8.高级装配(二)

8.高级装配(二)

3. 处理bean歧义性

1. 使用首选bean

1. 标识为primary的bean将被使用，如果有多个bean标识为primary,这仍会有冲突

2. Bean

   @Component
   @Primary
   public class Man {}
   

3. XML

   <bean id="man" class="com.desmond.demo.Man" primary="true"></bean>
   

2. 使用Qualifier限定符

1. 限定符用于缩小bean的范围

   public interface B {
       
   }
   
   @Component
   public class B1 implements B {
       
   }
   
   @Component
   public class B2 implements B {
       
   }
   

   @Component
   public class A {
       @Qualifier("b2")
       @Autowire
       private B b;
   }
   

2. 为声明的bean创建自定义限定符

   public interface B {  
   }
   
   @Component
   public class B1 implements B {
   }
   
   @Qualifier("b2Custom")
   @Component
   public class B2 implements B {   
   }
   

   @Component
   public class A {
       @Qualifier("b2Custom")
       @Autowire
       private B b;
   }
   

3. 自定义限定符

4. 自定义一个注解，引入@Qualifier注解即可

   @Target(...)
   @Retention(...)
   @Qualifier
   public @interface B1Anno() {}
   
   @Target(...)
   @Retention(...)
   @Qualifier
   public @interface B2Anno() {}
   
   public interface B {  
   }
   
   @B1Anno
   @Component
   public class B1 implements B {
   }
   
   @B2Anno
   @Component
   public class B2 implements B {   
   }
   

   @Component
   public class A {
       @B2Anno
       @Autowire
       private B b;
   }
   

4. bean作用域

1. 作用域

   1. 单例(Singleton)
   2. 原型(Prototype)
   3. 会话(Session), web应用
   4. 请求(Request), web应用

2. Java

   @Scope(scopeName = WebApplicationContext.SCOPE_SESSION, proxyMode = ScopedProxyMode.INTERFACES)
   @Component
   public class ShoppingCar {
   }
   

3. Xml

   <bean id="car" class="com.desmond.springlearning.scope.ShoppingCar" scope="session">
           <aop:scoped-proxy proxy-target-class="true"></aop:scoped-proxy>
   </bean>
   

   相当于 @Scope里的 proxyMode作用.

5. 运行时注入

1. 占位符, ${xxx}
2. Spring表达式SpEL #{xxx}