2. spring 应用之IOC

  • 2019 年 10 月 18 日
  • 筆記

 本文是作者原创,版权归作者所有.若要转载,请注明出处

 

我们知道Spring Framework 最重要的功能就是IoC (Inversion of Control ),也叫DI(dependency injection),这不是我说的,是官网这么说的,截图如下

spring官网说IoC,也叫DI,是同一个意思.

 

首先复习一下spring的应用

1.用xml方式将对象交给spring管理

首先是测试类

public class UserService  {        private String userName;        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }    }

然后是applicationContext.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"         xsi:schemaLocation="http://www.springframework.org/schema/beans          https://www.springframework.org/schema/beans/spring-beans.xsd"      default-autowire="no">          <bean class="com.lusaisai.service.UserService" id="userService" >          <!--此处name的值与set方法要一致-->          <property name="userName" value="lusai"></property>      </bean>    </beans>

最后是测试

public static void main(String[] args) {            ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");          UserService userService = (UserService) context.getBean("userService");
   
　　　　　　System.out.println(userService.getUserName());
 }

 

 可以看到注入成功

 

 2.依赖注入

首先是UserService依赖的对象UserDao

public interface UserDao {      void test();  }

然后是它的实现类

public class UserDaoImpl implements UserDao {      @Override      public void test() {          System.out.println("UserDaoImpl");      }  }

在UserService增加依赖的对象UserDao和set方法,注意,这里需要UserService的空构造

public class UserService  {        private String userName;        private UserDao userDao;        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }        public UserDao getUserDao() {          return userDao;      }        public void setUserDao(UserDao userDao) {          this.userDao = userDao;      }        public void serviceTest(){          userDao.test();      }    }

然后是xml配置

<!--必须有空构造-->      <bean class="com.lusaisai.service.UserService" id="userService" >          <property name="userName" value="lusai"></property>          <!--这里的ref指定下方bean标签配置对象的id-->          <!--此处name的值与UserService的属性userDao的set方法名要一致-->          <property name="userDao" ref="userDao"></property>      </bean>        <bean class="com.lusaisai.dao.UserDaoImpl" id="userDao" ></bean>

然后是测试

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");          UserService userService = (UserService) context.getBean("userService");          System.out.println(userService.getUserName());          userService.serviceTest();

看下结果

 

好了,注入成功

 

3.我们发现一个问题,我们已经在代码里写了UserDao,还有它的set和get方法,为啥还要在xml里用配置告诉spring应该如何注入呢,其实spring提供了自动装配的功能,如下图

 我们可以看到default-autowire有5个可供选择

 

 单独的bean标签里也有5个供选择,这里截个官网的图

 

 

下面我们来测试一下,首先是byName,我们把手动装配注释掉,添加上default-autowire=”byName”

<?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
        https://www.springframework.org/schema/beans/spring-beans.xsd"
   default-autowire="byName" >

   <!--必须有空构造-->
   <bean class="com.lusaisai.service.UserService" id="userService" >
      <property name="userName" value="lusai"></property>
      <!--这里的ref指定下方bean标签配置对象的id-->
      <!--此处name的值与UserService的属性userDao的set方法名要一致-->
      <!--<property name="userDao" ref="userDao"></property>-->
   </bean>

   <bean class="com.lusaisai.dao.UserDaoImpl" id="userDao" ></bean>

</beans>

UserService中的代码没有改动,测试
ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");          UserService userService = (UserService) context.getBean("userService");          System.out.println(userService.getUserName());          UserDao userDao = userService.getUserDao();          System.out.println(userDao);

看下结果

 

 好的,成功了,我们改一下set方法的名字

public void setUserDao1(UserDao userDao) {          this.userDao = userDao;      }

重新运行一次

 

 

 可以看到,userDao没有注入进来, 我们把方法名复原再次修改属性名试一下

private String userName;        private UserDao userDao2;        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }        public UserDao getUserDao() {          return userDao2;      }        public void setUserDao(UserDao userDao) {          this.userDao2 = userDao;      }

重新运行

 

 

 可以看到,注入成功,因此byName的set方法名要和依赖对象的bean标签的id相同

 

