Using @Configurable in Spring Framework: inject dependency to any object

Honestly, I like Spring Framework: awesome dependency management combined with rich features and great community. Recently I encountered very nice feature - @Configurable. In short, it allows developer to inject dependency into any object (who defines this annotation) without explicit bean definition. It's pretty cool. Techniques behind - AspectJ with runtime weaving.

Let me show how it works by creating simple test project. Let's start with Maven's project descriptor (pom.xml):

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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemalocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">  <modelversion>4.0.0</modelversion>    <groupid>spring-configurable</groupid>  <artifactid>spring-configurable</artifactid>  <version>0.0.1-SNAPSHOT</version>  <packaging>jar</packaging>    <name>spring-configurable</name>  <url>http://maven.apache.org</url>    <properties>   <project.build.sourceencoding>UTF-8</project.build.sourceencoding>   <spring.framework.version>3.0.5.RELEASE</spring.framework.version>  </properties>     <dependencies>   <dependency>    <groupid>org.aspectj</groupid>    <artifactid>aspectjweaver</artifactid>    <version>1.6.5</version>   </dependency>       <dependency>    <groupid>org.springframework</groupid>    <artifactid>spring-beans</artifactid>    <version>${spring.framework.version}</version>   </dependency>       <dependency>    <groupid>org.springframework</groupid>    <artifactid>spring-aspects</artifactid>    <version>${spring.framework.version}</version>   </dependency>       <dependency>    <groupid>org.springframework</groupid>    <artifactid>spring-core</artifactid>    <version>${spring.framework.version}</version>   </dependency>       <dependency>    <groupid>org.springframework</groupid>    <artifactid>spring-context</artifactid>    <version>${spring.framework.version}</version>   </dependency>       <dependency>    <groupid>org.springframework</groupid>    <artifactid>spring-jdbc</artifactid>    <version>${spring.framework.version}</version>   </dependency>  </dependencies> </project>

Next one, let me create application context (applicationContext.xml) and place it inside src/main/resources:

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<!--xml version="1.0" encoding="UTF-8"?--> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:context="http://www.springframework.org/schema/context" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemalocation="   http://www.springframework.org/schema/beans   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd   http://www.springframework.org/schema/context   http://www.springframework.org/schema/context/spring-context-3.0.xsd">       <context:annotation-config />  <context:spring-configured />  <context:load-time-weaver />     <context:component-scan base-package="com.test.configurable" />     <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource" /> </beans>

Two key declarations here are <context:spring-configured /> and <context:load-time-weaver />. According to documentation, <context:spring-configured /> "... signals the current application context to apply dependency injection to non-managed classes that are
instantiated outside of the Spring bean factory (typically classes annotated with the @Configurable annotation)..." and <context:load-time-weaver /> turns on runtime weaving.

Respective Java code which uses power of @Configurable annotation is located into Starter.java, which itself is placed inside src/main/java:

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package com.test.configurable;   import javax.sql.DataSource;   import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.annotation.Configurable; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; import org.springframework.util.Assert;   public class Starter {     @Configurable  private static class Inner {   @Autowired private DataSource dataSource;   }     public static void main(String[] args) {   final ApplicationContext context = new ClassPathXmlApplicationContext( "/applicationContext.xml" );       final DataSource dataSource = context.getBean( DataSource.class );   Assert.notNull( dataSource );       Assert.notNull( new Inner().dataSource );  }   }

As we see, class Inner is not a bean, is nested into another class and is created simply by calling new. Nevertheless, dataSource bean is injected as expected. Last but not least, in order this example to work, application should be run using an agent (I am using Spring Framework 3.0.5): -javaagent:spring-instrument-3.0.5.RELEASE.jar