Spring入門之Bean的實例化方式

Bean的四種實例化方式（也可以說是三種）

bean的實例化方式：

　　①.構造器實例化（無參數構造器,與構造器的訪問權限無關），最標准，使用最多。

　　②.靜態工廠方法實例化(了解)

　　③.實例工廠方法實例化(了解)

　　④.實現FactoryBean接口實例化：實例工廠變種：集成其他框架使用：SqlSessionFactoryBean

 1、構造器實例化

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("App.xml")
//不寫名字默認為App-context.xml
public class App {
    @Autowired
    private ApplicationContext context;

    @Test
    public void testOld(){
        Teacher teacher1 = new Teacher();
        Teacher teacher2 = new Teacher();
        System.out.println(teacher1);
        System.out.println(teacher2);
    }
    @Test
    public void testSpring(){
        //用來檢驗scope是singleton或prototype的不同
        Teacher teacher1 = context.getBean(Teacher.class);
        Teacher teacher2 = context.getBean(Teacher.class);
        System.out.println(teacher1);
        System.out.println(teacher2);
    }
}

<?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="teacher" class="com.practice.test_04.constructor.Teacher" scope="singleton"/>
</beans>

public class Teacher {

    public Teacher(){
        System.out.println("======構造函數執行了=======");
    }
}

知識點補充：

　　scope作用域

　　　　

2、靜態工廠方法實例化

public class Teacher2 {
    public Teacher2(){
        System.out.println("======構造函數執行了=======");
    }
}

public class Teacher2Factory {
    public static Teacher2 getTeacher2(){
        System.out.println("====靜態工廠執行了=====");
        return new Teacher2();
    }
}

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("App.xml")
//不寫名字默認為App-context.xml
public class App {
    @Autowired
    private ApplicationContext context;

    @Test
    public void testOld(){
        Teacher2 teacher2 = new Teacher2();
        System.out.println(teacher2);
    }
    @Test
    public void testSpring(){
        Teacher2 teacher2 = context.getBean(Teacher2.class);
        System.out.println(teacher2);
    }
}

<?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="teacher2" class="com.practice.test_04.staticfactory.Teacher2Factory" factory-method="getTeacher2"/>

</beans>

3、實例工廠方法實例化

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("App.xml")
//不寫名字默認為App-context.xml
public class App {
    @Autowired
    private ApplicationContext context;
    @Test
    public void testOld(){
        Teacher3 teacher3 = new Teacher3();
        System.out.println(teacher3);
    }
    @Test
    public void testSpring(){
        Teacher3 teacher3 = context.getBean(Teacher3.class);
        System.out.println(teacher3);
    }
}

public class Teacher3 {
    public Teacher3(){
        System.out.println("======構造函數執行了=======");
    }
}

public class Teacher3Factory {

    public Teacher3 getObject(){
        System.out.println("====實例化工廠執行了=====");
        return new Teacher3();
    }
}

<?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="teacher3Factory" class="com.practice.test_04.instancefactory.Teacher3Factory"/>
    <bean id="teacher" factory-bean="teacher3Factory" factory-method="getObject"/>

</beans>

4、實現FactoryBean接口實例化

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("App.xml")
//不寫名字默認為App-context.xml
public class App {
    @Autowired
    private ApplicationContext context;
    @Test
    public void testSpring(){
        Teacher4 teacher4 = context.getBean(Teacher4.class);
        System.out.println(teacher4);
    }
}

public class Teacher4 {
    public Teacher4(){
        System.out.println("======構造函數執行了=======");
    }
}

public class Teacher4Factory implements FactoryBean<Teacher4> {

    public Teacher4 getObject(){
        System.out.println("====實例化工廠執行了=====");
        return new Teacher4();
    }

    public Class<?> getObjectType() {
        return Teacher4.class;
    }
}

<?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="teacher" class="com.practice.test_04.factorybean.Teacher4Factory"/>

</beans>

知識點補充：

　　BeanFactory和FactoryBean 的區別:

　　BeanFactory:Spring的容器對象,本質是一個factory，是Spring管理對象的工廠 FactoryBean：是Spring框架的一個接口，本質是一個bean，用來約束創建對象的工廠的的行為。

 bean的出始化和銷毀

1、<bean id="someBean" class="......" init-method="該類中初始化方法名" destroy-method="該類中銷毀方法名"> </bean>

2、init-method：bean生命周期初始化方法,對象創建后就進行調用

3、destroy-method:容器被銷毀的時候，如果bean被容器管理，會調用該方法。

4、default-init-method,default-destroy-method.配置文件中所有的bean元素的初始化方法和銷毀方法

5、分析原理: 如果bean的scope="prototype"，那么容器只負責創建和初始化，銷毀方法它並不會被spring容器管理。交給用戶自己調用。因為當bean的scope="prototype"時，Spring容器在啟動時，並不會將創建出來的對象放在容器當中。而是在每次獲取對象時，都來創建一個新的對象。因此，在容器銷毀的時候，並不知道要銷毀該對象。因此就不會調用對象的銷毀方法。

 6、代碼示例

public class Wow {
    public Wow(){
        System.out.println("創建對象");
    }
    public void doWork(){
        System.out.println("開始運行");
    }
    public void init(){
        System.out.println("初始化資源");
    }
    public void close(){
        System.out.println("關閉資源");
    }
}

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("App.xml")
public class App {
    @Autowired
    private ApplicationContext context;
    @Test
    public void testWow(){
        Wow wow1 = context.getBean(Wow.class);
        Wow wow2 = context.getBean(Wow.class);
        wow1.doWork();
    }
}

<?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="wow" class="com.practice.test_05.Wow" init-method="init" destroy-method="close" scope="prototype"/>
</beans>