bean的基本配置

bean的基本配置

bean的别名配置

bean作用范围配置

注意spring创建的bean默认是一个单例实例。类似于new的对象都是一个对象，内存地址都一样。
用scope可以配置 是否单例。

思考：为什么bean默认为单例？？

Bean实例化

1.构造方法

2.静态工厂

step1:创建静态工厂

public class BookDaoFactory {
    public  static BookDao getBookDao(){
        return  new BookDaoImpl();
    }
}
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测试对象是否创建成功

public class APP3 {
    public static void main(String[] args) {
        BookDao bookDao= BookDaoFactory.getBookDao();
        bookDao.save();
    }
}
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step2:添加配置文件

applicationContext.xml

<?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="bookDao" class="com.itheima.factory.BookDaoFactory" factory-method="getBookDao"></bean>
</beans>
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step3:run APP3.java

public class APP3 {
    public static void main(String[] args) {
//        BookDao bookDao= BookDaoFactory.getBookDao();
//        bookDao.save();

        ApplicationContext ctx=new ClassPathXmlApplicationContext("applicationContext.xml");
        //获取Bean
//        BookDao bookDao = (BookDao) ctx.getBean("bookDao");
//        bookDao.save();
        BookDao bookDao=(BookDao) ctx.getBean("bookDao");
        bookDao.save();
    }
}

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3.实例工厂

step1:实例工厂

public class BookDaoFactory {
    public   BookDao getBookDao(){
        return  new BookDaoImpl();
    }
}
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小run一下APP.java看看能不能跑出来

public class APP3 {
    public static void main(String[] args) {
        BookDaoFactory bookDaoFactory= new BookDaoFactory();
        BookDao bookDao=bookDaoFactory.getBookDao();
        bookDao.save();
    }
}
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step2:修改配置

<?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">

<!--    使用实例工厂实例化bean-->
    <bean id="bookDaoFactory" class="com.itheima.factory.BookDaoFactory"/>
    <bean id="bookDao" factory-method="getBookDao" factory-bean="bookDaoFactory"/>
</beans>
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step3:run APP3.java

public class APP3 {
    public static void main(String[] args) {

        ApplicationContext ctx=new ClassPathXmlApplicationContext("applicationContext.xml");
        //获取Bean
//        BookDao bookDao = (BookDao) ctx.getBean("bookDao");
//        bookDao.save();
        BookDao bookDao=(BookDao) ctx.getBean("bookDao");
        bookDao.save();
    }
}
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4.FactoryBean(方式3的变种) ※

step1:创建FactoryBean

BookDaoFactoryBean.java

public class BookDaoFactoryBean implements FactoryBean<BookDao> {
    //代替原始实例工厂中创建对象的方法
    public BookDao getObject() throws Exception {
        return new BookDaoImpl();
    }

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

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step2:配置文件

<?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="bookDao" class="com.itheima.factory.BookDaoFactoryBean"/>
</beans>
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step3：run APP3.java

public class APP3 {
    public static void main(String[] args) {

        ApplicationContext ctx=new ClassPathXmlApplicationContext("applicationContext.xml");
        //获取Bean
//        BookDao bookDao = (BookDao) ctx.getBean("bookDao");
//        bookDao.save();
        BookDao bookDao=(BookDao) ctx.getBean("bookDao");
        bookDao.save();
    }
}
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