xml方式bean的配置---实例化bean的方式

xml方式bean的配置—实例化bean的方式

• 构造函数
• 无参构造
• 有参构造
• 工厂方法
• 静态工厂
• 实例工厂
• 实现 FactoryBean 规范延迟实例化 Bean

项目结构

pom.xml 文件

<dependencies><dependency><groupId>org.springframework</groupId><artifactId>spring-context</artifactId><version>5.2.10.RELEASE</version></dependency>
</dependencies>

无参构造

默认调用无参构造

<?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="userDao" class="com.kaiming.dao.impl.UserDaoImpl"></bean><!-- userService中注入userDao--><bean id="userService" class="com.kaiming.service.impl.UserServiceImpl"><property name="userDao" ref="userDao"></property></bean></beans>    

public class UserServiceImpl implements UserService {public UserServiceImpl() {System.out.println("UserServiceImpl无参构造方法");}public void setUserDao(UserDao userDao) {System.out.println("userDao" + userDao);}
}

UserServiceImpl无参构造方法
userDaocom.kaiming.dao.impl.UserDaoImpl@319b92f3
com.kaiming.service.impl.UserServiceImpl@fcd6521

有参构造

beanx.xml 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="userDao" class="com.kaiming.dao.impl.UserDaoImpl"></bean><!-- userService中注入userDao--><bean id="userService" class="com.kaiming.service.impl.UserServiceImpl"><!-- 有参构造，不指定默认调用无参构造--><constructor-arg name="name" value="haohao"></constructor-arg><property name="userDao" ref="userDao"></property></bean></beans>    

public class UserServiceImpl implements UserService {public UserServiceImpl() {System.out.println("UserServiceImpl无参构造方法");}public UserServiceImpl (String name) {System.out.println("UserServiceImpl有参构造方法");}public void setUserDao(UserDao userDao) {System.out.println("userDao" + userDao);}
}

UserServiceImpl有参构造方法
userDaocom.kaiming.dao.impl.UserDaoImpl@319b92f3
com.kaiming.service.impl.UserServiceImpl@fcd6521

工厂方法实例化

静态工厂方法实例化bean

factory 包下创建一个 MyBeanFactory ，且静态方法为无参

public class MyBeanFactory {// 静态方法public static UserDao userDao() {// bean 创建前后可以做一些初始化的工作，执行一些业务逻辑return new UserDaoImpl();}
}

<?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="userDao1" class="com.kaiming.factory.MyBeanFactory" factory-method="userDao"></bean><bean id="userDao" class="com.kaiming.dao.impl.UserDaoImpl"></bean><!-- userService中注入userDao--><bean id="userService" class="com.kaiming.service.impl.UserServiceImpl"><constructor-arg name="name" value="haohao"></constructor-arg><property name="userDao" ref="userDao"></property></bean></beans>    

test 测试

public class ApplicationContextTest {public static void main(String[] args) {BeanFactory beanFactory = new ClassPathXmlApplicationContext("beans.xml");Object userDao1 = beanFactory.getBean("userDao1");System.out.println(userDao1);}
}

UserServiceImpl有参构造方法
com.kaiming.dao.impl.UserDaoImpl@436a4e4b

factory 包下创建的 MyBeanFactory ，且静态方法为有参 ，若有多个参数，配置多个 <constructor-arg>

public class MyBeanFactory {public static UserDao userDao(String name) {return new UserDaoImpl();}
}

<!--静态方法-->
<bean id="userDao1" class="com.kaiming.factory.MyBeanFactory" factory-method="userDao"><constructor-arg name="name" value="haohao"></constructor-arg>
</bean>

实例工厂

factory 包下创建一个 MyBeanFactory2 ，且实例方法为无参

public class MyBeanFactory2 {public  UserDao userDao() {return new UserDaoImpl();}
}

<?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="MyBeanFactory" class="com.kaiming.factory.MyBeanFactory2"></bean><bean id="userDao2" factory-bean="MyBeanFactory" factory-method="userDao"></bean><bean id="userDao1" class="com.kaiming.factory.MyBeanFactory" factory-method="userDao"></bean><bean id="userDao" class="com.kaiming.dao.impl.UserDaoImpl"></bean><!-- userService中注入userDao--><bean id="userService" class="com.kaiming.service.impl.UserServiceImpl"><constructor-arg name="name" value="haohao"></constructor-arg><property name="userDao" ref="userDao"></property></bean></beans>    

factory 包下创建的 MyBeanFactory2 ，且静态方法为有参 ，若有多个参数，配置多个 <constructor-arg>

<bean id="MyBeanFactory" class="com.kaiming.factory.MyBeanFactory2"></bean><bean id="userDao2" factory-bean="MyBeanFactory" factory-method="userDao"><constructor-arg name="name" value="haha"></constructor-arg>
</bean>

实现 FactoryBean 规范延迟实例化 Bean

对 bean 的创建有延迟加载的功能，只有用到时，才调用 getObject() 返回 bean ，并且存储到 FactoryBeanObjectCache 的 Map 当中，如果再次调用则直接从这个 Map 中获取并返回，而不会调用 getObject() 方法

public interface FactoryBean<T> {String OBJECT_TYPE_ATTRIBUTE = "factoryBeanObjectType";// 返回bean@NullableT getObject() throws Exception;// 返回对象类型@NullableClass<?> getObjectType();// 是否为单例default boolean isSingleton() {return true;}
}

factory 包下创建的 MyBeanFactory3 实现 FactoryBean 接口

public class MyBeanFactory3 implements FactoryBean<UserDao> {@Overridepublic UserDao getObject() throws Exception {return new UserDaoImpl();}@Overridepublic Class<?> getObjectType() {return UserDao.class;}
}

test 测试

public class ApplicationContextTest {public static void main(String[] args) {BeanFactory beanFactory = new ClassPathXmlApplicationContext("beans.xml");Object userDao3 = beanFactory.getBean("userDao3");System.out.println(userDao3);}
}

UserServiceImpl有参构造方法
com.kaiming.dao.impl.UserDaoImpl@3c153a1