Detailed explanation of the steps of JDBC connecting to the database

    Java Code  
 

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JDBC connection database
• Create a program to connect to the database with JDBC, including 7 steps:
1. Load the JDBC driver:
    Before connecting to the database, first load the driver of the database you want to connect to the JVM (Java Virtual Machine). The static method forName( String   className ) of the java.lang.Class class is implemented.
    For example:
         try
        {
             //Load the driver class of MySql
            Class.forName( "com.mysql.jdbc.Driver" ) ;
        }
         catch (ClassNotFoundException e)
        {
            System.out.println( "Could not find the driver class, failed to load the driver !" );
            e.printStackTrace() ;
        }
        After successful loading, the instance of the Driver class will be registered in the DriverManager class.
2. Provide the URL of JDBC connection
    • The connection URL defines the protocol, sub-protocol, and data source identification when connecting to the database.
    •Writing form: Protocol: Sub-Protocol: Data Source Identification
    Protocol: Always start with jdbc in JDBC
    Sub-Protocol: is the name of the bridge connection driver or database management system.
    Data source identification: mark the address and connection port where the database source is found.
    For example: (MySql connection URL)
    jdbc:mysql:
         //localhost:3306/test?useUnicode=true&characterEncoding=gbk ;
   useUnicode=true: indicates the use of the Unicode character set. If characterEncoding is set to
   gb2312 or GBK, this parameter must be set to true. characterEncoding=gbk: Character encoding method.
3. Create a database connection
    • To connect to a database, you need to request and obtain a Connection object from java.sql.DriverManager, which represents a database connection.
    • Use DriverManager's getConnectin( String url , String username , String password ) method to obtain by passing in the specified path of the database to be connected, the username and password of the database.
     For example:
         //Connect to MySql database, username and password are both root
String          url = "jdbc:mysql://localhost:3306/test" ;
         String username = "root" ;
         String password = "root" ;
         try
        {
            Connection con =
                DriverManager.getConnection(url , username , password ) ;
        }
         catch (SQLException se)
        {
            System.out.println( "Database connection failed!" );
            se.printStackTrace() ;
        }
4. Create a Statement
    • To execute a SQL statement, you must obtain an instance of java.sql.Statement, which is divided into the following 3 Types:
      1. Execute static SQL statements. Usually implemented through a Statement instance.
      2. Execute dynamic SQL statements. Usually implemented through a PreparedStatement instance.
      3. Execute the database stored procedure. Usually implemented through a CallableStatement instance.
        Specific implementation:
        Statement stmt = con.createStatement() ;
        PreparedStatement pstmt = con.prepareStatement(sql) ;
        CallableStatement cstmt = con.prepareCall( "{CALL demoSp(? , ?)}" ) ;
5. Execute SQL statement
    Statement The interface provides three methods for executing SQL statements: executeQuery, executeUpdate and execute
     1. ResultSet executeQuery( String sqlString): Execute the SQL statement querying the database and return a result set (ResultSet) object.
     2. int executeUpdate( String sqlString): used to execute INSERT, UPDATE or DELETE statements and SQL DDL statements, such as: CREATE TABLE and DROP TABLE, etc.
     3. execute(sqlString): used to execute multiple result sets, multiple updates count or a combination of both
        语句。
        具体实现的代码：
        ResultSet rs = stmt.executeQuery( "SELECT * FROM ..." ) ;
         int rows = stmt.executeUpdate( "INSERT INTO ..." ) ;
         boolean flag = stmt.execute( String sql) ;
6、处理结果
    两种情况：
     1、执行更新返回的是本次操作影响到的记录数。
     2、执行查询返回的结果是一个ResultSet对象。
    • ResultSet包含符合SQL语句中条件的所有行，并且它通过一套get方法提供了对这些行中数据的访问。
    • 使用结果集（ResultSet）对象的访问方法获取数据：
         while (rs.next())
        {
             String name = rs.getString( "name" ) ;
             String pass = rs.getString( 1 ) ; // 此方法比较高效
        }
        （列是从左到右编号的，并且从列1开始）
7、关闭JDBC对象
     操作完成以后要把所有使用的JDBC对象全都关闭，以释放JDBC资源，关闭顺序和声
     明顺序相反：
     1、关闭记录集
     2、关闭声明
     3、关闭连接对象
         if (rs != null)     // 关闭记录集
        {
             try
            {
                rs.close() ;
            }
             catch (SQLException e)
            {
                e.printStackTrace() ;
            }
        }
         if (stmt != null)     // 关闭声明
        {
             try
            {
                stmt.close() ;
            }
             catch (SQLException e)
            {
                e.printStackTrace() ;
            }
        }
         if (conn != null)    // 关闭连接对象
        {
             try
            {
                conn.close() ;
            }
             catch (SQLException e)
            {
                e.printStackTrace() ;
            }
        }

Detailed explanation of the steps of JDBC connecting to the database

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