接下来看下byType,我们将default-autowire=”byType” 再加上一个同一个类不同名的bean标签

<?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          https://www.springframework.org/schema/beans/spring-beans.xsd"      default-autowire="byType" >        <!--必须有空构造-->      <bean class="com.lusaisai.service.UserService" id="userService" >          <property name="userName" value="lusai"></property>          <!--这里的ref指定下方bean标签配置对象的id-->          <!--此处name的值与UserService的属性userDao的set方法名要一致-->          <!--<property name="userDao" ref="userDao"></property>-->      </bean>        <bean class="com.lusaisai.dao.UserDaoImpl" id="userDao" ></bean>        <bean class="com.lusaisai.dao.UserDaoImpl" id="userDao2" ></bean>    </beans>

userService代码

private String userName;        private UserDao userDao;        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }        public UserDao getUserDao() {          return userDao;      }        public void setUserDao(UserDao userDao) {          this.userDao = userDao;      }

再运行一下结果

十月 17, 2019 11:53:15 下午 org.springframework.context.support.AbstractApplicationContext refresh  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 [applicationContext.xml]: Unsatisfied dependency expressed through bean property 'userDao'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.lusaisai.dao.UserDao' available: expected single matching bean but found 2: userDao,userDao2  Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userService' defined in class path resource [applicationContext.xml]: Unsatisfied dependency expressed through bean property 'userDao'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.lusaisai.dao.UserDao' available: expected single matching bean but found 2: userDao,userDao2      at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1499)      at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1379)      at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:592)      at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515)      at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320)      at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)      at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318)      at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)      at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:849)      at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:877)      at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549)      at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:144)      at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:85)      at com.lusaisai.test.Test.main(Test.java:16)  Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.lusaisai.dao.UserDao' available: expected single matching bean but found 2: userDao,userDao2      at org.springframework.beans.factory.config.DependencyDescriptor.resolveNotUnique(DependencyDescriptor.java:221)      at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1225)      at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1167)      at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1484)      ... 13 more

报错信息,显示只要一个,但找到2个,我们注释掉一个

<!--<bean class="com.lusaisai.dao.UserDaoImpl" id="userDao" ></bean>-->

重新运行,看下结果

 

 

 注入成功了,说明byType的自动个装配方式中如果存在多个相同类型不同id的bean标签，则抛出异常,如果没有匹配的bean，则不自动装配

 

最后看下构造方法注入

首先

default-autowire="constructor"

然后在UserService中注释掉set方法,添加userDao的构造方法

private String userName;        private UserDao userDao;        public UserService(UserDao userDao) {          this.userDao = userDao;      }        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }        public UserDao getUserDao() {          return userDao;      }

,运行,看结果

 

 注入成功了

我们把userDao的构造方法注释了,再运行看下结果

 

 没注入成功,但也不报错

 

好,到此为止,我们的xml配置将对象交给spring管理就讲完了总结一下

可以看出,no和Default是不自动装配的,byName和byType是通过set方法自动装配的,同时要确保有空构造存在,我猜底层是用newInstance()实现的具体源码后面再看

byName是根据set方法名自动装配的,set方法名要和bean标签的id相对应,否则,注入不成功,但不会报错

byType是根据类型装配的,如果存在多个该属性类型的bean标签，则抛出异常,如果没有匹配的bean，则不自动装配

constructor是根据构造方法来装配的,如果容器中没有一个构造函数参数类型的bean，则不自动装配

 

可以看到这种xml格式其实是非常麻烦的,实际项目中我们一般通过注解来将对象交给spring管理

只需要将spring的配置文件按以下配置即可,加入包扫描,就能将包下的所有对象通过注解方式来注入

<?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:context="http://www.springframework.org/schema/context"         xsi:schemaLocation="http://www.springframework.org/schema/beans          https://www.springframework.org/schema/beans/spring-beans.xsd          http://www.springframework.org/schema/context           http://www.springframework.org/schema/context/spring-context-3.0.xsd"        >        <context:component-scan base-package="com.lusaisai"></context:component-scan>    </beans>

我们来看例子,注意上面的spring配置文件中一个bean标签都没有了,加入了@Component注解,

这里也可以用@Repository,@Service,@Controller,可以将对象注入到spring容器进行管理,效果是一样的

@Component  public class UserDaoImpl implements UserDao {      @Override      public void test() {          System.out.println("UserDaoImpl");      }  }

