can choose to back up before deleting , If you directly click the delete button , You will be prompted to back up first . This will solve the problem sql The file lacks table structure and data .
      After testing , The backed up database can restore its table structure and table data through the command line . Note that you should create a database with the same name before executing the command ！ The order is mysql -u user name -p Database name < Absolute path \\ file name , It's also going to be bin Execute command under directory .
     controller The layer code is ：

    // Backup database 
    @RequestMapping("/backupDB/{id}")
    public Map<String, Object> backupDB(@PathVariable int id) throws Exception {
    
        Map<String, Object> map = new HashMap<>();
        // Backup first ！
        System.out.println(" To the back end id:"+id);
        int bu=db.backupDB(id);
        System.out.println(" The result of backing up the user database ："+bu);

        if (bu>0) {
    
            map.put("state", true);
            map.put("msg", " Delete successful ！");
        } else {
    
            map.put("state", false);
            map.put("msg", " Delete failed ！");
        }

        return map;
    }

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