[JDBC] quick start tutorial

1. What is? JDBC？

JDBC API It's a Java API, You can access any type of table column data , In particular, data stored in relational databases .JDBC representative Java Database connection .
JDBC The library contains API Usually used with databases ：

• Connect to database
• establish SQL or MySQL sentence
• Execute... In the database SQL or MySQL Inquire about
• View and modify data records in the database

2.JDBC Environment configuration

• JAVA（JDK） install
• Installation of database system （ Such as MySQL,SQL Server Installation ）

3. establish JDBC Applications

Build a JDBC Applications , This tutorial uses java Connect SQL Server For example , It is carried out in six steps ：

1. Import package

Include in the program what is needed for database programming JDBC class . Most of the time , Use import java.sql.* That's enough

2. register JDBC The driver

Initialize the driver , Open communication with the database .

Class.forName("com.mysql.cj.jdbc.Driver");

3. Open the link

Use DriverManager.getConnection() Method to create a Connection object ,

String user="sa";
String pwd="123456";
System.out.println(" Connect to database ...");
Connection con=DriverManager.getConnection(url,user,pwd);

4. Execute a query

Use one Statement Type or PreparedStatement The object of , And submit a SQL Statement to the database to execute the query ：

System.out.println(" establish statement...");
Statement sm=con.createStatement();
String sql="SELECT * FROM Students";
ResultSet rs=sm.executeQuery(sql);

If you want to execute a SQL sentence ：UPDATE,INSERT,DELETE sentence , as follows ：

sm=con.createStatement();
String sql="DELETE FROM Students";
ResultSet rs=sm.executeUpdate(sql);

5. Extract data from the result set

This step demonstrates how to get the data of query results from the database . You can use the appropriate ResultSet.getXXX() Method to retrieve the data, and the results are as follows ：

//STEP 5: Extract data from result set
while(rs.next()){
    
    //Retrieve by column name
    int id  = rs.getInt("id");
    int age = rs.getInt("age");
    String first = rs.getString("first");
    String last = rs.getString("last");

    //Display values
    System.out.print("ID: " + id);
    System.out.print(", Age: " + age);
    System.out.print(", First: " + first);
    System.out.println(", Last: " + last);
}

6. Clean up environmental resources

In the use of JDBC After interacting with the data in the database , All database resources should be explicitly shut down to reduce the waste of resources , Depend on JVM The garbage collection of is as follows ：

//STEP 6: Clean-up environment
rs.close();
stmt.close();
con.close();

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