这里在依赖的对象上加入了@autowire注解,我猜底层是通过filed.set调用的，所以不需要set方法,这个以后看源码了再讲

@Component  public class UserService  {        private String userName="lusai";        @Autowired      private UserDao userDao;        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }        public UserDao getUserDao() {          return userDao;      }    }

当然也可以将注解加在set方法上,如下

@Component
public class UserService  {

    private String userName="lusai";


    private UserDao userDao;

    @Autowired
    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName1) {
        this.userName = userName1;
    }

    public UserDao getUserDao() {
        return userDao;
    }

测试一下

public static void main(String[] args) {            ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");          UserService userService = (UserService) context.getBean("userService");          System.out.println(userService.getUserName());          UserDao userDao = userService.getUserDao();          System.out.println(userDao);        }

看下结果

 

 可以看到,注入成功了

如果我们再给UserDao接口的另一个实现类也交给spring管理,会不会报错呢?如下

@Component  public class UserDaoImpl2 implements UserDao{      @Override      public void test() {          System.out.println("UserDaoImpl2");      }  }

运行一下看结果

Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.lusaisai.dao.UserDao' available: expected single matching bean but found 2: userDaoImpl,userDaoImpl2      at org.springframework.beans.factory.config.DependencyDescriptor.resolveNotUnique(DependencyDescriptor.java:221)      at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1225)      at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1167)      at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredMethodElement.inject(AutowiredAnnotationBeanPostProcessor.java:668)      ... 15 more

果然报错了,说明同一个接口,最好不要写多个实现类,那我非要写多个实现类怎么办呢

我们可以用@Resource,并指定它的name属性的别名为类名的首字母小写,如下

@Component  public class UserService  {        private String userName="lusai";          @Resource(name = "userDaoImpl2")      private UserDao userDao;        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }        public UserDao getUserDao() {          return userDao;      }    }

运行一下,看看结果

 

 成功了

 

总结:先来张网上的图

 

 @Autowired与@Resource都可以用来装配bean. 都可以写在字段上,或写在setter方法上。两者如果都写在字段上，那么就不需要再写setter方法

@Autowired默认按类型装配（这个注解是属业spring的）,需要导入包org.springframework.beans.factory.annotation.Autowired 默认按照类型来进行装配

@Resource（这个注解属于java的），需要导入包javax.annotation.Resource。默认按照名称进行装配，名称可以通过name属性进行指定

 

最后,现在流行用javaconfig而不是xml来配置spring,这里贴一下javaconfig的代码

第一种:相当于写bean标签,如下,这里使用@bean注解 将UserService 和UserDaoImpl对象交给spring管理

@Configuration  public class SpringConfig {        @Bean      public UserService userService(){          return new UserService();      }        @Bean      public UserDao userDao(){          return new UserDaoImpl();      }    }

这里注入依赖

public class UserService  {        private String userName="lusai";        @Autowired      private UserDao userDao;        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }        public UserDao getUserDao() {          return userDao;      }    }

这是测试demo

public static void main(String[] args) {            AnnotationConfigApplicationContext annotationContext = new AnnotationConfigApplicationContext(SpringConfig.class);          UserService userService = (UserService) annotationContext.getBean("userService");          System.out.println(userService.getUserName());          UserDao userDao = userService.getUserDao();          System.out.println(userDao);        }

看下结果

 

 

第二种:相当于扫描包,把上面的两个@bean注解注释了,开启扫描

@Configuration  @ComponentScan("com.lusaisai")  public class SpringConfig {        /*@Bean      public UserService userService(){          return new UserService();      }        @Bean      public UserDao userDao(){          return new UserDaoImpl();      }*/    }

在UserService 和UserDaoImpl对象上加上@Component,将他们交给spring管理,如下

@Component  public class UserDaoImpl implements UserDao {      @Override      public void test() {          System.out.println("UserDaoImpl");      }  }

@Component  public class UserService  {        private String userName="lusai";        @Autowired      private UserDao userDao;        public String getUserName() {          return userName;      }        public void setUserName(String userName1) {          this.userName = userName1;      }        public UserDao getUserDao() {          return userDao;      }    }

重新测试

 

 可以看到,注入成功了.

最后 @Autowired与@Resource 和xml中的 default-autowire=”byName” 和byType是不是相同的原理的呢

先说结论:两者不是同一套逻辑,这里就后面看源码的时候再来解释吧

 

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