Spring入门之四-------Spring实例化Bean的其他知识点

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一、懒加载

技术分享图片 
public class Bean1 {

    public Bean1() {
        System.out.println(this.getClass().getSimpleName() + ":" + this.toString() + " has been created");
    }
}
Bean1
技术分享图片 
public class Bean2 {

    public Bean2() {
        System.out.println(this.getClass().getSimpleName() + ":" + this.toString() + " has been created");
    }
}
Bean2 
<bean id="bean1" class="com.imooc.springClass4.others.Bean1" lazy-init="false"/>
<bean id="bean2" class="com.imooc.springClass4.others.Bean2" lazy-init="true"/>
@Test
public void testBean() throws Exception {
    final AbstractApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
    System.out.println("============ApplicationContext has been create============");

    Bean1 bean1 = context.getBean("bean1", Bean1.class);
    System.out.println("bean1 = " + bean1);
    System.out.println();

    Bean2 bean2 = context.getBean("bean2", Bean2.class);
    System.out.println("bean2 = " + bean2);
    System.out.println();
}

输出

Bean1:[email protected] has been created
============ApplicationContext has been create============
bean1 = [email protected]

Bean2:[email protected] has been created
bean2 = [email protected]

结论：bean1没有设定懒加载，所以Spring在加载上下文的时候就已经创建了bean1；bean2没有设定懒加载，所以bean2在被需要的时候才创建。

如果想设定当前xml中所有的bean都默认开启懒加载，可通过设定default-lazy-init="false"实现：

 

<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"
       default-lazy-init="false"
>
...
</beans>

 

二、Bean别名

技术分享图片 
public class Bean3 {

    public Bean3() {
        System.out.println(this.getClass().getSimpleName() + ":" + this.toString() + " has been created");
    }
}
Bean3

方式一：通过name属性创建别名

<bean id="bean3-1" name="bean3-2, bean3-3" class="com.imooc.springClass4.others.Bean3"/>

上面代码表示：创建一个Bean3，id为bean3-1，再给取两个别名：bean3-2、bean3-3

方式二：通过alias标签创建别名

<alias name="bean3-1" alias="bean3-4"/>

上面代码表示：给bean3-1取一个别名：bean3-4

测试

@Test
public void testBean() throws Exception {
    final AbstractApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");

    Bean3 bean3_1 = context.getBean("bean3-1", Bean3.class);
    System.out.println("bean3_1 = " + bean3_1);
    System.out.println();

    Bean3 bean3_2 = context.getBean("bean3-2", Bean3.class);
    System.out.println("bean3_2 = " + bean3_2);
    System.out.println();

    Bean3 bean3_3 = context.getBean("bean3-3", Bean3.class);
    System.out.println("bean3_3 = " + bean3_3);
    System.out.println();

    Bean3 bean3_4 = context.getBean("bean3-4", Bean3.class);
    System.out.println("bean3_4 = " + bean3_4);
    System.out.println();    
}

输出

bean3_1 = [email protected]
bean3_2 = [email protected]
bean3_3 = [email protected]
bean3_4 = [email protected]

可以看到所有的bean3_?的地址都是一样的。

三、引入其他xml

技术分享图片 
public class Bean4 {

    public Bean4() {
        System.out.println(this.getClass().getSimpleName() + ":" + this.toString() + " has been created");
    }
}
Bean4

resources目录下创建spring-1.xml，代码如下：

<?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="bean4" class="com.imooc.springClass4.others.Bean4"/>
</beans>

调整之前的spring.xml，增加

<import resource="spring-1.xml"/>

测试

@Test
public void testBean() throws Exception {
    final AbstractApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");

    Bean4 bean4 = context.getBean("bean4", Bean4.class);
    System.out.println("bean4 = " + bean4);
    System.out.println();
}

输出

bean4 = [email protected]

可以看到我们通过new ClassPathXmlApplicationContext("spring.xml")的方式引用spring.xml，由于spring.xml中import了spring-1.xml，所以spring-1.xml中定义的bean4也被实例化了。

