How to start spring-boot app without depending on Database?

Question

I am using "Spring-boot + Hibernate4 + mysql" for my application. As part of which I have a requirement where my sprint-boot app should be able to start even when database is down. Currently it gives the below exception when I try to start my spring boot app without DB being up.

I researched a lot and found out that this exception has to do with hibernate.temp.use_jdbc_metadata_defaults property.

I tried setting this in "application.yml" of spring boot but this property's value is not being reflected at runtime.

Exception Stack Trace:

2014-05-25 04:09:43.193  INFO 59755 --- [           main] o.hibernate.annotations.common.Version   : HCANN000001: Hibernate Commons Annotations {4.0.4.Final}
2014-05-25 04:09:43.250  WARN 59755 --- [           main] o.h.e.jdbc.internal.JdbcServicesImpl     : HHH000342: Could not obtain connection to query metadata : Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
2014-05-25 04:09:43.263  INFO 59755 --- [           main] o.apache.catalina.core.StandardService   : Stopping service Tomcat

Error starting ApplicationContext. To display the auto-configuration report enabled debug logging (start with --debug)


Exception in thread "main" 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 org.hibernate.HibernateException: Access to DialectResolutionInfo cannot be null when 'hibernate.dialect' not set
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1553)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:539)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:475)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:304)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:300)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:195)
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:973)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:750)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:482)
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:120)
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:648)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:311)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:909)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:898)
    at admin.Application.main(Application.java:36)
Caused by: org.hibernate.HibernateException: Access to DialectResolutionInfo cannot be null when 'hibernate.dialect' not set
    at org.hibernate.engine.jdbc.dialect.internal.DialectFactoryImpl.determineDialect(DialectFactoryImpl.java:104)
    at org.hibernate.engine.jdbc.dialect.internal.DialectFactoryImpl.buildDialect(DialectFactoryImpl.java:71)
    at org.hibernate.engine.jdbc.internal.JdbcServicesImpl.configure(JdbcServicesImpl.java:205)
    at org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.configureService(StandardServiceRegistryImpl.java:89)
    at org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:206)
    at org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:178)
    at org.hibernate.cfg.Configuration.buildTypeRegistrations(Configuration.java:1885)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1843)
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl$4.perform(EntityManagerFactoryBuilderImpl.java:850)
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl$4.perform(EntityManagerFactoryBuilderImpl.java:843)
    at org.hibernate.boot.registry.classloading.internal.ClassLoaderServiceImpl.withTccl(ClassLoaderServiceImpl.java:399)
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:842)
    at org.hibernate.jpa.HibernatePersistenceProvider.createContainerEntityManagerFactory(HibernatePersistenceProvider.java:150)
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:336)
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:318)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1612)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1549)
    ... 15 more

application.yml:

spring:   
  jpa:
show-sql: true
hibernate:
  ddl-auto: none
  naming_strategy: org.hibernate.cfg.DefaultNamingStrategy
  temp:
    use_jdbc_metadata_defaults: false

Answer 1

It was indeed a tough nut to crack.

After lot and lot of research and actually debugging the spring-boot, spring, hibernate, tomcat pool, etc to get it done.

I do think that it will save lot of time for people trying to achieve this type of requirement.

Below are the settings required to achieve the following requirement

1. Spring boot apps will start fine even if DB is down or there is no DB.
2. Apps will pick up the connections on the fly as DB comes up which means there is no need to restart the web server or redeploy the apps.
3. There is no need to start the tomcat or redeploy the apps, if DB goes down from running state and comes up again.

application.yml :

spring:
  datasource:
    driverClassName: com.mysql.jdbc.Driver
    url: jdbc:mysql://localhost:3306/schema
    username: root
    password: root
    continueOnError: true
    initialize: false
    initialSize: 0
    timeBetweenEvictionRunsMillis: 5000
    minEvictableIdleTimeMillis: 5000
    minIdle: 0

  jpa:
    show-sql: true
    hibernate:
      ddl-auto: none
      naming_strategy: org.hibernate.cfg.DefaultNamingStrategy
    properties:
      hibernate:   
        dialect: org.hibernate.dialect.MySQL5Dialect
        hbm2ddl:
          auto: none
        temp:
          use_jdbc_metadata_defaults: false