Spring之使用注解实例化Bean并注入属性

以你之姓@ 2021-12-16 03:55 365阅读 0赞

## 1.准备工作 ##

**（1）导入jar包**

除了上篇文章使用到的基本jar包外，还得加入aop的jar包，所有jar包如下

![Image 1][]

所需jar包

**（2）配置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:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">  <context:component-scan base-package="com.codeliu"/> </beans>

## 2.注解实例化Bean ##

**（1）实例化Bean有四个注解**

*  **@Component**
 *  **@Service**：业务层
 *  **@Controller**：WEB层
 *  **@Repository**：持久层

虽然分了层，但目前这四个注解的功能是一样的。

@Service(value = "user") //相当于bean标签中的id,四种方式功能一样 // @Component(value = "user") // @Controller(value = "user") // @Repository(value = "user") @Scope(value = "singleton") public class User { public void print() { System.out.println("user......"); } }

@Test /** * 使用注解实例化User类 */ public void testUser() { // 读取配置文件 @SuppressWarnings("resource") ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml"); User user = (User)context.getBean("user"); user.print(); }

## bean的作用域配置 ##

## 　　Spring中可以使用scope属性来配置bean的作用域： ##

## 　　singleton:单例，在初始化配置文件时生成单例bean对象 ##

## 　　prototype：原型的，在初始化配置文件时不生成bean对象，使用时返回不同的bean对象 ##

## 　　request：web环境下每一个request请求都会返回一个不同的bean，只在本次请求中有效 ##

## 　　session：web环境下每一个request请求都会返回一个不同的bean，在session中有效 ##

## 3.注解为属性赋值 ##

首先来个UserDao

@Component(value = "userDao") public class UserDao { public void print() { System.out.println("userdao......"); } }

再来个service

@Service(value = "userService") public class UserService { // 注入对象类型的属性,不用提供set方法 // 1.使用自动装配 // @Autowired // 为byType类型，如果有多个相同类型的，得配合@Qualifier注解 // private UserDao userDao; // 2.不使用自动装配 @Resource(name = "userDao") private UserDao userDao; // 注入普通类型的属性 @Value(value = "CodeTiger") private String name; public void print() { System.out.println("UserService......"); userDao.print(); System.out.println(name); } }

为属性赋值，我们可以使用自动装配，也可以手动赋值。

@Test /** * 使用注解注入属性 */ public void testUserService() { @SuppressWarnings("resource") ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml"); UserService service = (UserService)context.getBean("userService"); service.print(); }

## 4.注解和xml结合使用 ##

当然我们也可以同时使用注解和xml，**一般我们在xml中实例化Bean，使用注解为属性赋值。**

--------------------

**Spring@Autowired注解与自动装配**

**1   配置文件的方法**

我们编写spring 框架的代码时候。一直遵循是这样一个规则：所有在spring中注入的bean 都建议定义成私有的域变量。并且要配套写上 get 和 set方法。

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 Boss 拥有 Office 和 Car 类型的两个属性：&nbsp;&nbsp;&nbsp; &nbsp;&nbsp; 清单 3. Boss.java 
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 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">package&nbsp;com.baobaotao;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">public&nbsp;class&nbsp;Boss&nbsp;{&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;private&nbsp;Car&nbsp;car;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;private&nbsp;Office&nbsp;office;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;//&nbsp;省略&nbsp;get/setter&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;@Override&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;public&nbsp;String&nbsp;toString()&nbsp;{&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;"car:"&nbsp;+&nbsp;car&nbsp;+&nbsp;"/n"&nbsp;+&nbsp;"office:"&nbsp;+&nbsp;office;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
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 System.out.println必须实现toString方法 
 &nbsp;&nbsp; 
 我们在 Spring 容器中将 Office 和 Car 声明为 Bean，并注入到 Boss Bean 中：下面是使用传统 XML 完成这个工作的配置文件 beans.xml：&nbsp;&nbsp;&nbsp; 
 &nbsp;&nbsp; 
 清单 4. beans.xml 将以上三个类配置成 Bean&nbsp;&nbsp;&nbsp; 
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 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&lt;?xml&nbsp;version="1.0"&nbsp;encoding="UTF-8"&nbsp;?&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&lt;beans&nbsp;xmlns="http://www.springframework.org/schema/beans"&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;xsi:schemaLocation="http://www.springframework.org/schema/beans&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">http://www.springframework.org/schema/beans/spring-beans-2.5.xsd"&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&lt;bean&nbsp;id="boss"&nbsp;class="com.baobaotao.Boss"&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;property&nbsp;name="car"&nbsp;ref="car"/&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;property&nbsp;name="office"&nbsp;ref="office"&nbsp;/&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&lt;/bean&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&lt;bean&nbsp;id="office"&nbsp;class="com.baobaotao.Office"&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;property&nbsp;name="officeNo"&nbsp;value="002"/&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&lt;/bean&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&lt;bean&nbsp;id="car"&nbsp;class="com.baobaotao.Car"&nbsp;scope="singleton"&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;property&nbsp;name="brand"&nbsp;value="&nbsp;红旗&nbsp;CA72"/&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;property&nbsp;name="price"&nbsp;value="2000"/&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&lt;/bean&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&lt;/beans&gt;&nbsp; &nbsp;&nbsp;</li> 
 </ol> 
 </div> 当我们运行以下代码时，控制台将正确打出 boss 的信息：&nbsp;&nbsp;&nbsp; 
 &nbsp;&nbsp; 
 清单 5. 测试类：AnnoIoCTest.java&nbsp;&nbsp;&nbsp; 
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 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">import&nbsp;org.springframework.context.ApplicationContext;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">import&nbsp;org.springframework.context.support.ClassPathXmlApplicationContext;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">public&nbsp;class&nbsp;AnnoIoCTest&nbsp;{&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;public&nbsp;static&nbsp;void&nbsp;main(String[]&nbsp;args)&nbsp;{&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;String[]&nbsp;locations&nbsp;=&nbsp;{ "beans.xml"};&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ApplicationContext&nbsp;ctx&nbsp;=&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;new&nbsp;ClassPathXmlApplicationContext(locations);&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Boss&nbsp;boss&nbsp;=&nbsp;(Boss)&nbsp;ctx.getBean("boss");&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(boss);&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;line-height:18px;">}&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 <li style="border-top:none;border-right:none;border-bottom:none;border-left:3px solid #6ce26c;list-style:decimal outside;color:inherit;line-height:18px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li> 
 </ol> 
 </div> 
 &nbsp;&nbsp; 
 这说明 Spring 容器已经正确完成了 Bean 创建和装配的工作。&nbsp;&nbsp;&nbsp; 
 &nbsp; 
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**2   @Autowired **

