JDBC Query Record

This chapter provides information on how to select data from a table using a JDBC application/Example of getting records. Before executing the following example, please ensure that you have the following conditions:

• To execute the following example, you can useUsernameAndPasswordReplace with actual username and password.

• Your MySQL or any database you are using has already started and is running.

Necessary steps

To create a new database using a JDBC application, you need to perform the following steps-

• Import package:It requires you to include the software package that contains the JDBC classes required for database programming. Typically, use import java.sql.* That's enough.

• Register JDBC driver: It requires you to initialize the driver so that you can open a communication channel with the database.

• Establish a connection:It is necessary to use　DriverManager.getConnection() Methods to create a Connection object that represents a physical connection to the database server.

• Execute the query: It is necessary to use an object of the Statement type to construct and submit SQL statements to select (i.e., obtain) records from the table.

• Get data: Once an SQL query is executed, records can be obtained from the table.

• Clean up the environment: It is necessary to explicitly close all database resources instead of relying on JVM's garbage collection.

Sample code

Copy and paste the following example into JDBCExample.java, compile and run as follows-

//Step1Import the required software packages
import java.sql.*;
public class JDBCExample {
　　　//　JDBC driver program name and database URL
　　　static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";　　
　　　static final String DB_URL = "jdbc:mysql:"//localhost/STUDENTS";
　　　//　　Database credentials
　　　static final String USER = "username";
　　　static final String PASS = "password";
　　　
　　　public static void main(String[] args) {
　　　Connection conn = null;
　　　Statement stmt = null;
　　　try{
　　　　　　//Step2Register the JDBC driver
　　　　　　Class.forName("com.mysql.jdbc.Driver");
　　　　　　//Step3Establish the connection
　　　　　　System.out.println("Connecting to a selected database...");
　　　　　　conn = DriverManager.getConnection(DB_URL, USER, PASS);
　　　　　　System.out.println("Connected to the database successfully...");
　　　　　　
　　　　　　//Step4Execute the query
　　　　　　System.out.println("Creating statement...");
　　　　　　stmt = conn.createStatement();
　　　　　　String sql = "SELECT id, first, last, age FROM Registration";
　　　　　　ResultSet rs = stmt.executeQuery(sql);
　　　　　　//Step5Extract data from the result set
　　　　　　while(rs.next()){
　　　　　　　　　//Search by column name
　　　　　　　　　int id = rs.getInt("id");
　　　　　　　　　int age = rs.getInt("age");
　　　　　　　　　String first = rs.getString("first");
　　　　　　　　　String last = rs.getString("last");
　　　　　　　　　//Display Value
　　　　　　　　　System.out.print("ID: ",　+　id);
　　　　　　　　　System.out.print(", Age: ",　+　age);
　　　　　　　　　System.out.print(", First: ",　+　first);
　　　　　　　　　System.out.println(", Last: ",　+　last);
　　　　　　}
　　　　　　rs.close();
　　　catch(SQLException se){
　　　　　　//Handle JDBC error
　　　　　　se.printStackTrace();
　　　}
　　　　　　//Handle Class.forName error
　　　　　　e.printStackTrace();
　　　}finally{
　　　　　　//Used for closing resources
　　　　　　try{
　　　　　　　　　if(stmt!=null)
　　　　　　　　　　　　conn.close();
　　　　　　catch(SQLException se){
　　　　　　}//　Nothing to do
　　　　　　try{
　　　　　　　　　if(conn!=null)
　　　　　　　　　　　　conn.close();
　　　　　　catch(SQLException se){
　　　　　　　　　se.printStackTrace();
　　　　　　}
　　　}//End try
　　　System.out.println("Goodbye!");
}//End main
}//End JDBCExample

Now, let's compile the above example as follows:

C:\>javac JDBCExample.java
C:\>

RuntimeJDBCExampleIt will produce the following result-

C:\>java JDBCExample
Connecting to a selected database...
Connected database successfully...
Creating statement...
ID:　10, Age:　18, First: Zara, Last: Ali
ID:　101, Age:　25, First: Mahnaz, Last: Fatma
ID:　102, Age:　3, First: Zaid, Last: Khan
ID:　103, Age:　28, First: Sumit, Last: Mittal
Goodbye!
C:\>