四、方法注入

可能存在如下场景：Class A 的某个方法依赖于Class B的实例，Class A使用scope=singleton单例模式，但是Class A每次执行方法的时候都希望获取一个新的Class B的实例，这个时候就用到了方法注入。举例：

public class Bean5 {
    public Bean5() {
        System.out.println(this.getClass().getSimpleName() + ":" + this.toString() + " has been created");
    }
}
public abstract class Bean6 {

    public Bean6() {
        System.out.println(this.getClass().getSimpleName() + ":" + this.toString() + " has been created");
    }

    protected abstract Bean5 createBean5();
    
    public void printBean5() {
        System.out.println("createBean5().toString() = " + createBean5().toString());
    }
}

从上面代码我们看到，Bean6的printBean5方法是依赖于Bean5的实例的，如果该方法每次执行都想获得一个Bean5的实例，那么：

  1. Bean6中声明一个abstract方法，返回Bean5
  2. Bean6的printBean5方法需要使用Bean5时直接饮用上面的abstract方法

xml配置如下：注意bean5需要时prototype模式

<bean id="bean5" class="com.imooc.springClass4.others.Bean5" scope="prototype"/>
<bean id="bean6" class="com.imooc.springClass4.others.Bean6">
    <lookup-method name="createBean5" bean="bean5"/>
</bean>

测试：

@Test
public void testBean() throws Exception {
    final AbstractApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
   
    for (int i = 0; i < 10; i++) {
        Bean6 bean6 = context.getBean("bean6", Bean6.class);
        bean6.printBean5();
    }
}

输出：

Bean5:[email protected] has been created
createBean5().toString() = [email protected]
Bean5:[email protected] has been created
createBean5().toString() = [email protected]
Bean5:[email protected] has been created
createBean5().toString() = [email protected]
Bean5:[email protected] has been created
createBean5().toString() = [email protected]
Bean5:[email protected] has been created
createBean5().toString() = [email protected]
......

可以看到Bean6.printBean5()方法每次拿到的Bean5都是不同的实例

五、init-method和destroy-method

1. 如果需要在Bean实例化完成之后执行一些逻辑，可以有如下两种方法：

（1）使用init-method

（2）让Bean实现InitializingBean接口

2. 如果需要在Bean销毁之前执行一些逻辑，也有两种方法：

（1）使用destroy-method

（2）让Bean实现DisposableBean接口

例如：

public class Bean7 implements InitializingBean, DisposableBean {

    public Bean7() {
        System.out.println(this.getClass().getSimpleName() + ":" + this.toString() + " has been created");
    }

    public void onInit() {
        System.out.println(this.getClass().getSimpleName() + ":" + "onInit");
    }

    public void onDestroy() {
        System.out.println(this.getClass().getSimpleName() + ":" + "onDestroy");
    }

    public void afterPropertiesSet() throws Exception {
        System.out.println(this.getClass().getSimpleName() + ":" + "afterPropertiesSet");
    }

    public void destroy() throws Exception {
        System.out.println(this.getClass().getSimpleName() + ":" + "destroy");
    }
}

afterPropertiesSet()和destroy()是针对接口的实现。相应的xml配置：

<bean id="bean7" class="com.imooc.springClass4.others.Bean7" init-method="onInit" destroy-method="onDestroy"/>

测试：

@Test
public void testBean() throws Exception {
    final AbstractApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");

    Bean7 bean7 = context.getBean("bean7", Bean7.class);
    System.out.println("bean7 = " + bean7);
    
    context.close();
}

输出：

Bean7:[email protected] has been created
Bean7:afterPropertiesSet
Bean7:onInit
bean7 = [email protected]
Bean7:destroy
Bean7:onDestroy

如果想设定当前xml中所有的bean都有相同的init-method和destroy-method，可通过设定default-init-method="????"、default-destroy-method="????"实现：

 

<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"
       default-init-method="onInit"
       default-destroy-method="onDestroy"
>
</beans>

 

