Spring Boot 2 Tips & FAQ

JPA

Issue: Field xxx in xxx required a bean named 'entityManagerFactory' that could not be found.

Symptoms:

When using Spring Boot2 with JPA, I encountered a weird issue, where if I'm using H2 as the embedded DB, everything worked fine, but once I switched to external MySQL under "prod" profile, it kept failing:

$ SPRING_PROFILES_ACTIVE=prod \
    mvn -e clean spring-boot:run -Dmaven.test.skip=true

...
***************************
APPLICATION FAILED TO START
***************************

Description:

Field repository in app.controller.StudentController required a bean named 'entityManagerFactory' that could not be found.

The injection point has the following annotations:
	- @org.springframework.beans.factory.annotation.Autowired(required=true)


Action:

Consider defining a bean named 'entityManagerFactory' in your configuration.

Analysis & Solutions:

This was because I excluded HikariCP as I found it's really unfamiliar to me and didn't know what it was.

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-data-jpa</artifactId>
			<exclusions>
				<exclusion>
					<groupId>com.zaxxer</groupId>
					<artifactId>HikariCP</artifactId>
				</exclusion>
			</exclusions>
		</dependency>

Unfortunately, this was exactly what caused the problem.

Check out the Spring Boot doc, here, and it clearly states that:

Production database connections can also be auto-configured by using a pooling DataSource. Spring Boot uses the following algorithm for choosing a specific implementation: 1. We prefer HikariCP for its performance and concurrency. If HikariCP is available, we always choose it. 2. Otherwise, if the Tomcat pooling DataSource is available, we use it. 3. If neither HikariCP nor the Tomcat pooling datasource are available and if Commons DBCP2 is available, we use it. If you use the spring-boot-starter-jdbc or spring-boot-starter-data-jpa “starters”, you automatically get a dependency to HikariCP.

So we either use the default by simply adding org.springframework.boot:spring-boot-starter-data-jpa dependency without excluding HikariCP, or explicitly adding your preferred pooling library.

Debug

Start Spring Boot App in Debug Mode

It's very easy to start Spring Boot appp in debug mode when using org.springframework.boot:spring-boot-maven-plugin Maven plugin:

$ mvn -Dmaven.test.skip=true \
    -Dspring-boot.run.jvmArguments="-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=5005" \
    spring-boot:run