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

ゞ浴缸里的玫瑰 2022-12-31 13:20 92阅读 0赞

# 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 ##

<table> 
 <thead> 
  <tr> 
   <th>名称</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>byName</td> 
   <td>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</td> 
  </tr> 
  <tr> 
   <td>byType</td> 
   <td>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。</td> 
  </tr> 
  <tr> 
   <td>constructor</td> 
   <td>根据构造方法的参数的数据类型，进行 byType 模式的自动装配。</td> 
  </tr> 
  <tr> 
   <td>autodetect</td> 
   <td>如果发现默认的构造方法，则用 constructor 模式，否则用 byType 模式</td> 
  </tr> 
  <tr> 
   <td>no</td> 
   <td>默认情况下，不使用自动装配，Bean 依赖必须通过 ref 元素定义。</td> 
  </tr> 
 </tbody> 
</table>

## 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>
    
    
    
    <?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：  
![在这里插入图片描述][2020122922245092.png]  
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） ##

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

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：

执行结果：  
![在这里插入图片描述][20201229224220229.png]

[2020122922245092.png]: /images/20221120/5924843fe8b14e96901ea480a864e441.png
[20201229224220229.png]: /images/20221120/dcfb2ce0518941ecad36f815e202bf76.png