How Can I Connect to a PostgreSQL Database Through JDBC?

Prerequisites

Familiarize yourself with:

• Computer basics.
• Java programming language.
• JDBC knowledge.

Obtaining and Using JDBC

• JDBC driver download address: https://jdbc.postgresql.org/download.html
• JDBC Interface: https://jdbc.postgresql.org/documentation/head/index.html

Connection with the SSL Certificate

Download the SSL certificate and verify the certificate before connecting to databases.

In the DB Information area on the Basic Information page, click in the SSL field to download the root certificate or certificate bundle.

1. Connect to the RDS PostgreSQL DB instance through JDBC.

   jdbc:postgresql://<instance_ip>:<instance_port>/<database_name>?sslmode=verify-full&sslrootcert=<ca.pem>

   Table 1 Parameter description

   Parameter	Description
   <instance_ip>	If you attempt to access the RDS DB instance through an ECS, set instance_ip to the floating IP address displayed on the Basic Information page of the DB instance to which you intend to connect.
   	If you attempt to access the RDS DB instance through an EIP, set instance_ip to the EIP that has been bound to the DB instance.
   <instance_port>	Enter the database port displayed on the Basic Information page. Default value: 5432
   <database_name>	Enter the name of the database to which you intend to connect. Default value: postgres
   sslmode	Enter the SSL connection mode. Default value: verify-full
   sslrootcert	Enter the directory of the CA certificate for the SSL connection. The certificate should be stored in the directory where the command is executed.

   Example script in Java:

   import java.sql.Connection;
   import java.sql.DriverManager;
   import java.sql.ResultSet;
   import java.sql.Statement;
   
   public class MyConnTest {
   	final public static void main(String[] args) {
   		Connection conn = null;
   		// set sslmode here.
   		// with ssl certificate and path.
   		String url = "jdbc:postgresql://192.168.0.225:5432/my_db_test?sslmode=verify-full&sslrootcert=/home/Ruby/ca.pem";
   
   		try {
   			Class.forName("org.postgresql.Driver");
   			conn = DriverManager.getConnection(url, "root", "password");
   			System.out.println("Database connected");
   
   			Statement stmt = conn.createStatement();
   			ResultSet rs = stmt.executeQuery("SELECT * FROM mytable WHERE columnfoo = 500");
   			while (rs.next()) {
   				System.out.println(rs.getString(1));
   			}
   
   			rs.close();
   			stmt.close();
   			conn.close();
   		} catch (Exception e) {
   			e.printStackTrace();
   			System.out.println("Test failed");
   		} finally {
   			// release resource ....
   		}
   	}
   }

Connection Without the SSL Certificate

You do not need to download the SSL certificate because the certificate verification on the server is not required.

1. Connect to the RDS PostgreSQL DB instance through JDBC.

   jdbc:postgresql://<instance_ip>:<instance_port>/<database_name>?sslmode=disable

   Table 2 Parameter description

   Parameter	Description
   <instance_ip>	If you attempt to access the RDS DB instance through an ECS, set instance_ip to the floating IP address displayed on the Basic Information page of the DB instance to which you intend to connect.
   	If you attempt to access the RDS DB instance through an EIP, set instance_ip to the EIP that has been bound to the DB instance.
   <instance_port>	Enter the database port displayed on the Basic Information page. Default value: 5432
   <database_name>	Enter the name of the database to which you intend to connect. Default value: postgres
   sslmode	Enter the SSL connection mode. disable means data is not encrypted.

   Example script in Java:

   import java.sql.Connection;
   import java.sql.DriverManager;
   import java.sql.ResultSet;
   import java.sql.Statement;
   
   public class MyConnTest {
   	final public static void main(String[] args) {
   		Connection conn = null;
   		// set sslmode here.
   		// no ssl certificate, so do not specify path.
   		String url = "jdbc:postgresql://192.168.0.225:5432/my_db_test?sslmode=disable";
   		try {
   			Class.forName("org.postgresql.Driver");
   			conn = DriverManager.getConnection(url, "root", "password");
   			System.out.println("Database connected");
   
   			Statement stmt = conn.createStatement();
   			ResultSet rs = stmt.executeQuery("SELECT * FROM mytable WHERE columnfoo = 500");
   			while (rs.next()) {
   				System.out.println(rs.getString(1));
   			}
   			rs.close();
   			stmt.close();
   			conn.close();
   		} catch (Exception e) {
   			e.printStackTrace();
   			System.out.println("Test failed");
   		} finally {
   			// release resource ....
   		}
   	}
   }