Remember that an in-memory database is created/initialized when an application starts up; and destroyed when the application shuts down.
- 1. What is H2 Database?
- 2. Maven Dependency
- 3. H2 Configuration Options
- 4. Creating Schema and Inserting Data on Initialization
- 5. H2 Console
- 6. Conclusion
1. What is H2 Database?
H2 is one of the popular in-memory databases written in Java. H2 can be embedded in Java applications or run in the client-server mode.
Spring Boot provides excellent integration support for H2 using simple properties configuration.
To make itself even more helpful, H2 also provides a console view to maintain and interact with the database tables and data using the GUI interface.
2. Maven Dependency
To use H2 in the Spring boot application, we need to add the H2 runtime jar into dependencies. The best way to add is through maven.
<dependency> <groupId>com.h2database</groupId> <artifactId>h2</artifactId> <scope>runtime</scope> </dependency>
3. H2 Configuration Options
3.1. In-Memory Database Configuration
Spring provides effortless configuration options to connect to any database using properties. Below are the configuration properties, we shall have in
application.properties file for the most straightforward H2 configuration.
spring.datasource.url=jdbc:h2:mem:testdb spring.datasource.driverClassName=org.h2.Driver spring.datasource.username=sa spring.datasource.password= spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
Please note by default, spring boot configures the in-memory database connection with the username
'sa' and an empty password. If you wish to change the username and password, override them in the above properties options.
3.2. Persistent Database Configuration
By default, the in-memory databases are volatile, and all stored data will be lost when we restart the application. In this case, data is written in temporary memory, and as soon as JVM is stopped, data is flushed.
To have a persistent data store capable of storing data between application start/stop, we should hold the data in files. For this change the
# temporary data storage spring.datasource.url = jdbc:h2:mem:testdb # temporary data storage spring.datasource.url = jdbc:h2:file:/data/sample spring.datasource.url = jdbc:h2:file:C:/data/sample
4. Creating Schema and Inserting Data on Initialization
We may want to initialize the database with some fixed schema (DDL) and insert default data (DML) into tables before the application is ready for business usecases.
We can achieve this by putting SQL files into the resources folder (
- schema.sql – To initialize the schema ie.create tables and dependencies.
- data.sql – To insert default data rows.
DROP TABLE IF EXISTS TBL_EMPLOYEES; CREATE TABLE TBL_EMPLOYEES ( id INT AUTO_INCREMENT PRIMARY KEY, first_name VARCHAR(250) NOT NULL, last_name VARCHAR(250) NOT NULL, email VARCHAR(250) DEFAULT NULL );
INSERT INTO TBL_EMPLOYEES (first_name, last_name, email) VALUES ('Lokesh', 'Gupta', 'email@example.com'), ('Deja', 'Vu', 'firstname.lastname@example.org'), ('Caption', 'America', 'email@example.com');
5. H2 Console
5.1. Enabling H2 Console
By default, the console view of the H2 database is disabled. We must enable it to view and access it in the browser. Note that we can customize the URL of the H2 console, which, by default, is
# Enabling H2 Console spring.h2.console.enabled=true # Custom H2 Console URL spring.h2.console.path=/h2
5.2. Accessing H2 Console
Start the spring boot application and access the console in the browser with this URL :
We can see the console like this.
Now enter the configured username and password. We can verify the table structure and default data inserted through SQL files.
5.3. Other Configuration Options
Spring boot provides two more properties to customize the behavior of the H2 console further. We can enable/disable the database trace logs, and we can enable/disable the remote access of H2 console.
By default, both properties are
# Whether to enable trace output. spring.h2.console.settings.trace=false # Whether to enable remote access. spring.h2.console.settings.web-allow-others=false
In this Spring boot with H2 database tutorial, we learned to configure, initialize and access the H2 database through a spring boot application using simple properties configuration options.
Happy Learning !!