JDBC get connection (Mysql example)

Method one ( not recommended ): directly by creating the implementation class of java.sql.Driver implemented by Mysql.

@Test
 public  void testConnection () {
     try {
         // 1. Provide java.sql.Driver interface implementation class 
        Driver driver = null ; 
        driver = new com.mysql.jdbc.Driver (); 

        // 2. Provide url, Specify the data for specific operations 
        String url = "jdbc: mysql: // localhost: 3306 / test" ; 

        // 3. Provide an object of Properties, specify the user name and password 
        Properties info = new Properties (); 
        info.setProperty ( "user" , "root" ); 
        info.setProperty ( "password", "abc123" ); 

        // 4. Call driver's connect () to get the connection
        Connection conn = driver.connect(url, info);
        System.out.println(conn);
    } catch (SQLException e) {
        e.printStackTrace();
    }
}

Method two ( not recommended ): Get the connection by reflecting the Driver class implemented by Mysql.

@Test
 public  void testConnection () {
     try {
         // 1. Instantiate Driver 
        String className = "com.mysql.jdbc.Driver" ; 
        Class clazz = Class.forName (className); 
        Driver driver = (Driver) clazz.newInstance ( ); 

        // 2. Provide the url, indicating the specific operation data 
        String url = "jdbc: mysql: // localhost: 3306 / test" ; 

        // 3. Provide the Properties object, indicating the user name and password 
        Properties info = new Properties ( ); 
        info.setProperty ( "user", "root" ); 
        info.setProperty ( "password", "abc123"); 

        // 4. Call connect () of the driver to get the connection 
        Connection conn = driver.connect (url, info); 
        System.out.println (conn); 
    } catch (Exception e) { 
        e.printStackTrace (); 
    } 
}

Method 3: To achieve database connection through java.sql.Manager, Driver needs to be registered in DriverManager.

@Test
 public  void testConnection () {
     try {
         // 1. 4 basic elements of database connection: 
        String url = "jdbc: mysql: // localhost: 3306 / test" ; 
        String user = "root" ; 
        String password = " abc123 " ; 
        String driverName =" com.mysql.jdbc.Driver " ; 

        // 2. Instantiate Driver 
        Class clazz = Class.forName (driverName); 
        Driver driver = (Driver) clazz.newInstance (); 

        // 3. Register Drive 
        DriverManager.registerDriver (driver); 

        // 4. Get connection
        Connection conn = DriverManager.getConnection(url, user, password);
        System.out.println(conn);
    } catch (Exception e) {
        e.printStackTrace();
    }
}
      

Method 4: In the implementation class of Driver in Mysql, Driver is instantiated in the static code block and registered in DriverManager.

@Test
  public  void testConnection () {
     try {
         // 1. 4 basic elements of database connection: 
        String url = "jdbc: mysql: // localhost: 3306 / test" ; 
        String user = "root" ; 
        String password = " abc123 " ; 
        String driverName =" com.mysql.jdbc.Driver " ;
 
        // 2. Load driver 
        (①Instantiate 

        Driver ②Register driver) Class.forName (driverName); // Driver driver = (Driver) clazz.newInstance ( );
         // 3. Register Driver
         // DriverManager.registerDriver (driver); 
        / *  
        The reason why the above code can be commented out is because the driver class in mysql declares:
        static { 
            try { DriverManager.registerDriver (new Driver ()); // Driver is instantiated by default, and the instantiated Driver is registered in DriverManager 
            } catch (SQLException var1) { 
                throw new RuntimeException ("Can't register driver!" ); 
            } 
        } 
                

         * / 

        // 3. Get connection 
        Connection conn = DriverManager.getConnection (url, user, password); 
        System.out.println (conn); 
    } catch (Exception e) { 
        e.printStackTrace (); 
    } 
}

Method 5 ( recommended ): Use the configuration file to obtain the database connection, so that the code and the specific database are decoupled. (The configuration file jdbc.properties should be placed in the src directory)

@Test
public  void testConnection() throws Exception {
    //1.加载配置文件
    InputStream is = ConnectionTest.class.getClassLoader().getResourceAsStream("jdbc.properties");
    Properties pros = new Properties();
    pros.load(is);
        
    //2.读取配置信息
    String user = pros.getProperty("user");
    String password = pros.getProperty("password");
    String url = pros.getProperty("url");
    String driverClass = pros.getProperty("driverClass");

    //3.Load driver
    Class.forName(driverClass);

    //4.获取连接
    Connection conn = DriverManager.getConnection(url,user,password);
    System.out.println(conn); 
}