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Spring注入内部bean

如你所知道的Java内部类是其他类的范围内定义的，同样，内部bean是被其他bean的范围内定义的bean。因此<property/>或<constructor-arg/>元素内<bean/>元件被称为内部bean和它如下所示。

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"
    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">

   <bean id="outerBean" class="...">
      <property name="target">
         <bean id="innerBean" class="..."/>
      </property>
   </bean>

</beans>
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例如：

我们使用Eclipse IDE，然后按照下面的步骤来创建一个Spring应用程序：

步骤描述
1Create a project with a name SpringExample and create a package com.zhishitu under the src folder in the created project.
2Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter.
3Create Java classes TextEditor, SpellChecker and MainApp under the com.zhishitupackage.
4Create Beans configuration file Beans.xml under the src folder.
5The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below.

这里是TextEditor.java文件的内容：

package com.zhishitu;

public class TextEditor {
   private SpellChecker spellChecker;

   // a setter method to inject the dependency.
   public void setSpellChecker(SpellChecker spellChecker) {
      System.out.println("Inside setSpellChecker." );
      this.spellChecker = spellChecker;
   }
   // a getter method to return spellChecker
   public SpellChecker getSpellChecker() {
      return spellChecker;
   }

   public void spellCheck() {
      spellChecker.checkSpelling();
   }
}
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下面是另外一个相关的类文件SpellChecker.java内容：

package com.zhishitu;

public class SpellChecker {
   public SpellChecker(){
      System.out.println("Inside SpellChecker constructor." );
   }

   public void checkSpelling(){
      System.out.println("Inside checkSpelling." );
   }
   
}
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以下是MainApp.java文件的内容：

package com.zhishitu;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext context = 
             new ClassPathXmlApplicationContext("Beans.xml");

      TextEditor te = (TextEditor) context.getBean("textEditor");

      te.spellCheck();
   }
}
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以下是配置文件beans.xml文件里面有配置为基于setter 注入，但使用内部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"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

   <!-- Definition for textEditor bean using inner bean -->
   <bean id="textEditor" class="com.zhishitu.TextEditor">
      <property name="spellChecker">
         <bean id="spellChecker" class="com.zhishitu.SpellChecker"/>
       </property>
   </bean>

</beans>
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创建源代码和bean配置文件来完成，让我们运行应用程序。如果一切顺利，这将打印以下信息：

Inside SpellChecker constructor.
Inside setSpellChecker.
Inside checkSpelling.
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