六、parent bean

可能存在如下场景：有很多Class继承于Class B，且Class B有很多的property，当我们需要实例化很多Class B子类的时候，如果这些子类从Class B继承的propertiy值基本相同，那么通过xml创建这些子类是一件很繁重的事情，并且会存在很多类似的重复性的代码出现。这种情况下，有如下解决办法，举例说明：

public class Bean8 {

    public Bean8() {
        System.out.println(this.getClass().getSimpleName() + ":" + this.toString() + " has been created");
    }
    private String name;
    private Integer age;
    //get/set...
}
public class Bean8_1 extends Bean8{

    public Bean8_1() {
        System.out.println(this.getClass().getSimpleName() + ":" + this.toString() + " has been created");
    }
    private String address;
    private Integer height;
    //get/set/toString...    
}
public class Bean8_2 extends Bean8{

    public Bean8_2() {
        System.out.println(this.getClass().getSimpleName() + ":" + this.toString() + " has been created");
    }
    private String email;
    private Integer weight;
    //get/set/toString...
}
<bean id="bean8" class="com.imooc.springClass4.others.Bean8" abstract="true">
    <property name="name" value="zhang3"/>
    <property name="age" value="33"/>
</bean>
<bean id="bean8_1" class="com.imooc.springClass4.others.Bean8_1" parent="bean8">
    <property name="age" value="34"/>
    <property name="address" value="JiangSu SuZhou"/>
    <property name="height" value="155"/>
</bean>
<bean id="bean8_2" class="com.imooc.springClass4.others.Bean8_2" parent="bean8">
    <property name="age" value="35"/>
    <property name="email" value="[email protected]"/>
    <property name="weight" value="65"/>
</bean>

在xml中：

  1. 定义bean8，且设定abstracy=true，设定name和age的值
  2. 实例化bean8-1，且设定parent=bean8，重新设定age=34，设定address和height的值
  3. 实例化bean8-2，且设定parent=bean8，重新设定age=35，设定email和weight的值

测试：

@Test
public void testBean() throws Exception {
    final AbstractApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
  
    Bean8_1 bean8_1 = context.getBean("bean8_1", Bean8_1.class);
    System.out.println("bean8_1 = " + bean8_1);
    Bean8_2 bean8_2 = context.getBean("bean8_2", Bean8_2.class);
    System.out.println("bean8_2 = " + bean8_2);
}

输出

bean8_1 = Bean8_1{address=‘JiangSu SuZhou‘, height=155‘, name=zhang3‘, age=34}
bean8_2 = Bean8_1{email=‘[email protected]‘, weight=65‘, name=zhang3‘, age=35}

这样，我们就可以将Bean8子类的属性值统一在bean8中赋值进去，且由于bean8被标注的abstract所以并不会被创建。

 

另外，即使Bean8_1和Bean8_2没有继承于Bean8，但是Bean8_1和Bean8_2都有name和age属性，也可以用过类似的手段简化我们的代码，示例如下：

public class Bean9_1 {

    public Bean9_1() {
        System.out.println(this.getClass().getSimpleName() + ":" + this.toString() + " has been created");
    }

    private String name;
    private Integer age;
    private String address;
    private Integer height;

    // get/set/toString......
}
public class Bean9_2{

    public Bean9_2() {
        System.out.println(this.getClass().getSimpleName() + ":" + this.toString() + " has been created");
    }

    private String name;
    private Integer age;
    private String email;
    private Integer weight;

    // get/get/toString...
}
<bean id="bean9" abstract="true">
    <property name="name" value="zhang3"/>
    <property name="age" value="33"/>
</bean>
<bean id="bean9_1" class="com.imooc.springClass4.others.Bean9_1" parent="bean9">
    <property name="age" value="34"/>
    <property name="address" value="JiangSu SuZhou"/>
    <property name="height" value="155"/>
</bean>
<bean id="bean9_2" class="com.imooc.springClass4.others.Bean9_2" parent="bean9">
    <property name="age" value="35"/>
    <property name="email" value="[email protected]"/>
    <property name="weight" value="65"/>
</bean>

和之前bean8的区别就是，定义bean9的时候没有对应的Class

测试：

@Test
public void testBean() throws Exception {
    final AbstractApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
 
    Bean9_1 bean9_1 = context.getBean("bean9_1", Bean9_1.class);
    System.out.println("bean9_1 = " + bean9_1);
    Bean9_2 bean9_2 = context.getBean("bean9_2", Bean9_2.class);
    System.out.println("bean9_2 = " + bean9_2);
}

输出

bean9_1 = Bean9_1{name=‘zhang3‘, age=34, address=‘JiangSu SuZhou‘, height=155}
bean9_2 = Bean9_2{name=‘zhang3‘, age=35, email=‘[email protected]‘, weight=65}

 




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