Spring Autowired注解与省去get和set方法,对注解Autowired放在setter方法上的情况

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<?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:aop="http://www.springframework.org/schema/aop"	xmlns:c="http://www.springframework.org/schema/c"	xmlns:context="http://www.springframework.org/schema/context"	xmlns:jdbc="http://www.springframework.org/schema/jdbc"	xmlns:jee="http://www.springframework.org/schema/jee"	xmlns:mvc="http://www.springframework.org/schema/mvc"	xmlns:p="http://www.springframework.org/schema/p"	xmlns:tx="http://www.springframework.org/schema/tx"	xmlns:util="http://www.springframework.org/schema/util"	xmlns:websocket="http://www.springframework.org/schema/websocket"	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd		http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.3.xsd		http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.3.xsd		http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-4.3.xsd		http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-4.3.xsd		http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-4.3.xsd		http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.3.xsd		http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-4.3.xsd		http://www.springframework.org/schema/websocket http://www.springframework.org/schema/websocket/spring-websocket-4.3.xsd">           <bean id="autotest" class="autotest" autowire="constructor">                       </bean>                  <!--          当 Spring 容器启动时,AutowiredAnnotationBeanPostProcessor 将扫描 Spring 容器中所有 Bean,当发现 Bean 中拥有 @Autowired 注释时就找到和其匹配(默认按类型匹配)的 Bean,并注入到对应的地方中去          -->         <bean class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor"/>                  <bean id="person" class="Person">              <property name="age" value="21"></property>              <property name="name" value="李跃"></property>               <property name="sex" value="男"></property>           </bean>     </beans>
import org.springframework.beans.factory.annotation.Autowired;import org.springframework.context.ConfigurableApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext; public class autotest {                 @Autowired//这里用了这个注释就省去了构造方法或者get,set方法来设置person属性      private Person person;        	public void fun(){             ConfigurableApplicationContext cf=new ClassPathXmlApplicationContext("spring-mvc.xml");                 autotest autotest=(autotest)cf.getBean("autotest");              System.out.println(autotest);             System.out.println(autotest.person);       }                 public static void main(String args[]){              new autotest().fun();          }  }  

否则如下

<?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:aop="http://www.springframework.org/schema/aop"	xmlns:c="http://www.springframework.org/schema/c"	xmlns:context="http://www.springframework.org/schema/context"	xmlns:jdbc="http://www.springframework.org/schema/jdbc"	xmlns:jee="http://www.springframework.org/schema/jee"	xmlns:mvc="http://www.springframework.org/schema/mvc"	xmlns:p="http://www.springframework.org/schema/p"	xmlns:tx="http://www.springframework.org/schema/tx"	xmlns:util="http://www.springframework.org/schema/util"	xmlns:websocket="http://www.springframework.org/schema/websocket"	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd		http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.3.xsd		http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.3.xsd		http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-4.3.xsd		http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-4.3.xsd		http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-4.3.xsd		http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.3.xsd		http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-4.3.xsd		http://www.springframework.org/schema/websocket http://www.springframework.org/schema/websocket/spring-websocket-4.3.xsd">           <bean id="autotest" class="autotest" >              <property name="person" ref="person"></property>           </bean>                         <bean id="person" class="Person">              <property name="age" value="21"></property>              <property name="name" value="李跃"></property>               <property name="sex" value="男"></property>           </bean>     </beans>
import org.springframework.beans.factory.annotation.Autowired;import org.springframework.context.ConfigurableApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext; public class autotest {                    private Person person;         public Person getPerson() {		return person;	} 	public void setPerson(Person person) {		this.person = person;	} 	public void fun(){             ConfigurableApplicationContext cf=new ClassPathXmlApplicationContext("spring-mvc.xml");                 autotest autotest=(autotest)cf.getBean("autotest");              System.out.println(autotest);             System.out.println(autotest.person);       }                 public static void main(String args[]){              new autotest().fun();          }  }  

