Connect a Kotlin application to Neon Postgres

This guide describes how to create a Neon project and connect to it from a Kotlin application using Java Database Connectivity (JDBC), the standard API for interacting with relational databases on the JVM.

You will learn how to set up a project, connect to your database, and perform basic create, read, update, and delete (CRUD) operations.

Prerequisites

A Neon account. If you do not have one, see Sign up.
Java Development Kit (JDK) 17 or later.
Gradle to manage the project and dependencies.

Create a Neon project
If you do not have one already, create a Neon project.
1. Navigate to the Projects page in the Neon Console.
2. Click New Project.
3. Specify your project settings and click Create Project.
Your project is created with a ready-to-use database named neondb. In the following steps, you will connect to this database from your Kotlin application.
Create a Kotlin project
Create a project using the Gradle init command. This sets up a standard Kotlin application structure.
1. Run the following command in your terminal to generate a new Kotlin application project.
```
gradle init \
    --type kotlin-application \
    --dsl kotlin \
    --project-name neon-kotlin-jdbc \
    --package com.neon.quickstart
```
2. Change into the newly created project directory.
```
cd neon-kotlin-jdbc
```
  Open this directory in your preferred code editor (for example, VS Code, IntelliJ IDEA).
3. Add the postgresql driver and dotenv-kotlin libraries. With a Gradle version catalog (created by gradle init), declare the libraries in gradle/libs.versions.toml, then reference them from app/build.gradle.kts.
  
  Add the versions and library entries to gradle/libs.versions.toml:
```
[versions]
postgresql = "42.7.7"
dotenv = "6.5.1"

[libraries]
postgresql = { module = "org.postgresql:postgresql", version.ref = "postgresql" }
dotenv = { module = "io.github.cdimascio:dotenv-kotlin", version.ref = "dotenv" }
```
  Then add the dependencies in app/build.gradle.kts inside the dependencies block:
```
dependencies {
    implementation(libs.postgresql)
    implementation(libs.dotenv)
}
```
  Save both files.
4. Compile the project to download the dependencies.
```
./gradlew build
```
  On Windows, use gradlew.bat build.
  
  This command compiles your Kotlin code and downloads the required dependencies.
Store your Neon connection string
Create a file named .env in the app directory. This file will securely store your database connection string. Place it next to the application module so dotenv-kotlin can load it when you run the app with Gradle.
1. In the Neon Console, select your project on the Dashboard.
2. Click Connect on your Project Dashboard to open the Connect to your database modal.
3. Select Java as your programming language. Kotlin uses the same JDBC connection string format.
4. Copy the connection string, which includes your password.
5. Create a file named .env in the app directory and add the connection string to it as shown below:
```
DATABASE_URL="jdbc:postgresql://[neon_hostname]/[dbname]?user=[user]&password=[password]&sslmode=require&channelBinding=require"
```
  Replace [user], [password], [neon_hostname], and [dbname] with your actual database credentials.

Examples

This section provides code examples for performing CRUD operations. Place the example files inside app/src/main/kotlin/com/neon/quickstart/.

You can also clone the complete example project from GitHub: neon-kotlin-jdbc.

Each example is a package-level function. Select which one to run by uncommenting it in App.kt:

package com.neon.quickstart

fun main() {
    // Uncomment the example you want to run.

    createTable()
    // readData()
    // updateData()
    // deleteData()
    // transactionExample()
}

Then run the selected example with:

./gradlew run

On Windows, use gradlew.bat run.

Create a table and insert data

Create a file named CreateTable.kt. This function connects to your database, creates a table, and inserts data.

package com.neon.quickstart

import io.github.cdimascio.dotenv.dotenv
import java.sql.DriverManager

fun createTable() {
    val dotEnv = dotenv()
    val connString = dotEnv["DATABASE_URL"]

    try {
        DriverManager.getConnection(connString).use { conn ->
            println("Connection established")

            conn.createStatement().use { stmt ->
                // Drop the table if it already exists
                stmt.execute("DROP TABLE IF EXISTS books;")
                println("Finished dropping table (if it existed).")

                // Create a new table
                stmt.execute(
                    """
                    CREATE TABLE books (
                        id SERIAL PRIMARY KEY,
                        title VARCHAR(255) NOT NULL,
                        author VARCHAR(255),
                        publication_year INT,
                        in_stock BOOLEAN DEFAULT TRUE
                    );
                    """.trimIndent()
                )
                println("Finished creating table.")

