Six steps of JDBC programming

JDBC Six steps to programming

​

The overall steps

​ First step ： Registration drive （ tell java, What database are you about to connect to ）

​ The second step ： Get the connection （ Express JVM The channel between the database process and the database process is opened , This belongs to the communication between processes Letter , heavyweight , Be sure to turn it off after use ）

​ The third step ： Get database operation object （ Special execution sql Object of statement ）

​ Step four ： perform SQL sentence （DQL DML …）

​ Step five ： Process query result set （ Only if step four is select At the time of statement , The fifth step is to process the query result set ）

​ Step six ： Release resources （java And database belong to the communication between processes , After opening, be sure to close ）

First step 、 Registration drive

​ Code

new How to write it （ Not commonly used ）

//1、 Registration drive  
Driver driver = new com.mysql.cj.jdbc.Driver(); // polymorphic , A parent type reference points to a child type 
// Driver driver = new oracle.jdbc.driver.OracleDriver(); oracle  drive 
DriverManager.registerDriver(driver);

Reflective writing （ Commonly used ）

 //1、 Registration drive 
            Class.forName(com.mysql.cj.jdbc.Driver);

The second step ： Get the connection

URL Which parts are included
agreement
ip
PORT Port number
Resource name
http://182.61.22.7:80/index.html
http:// Communication protocol
182.61.22.7 The server ip Address
80 The port of the software on the server
index.html Is the name of a resource on the server

 explain ：localhost and 127.0.0.1 It's all local ip

What is communication protocol , What's the usage? ？
Communication protocol is the data transmission format set in advance before communication .
How does the data packet transmit data , The format is set in advance

//Oracel url
Oracle JDBC: Oracle:thin:@localhost:1521:orcl

​ Code

//2、 Get the connection 
String url = "jdbc:mysql://127.0.0.1:3306/csdb?serverTimezone=UTC";
String user = "root";
String password = "******";
Connection conn = DriverManager.getConnection(url, user, password);
//[email protected]
System.out.println(" Connection object ：" + conn);

The third step ： Get database operation object

​ Code

//3、 Get database operation object 
//Startement Special execution sql sentence .
Statement stmt = conn.createStatement();

Step four ： perform SQL sentence

​ Be careful ：JDBC Medium sql Statement does not need to provide a semicolon end

//4、 perform sql
//insert
String sql = "insert into dept values(50,' The personnel department ',' Beijing ')";
// Special execution DML Of the statement （insert ,delete ,update）
// The return value is “ Affect the number of records in your database ”
int count = stmt.executeUpdate(sql);
System.out.println(count == 1 ? " Saved successfully " : " Save failed ");

//delete
String sql = "delete from dept where deptno = 50";
int count = stmt.executeUpdate(sql);
System.out.println(count == 1 ? " Delete successful " : " Delete failed ");

//updata
String sql = "update dept set deptno = 60 where deptno = 50 ";
System.out.println(count == 1 ? " The update is successful " : " Update failed ");
System.out.println(count == 1 ? " The update is successful " : " Update failed ");

//create
String sql = "select empno ,ename,sal from emp";
ResultSet rs = stmt.executeQuery(sql);

Step five ： Process query result set

​ 5、 Processing result set
​ rs.next Will move the result set cursor down one , If there is data return at the moved position true, Otherwise return to false
​ rs.getString, Take out the data , No matter what type , All converted into String type , Which columns of the database are from 1 Start

while (rs.next()) {
    
    // It is best to use the name of the column name of the query result here 
    int empno = rs.getInt("empno");
    String ename = rs.getString("ename");
    double sal = rs.getDouble("sal");
    System.out.println(empno + ',' + ename + ',' + sal);
}

Traverse rs Schematic diagram

Step six ： Release resources

Release resources
In order to ensure the release of resources , stay finally Close the resource in the statement block
And it should be closed from the largest to the largest
The results were analyzed respectively try..catch

try {
    
    if (rs != null) {
    
        rs.close();
    }
} catch (SQLException throwables) {
    
    throwables.printStackTrace();
}
try {
    
    if (stmt != null) {
    
        stmt.close();
    }
} catch (SQLException throwables) {
    
    throwables.printStackTrace();
}
try {
    
    if (conn != null) {
    
        conn.close();
    }
} catch (SQLException throwables) {
    
    throwables.printStackTrace();
}

Use the resource binder to write jdbc Programming

​ jdbc.properties file

driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://127.0.0.1:3306/csdb?serverTimezone=UTC
user=root
password=lh051920

​ Code file

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ResourceBundle;


public class jdbc Resource binder configuration  {
    

    public static void main(String[] args) {
    
        ResourceBundle bundle = ResourceBundle.getBundle("JDBC Register driver and acquire driver /jdbc");
        Connection conn = null;
        Statement stmt = null;

        String driver = bundle.getString("driver");
        String url = bundle.getString("url");
        String user = bundle.getString("user");
        String password = bundle.getString("password");
        try {
    
            //1、 Registration drive 
            Class.forName(driver);

            conn = DriverManager.getConnection(url, user, password);
            //[email protected]
            System.out.println(" Connection object ：" + conn);

            //3、 Get database operation object 
            //Startement Special execution sql sentence .
            stmt = conn.createStatement();

            //4、 perform sql
            String sql = "delete from dept where deptno = 60 or deptno = 70 or deptno = 90";
            // Special execution DML Of the statement （insert ,delete ,update）
            // The return value is “ Affect the number of records in your database ”
            int count = stmt.executeUpdate(sql);
            System.out.println(count == 1 ? " Saved successfully " : " Save failed ");

            //5、 Processing result set 


        } catch (Exception throwables) {
    
            throwables.printStackTrace();
        } finally {
    
            //6、 Release resources 
            // In order to ensure the release of resources , stay finally Close the resource in the statement block 
            // And it should be closed from the largest to the largest 
            // The results were analyzed respectively try..catch
            try {
    
                if (stmt != null) {
    
                    stmt.close();
                }
            } catch (SQLException throwables) {
    
                throwables.printStackTrace();
            }
            try {
    
                if (conn != null) {
    
                    conn.close();
                }
            } catch (SQLException throwables) {
    
                throwables.printStackTrace();
            }
        }
    }


}