Six-step example code for JDBC connection (connecting to MySQL)

//Exceptions must be handled //The code may vary depending on the version. The old version is DriverManager.register(new com.mysql.jdbc.Driver());
//or Class.forName("com.mysql.jdbc.Driver");
 
 
//The new version is DriverManager.register(new com.mysql.cj.jdbc.Driver());
//or Class.forName("com.mysql.cj.jdbc.Driver");

//Because we need to perform try..catch and close the resource, we write it outside try and assign it a value of null Connection conn = null;
...
//The return value is Connection. The url writing of the old and new versions is also different. // jdbc:mysql://localhost:3306/t_use is the same as before. Change t_use to your own database name. //Old version conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/t_use","user name","password");
 
 
//New versionconn = DriverManager.getConnection("jdbc:mysql://localhost:3306/t_use?serverTimezone=GMT%2B8","user name","password");

//This is the same Connection as before Statement st = null;
...
//This way the object is created st = conn.createStatement();

//Write the sql statement in quotation marks String sql = " ";
//Use the object just created to access this sql statement //There is something else to say here. If it is not a select statement, use the following one. The return value is an int, so there is no need for step 5. st.executeUpdate(sql);
 
//If the sql statement is select, you need to use the following statement, and you also need to define a ResultSet object to receive this value //Then proceed to step 5 ResultSet rs = null; //Same as Connection rs = st.executeQuery(sql);

//This is only processed by the select statement, not only can getString but also getInt, etc. while (rs.next()) {
    String str = rs.getString("The name of the field to be output");
}

//The first five steps are all performed in try, and the sixth step is performed in finally //Close the connection if (rs != null) {
                try {
                    rs.close();
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }
 
            if (st != null) {
                try {
                    st.close();
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }
 
            if (conn != null) {
                try {
                    conn.close();
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }

package jdbc.com;
import com.mysql.cj.protocol.Resultset;
 
import java.sql.*;
public class Test02 {
    public static void main(String[] args) {
 
        Connection conn = null;
        Statement st = null;
        ResultSet rt = null;
        try {
            //Register the connection (can be written in one line)
            //com.mysql.cj.jdbc.Driver Driver = new com.mysql.cj.jdbc.Driver();
            DriverManager.registerDriver(new com.mysql.cj.jdbc.Driver());
            //Get database connection conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/liu2?serverTimezone=GMT%2B8","user name","password");
            //Get the database operation object st = conn.createStatement();
            //Execute sql statement String sql = "select ename,sal from emp order by sal desc";
            rt = st.executeQuery(sql);
            //Processing query statements while (rt.next()) {
               String ename = rt.getString("ename");
               String sal = rt.getString("sal");
               System.out.println(ename + "," + sal);
           }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }finally {
            //Close the connection if (rt != null) {
                try {
                    rt.close();
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }
 
            if (st != null) {
                try {
                    st.close();
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }
 
            if (conn != null) {
                try {
                    conn.close();
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }
 
 
        }
    }
}