Connecting with Java

This guide shows how to connect your Java app to a Hydra database using the PostgreSQL JDBC driver, parse command-line arguments, and run a basic query.

Variables

To connect to a Hydra database, the following parameters are required. You can find these details in the Elestio service overview page of your Hydra service.

These values can usually be found in the Elestio service overview details as shown in the image below, make sure to take a copy of these details and add it to the code moving ahead.

Prerequisites

Install Java & JDBC driver

Check if Java is installed by running:

java -version

If not installed, install it first and then download and install JDBC driver from https://jdbc.postgresql.org/download/ or if you have Maven installed, run the following command with updated version of the driver:

mvn org.apache.maven.plugins:maven-dependency-plugin:2.8:get \  
  -Dartifact=org.postgresql:postgresql:42.7.5:jar \
  -Ddest=postgresql-42.7.5.jar

Code

Once all prerequisites are set up, create a new file named HydraPg.java and add the following code:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.HashMap;
import java.util.Map;

public class HydraPg {

    static class Config {
        String host, port, database, username, password;

        Config(String host, String port, String database, String username, String password) {
            this.host = host;
            this.port = port;
            this.database = database;
            this.username = username;
            this.password = password;
        }

        String getJdbcUrl() {
            return String.format("jdbc:postgresql://%s:%s/%s?sslmode=require", host, port, database);
        }

        boolean isComplete() {
            return host != null && port != null && database != null && username != null && password != null;
        }
    }

    static Map<String, String> parseArgs(String[] args) {
        Map<String, String> map = new HashMap<>();
        for (int i = 0; i < args.length - 1; i += 2) {
            map.put(args[i], args[i + 1]);
        }
        return map;
    }

    public static void main(String[] args) {
        try {
            Class.forName("org.postgresql.Driver");

            Map<String, String> argMap = parseArgs(args);
            Config cfg = new Config(
                argMap.get("-host"),
                argMap.get("-port"),
                argMap.get("-database"),
                argMap.get("-username"),
                argMap.get("-password")
            );

            if (!cfg.isComplete()) {
                System.err.println("Missing required arguments. Example usage:");
                System.err.println("java -cp postgresql-42.7.5.jar:. HydraPg -host <HOST> -port <PORT> -database <DB> -username <USER> -password <PASS>");
                return;
            }

            try (Connection conn = DriverManager.getConnection(cfg.getJdbcUrl(), cfg.username, cfg.password)) {
                System.out.println("Connected to Hydra database successfully.");

                Statement stmt = conn.createStatement();
                ResultSet rs = stmt.executeQuery("SELECT current_database(), current_user, version()");

                while (rs.next()) {
                    System.out.println("Database: " + rs.getString(1));
                    System.out.println("User: " + rs.getString(2));
                    System.out.println("Version: " + rs.getString(3));
                }

                rs.close();
                stmt.close();
            }

        } catch (ClassNotFoundException e) {
            System.err.println("PostgreSQL JDBC driver not found.");
            e.printStackTrace();
        } catch (SQLException e) {
            System.err.println("Connection or query error:");
            e.printStackTrace();
        }
    }
}

To execute the script, open the terminal or command prompt and navigate to the directory where HydraPg.java. Once in the correct directory, run the script with the command (Update the variables with actual values acquired from previous steps).

javac HydraPg.java

java -cp postgresql-42.7.5.jar:. HydraPg -host HOST -port PORT -database DATABASE -username USERNAME -password PASSWORD

If the connection is successful, the terminal will display output similar to:

Connected to Hydra database successfully.
Database: elestio
User: postgres
Version: PostgreSQL 14.13 (Debian 14.13-1.pgdg120+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit