J and I and Me
2010-07-07
  Limiting the Visibility of Spring Beans
Lately I have been working on concepts for the configuration of large Spring applications. The basic concept to build large system is well established in computer science: Break the system down in smaller blocks and build each of the blocks. Have the blocks talk to each other only in defined ways to decouple. This means that the blocks can easily be changed internally as long as the external properties stay the same. Transferred to Spring this means that the Spring configuration of the system must be broken down into parts. This is very well possible and actually already a best practice.

However, there is one problem: The Spring configuration has only a global visibility. I.e. every Spring bean can be used anywhere in the configuration. There are some ways to tackle this problem - that is beyond the scope of this posting.

There used to be a very elegant solution to this in the Spring Java Configuration introduced in Spring 3.0:

@Configuration
public class JavaConfiguration {

 @Bean(destroyMethod = "close")
 protected DataSource dataSource() {...}

 @Bean
 public EntityManagerFactory entityManagerFactory() {...}

 @Bean
 protected JpaVendorAdapter jpaVendorAdapter() {...}
}


This configuration creates Spring beans called dataSource, entityManagerFactory and jpaVendoreAdapter by calling the respective methods. Now the trick is: If you use the protected keyword the beans are not visible outside this class i.e. in particular they are not visible in an XML configuration that uses this class or in other Spring configuration classes. At least that is how it used to be - this feature is gone now. If you agree with me that this is an important feature - please vote for http://jira.springframework.org/browse/SPR-7170 to bring it back!

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  Changing Languages
For the future I plan to continue this blog in English. German limits the audience significantly. Also I am not concerned about only the German market - I am working on consulting and trainings products for the global market. I believe most Germans know enough English to still follow the blog. Let me know your opinion.

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Eberhard Wolff
Leobschützer Strasse 22
13125 Berlin
E-Mail-Adresse: eberhard.wolff@gmail.com

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Eberhard Wolff