Spring 2.5 引入了 @Autowired 注释，它可以对类成员变量、方法及构造函数进行标注，完成自动装配的工作。 通过 @Autowired的使用来消除 set ，get方法。

要实现我们要精简程序的目的。需要这样来处理：   
**\* 在applicationContext.xml中加入：**

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1.      
2.   <bean **class**="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor"/>

Spring 通过一个 BeanPostProcessor 对 @Autowired 进行解析，所以要让 @Autowired 起作用必须事先在 Spring 容器中声明 AutowiredAnnotationBeanPostProcessor Bean。

**\* 修改在原来注入spirng容器中的bean的方法。**   
     在域变量上加上标签@Autowired,并且去掉 相应的get 和set方法

清单 6. 使用 @Autowired 注释的 Boss.java   *                *

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1.  **package** com.baobaotao;     
2.  **import** org.springframework.beans.factory.annotation.Autowired;     
3.      
4.  **public** **class** Boss \{     
5.      
6.      @Autowired    
7.      **private** Car car;     
8.      
9.      @Autowired    
10.     **private** Office office;     
11.     
12.     …     
13. \}

**\* 在applicatonContext.xml中 把原来 引用的<porpery >标签也去掉。**

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1.             
2. **<?****xml** version="1.0" encoding="UTF-8" **?>**     
3. **<****beans** xmlns="http://www.springframework.org/schema/beans"    
4.     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    
5.     xsi:schemaLocation="http://www.springframework.org/schema/beans      
6. http://www.springframework.org/schema/beans/spring-beans-2.5.xsd"**>**     
7.     
8.          
9.     **<****bean** class="org.springframework.beans.factory.annotation.     
10.         AutowiredAnnotationBeanPostProcessor"**/>**     
11.     
12.          
13.     **<****bean** id="boss" class="com.baobaotao.Boss"**/>**     
14.       
15.     **<****bean** id="office" class="com.baobaotao.Office"**>**     
16.         **<****property** name="officeNo" value="001"**/>**     
17.     **</****bean****>**     
18.     **<****bean** id="car" class="com.baobaotao.Car" scope="singleton"**>**     
19.         **<****property** name="brand" value=" 红旗 CA72"**/>**     
20.         **<****property** name="price" value="2000"**/>**     
21.     **</****bean****>**     
22. **</****beans****>**

这样，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。     
    
按照上面的配置，Spring 将直接采用 Java 反射机制对 Boss 中的 car 和 office 这两个私有成员变量进行自动注入。所以对成员变量使用 @Autowired 后，您大可将它们的 setter 方法（setCar() 和 setOffice()）从 Boss 中删除。     
    
当然，您也可以通过 @Autowired 对方法或构造函数进行标注，如果构造函数有两个入参，分别是 bean1 和 bean2，@Autowired 将分别寻找和它们类型匹配的 Bean，将它们作为 CountryService (Bean1 bean1 ,Bean2 bean2) 的入参来创建 CountryService Bean。来看下面的代码：  对方法

\[java\]  [view plain][]  [copy][view plain]

1.  **package** com.baobaotao;     
2.      
3.  **public** **class** Boss \{     
4.      **private** Car car;     
5.      **private** Office office;     
6.      
7.       @Autowired    
8.      **public** **void** setCar(Car car) \{     
9.          **this**.car = car;     
10.     \}     
11.       
12.     @Autowired    
13.     **public** **void** setOffice(Office office) \{     
14.         **this**.office = office;     
15.     \}     
16.     …     
17. \}

这时，@Autowired 将查找被标注的方法的入参类型的 Bean，并调用方法自动注入这些 Bean。而下面的使用方法则对构造函数进行标注：

\[java\]  [view plain][]  [copy][view plain]

1.  **package** com.baobaotao;     
2.      
3.  **public** **class** Boss \{     
4.      **private** Car car;     
5.      **private** Office office;     
6.        
7.      @Autowired    
8.      **public** Boss(Car car ,Office office)\{     
9.          **this**.car = car;     
10.         **this**.office = office ;     
11.     \}     
12.       
13.     …     
14. \}

由于 Boss() 构造函数有两个入参，分别是 car 和 office，@Autowired 将分别寻找和它们类型匹配的 Bean，将它们作为 Boss(Car car ,Office office) 的入参来创建 Boss Bean。

附：https://www.jianshu.com/p/80df0a6daf65

https://blog.csdn.net/l1212xiao/article/details/80424064

转载于:https://www.cnblogs.com/myseries/p/10825540.html

[Image 1]: 
[view plain]: https://blog.csdn.net/HEYUTAO007/article/details/5981555#