Spring内部bean实例 - Spring教程

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.yiibai.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.yiibai.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.yiibai.common.Customer">
        <property name="person" ref="PersonBean" />
    </bean>

    <bean id="PersonBean" class="com.yiibai.common.Person">
        <property name="name" value="yiibai" />
        <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“yiibai” persion bean 只用于Customer bean，这是更好地声明 “yiibai” 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.yiibai.common.Customer">
        <property name="person">
            <bean class="com.yiibai.common.Person">
                <property name="name" value="yiibai" />
                <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.yiibai.common.Customer">
        <constructor-arg>
            <bean class="com.yiibai.common.Person">
                <property name="name" value="yiibai" />
                <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.yiibai.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=yiibai]]