                // Insert a single book record
                val insertOneSql = """
                    INSERT INTO books (title, author, publication_year, in_stock)
                    VALUES (?, ?, ?, ?);
                """.trimIndent()

                conn.prepareStatement(insertOneSql).use { pstmt ->
                    pstmt.setString(1, "The Catcher in the Rye")
                    pstmt.setString(2, "J.D. Salinger")
                    pstmt.setInt(3, 1951)
                    pstmt.setBoolean(4, true)
                    pstmt.executeUpdate()

                    println("Inserted a single book.")
                }

                // Insert multiple books
                val insertManySql = """
                    INSERT INTO books (title, author, publication_year, in_stock)
                    VALUES (?, ?, ?, ?);
                """.trimIndent()

                conn.prepareStatement(insertManySql).use { pstmt ->
                    val booksToInsert = listOf(
                        listOf("The Hobbit", "J.R.R. Tolkien", 1937, true),
                        listOf("1984", "George Orwell", 1949, true),
                        listOf("Dune", "Frank Herbert", 1965, false)
                    )

                    for (book in booksToInsert) {
                        pstmt.setString(1, book[0] as String)
                        pstmt.setString(2, book[1] as String)
                        pstmt.setInt(3, book[2] as Int)
                        pstmt.setBoolean(4, book[3] as Boolean)
                        pstmt.addBatch()
                    }

                    pstmt.executeBatch()
                    println("Inserted 3 rows of data.")
                }
            }
        }
    } catch (e: Exception) {
        println("Connection failed.")
        e.printStackTrace()
    }
}

The above code does the following:

Connects to the Neon database using the connection string from the .env file.
Drops the books table if it already exists.
Creates a new books table with columns for id, title, author, publication_year, and in_stock.
Inserts a single book record.
Inserts multiple book records in a batch operation.

In App.kt, ensure only createTable() is uncommented, then run:

./gradlew run

When the code runs successfully, it produces the following output:

Connection established
Finished dropping table (if it existed).
Finished creating table.
Inserted a single book.
Inserted 3 rows of data.

Read data

Create a file named ReadData.kt. This function fetches all rows from the books table and prints them.

package com.neon.quickstart

import io.github.cdimascio.dotenv.dotenv
import java.sql.DriverManager

fun readData() {
    val dotenv = dotenv()
    val connString = dotenv["DATABASE_URL"]

    try {
        DriverManager.getConnection(connString).use { conn ->
            conn.createStatement().use { stmt ->
                println("Connection established")

                val sql = "SELECT * FROM books ORDER BY publication_year;"

                stmt.executeQuery(sql).use { rs ->
                    println("\n--- Book Library ---")

                    while (rs.next()) {
                        println(
                            "ID: ${rs.getInt("id")}, " +
                                    "Title: ${rs.getString("title")}, " +
                                    "Author: ${rs.getString("author")}, " +
                                    "Year: ${rs.getInt("publication_year")}, " +
                                    "In Stock: ${rs.getBoolean("in_stock")}"
                        )
                    }

                    println("--------------------\n")
                }
            }
        }
    } catch (e: Exception) {
        println("Connection failed.")
        e.printStackTrace()
    }
}

The above code does the following:

Connects to the Neon database using the connection string from the .env file.
Executes a SQL query to select all rows from the books table, ordered by publication_year.
Iterates through the result set and prints each book's details.

In App.kt, uncomment readData() (and comment out the other calls), then run:

./gradlew run

When the read logic runs, it produces the following output:

Connection established

--- Book Library ---
ID: 2, Title: The Hobbit, Author: J.R.R. Tolkien, Year: 1937, In Stock: true
ID: 3, Title: 1984, Author: George Orwell, Year: 1949, In Stock: true
ID: 1, Title: The Catcher in the Rye, Author: J.D. Salinger, Year: 1951, In Stock: true
ID: 4, Title: Dune, Author: Frank Herbert, Year: 1965, In Stock: false
--------------------

Update data

Create a file named UpdateData.kt to update the stock status of 'Dune' to true.

package com.neon.quickstart

import io.github.cdimascio.dotenv.dotenv
import java.sql.DriverManager

fun updateData() {
    val dotenv = dotenv()
    val connString = dotenv["DATABASE_URL"]
    val sql = "UPDATE books SET in_stock = ? WHERE title = ?;"

    try {
        DriverManager.getConnection(connString).use { conn ->
            conn.prepareStatement(sql).use { pstmt ->
                println("Connection established")

                pstmt.setBoolean(1, true)
                pstmt.setString(2, "Dune")

                val rowsAffected = pstmt.executeUpdate()

                if (rowsAffected > 0) {
                    println("Updated stock status for 'Dune'.")
                }
            }
        }
    } catch (e: Exception) {
        println("Connection failed.")
        e.printStackTrace()
    }
}

The above code does the following:

Connects to the Neon database.
Prepares an SQL UPDATE statement to set the in_stock status of the book 'Dune' to true.
Executes the update and prints a confirmation message if successful.

In App.kt, uncomment updateData(), then run:

./gradlew run

After running the update, verify the change by switching App.kt to call readData() and running again.

