How to access in memory h2 database of one spring boot application from another spring boot application

Question

In my project, i have created 3 spring boot application. First spring boot application has h2 embedded database. Now i want to access this database from my 2nd and 3rd sprin

Answer 1

You can setup H2 Server as Spring Bean.

First edit pom.xml - delete <scope>runtime</scope> from h2 dependency:

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
</dependency>

Then add H2 server bean to SpringBootApplication or Configuration class:

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    /**
     * Start internal H2 server so we can query the DB from IDE
     *
     * @return H2 Server instance
     * @throws SQLException
     */
    @Bean(initMethod = "start", destroyMethod = "stop")
    public Server h2Server() throws SQLException {
        return Server.createTcpServer("-tcp", "-tcpAllowOthers", "-tcpPort", "9092");
    }
}

Last - edit application.properties - set the name of the database:

spring.datasource.url=jdbc:h2:mem:dbname
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=
spring.jpa.hibernate.ddl-auto=create

Then you can connect to this H2 Server from outside (e.g. to your application with H2 DB) using this connection:

jdbc:h2:tcp://localhost:9092/mem:dbname

As a bonus using this url you can connect to the database of your app right from your IDE.

UPDATE

There is a chance of getting an error when trying to connect to the H2 for Spring Boot app of 1.5.x version. In this case just change a version of H2 to previous one, for example:

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <version>1.4.193</version>
</dependency>

UPDATE 2

If you need to run several apps with H2 simultaneously on the same host you should set the different H2 ports on them in Server.createTcpServer mothod, for example: 9092, 9093, etc..

// First App
@Bean(initMethod = "start", destroyMethod = "stop")
public Server h2Server() throws SQLException {
    return Server.createTcpServer("-tcp", "-tcpAllowOthers", "-tcpPort", "9092");
}

// Second App
@Bean(initMethod = "start", destroyMethod = "stop")
public Server h2Server() throws SQLException {
    return Server.createTcpServer("-tcp", "-tcpAllowOthers", "-tcpPort", "9093");
}

Then you can connect to the H2 DB of these apps with following urls:

App1 H2: jdbc:h2:tcp://localhost:9092/mem:dbname
App2 H2: jdbc:h2:tcp://localhost:9093/mem:dbname

Answer 2

You can run H2 in the server mode.

import org.h2.tools.Server;
...
// start the TCP Server
server = Server.createTcpServer("-tcpAllowOthers").start();
...
// stop the TCP Server
server.stop();

Usage: java org.h2.tools.Server 
When running without options, -tcp, -web, -browser and -pg are started.
Options are case sensitive. Supported options are:
[-help] or [-?]         Print the list of options
[-web]                  Start the web server with the H2 Console
[-webAllowOthers]       Allow other computers to connect - see below
[-webDaemon]            Use a daemon thread
[-webPort ]       The port (default: 8082)
[-webSSL]               Use encrypted (HTTPS) connections
[-browser]              Start a browser connecting to the web server
[-tcp]                  Start the TCP server
[-tcpAllowOthers]       Allow other computers to connect - see below
[-tcpDaemon]            Use a daemon thread
[-tcpPort ]       The port (default: 9092)
[-tcpSSL]               Use encrypted (SSL) connections
[-tcpPassword ]    The password for shutting down a TCP server
[-tcpShutdown ""]  Stop the TCP server; example: tcp://localhost
[-tcpShutdownForce]     Do not wait until all connections are closed
[-pg]                   Start the PG server
[-pgAllowOthers]        Allow other computers to connect - see below
[-pgDaemon]             Use a daemon thread
[-pgPort ]        The port (default: 5435)
[-properties ""]   Server properties (default: ~, disable: null)
[-baseDir ]        The base directory for H2 databases (all servers)
[-ifExists]             Only existing databases may be opened (all servers)
[-trace]                Print additional trace information (all servers)
The options -xAllowOthers are potentially risky.
For details, see Advanced Topics / Protection against Remote Access.
See also http://h2database.com/javadoc/org/h2/tools/Server.html

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