Spring的《XML显式装配bean》之Bean的创建与销毁操作

比眉伴天荒 2022-07-11 08:46 199阅读 0赞

> 这一节主要介绍bean的创建和销毁过程

在xml的配置里面，我们可以配置Bean的创建与销毁操作。

(1)厨师类Chief，里面增加了create()和destroy() 方法。

package spring.ch1.topic6;
    
    /** * Created by louyuting on 17/1/20. */
    public class Chief { 
        private final int id = index++;
    
        public int getId() {
            return id;
        }
    
        public void create() {
            System.out.println("chief created");
        }
    
        public void destroy() {
            System.out.println("chief destroy");
        }
        private static int index=0;
    }

(2)配置xml里面的Bean时，我们需要配置init-method=”create” destroy-method=”destroy”

<?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-3.1.xsd http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    
        <bean id="chief" class="spring.ch1.topic6.Chief" scope="prototype" init-method="create" destroy-method="destroy" />
    </beans>

(3)测试类

package spring.ch1.topic6;
    
    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.context.ApplicationContext;
    import org.springframework.test.context.ContextConfiguration;
    import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
    
    /** * Created by louyuting on 17/1/20. */
    @RunWith(SpringJUnit4ClassRunner.class)
    @ContextConfiguration(locations = {
       "/spring/ch1/topic6/ApplicationContext-test.xml"})
    public class ChiefTest { 
        @Autowired
        private ApplicationContext applicationContext;
    
        @Test
        public void testSinger(){
            Chief chief = (Chief)applicationContext.getBean("chief");
            System.out.println("chief id=" + chief.getId());
            System.gc();
        }
    }

（4）输出：

//output:
    chief created
    chief id=0

这里只执行了create方法，没有执行destroy方法，这是让我纳闷的地方？也没找到原因。

但是当我们修改一下Chief类：增加了优先执行的静态代码块，以及在构造器里面增加了输出

package spring.ch1.topic6;
    
    public class Chief {   
        static {  
            System.out.println("before chief create");  
        }  
    
        public Chief() {  
            System.out.println("chief construtor");  
        }  
    
        private final int id = index++;  
    
        public int getId() {  
            return id;  
        }  
    
        public void create() {  
            System.out.println("chief created");  
        }  
    
        public void destroy() {  
            System.out.println("chief destroy");  
        }  
    
        private static int index = 0;  
    
    }

测试类也做一个修改：

package spring.ch1.topic6;
    
    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.context.ApplicationContext;
    import org.springframework.test.context.ContextConfiguration;
    import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
    
    /** * Created by louyuting on 17/1/20. */
    @RunWith(SpringJUnit4ClassRunner.class)
    @ContextConfiguration(locations = {
       "/spring/ch1/topic6/ApplicationContext-test.xml"})
    public class ChiefTest { 
        @Autowired
        private ApplicationContext applicationContext;
    
        @Test
        public void testSinger(){
            for (int i = 0; i < 3; i++) {  
                Chief chief = applicationContext.getBean(Chief.class);  
                System.out.println("chief id:" + chief.getId());  
            } 
        }
    
    }

在测试类里面我们增加了循环取id的操作。

测试输出：  
before chief create  
chief construtor  
chief created  
chief id:0  
chief id:0  
chief id:0

bean默认的是singleton，所以输出的三个id都是0， 也只执行了一次创建函数。

有输出可以看出，执行顺序是：  
（1）静态代码块  
（2）构造函数，创建对象  
（3）创建操作  
（4）执行业务操作  
（5）销毁操作

完整代码的[github地址][github]

[github]: https://github.com/louyuting/nettyRPC/tree/master/Spring/spring/spring/ch1/topic6