jpa - Spring Boot 1.4 : class path resource [] cannot be resolved to URL because it does not exist

Question

The project without JPA works fine with 1.3, but throws the following exception with 1.4:

2016-07-31_19:29:21.758 [main] ERROR org.springframework.boot.SpringApplication - Application startup failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class path resource [org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaAutoConfiguration.class]: Invocation of init method failed; nested exception is javax.persistence.PersistenceException: Unable to resolve persistence unit root URL
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1578) ~[spring-beans-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:545) ~[spring-beans-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482) ~[spring-beans-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) ~[spring-beans-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) ~[spring-beans-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) ~[spring-beans-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197) ~[spring-beans-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1076) ~[spring-context-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:851) ~[spring-context-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:541) ~[spring-context-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122) ~[spring-boot-1.4.0.RELEASE.jar!/:1.4.0.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:759) [spring-boot-1.4.0.RELEASE.jar!/:1.4.0.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:369) [spring-boot-1.4.0.RELEASE.jar!/:1.4.0.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:313) [spring-boot-1.4.0.RELEASE.jar!/:1.4.0.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1185) [spring-boot-1.4.0.RELEASE.jar!/:1.4.0.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1174) [spring-boot-1.4.0.RELEASE.jar!/:1.4.0.RELEASE]
    at at.oebb.ticketshop.automat.backend.Application.main(Application.java:21) [classes!/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_31]
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_31]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_31]
    at java.lang.reflect.Method.invoke(Unknown Source) ~[na:1.8.0_31]
    at org.springframework.boot.loader.MainMethodRunner.run(MainMethodRunner.java:48) [ts-automat-0.0.1.jar:na]
    at org.springframework.boot.loader.Launcher.launch(Launcher.java:87) [ts-automat-0.0.1.jar:na]
    at org.springframework.boot.loader.Launcher.launch(Launcher.java:50) [ts-automat-0.0.1.jar:na]
    at org.springframework.boot.loader.JarLauncher.main(JarLauncher.java:58) [ts-automat-0.0.1.jar:na]
Caused by: javax.persistence.PersistenceException: Unable to resolve persistence unit root URL
    at org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager.determineDefaultPersistenceUnitRootUrl(DefaultPersistenceUnitManager.java:603) ~[spring-orm-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager.preparePersistenceUnitInfos(DefaultPersistenceUnitManager.java:443) ~[spring-orm-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager.afterPropertiesSet(DefaultPersistenceUnitManager.java:424) ~[spring-orm-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:310) ~[spring-orm-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:373) ~[spring-orm-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:362) ~[spring-orm-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1637) ~[spring-beans-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1574) ~[spring-beans-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    ... 24 common frames omitted
Caused by: java.io.FileNotFoundException: class path resource [] cannot be resolved to URL because it does not exist
    at org.springframework.core.io.ClassPathResource.getURL(ClassPathResource.java:187) ~[spring-core-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    at org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager.determineDefaultPersistenceUnitRootUrl(DefaultPersistenceUnitManager.java:600) ~[spring-orm-4.3.1.RELEASE.jar!/:4.3.1.RELEASE]
    ... 31 common frames omitted

Answer 1

This happens in spring boot version 1.4 when you have spring data JPA jars on your dependency and you have no classes in your project annotated with @entity.

In order to resolve the issue, you can use jdbc starter instead of jpa in your pom file.

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>