./gradlew run

The updated output will be:

--- Book Library ---
ID: 2, Title: The Hobbit, Author: J.R.R. Tolkien, Year: 1937, In Stock: true
ID: 3, Title: 1984, Author: George Orwell, Year: 1949, In Stock: true
ID: 1, Title: The Catcher in the Rye, Author: J.D. Salinger, Year: 1951, In Stock: true
ID: 4, Title: Dune, Author: Frank Herbert, Year: 1965, In Stock: true
--------------------

You can see that the stock status for 'Dune' has been updated to true.

Delete data

Create a file named DeleteData.kt to delete the book '1984' from the table.

package com.neon.quickstart

import io.github.cdimascio.dotenv.dotenv
import java.sql.DriverManager

fun deleteData() {
    val dotenv = dotenv()
    val connString = dotenv["DATABASE_URL"]
    val sql = "DELETE FROM books WHERE title = ?;"

    try {
        DriverManager.getConnection(connString).use { conn ->
            conn.prepareStatement(sql).use { pstmt ->
                println("Connection established")

                pstmt.setString(1, "1984")

                val rowsAffected = pstmt.executeUpdate()

                if (rowsAffected > 0) {
                    println("Deleted the book '1984' from the table.")
                }
            }
        }
    } catch (e: Exception) {
        println("Connection failed.")
        e.printStackTrace()
    }
}

The above code does the following:

Connects to the Neon database.
Prepares an SQL DELETE statement to remove the book '1984'.
Executes the delete and prints a confirmation message if successful.

In App.kt, uncomment deleteData(), then run:

./gradlew run

After running the delete, verify the change by switching App.kt to call readData() and running again.

./gradlew run

The final output will be:

--- Book Library ---
ID: 2, Title: The Hobbit, Author: J.R.R. Tolkien, Year: 1937, In Stock: true
ID: 1, Title: The Catcher in the Rye, Author: J.D. Salinger, Year: 1951, In Stock: true
ID: 4, Title: Dune, Author: Frank Herbert, Year: 1965, In Stock: true
--------------------

You can see that the book '1984' has been successfully deleted from the books table.

Using transactions

The examples above execute each operation independently. For production code where multiple operations must succeed or fail together, wrap them in a transaction. Set autoCommit = false to start a transaction, call commit() on success, and rollback() in the catch block on failure.

package com.neon.quickstart

import io.github.cdimascio.dotenv.dotenv
import java.sql.DriverManager
import java.sql.SQLException

fun transactionExample() {
    val dotenv = dotenv()
    val connString = dotenv["DATABASE_URL"]

    DriverManager.getConnection(connString).use { conn ->
        try {
            conn.autoCommit = false // Begin Transaction

            // Insert
            conn.prepareStatement(
                "INSERT INTO books (title, author, publication_year) VALUES (?, ?, ?)"
            ).use { pstmt ->
                pstmt.setString(1, "Brave New World")
                pstmt.setString(2, "Aldous Huxley")
                pstmt.setInt(3, 1932)
                pstmt.executeUpdate()

                println("Inserted book.")
            }

            // Update
            conn.prepareStatement(
                "UPDATE books SET in_stock = ? WHERE title = ?"
            ).use { pstmt ->
                pstmt.setBoolean(1, false)
                pstmt.setString(2, "Brave New World")
                pstmt.executeUpdate()

                println("Updated stock status.")
            }

            conn.commit() // Commit transaction
            println("Transaction committed successfully.")

        } catch (e: SQLException) {
            println("Transaction failed. Rolling back.")

            conn.rollback()
            e.printStackTrace()
        }
    }
}

In App.kt, uncomment transactionExample(), then run:

./gradlew run

Notes for AI-assisted setup

Always use PreparedStatement (with ? placeholders) for INSERT, UPDATE, and DELETE operations. Do not use Statement for queries with user-provided data, as this is vulnerable to SQL injection.
Add library versions to gradle/libs.versions.toml and reference them with implementation(libs.*) in app/build.gradle.kts.
Wrap related database operations in a transaction (autoCommit = false / commit() / rollback()). Always call rollback() in a catch block to ensure atomicity on failure.
Close JDBC connections and statements using Kotlin's .use { } (equivalent to Java try-with-resources) to prevent connection leaks.
Do not hardcode credentials in .kt files. Use environment variables via dotenv-kotlin. For more information, see Security overview.

Next steps: Using a framework

While this guide demonstrates how to connect to Neon using raw SQL queries, for more advanced and maintainable data interactions in your Kotlin applications, consider using a framework or ORM. Frameworks help you manage schema changes and keep your database structure in sync with your application models.

Explore the following resources to learn how to integrate frameworks with Neon:

Next steps: Neon backend services

Add Object Storage: S3-compatible file storage that branches with your database
Call an LLM with AI Gateway: Access foundation models from Anthropic, OpenAI, Google, and more with one credential

Resources

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Connect a Kotlin application to Neon Postgres

Prerequisites

Create a Neon project

Create a Kotlin project

Store your Neon connection string

Examples

Create a table and insert data

Read data

Update data

Delete data

Using transactions

Next steps: Using a framework

Next steps: Neon backend services

Resources

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