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Create the Java project

Table of contents

Set up the Maven project

Create a Java project with Maven from your preferred IDE. This guide uses Maven, but you can use Gradle if you prefer. Add the following dependencies to pom.xml:

<dependencies>
    <dependency>
        <groupId>org.postgresql</groupId>
        <artifactId>postgresql</artifactId>
        <version>42.7.3</version>
    </dependency>
    <dependency>
        <groupId>ch.qos.logback</groupId>
        <artifactId>logback-classic</artifactId>
        <version>1.5.6</version>
    </dependency>
    <dependency>
        <groupId>org.junit.jupiter</groupId>
        <artifactId>junit-jupiter</artifactId>
        <version>5.10.2</version>
        <scope>test</scope>
    </dependency>
</dependencies>

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-surefire-plugin</artifactId>
            <version>3.2.5</version>
        </plugin>
    </plugins>
</build>

This adds the Postgres JDBC driver, logback for logging, JUnit 5 for testing, and the latest maven-surefire-plugin for JUnit 5 support.

Implement the business logic

Create a Customer record:

package com.testcontainers.demo;

public record Customer(Long id, String name) {}

Create a DBConnectionProvider class to hold JDBC connection parameters and provide a database Connection:

package com.testcontainers.demo;

import java.sql.Connection;
import java.sql.DriverManager;

class DBConnectionProvider {

  private final String url;
  private final String username;
  private final String password;

  public DBConnectionProvider(String url, String username, String password) {
    this.url = url;
    this.username = username;
    this.password = password;
  }

  Connection getConnection() {
    try {
      return DriverManager.getConnection(url, username, password);
    } catch (Exception e) {
      throw new RuntimeException(e);
    }
  }
}

Create the CustomerService class:

package com.testcontainers.demo;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class CustomerService {

  private final DBConnectionProvider connectionProvider;

  public CustomerService(DBConnectionProvider connectionProvider) {
    this.connectionProvider = connectionProvider;
    createCustomersTableIfNotExists();
  }

  public void createCustomer(Customer customer) {
    try (Connection conn = this.connectionProvider.getConnection()) {
      PreparedStatement pstmt = conn.prepareStatement(
        "insert into customers(id,name) values(?,?)"
      );
      pstmt.setLong(1, customer.id());
      pstmt.setString(2, customer.name());
      pstmt.execute();
    } catch (SQLException e) {
      throw new RuntimeException(e);
    }
  }

  public List<Customer> getAllCustomers() {
    List<Customer> customers = new ArrayList<>();

    try (Connection conn = this.connectionProvider.getConnection()) {
      PreparedStatement pstmt = conn.prepareStatement(
        "select id,name from customers"
      );
      ResultSet rs = pstmt.executeQuery();
      while (rs.next()) {
        long id = rs.getLong("id");
        String name = rs.getString("name");
        customers.add(new Customer(id, name));
      }
    } catch (SQLException e) {
      throw new RuntimeException(e);
    }
    return customers;
  }

  private void createCustomersTableIfNotExists() {
    try (Connection conn = this.connectionProvider.getConnection()) {
      PreparedStatement pstmt = conn.prepareStatement(
        """
        create table if not exists customers (
            id bigint not null,
            name varchar not null,
            primary key (id)
        )
        """
      );
      pstmt.execute();
    } catch (SQLException e) {
      throw new RuntimeException(e);
    }
  }
}

Here's what CustomerService does:

  • The constructor calls createCustomersTableIfNotExists() to ensure the table exists.
  • createCustomer() inserts a customer record into the database.
  • getAllCustomers() fetches all rows from the customers table and returns a list of Customer objects.
Write tests with Testcontainers »