2.对注解Autowired放在setter方法上的情况,这种情况要注意几种情况,先看代码

<?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:aop="http://www.springframework.org/schema/aop"	xmlns:c="http://www.springframework.org/schema/c"	xmlns:context="http://www.springframework.org/schema/context"	xmlns:jdbc="http://www.springframework.org/schema/jdbc"	xmlns:jee="http://www.springframework.org/schema/jee"	xmlns:mvc="http://www.springframework.org/schema/mvc"	xmlns:p="http://www.springframework.org/schema/p"	xmlns:tx="http://www.springframework.org/schema/tx"	xmlns:util="http://www.springframework.org/schema/util"	xmlns:websocket="http://www.springframework.org/schema/websocket"	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd		http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.3.xsd		http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.3.xsd		http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-4.3.xsd		http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-4.3.xsd		http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-4.3.xsd		http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.3.xsd		http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-4.3.xsd		http://www.springframework.org/schema/websocket http://www.springframework.org/schema/websocket/spring-websocket-4.3.xsd">           <bean id="autotest" class="autotest"/>                     <!--                             当 Spring 容器启动时,AutowiredAnnotationBeanPostProcessor 将扫描 Spring 容器中所有 Bean,当发现 Bean 中拥有 @Autowired 注释时就找到和其匹配(默认按类型匹配)的 Bean,并注入到对应的地方中去          -->        <bean class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor"/>                  <bean id="person" class="Person">               <property name="age" value="21"></property>               <property name="name" value="李跃"></property>               <property name="sex" value="男"></property>           </bean>     </beans>
import org.springframework.beans.factory.annotation.Autowired;import org.springframework.context.ConfigurableApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext; //A:public class autotest{  //C:    private Person person;		public void fun(){             ConfigurableApplicationContext cf=new ClassPathXmlApplicationContext("spring-mvc.xml");                 autotest autotest=(autotest)cf.getBean("autotest");                        System.out.println(autotest.person); //Person@4f970963           System.out.println(this); //autotest@2f92e0f4           System.out.println(autotest); //autotest@7b49cea0           System.out.println(this.person);//null,                }             public Person getPerson() {    	System.out.println(person); 		return person;	}        @Autowired	public void setPerson(Person person) {		this.person = person;	}    public static void main(String args[]){  	       new autotest().fun(); // (new autotest()==B)调用A==b.a.fun()         }  }  

上面要注意区分几个对象this,autotest,是有区别的,对this和autotest来说person都是他们的属性,但是真正通过注解和配置文件配合工作的却是autotest,所以对于注解在setter方法上的情况,只有autotest.person不是空,单独的this.person或者new 一个对象.person是空的。这里我是来自http://blog.csdn.net/badboy_qiao/article/details/52713257最后总结的启发。

结论:注入的对象,只会调用空参构造函数,且这个对象的所有属性都是默认值,自己手动赋予的值不会被使用,

所以在A中的C类,在B中调用A的时候,创建的A对象的属性都是默认值,所以A对象虽然有了,但是A的属性C却是null,所以在B中直接this.a.c.method()是会报null指针异常的,且是c是null的发生原因。

解决方式:C在A中添加get方法,然后B中使用a.getC()即可获得c的对象,且c的对象也是spring注入的。

再顺便谈一个问题做下记录,为了更好理解上面的几句话看下面对象的输出,this对象始终和第一次真正new出来的对象(autotest test=new autotest();不是new autotest();)是同一个东西

import org.springframework.beans.factory.annotation.Autowired;import org.springframework.context.ConfigurableApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext; //A:public class autotest{  //C:    private Person person;		public void fun(){             ConfigurableApplicationContext cf=new ClassPathXmlApplicationContext("spring-mvc.xml");                 autotest autotest=(autotest)cf.getBean("autotest");              autotest test=new autotest();           System.out.println(test);//D autotest@7b49cea0            System.out.println(this); //C autotest@28a418fc           System.out.println(this.person);//null           System.out.println(test.person);//null           System.out.println(autotest.person);//Person@887af79     }             public Person getPerson() {    	System.out.println(person); 		return person;	}        @Autowired	public void setPerson(Person person) {		this.person = person;	}    public static void main(String args[]){ 	      System.out.println(new autotest());//B autotest@2f92e0f4	      autotest test=new autotest();	      System.out.println(test.person);//null	      System.out.println(test);//A autotest@28a418fc	      test.fun();         }  }  

还有一个地方就是如果所有bean在容器中已经存在,那么我们某个Java类中如果用到其它对象,我们可以省去在当前这个Java类的bean配置文件中用property来配置它包含的属性,它会自动注入这些属性对象,直接使用就行。

如下面这里使用到这个对象

这个类的bean中可以直接

<bean name=”shopManagerController” class=”com.xxxx.ShopManagerController””>

</bean>不用property来配置shopManagerService,可以省去,用了resource注解settter方法也可以省去,但是要在接口实现类或者类的上面使用@Service(“resource右边的name或者接口或者类的首字母小写”)

<!– 把标记了@Controller等注解的类转换为bean –>
<context:component-scan base-package=”com.XXX” />

XML中也不需要配置controller的bean

1.bean的实例化,个人理解

1.通过自动扫包,注解方式配置bean,不用繁琐的在xml文件中进行配置很多bean,
这种bean当tomcat启动项目的时候,bean对象是null,当我调用相应方法时,
它会首先被实例化然后被调用,如下面只有当我我调用selectpage方法时,handle通过afterPropertiesSet方法调用子类的
的initService方法被实例化,然后handle对象不再为空


protected abstract void initService();


@Override
public void afterPropertiesSet() throws Exception {
initService();
System.out.println(“初始化handle”+handle);
if (handle == null) {
logger.info(“Generic handle is not set. Please set it in the initService method if handle access is desired!”);
}


}




public SearchCriteria<T> selectPage(SearchCriteria<T> sc) {
return handle.selectPage(sc);
}




2.xml中配置bean,这种bean当tomcat启动项目的时候,bean对象就被实例化放入到一个容器中,当我调用相应方法时,
它会被直接取出来,如上面当我我调用selectpage方法时,不需要再进行afterPropertiesSet方法调用子类的
的initService方法对handle进行实例化,然后handle对象不会为空。

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