在Spring框架中，一个bean仅用于一个特定的属性，这是提醒其声明为一个内部bean。内部bean支持setter注入“property”和构造器注入"constructor-arg“。
下面来看看一个详细的例子，演示使用 Spring 内部 bean 。
package com.xuhuhu.common;
public class Customer
{
private Person person;
public Customer(Person person) {
this.person = person;
}
public void setPerson(Person person) {
this.person = person;
}
@Override
public String toString() {
return "Customer [person=" + person + "]";
}
}
package com.xuhuhu.common;
public class Person
{
private String name;
private String address;
private int age;
//getter and setter methods
@Override
public String toString() {
return "Person [address=" + address + ",
age=" + age + ", name=" + name + "]";
}
}
很多时候，可以使用 'ref' 属性来引用“Person” bean到“Customer” Bean，person的属性如下：
<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-2.5.xsd"> <bean id="CustomerBean" class="com.xuhuhu.common.Customer"> <property name="person" ref="PersonBean" /> </bean> <bean id="PersonBean" class="com.xuhuhu.common.Person"> <property name="name" value="zaixian" /> <property name="address" value="address1" /> <property name="age" value="28" /> </bean> </beans>
在一般情况下，引用这样也没有问题，但由于“zaixian” persion bean 只用于Customer bean，这是更好地声明 “zaixian” person 作为一个内部 bean，如下：
<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-2.5.xsd"> <bean id="CustomerBean" class="com.xuhuhu.common.Customer"> <property name="person"> <bean class="com.xuhuhu.common.Person"> <property name="name" value="zaixian" /> <property name="address" value="address1" /> <property name="age" value="28" /> </bean> </property> </bean> </beans>
内部 bean 也支持构造器注入如下：
<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-2.5.xsd"> <bean id="CustomerBean" class="com.xuhuhu.common.Customer"> <constructor-arg> <bean class="com.xuhuhu.common.Person"> <property name="name" value="zaixian" /> <property name="address" value="address1" /> <property name="age" value="28" /> </bean> </constructor-arg> </bean> </beans>
注意：
id 或 name 值在bean类是没有必要以一个内部 bean 呈现，它会简单地忽略Spring容器。
执行结果：
package com.xuhuhu.common;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class App
{
public static void main( String[] args )
{
ApplicationContext context =
new ClassPathXmlApplicationContext(new String[] {"Spring-Customer.xml"});
Customer cust = (Customer)context.getBean("CustomerBean");
System.out.println(cust);
}
}
输出结果：
Customer [person=Person [address=address1, age=28, name=zaixian]]
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