How to Configure H2 Database in Struts

August 23, 2025

Struts still holds its place as an intuitive Java web framework, and pairing it with H2 Database gives you a powerful yet lightweight solution. In this tutorial, we’ll stick strictly to configuring H2 for Struts using Docker for local development and Kubernetes for production while keeping your code clean, secure, and consistent.

1. Add Dependencies in `pom.xml`

First, include the essential libraries needed for Struts and H2 connectivity:

<dependencies>
  <!-- Struts framework -->
  <dependency>
    <groupId>org.apache.struts</groupId>
    <artifactId>struts2-core</artifactId>
    <version>${struts.version}</version>
  </dependency>

  <!-- H2 Database JDBC driver -->
  <dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <version>${h2.version}</version>
  </dependency>

  <!-- Kubernetes client for production config -->
  <dependency>
    <groupId>io.fabric8</groupId>
    <artifactId>kubernetes-client</artifactId>
    <version>${fabric8.version}</version>
  </dependency>
</dependencies>

This setup ensures your Struts app can talk to H2 via JDBC and that you have optional Kubernetes support for production builds.

2. Run H2 Using Docker for Development

H2 can run in server mode using Docker:

docker run -d \
  --name h2-dev \
  -p 9092:9092 \
  -e H2_OPTIONS=-ifNotExists \
  oscarfonts/h2

This spins up an H2 server on port 9092. It’s ready for local testing and development.

3. Create Development Configuration: `h2-dev.properties`

Create this file under src/main/resources:

db.driver=org.h2.Driver
db.url=jdbc:h2:tcp://localhost:9092/~/devdb;DB_CLOSE_DELAY=-1;AUTO_SERVER=TRUE
db.user=sa
db.password=
db.validationQuery=SELECT 1

Notice the AUTO_SERVER=TRUE flag lets multiple connections access the same database file simultaneously.
Load it in your Struts DAO or helper:

Properties props = new Properties();
props.load(getClass().getResourceAsStream("/h2-dev.properties"));
Class.forName(props.getProperty("db.driver"));
try (Connection conn = DriverManager.getConnection(
        props.getProperty("db.url"),
        props.getProperty("db.user"),
        props.getProperty("db.password"));
     Statement stmt = conn.createStatement()) {
  stmt.executeQuery(props.getProperty("db.validationQuery"));
}

Now your Struts application is connected to H2 in development.

4. Prepare Kubernetes Config for Production

For production, externalize path and settings via ConfigMaps and Secrets:

kubectl create configmap h2-config \
  --from-literal=DB_DRIVER=org.h2.Driver \
  --from-literal=DB_URL=jdbc:h2:tcp://h2-svc:9092/proddb;FILE_LOCK=FS \
  --from-literal=DB_VALIDATION_QUERY=SELECT 1

kubectl create secret generic h2-secret \
  --from-literal=DB_USER=sa \
  --from-literal=DB_PASSWORD=

These environment variables allow you to avoid pushing database details into code.

5. Add Production Configuration: `h2-prod.properties`

Place this in your packaged resources:

db.driver=${DB_DRIVER}
db.url=${DB_URL}
db.user=${DB_USER}
db.password=${DB_PASSWORD}
db.validationQuery=${DB_VALIDATION_QUERY}

Spring boot or Struts reads these environment variables automatically—no code changes needed.

6. Kubernetes Deployment Snippet

In your Deployment manifest, specify:

env:
  - name: DB_DRIVER
    valueFrom:
      configMapKeyRef:
        name: h2-config
        key: DB_DRIVER
  - name: DB_URL
    valueFrom:
      configMapKeyRef:
        name: h2-config
        key: DB_URL
  - name: DB_VALIDATION_QUERY
    valueFrom:
      configMapKeyRef:
        name: h2-config
        key: DB_VALIDATION_QUERY
  - name: DB_USER
    valueFrom:
      secretKeyRef:
        name: h2-secret
        key: DB_USER
  - name: DB_PASSWORD
    valueFrom:
      secretKeyRef:
        name: h2-secret
        key: DB_PASSWORD

Mount a PersistentVolumeClaim to store the .mv.db file, so your data survives pod restarts.

7. Example Struts Health Check Action

Try this quick health-check action:

public class DbHealthAction extends ActionSupport {
  public String execute() {
    String file = System.getenv("DB_URL") != null ? "/h2-prod.properties" : "/h2-dev.properties";
    Properties p = new Properties();
    p.load(getClass().getResourceAsStream(file));
    Class.forName(p.getProperty("db.driver"));
    try (Connection conn = DriverManager.getConnection(
             p.getProperty("db.url"),
             p.getProperty("db.user"),
             p.getProperty("db.password"));
         Statement stmt = conn.createStatement()) {
      stmt.executeQuery(p.getProperty("db.validationQuery"));
      addActionMessage("Connected to H2 successfully!");
      return SUCCESS;
    } catch (Exception e) {
      addActionError("Connection failed: " + e.getMessage());
      return ERROR;
    }
  }
}

This works the same way in both local and production builds—thanks to property switching.

Why This Works

Fast local iteration: H2 in Docker means no heavy installations.
Clean production config: Kubernetes manages environment values securely.
One codebase: No conditionals, just different .properties files.
Data persistence: Use mounting in Docker dev and PVC in Kubernetes prod.

1. Add Dependencies in pom.xml