# Connecting with Java

This guide explains how to establish a connection between a **Java** application and a **PostgreSQL** database using the **JDBC driver**. It walks through the necessary setup, configuration, and execution of a simple SQL query.

## **Variables**

Certain parameters must be provided to establish a successful connection to a PostgreSQL database. Below is a breakdown of each required variable, its purpose, and where to find it. Here’s what each variable represents:

<table border="1" id="bkmrk-variable-description" style="width: 100%;"><colgroup><col style="width: 10.7229%;"></col><col style="width: 39.0983%;"></col><col style="width: 50.1788%;"></col></colgroup><thead><tr><td>**Variable**  
</td><td>**Description**  
</td><td>**Purpose**</td></tr></thead><tbody><tr><td>`USER`</td><td>PostgreSQL username, from the Elestio service overview page</td><td>Identifies the database user who has permission to access the PostgreSQL database.</td></tr><tr><td>`PASSWORD`</td><td>PostgreSQL password, from the Elestio service overview page</td><td>The authentication key required for the specified `USER` to access the database</td></tr><tr><td>`HOST`</td><td>Hostname for PostgreSQL connection, from the Elestio service overview page</td><td>The address of the server hosting the PostgreSQL database.</td></tr><tr><td>`PORT`</td><td>Port for PostgreSQL connection, from the Elestio service overview page</td><td>The network port is used to connect to PostgreSQL. The default port is `5432`.</td></tr><tr><td>`DATABASE`</td><td>Database Name for PostgreSQL connection, from the Elestio service overview page</td><td>The name of the database being accessed. A PostgreSQL instance can contain multiple databases.</td></tr></tbody></table>

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 them to the code moving ahead.

![Screenshot 2025-03-20 at 12.34.30 PM.jpg](https://docs.elest.io/uploads/images/gallery/2025-03/scaled-1680-/screenshot-2025-03-20-at-12-34-30-pm.jpg)

### **Prerequisites**

##### **Install Java &amp; JDBC driver**

Check if Java is installed by running:

```bash
java -version
```

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

```bash
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 `Pg.java` and add the following code:

```java
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 Pg {
    private static class ConnectionConfig {
        private final String host;
        private final String port;
        private final String database;
        private final String username;
        private final String password;

        public ConnectionConfig(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;
        }

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

        public boolean isValid() {
            return host != null && !host.isEmpty() && 
                   port != null && !port.isEmpty() && 
                   database != null && !database.isEmpty();
        }
    }

    private static Map<String, String> parseArguments(String[] args) {
        Map<String, String> config = new HashMap<>();
        for (int i = 0; i < args.length - 1; i++) {
            String key = args[i].toLowerCase();
            String value = args[++i];
            config.put(key, value);
        }
        return config;
    }

    private static ConnectionConfig createConfig(Map<String, String> args) {
        return new ConnectionConfig(
            args.get("-host"),
            args.get("-port"),
            args.get("-database"),
            args.get("-username"),
            args.get("-password")
        );
    }

    private static void validateConnection(Connection connection) throws SQLException {
        try (Statement stmt = connection.createStatement();
             ResultSet rs = stmt.executeQuery("SELECT version()")) {
            if (rs.next()) {
                System.out.println("Database Version: " + rs.getString("version"));
            }
        }
    }

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

            // Parse and validate configuration
            Map<String, String> parsedArgs = parseArguments(args);
            ConnectionConfig config = createConfig(parsedArgs);

            if (!config.isValid()) {
                System.err.println("Error: Missing required connection parameters (host, port, database)");
                return;
            }

            // Establish connection and validate
            try (Connection conn = DriverManager.getConnection(
                    config.getConnectionUrl(),
                    config.username,
                    config.password)) {
                
                System.out.println("Successfully connected to the database!");
                validateConnection(conn);
            }

        } catch (ClassNotFoundException e) {
            System.err.println("Error: PostgreSQL JDBC Driver not found");
            e.printStackTrace();
        } catch (SQLException e) {
            System.err.println("Database connection error:");
            e.printStackTrace();
        }
    }
}
```

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

```bash
javac Pg.java && java -cp postgresql-42.7.5.jar:. Pg -host HOST -port PORT -database DATABASE -username avnadmin -password PASSWORD
```

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

```bash
Successfully connected to the database!
Database Version: PostgreSQL 16.8 (Debian 16.8-1.pgdg120+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit
```