Spring 3: JavaConfig vs XML Config

Spring JavaConfig allows you to configure the Spring IoC container and define your beans purely in Java rather than XML. I have been using Java-based configuration in all my new projects now and prefer it over the traditional XML-based configuration.

Here is a small example illustrating what the XML and Java configurations look like:

XML Config

<beans>
  <bean id="personDataSource" destroy-method="close" class="org.apache.commons.dbcp.BasicDataSource">
    <property name="driverClassName" value="oracle.jdbc.driver.OracleDriver"/>
    <property name="url" value="jdbc:oracle:thin:@firefly:1521:HRP2"/>
    <property name="username" value="scott"/>
    <property name="password" value="tiger"/>
  </bean>
  <bean id="personDao" class="com.example.PersonDao">
    <property name="dataSource" ref="personDataSource"/>
  </bean>
</beans>

Java Config

import javax.sql.DataSource;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class AppConfig {
  
  @Bean
  public DataSource personDataSource(){
    DataSource ds = new org.apache.commons.dbcp.BasicDataSource();
    ds.setDriverClassName("oracle.jdbc.driver.OracleDriver");
    ds.setUrl("jdbc:oracle:thin:@firefly:1521:HRP2");
    ds.setUsername("scott");
    ds.setPassword("tiger");
    return ds;
  }
  
  @Bean
  public PersonDao personDao() {
    return new PersonDao(personDataSource());
  }
}

Why I like JavaConfig:

Here are a few reasons, in no particular order, as to why I like the Java-based configuration:

1. Easy to learn: With XML, I have always found myself copying the app-context.xml from the last project I did, to start off with. I also have a hard time remembering what the XML schema is. However, JavaConfig is so intuitive that you can easily start writing your configuration from scratch - all you need to remember are a few annotations. Java-based configuration is more succint than XML. It is also more "readable". This makes it easier to see, at a glance, how your spring container is configured as compared to reading a lot of XML.


2. Quicker to write: It is faster to write JavaConfig because your Java IDE will help you complete class names and methods.


3. Type safety: In XML, it is easy to type the name of a class or property incorrectly, but with JavaConfig this is not possible because you will be using code completion in your Java IDE. Even if you are not, you will get a compiler error and can fix it straightaway.


4. Faster navigation: It is quicker to jump from one bean to another, track bean references etc because, since they are just Java classes and methods, you can use your IDE shortcuts to find types, go into method declarations and view call hierarchies.


5. No context switching: Another advantage of JavaConfig is that your brain (and IDE) does not have to keep switching between XML and Java. You can stay happily in the Java world.


6. No more XML! I hate XML in general. I find Spring XML verbose and hard to follow. It does not "belong" in a Java project. Sorry, but I don't think I will ever be using it again.

Oh, and YMMV :)