3.The IoC container(2)

http://static.springsource.org/spring/docs/3.1.x/spring-framework-reference/html/beans.html#beans-factory-nature

4.6.1 Lifecycle callbacks

4.6.1.1 Initialization callbacks

The org.springframework.beans.factory.InitializingBean interface allows a bean to perform initialization work after all necessary properties on the bean have been set by the container.接口InitializingBean只有一个方法

void afterPropertiesSet() throws Exception;

然而，更推荐用XML-based configuration metadata去配置，For example：

<bean id="exampleInitBean" class="examples.ExampleBean" init-method="init"/>
//////////////////////推荐////////////////////////////////////

public class ExampleBean {

  public void init() {
      // do some initialization work
  }
}

//==========等同于：======
<bean id="exampleInitBean" class="examples.AnotherExampleBean"/>

public class AnotherExampleBean implements InitializingBean {

  public void afterPropertiesSet() {
      // do some initialization work
  }
}

同样，Implementing the org.springframework.beans.factory.DisposableBean interface allows a bean to get a callback when the container containing it is destroyed. The DisposableBean interface specifies 只有一个方法:

void destroy() throws Exception;

推荐：

<bean id="exampleInitBean" class="examples.ExampleBean" destroy-method="cleanup"/>

public class ExampleBean {

  public void cleanup() {
      // do some destruction work (like releasing pooled connections)
  }
}

//============等同于========
<bean id="exampleInitBean" class="examples.AnotherExampleBean"/>

public class AnotherExampleBean implements DisposableBean {

  public void destroy() {
      // do some destruction work (like releasing pooled connections)
  }
}

4.7 Bean definition inheritance(继承)

<bean id="inheritedTestBean" abstract="true"
    class="org.springframework.beans.TestBean">
  <property name="name" value="parent"/>
  <property name="age" value="1"/>
</bean>

<bean id="inheritsWithDifferentClass"
      class="org.springframework.beans.DerivedTestBean"
      parent="inheritedTestBean" init-method="initialize">

  <property name="name" value="override"/>
  <!-- the age property value of 1 will be inherited from  parent -->

</bean>

4.8.1.1 Example: Hello World, BeanPostProcessor-style

package scripting;

import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.beans.BeansException;

public class InstantiationTracingBeanPostProcessor implements BeanPostProcessor {

  // simply return the instantiated bean as-is
  public Object postProcessBeforeInitialization(Object bean, String beanName)
                                                                     throws BeansException {
      return bean; // we could potentially return any object reference here...
  }

  public Object postProcessAfterInitialization(Object bean, String beanName)
                                                                     throws BeansException {
      System.out.println("Bean '" + beanName + "' created : " + bean.toString());
      return bean;
  }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns:lang="http://www.springframework.org/schema/lang"
     xsi:schemaLocation="http://www.springframework.org/schema/beans
         http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
         http://www.springframework.org/schema/lang
         http://www.springframework.org/schema/lang/spring-lang-3.0.xsd">

  <lang:groovy id="messenger"
        script-source="classpath:org/springframework/scripting/groovy/Messenger.groovy">
      <lang:property name="message" value="Fiona Apple Is Just So Dreamy."/>
  </lang:groovy>

  <!--
      when the above bean (messenger) is instantiated, this custom
      BeanPostProcessor implementation will output the fact to the system console
   -->
  <bean class="scripting.InstantiationTracingBeanPostProcessor"/>

</beans>
///////////////////////////////////
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.scripting.Messenger;

public final class Boot {

  public static void main(final String[] args) throws Exception {
      ApplicationContext ctx = new ClassPathXmlApplicationContext("scripting/beans.xml");
      Messenger messenger = (Messenger) ctx.getBean("messenger");
      System.out.println(messenger);
  }
}

//The output of the preceding application resembles the following:

Bean 'messenger' created : org.springframework.scripting.groovy.GroovyMessenger@272961
59 org.springframework.scripting.groovy.GroovyMessenger@272961

4.8.1.2 Example: The PropertyPlaceholderConfigurer

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
  <property name="locations" value="classpath:com/foo/jdbc.properties"/>
</bean>

<bean id="dataSource" destroy-method="close"
    class="org.apache.commons.dbcp.BasicDataSource">
  <property name="driverClassName" value="${jdbc.driverClassName}"/>
  <property name="url" value="${jdbc.url}"/>
  <property name="username" value="${jdbc.username}"/>
  <property name="password" value="${jdbc.password}"/>
</bean>

classpath:com/foo/jdbc.properties
jdbc.driverClassName=org.hsqldb.jdbcDriver
jdbc.url=jdbc:hsqldb:hsql://production:9002
jdbc.username=sa
jdbc.password=root

从Spring 2.5开始，it is possible to configure property placeholders with a dedicated configuration element. 多个地址用逗号分隔。

<context:property-placeholder location="classpath:com/foo/jdbc.properties"/>