实例化Bean的三种方式

一、构造方法方式

1.1 BookDaoImpl

package com.lin.dao.daoimpl;import com.lin.dao.BookDao;public class BookDaoImpl implements BookDao {public BookDaoImpl() {System.out.println("BookDao的无参构造器");}/*** 数据层实现*/public String queryBooks() {System.out.println("数据层查询书本方法");return "数据层查询书本方法";}
}

1.2 applicationContext.xml配置

   <!--bean标签：表示配置bean,id属性:bean的id,使用容器可以通过id值获取对应的bean,在一个容器中id值唯一class属性：表示给bean定义类型,即配置的bean的全路径类名--><!--方式一：构造方法实例化bean--><bean id="bookDao"  class="com.lin.dao.daoimpl.BookDaoImpl"></bean>

1.3 ConstructorMethodForInstance

package com.lin.beaninstance;import com.lin.dao.BookDao;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;/*** bean实例化方式一：构造方法方式*/
public class ConstructorMethodForInstance {public static void main(String[] args) {//1.创建IoC容器对象，加载spring核心配置文件ApplicationContext springcontext = new ClassPathXmlApplicationContext("applicationContext.xml");//2 从IOC容器中获取Bean对象(BookDao对象)BookDao bookDao = (BookDao) springcontext.getBean("bookDao");//3 调用Bean对象(BookDao对象)的方法bookDao.queryBooks();}
}

运行结果

注意：无参构造方法如果不存在，将抛出异常BeanCreationException

二、静态工厂方式

2.1 BookDaoStaticFactory静态工厂

package com.lin.factory;import com.lin.dao.BookDao;
import com.lin.dao.daoimpl.BookDaoImpl;public class BookDaoStaticFactory {//静态工厂创建对象public static BookDao getBookDao(){return new BookDaoImpl();}}

2.2 applicationContext.xml配置

 <!--方式二：使用静态工厂实例化bean-->
<bean id="bookDao" class="com.lin.factory.BookDaoStaticFactory" factory-method="getBookDao"></bean>

2.3 关系图

2.4 StaticFactoryForInstance

package com.lin.beaninstance;import com.lin.dao.BookDao;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;/*** bean实例化方式二：静态工厂方式*/
public class StaticFactoryForInstance {public static void main(String[] args) {//1.创建IoC容器对象，加载spring核心配置文件ApplicationContext springContext = new ClassPathXmlApplicationContext("applicationContext.xml");//2 从IOC容器中获取Bean对象(BookDao对象)BookDao bookDao = (BookDao) springContext.getBean("bookDao");//3 调用Bean对象(BookDao对象)的方法bookDao.queryBooks();}
}

2.4 运行结果

三 、实例工厂方式

3.1 BookDaoFactory工厂类

package com.lin.factory;import com.lin.dao.BookDao;
import com.lin.dao.daoimpl.BookDaoImpl;public class BookDaoFactory {//实例工厂创建对象public BookDao getBookDao(){return new BookDaoImpl();}
}

3.2 applicationContext.xml配置

     <!--方式三：使用实例工厂实例化bean--><bean id="bookDaoFactory" class="com.lin.factory.BookDaoFactory"></bean><bean id="bookDao" factory-bean="bookDaoFactory" factory-method="getBookDao"></bean>

3.3 关系图

3.4 实现FactoryBean<T>方式

定义BookDaoFactoryBean实现FactoryBean

package com.lin.beaninstance;import com.lin.dao.BookDao;
import com.lin.dao.daoimpl.BookDaoImpl;
import org.springframework.beans.factory.FactoryBean;public class BookDaoFactoryBean implements FactoryBean<BookDao> {@Overridepublic BookDao getObject() throws Exception {return new BookDaoImpl();}@Overridepublic Class<?> getObjectType() {return BookDao.class;}
}

applicationContext.xml配置

    <bean id="bookDao" class="com.lin.beaninstance.BookDaoFactoryBean"></bean>

getObjectType() {
return BookDao.class;
}
}

####  applicationContext.xml配置~~~xml<bean id="bookDao" class="com.lin.beaninstance.BookDaoFactoryBean"></bean>