bean 实例化的三种方式与生命周期

构造方法（常用）

提供可访问的构造方法

public class BookDaoImpl implements BookDao {public BookDaoImpl() {// ...}  // 写不写这个空参构造都可以public void save() {// sout();}
}

配置

<bean id="bookDao"class="com.itheima.dap.impl.BookDaoImpl"/>

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

静态工厂

静态工厂

public class OrderDaoFactory {public static OrderDao getOrderDao(){return new OrderDaoImpl();}
}

配置

<bean id="orderDao"factory-method="getOrderDao"class="com.itheima.factory.OrderDaoFactory"/>

实例工厂与 FactoryBean

实例工厂

public class UserDaoFactory {public UserDao getUserDao(){return new UserDaoImpl();}
}

配置
userDaoFactory 配合使用，实际无意义
getUserDao 方法名不固定

<bean id="userDaoFactory" class="com.itheima.factory.UserDaoFactory"/> <bean id="userDao"factory-mathod="getUserDao"factory-bean="userDaoFactory "/>

FactoryBean

public class UserDaoFactoryBean implements FactoryBean<UserDao> {public UserDao getObject() throws Exception{return new UserDaoImpl();}public Class<?> getObjectType() {return UserDao.class;}
}

<beanid="userDao"class="com.itheima.factory.UserDaoFactoryBean"/>

bean 生命周期控制

在 bean 创建后到销毁前做的一些事情

配置方法

提供生命周期控制方法

publci class BookDaoImpl implements BookDao {public void save() {sout("book dao save");}public void init() {sout("book init");}public void destory() {sout("book destory");}
}

配置生命周期控制方法

<bean id="bookDao"class="com.itheima.dao.impl.BookDaoImpl"init-method="init"destroy-method="destory"/>

接口方法

public class BookServiceImpl implements BookService, InitializingBean, DisposableBean {private BookDao bookDao;public void setBookDao(BookDao bookDao) {System.out.println("set .....");this.bookDao = bookDao;}public void save() {System.out.println("book service save ...");bookDao.save();}public void destroy() throws Exception {System.out.println("service destroy");}public void afterPropertiesSet() throws Exception {System.out.println("service init");}
}