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{//加載MySql的驅(qū)動類    
         Class.forName("com.mysql.jdbc.Driver") ;    
    }catch(ClassNotFoundException e){    
         System.out.println("找不到驅(qū)動程序類 ，加載驅(qū)動失??！");    
         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: ?

//連接MySql數(shù)據(jù)庫，用戶名和密碼都是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("數(shù)據(jù)庫連接失?。?quot;);    
          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

兩種情況：
1、執(zhí)行更新返回的是本次操作影響到的記錄數(shù)。
2、執(zhí)行查詢返回的結果是一個ResultSet對象。
? ResultSet包含符合SQL語句中條件的所有行，并且它通過一套get方法提供了對這些
行中數(shù)據(jù)的訪問。
? 使用結果集（ResultSet）對象的訪問方法獲取數(shù)據(jù)：
while(rs.next()){
String name = rs.getString("name") ;
String pass = rs.getString(1) ; // 此方法比較高效
}
（列是從左到右編號的，并且從列1開始）

6、處理異常，關閉JDBC對象資源

?操作完成以后要把所有使用的JDBC對象全都關閉，以釋放JDBC資源，關閉順序和聲 明順序相反：
1、先關閉requestSet
2、再關閉preparedStatement
3、最后關閉連接對象connection

if(rs !=null){   // 關閉記錄集    
   try {
      rs.close();
   } catch (SQLException e) {
      e.printStackTrace();
   }
}    
  if(stmt !=null){   // 關閉聲明    
   try {
      stmt.close();
   } catch (SQLException e) {
      e.printStackTrace();
   }
}
if(conn !=null){  // 關閉連接對象    
   try {
      conn.close();
   } catch (SQLException e) {
      e.printStackTrace();
   }
}

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