07_Spring Bean 自动装配 byName byType constructor autodetect no ＜bean＞ 元素的 autowire 属性

Spring Bean 自动装配

spring自动装配可以简化spring配置。

<bean> 元素的 autowire 属性。autowire 属性有五个值

自动装配的5中类型

名称	说明
byName	根据 Property 的 name 自动装配 ，如果一个 Bean 的 name 和另一个 Bean 中的 Property 的 name 相同，则自动装配这个 Bean 到 Property 中。注意：set方法名
byType	根据 Property 的数据类型（Type）自动装配，如果一个 Bean 的数据类型兼容另一个 Bean 中 Property 的数据类型，则自动装配。
constructor	根据构造方法的参数的数据类型，进行 byType 模式的自动装配。
autodetect	如果发现默认的构造方法，则用 constructor 模式，否则用 byType 模式
no	默认情况下，不使用自动装配，Bean 依赖必须通过 ref 元素定义。

ByName自动装配

Java代码

public class User {
	private String name;
	public User(String name) {
		this.name = name;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	@Override
	public String toString() {
		return "User name=" + name ;
	}
}

public class UserDaoImpl implements UserDao{
	@Override
	public User getUser() {
		return new User("自动装配ByName");
	}
}

public class UserServiceImpl implements UserService{
	private UserDao userDao;
	public UserDao getUserDao() {
		return userDao;
	}
	public void setUserDao(UserDao userDao) {
		this.userDao = userDao;
	}
	@Override
	public User getUser() {
		return userDao.getUser();
	}
}


public class TestSpringAutowire {
	public static void main(String[] args) {
		ApplicationContext act= new ClassPathXmlApplicationContext("/config/spring.xml");
		UserServiceImpl userService=(UserServiceImpl)act.getBean("userService");
		User user = userService.getUser();
		System.out.println(user.getName());
	}
}

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"
	xmlns:p="http://www.springframework.org/schema/p"
	xmlns:c="http://www.springframework.org/schema/c"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">
	<bean id ="userDao" class="cn.lingyiwin.dao.impl.UserDaoImpl"/>
	<bean id ="userService" class="cn.lingyiwin.service.impl.UserServiceImpl" autowire="byName"/>
</beans>

<!--或-->

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:p="http://www.springframework.org/schema/p"
	xmlns:c="http://www.springframework.org/schema/c"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd" default-autowire="byName">
	<bean id ="userDao" class="cn.lingyiwin.dao.impl.UserDaoImpl"/>
	<bean id ="userService" class="cn.lingyiwin.service.impl.UserServiceImpl"/>
</beans>

执行结果：

注意：ByName自动装配 service 中的userDao 是通过set方法设置的，xml中userDao要和sevice中属性名称一样。

ByType自动装配（一般不用）

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:p="http://www.springframework.org/schema/p"
	xmlns:c="http://www.springframework.org/schema/c"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">
        
	<bean class="cn.lingyiwin.dao.impl.UserDaoImpl"/>
	<bean id ="userService" class="cn.lingyiwin.service.impl.UserServiceImpl" autowire="byType"/>
</beans>

注意：通过类型装配，需要确保类型只有一个，如果有多个类型，就报错了，举例如下：

UserDao增加一个实现类：

public class UserDaoMySqlImpl implements UserDao{
	@Override
	public User getUser() {
		return null;
	}
}

xml注入

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:p="http://www.springframework.org/schema/p"
	xmlns:c="http://www.springframework.org/schema/c"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">
        
	<bean class="cn.lingyiwin.dao.impl.UserDaoImpl"/>
	<bean class="cn.lingyiwin.dao.impl.UserDaoMySqlImpl"/>
	<bean id ="userService" class="cn.lingyiwin.service.impl.UserServiceImpl" autowire="byType"/>
</beans>

执行结果：

警告: Exception encountered during context initialization - cancelling refresh attempt
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userService' defined in class path resource [config/spring.xml]: Unsatisfied dependency expressed through bean property 'userDao': : No qualifying bean of type [cn.lingyiwin.dao.UserDao] is defined: expected single matching bean but found 2: cn.lingyiwin.dao.impl.UserDaoImpl#0,cn.lingyiwin.dao.impl.UserDaoMySqlImpl#0; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [cn.lingyiwin.dao.UserDao] is defined: expected single matching bean but found 2: cn.lingyiwin.dao.impl.UserDaoImpl#0,cn.lingyiwin.dao.impl.UserDaoMySqlImpl#0
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1303)

constructor 装配

修改java代码：

public class UserServiceImpl implements UserService{
	private UserDao userDao;
	public UserServiceImpl(UserDao userDao) {
		this.userDao = userDao;
	}
	@Override
	public User getUser() {
		return userDao.getUser();
	}
}

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"
	xmlns:p="http://www.springframework.org/schema/p"
	xmlns:c="http://www.springframework.org/schema/c"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">
        
	<bean class="cn.lingyiwin.dao.impl.UserDaoImpl"/>
	<bean id ="userService" class="cn.lingyiwin.service.impl.UserServiceImpl" autowire="constructor"/>
</beans>

执行结果：