Basic introduction of JDBC

JDBC summary

1、 Database classification

• Hierarchical database system （ from IBM The company has successfully developed ）
• A mesh database system
• Relational database system （ The type of database currently applied ）
  • FoxBase,FoxPro,Access（ Small database ）
  • MySQL,SQL Server,Informix（ Medium database ）
  • Oracle,DB2,Sybase（ Large databases ）

2、JDBC What is it? ？

• jdbc yes Java Database connection （Java Database Connectivity,JDBC） It's a kind of execution SQL Of the statement java API（Application Programming Interface Application programming interface ）, By a group java Language written classes and interfaces .
• It is a general database access interface , Can access any database .
• It provides a standard application programming interface for programmers , Developers can use pure java Language to write a complete database application
  

3、JDBC The role of

• Establish a connection to the database

• perform SQL sentence

• Handle SQL The result set returned by the statement

  * My summary is ： Build a data path , It allows both sides to interact

4、JDBC Operating environment

​ Each database type needs to correspond to its own unique database driver package , such as mysql Of mysql-connector-java-5.0.4-bin.jar Driver package . other SQL Serve、DB2 And so on have their own corresponding driver packages

5、JDBC Six steps to access data

1. Load the database driver

   // With mysql For example 
   Class.forName("com.mysql.jdbc.Driver");
   

2. Establishing a connection

   String url = "jdbc:mysql://localhost:3306/test";
   String username = "root";
   String password = "lvzhiqi*****";
   Connection conn = DriverManager.getConnection(url,username,password);
   //url by ："jdbc:mysql://localhost:3306/ Database name "
   //username by ：root（ Database name , Generally, the local database name is root）
   //password by ： Database password 
   

3. establish Statement object

   Statement state = conn.createStatement();
   

4. establish ResultSet Object to perform SQL sentence

   String sql = "sql sentence "
   ResultSet rs = state.executeQuery(sql);
   

5. Processing result set

   while(rs.next()){
         
    	rs.getString(1);//1 Represents the position of the column in the database table 
   	rs.getString(2);
    	rs.getString(3);
    }
   

6. Release resources

   // Create before release , Create before release 
   try{
         
       if(rs!=null){
         
           rs.close();
       }
       if(state!=null){
         
           state.close();
       }
       if(conn!=null){
         
           conn.close();
       }
   }
   

6、 Load driver and connection of other databases

//Oracle Mode of connection 
Class.forName("oracle.jdbc.driver.OracleDriver").newInstance();
String url = "jdbc:oracle:thin:@localhost:1521:orcl"; //orcl Name the database 
//DB2 Mode of connection 
Class.forName("com.ibm.db2.jdbc.app.DB2Driver").newInstance();
String url = "jdbc:db2://localhost:5000/test";  //test Name the database 
//Sybase Mode of connection 
Class.forName("com.sybase.jdbc.SybDriver").newInstance();
String url = "jdbc:sybase:Tds:localhost:5007/test"; //test Name the database 
//SQL Server Mode of connection 
Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver").newInstance();
String url = "jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=test";  //test Name the database 
//Accessd Mode of connection 
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Connection connection = DriverManager.getConnection("jdbc:odbc:test");  //test Name the database 

summary ：JDBC It is a general access mechanism for accessing databases , Remember the six steps ：
1. Load the database driver
2. Establishing a connection
3. establish Statement object
4. establish ResultSet Object to perform SQL sentence
5. Processing result set
6. Release resources （ Create before release , Create before release ）