Spring 注入不同作用域对象

– Start
当你想把短生命周期的对象(如: prototype)注入到长生命周期的对象(如：singleton)时需要特别注意，Spring 提供了如下的解决办法。

使用代理

package shangbo.spring.example29;public interface MessageService {    String getMessage();}

package shangbo.spring.example29;public class MessageServiceImpl implements MessageService {    private int times = 0;    public String getMessage() {        times++;        return "Hello World-" + times;    }}

package shangbo.spring.example29;public class MessagePrinter {    final private MessageService service;    public MessagePrinter(MessageService service) {        this.service = service;    }    public void printMessage() {        System.out.println(this.service.getMessage());    }}

<?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:aop="http://www.springframework.org/schema/aop"    xsi:schemaLocation="http://www.springframework.org/schema/beans        http://www.springframework.org/schema/beans/spring-beans.xsd        http://www.springframework.org/schema/aop        http://www.springframework.org/schema/aop/spring-aop.xsd">    <!--         注意messageService对象是 prototype        <aop:scoped-proxy/> 指示容器生成代理对象    -->    <bean id="messageService" class="shangbo.spring.example29.MessageServiceImpl" scope="prototype">        <aop:scoped-proxy/>    </bean>    <!--         MessagePrinter 是 singleton 对象    -->    <bean class="shangbo.spring.example29.MessagePrinter">        <constructor-arg ref="messageService"/>    </bean></beans>

package shangbo.spring.example29;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;public class App {    public static void main(String[] args) {        // 实例化 Spring IoC 容器        ApplicationContext context = new ClassPathXmlApplicationContext("example.xml", MessagePrinter.class);        // 从容器中获得 MessagePrinter 的实例        MessagePrinter printer1 = context.getBean(MessagePrinter.class);        printer1.printMessage();        // 再次在容器中获得 MessagePrinter 的实例        MessagePrinter printer2 = context.getBean(MessagePrinter.class);        printer2.printMessage();    }}

使用 lookup 方法

package shangbo.spring.example30;public interface MessageService {    String getMessage();}

package shangbo.spring.example30;public class MessageServiceImpl implements MessageService {    private int times = 0;    public String getMessage() {        times++;        return "Hello World-" + times;    }}

package shangbo.spring.example30;public abstract class MessagePrinter {    public void printMessage() {        MessageService service = createMessageService();        System.out.println(service.getMessage());    }    // 注意，这是传说中的 lookup 方法    protected abstract MessageService createMessageService();}

<?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.xsd">    <bean id="messageService" class="shangbo.spring.example30.MessageServiceImpl" scope="prototype"/>    <!--         注入 lookup 方法    -->    <bean class="shangbo.spring.example30.MessagePrinter">        <lookup-method name="createMessageService" bean="messageService"/>    </bean></beans>

package shangbo.spring.example30;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;import shangbo.spring.example29.MessagePrinter;public class App {    public static void main(String[] args) {        // 实例化 Spring IoC 容器        ApplicationContext context = new ClassPathXmlApplicationContext("example.xml", MessagePrinter.class);        // 从容器中获得 MessagePrinter 的实例        MessagePrinter printer1 = context.getBean(MessagePrinter.class);        printer1.printMessage();        // 再次在容器中获得 MessagePrinter 的实例        MessagePrinter printer2 = context.getBean(MessagePrinter.class);        printer2.printMessage();    }}

Spring 还提供了其他方法，如注入 ，或实现 ApplicationContextAware 接口，但是它们需要继承 Spring 的接口，与 Spring 耦合在一起，不推荐使用。

– 更多参见：Spring Framework 精萃
– 声 明：转载请注明出处
– Last Updated on 2017-05-23
– Written by ShangBo on 2017-05-23
– End