What are the steps to connect to the database using jdbc?

The steps for jdbc to connect to the database: 1. Load the jdbc driver; 2. Create a database connection; 3. Create a preparedStatement; 4. Execute SQL statements; 5. Traverse the result set; 6. Handle exceptions and close JDBC Object resources.

The operating environment of this article: windows10 system, java 1.8, thinkpad t480 computer.

JDBC connects to the database and creates a program to connect to the database with JDBC, including the following steps:

First prepare the four parameters required by JDBC (user, password, url, driverClass)

(1) user name

(2) password

(3) URL defines the protocol, sub-protocol, and data source identifier when connecting to the database. Separate with colons. Writing form: Protocol: Subprotocol: Data source identifier

Protocol: Always starts with jdbc in JDBC
Subprotocol: It is the driver of the bridge connection or the name of the 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.

(4) driverClass driver required to connect to the database.

1. Load the JDBC driver:

Before connecting to the database, you must first load the driver of the database you want to connect to the JVM (Java Virtual Machine), which is done through the java.lang.Class class The static method forName(String className) is implemented.​​

For example: ​​

try{//加载MySql的驱动类    
         Class.forName("com.mysql.jdbc.Driver") ;    
    }catch(ClassNotFoundException e){    
         System.out.println("找不到驱动程序类 ，加载驱动失败！");    
         e.printStackTrace() ;    
    }

After successful loading, the instance of the Driver class will be registered to the DriverManager class.​

2. Create a database connection ​

​ •To connect to the 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 the path to the specified database to be connected, the username and password of the database.

For example: ​

//连接MySql数据库，用户名和密码都是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("数据库连接失败！");    
          se.printStackTrace() ;    
     }

3. Create a preparedStatement ​

​ •To execute a SQL statement, you must obtain a java.sql.Statement instance. The Statement instance is divided into the following 3 Types: ​

1. Execute static SQL statements. Usually implemented through Statement instances.​​
​ 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 method:
Statement stmt = con.createStatement();
PreparedStatement pstmt = con.prepareStatement(sql);
CallableStatement cstmt = con.prepareCall("{CALL demoSp(? , ?)}") ;

4. Execute SQL statements

•The Statement interface provides three methods for executing SQL statements: executeQuery, executeUpdate and execute

1. ResultSet executeQuery( String sqlString): Execute the SQL statement to query 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 returns Statements with result sets, multiple update counts, or a combination of both.
• Specific implementation code:
ResultSet rs = stmt.executeQuery("SELECT * FROM ...");
int rows = stmt.executeUpdate("INSERT INTO ...");
boolean flag = stmt.execute(String sql);

5. Traverse the result set

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）

6、处理异常，关闭JDBC对象资源

•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、先关闭requestSet
2、再关闭preparedStatement
3、最后关闭连接对象connection

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();
   }
}

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