Spring configuration from database

Question

We have an application which is deployed 120 times with slightly different configurations for each. We would like the configuration to be stored in the database for auditing and management purposes.

How can you instantiate Spring beans directly from the database without using XML?

Thanks

Answer 1

You can't have zero XML config (unless you use JavaConfig, which doesn't make things different in your case) . You can externalize some of it to the database, and use a custom PropertyPlaceholderConfigurer. See this article on how to achieve this.

Answer 2

@Bozho's suggestion is almost certainly the most practical solution, especially if the differences between the deployments is minimal and can be expressed via simple scalar properties.

The alternative is to write your own BeanFactory implementation. This is a non-trivial exercise, and you want to be sure that it's what you need. A good starting point would be to look at the source for XmlBeanFactory, and then write your own (DatabaseBeanFactory, perhaps) which does something similar, but fetching the bean definitions from the database, rather than from local XML files.

It's going to be quite a lot of extra work, though.

Answer 3

There are some options which are simplier than skaffman's suggestion:

• If your configuration is stored in the database in XML form, you can implement a custom resource fetching strategy by overriding AbstractApplicationContext.getResource(), so that you can load XML configs from the database. See here for some sample code. Using this approach you can also generate XML config on the fly.

• If your configuration is stored in the "disassembled" form, you can build BeanDefinitions and add them to the BeanDefinitionRegistry during initialization of the context using one of the following approaches:

  • Implement a namespace extension
  • Implement a BeanFactoryPostProcessor (you will need to downcast ConfigurableListableBeanFactory to BeanDefinitionRegistry, which work for most of application contexts types)
  • Since Spring 3.0.1 the previous approach was rectified by introduction of BeanDefinitionRegistryPostProcessor