Spring定义bean的三种方式和自动注入

一、定义bean的三种途径：        

• 首先编写Student和Teacher两个类

• public class Student {  
    
      private String name;  
    
      private Teacher teacher;  
    
      public String getName() {  
          return name;  
      }  
    
      public void setName(String name) {  
          this.name = name;  
      }  
    
      public Teacher getTeacher() {  
          return teacher;  
      }  
    
      public void setTeacher(Teacher teacher) {  
          this.teacher = teacher;  
      }  
    
  }  

  public class Teacher {  
    
      private String name;  
    
      public String getName() {  
          return name;  
      }  
    
      public void setName(String name) {  
          this.name = name;  
      }  
    
  }  

• • 方法一：基于XML的bean定义（需要提供setter方法）

  • <?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 http://www.springframework.org/schema/beans/spring-beans.xsd">  
      
        <bean id="student" class="test.Student">  
            <property name="name" value="张三"/>  
            <property name="teacher" ref="teacher"/>  
        </bean>  
      
        <bean id="teacher" class="test.Teacher">  
            <property name="name" value="李四"/>  
        </bean>  
      
    </beans>  
    [java] view plain copy
    public class Main {  
      
        public static void main(String args[]){  
            FileSystemXmlApplicationContext context=new FileSystemXmlApplicationContext("applicationContext.xml的绝对路径");  
            Student student= (Student) context.getBean("student");  
            Teacher teacher= (Teacher) context.getBean("teacher");  
            System.out.println("学生的姓名："+student.getName()+"。老师是"+student.getTeacher().getName());  
            System.out.println("老师的姓名："+teacher.getName());  
        }  
      
    }  

    • 方法二：基于注解的bean定义（不需要提供setter方法）
    Spring为此提供了四个注解，这些注解的作用与上面的XML定义bean效果一致，在于将组件交给Spring容器管理。组件的名称默认是类名（首字母变小写），也可以自己修改：
    @Component：当对组件的层次难以定位的时候使用这个注解
    @Controller：表示控制层的组件
    @Service：表示业务逻辑层的组件
    @Repository：表示数据访问层的组件
    使用这些注解的时候还有一个地方需要注意，就是需要在applicationContext.xml中声明<contex:component-scan...>一项，指明Spring容器扫描组件的包目录。

  • @Component("teacher")  
    public class Teacher {  
      
        @Value("李四")  
        private String name;  
      
        public String getName() {  
            return name;  
        }  
      
    }  
    [java] view plain copy
    @Component("student")  
    public class Student {  
      
        @Value("张三")  
        private String name;  
      
        @Resource  
        private Teacher teacher;  
      
        public String getName() {  
            return name;  
        }  
      
        public Teacher getTeacher() {  
            return teacher;  
        }  
      
    }  
    [html] view plain copy
    <?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">  
      
        <!--扫描组件的包目录-->  
        <context:component-scan base-package="test"/>  
      
    </beans>  
    [java] view plain copy
    public class Main {  
      
        public static void main(String args[]){  
            FileSystemXmlApplicationContext context=new FileSystemXmlApplicationContext("applicationContext.xml的绝对路径");  
            Student student= (Student) context.getBean("student");  
            Teacher teacher= (Teacher) context.getBean("teacher");  
            System.out.println("学生的姓名："+student.getName()+"。老师是"+student.getTeacher().getName());  
            System.out.println("老师的姓名："+teacher.getName());  
        }  
      
    }  

    • 方法三：基于Java类的bean定义（需要提供setter方法）

    • @Configuration  
      public class BeansConfiguration {  
        
          @Bean  
          public Student student(){  
              Student student=new Student();  
              student.setName("张三");  
              student.setTeacher(teacher());  
              return student;  
          }  
        
          @Bean  
          public Teacher teacher(){  
              Teacher teacher=new Teacher();  
              teacher.setName("李四");  
              return teacher;  
          }  
        
      }  
      [java] view plain copy
      public class Main {  
        
          public static void main(String args[]){  
              AnnotationConfigApplicationContext context=new AnnotationConfigApplicationContext(BeansConfiguration.class);  
              Student student= (Student) context.getBean("student");  
              Teacher teacher= (Teacher) context.getBean("teacher");  
              System.out.println("学生的姓名："+student.getName()+"。老师是"+student.getTeacher().getName());  
              System.out.println("老师的姓名："+teacher.getName());  
          }  
        
      }  

      二、Spring的自动注入

      • Spring提供了五种自动装配的类型

      no：顾名思义， 显式指明不使用Spring的自动装配功能
      byName：根据属性和组件的名称匹配关系来实现bean的自动装配
      byType：根据属性和组件的类型匹配关系来实现bean的自动装配，有多个适合类型的对象时装配失败
      constructor：与byType类似是根据类型进行自动装配，但是要求待装配的bean有相应的构造函数
      autodetect：利用Spring的自省机制判断使用byType或是constructor装配
      • 基于XML的自动装配
      
      

       

      <?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  
             http://www.springframework.org/schema/beans/spring-beans.xsd">  
        
          <bean id="student" class="test.Student" autowire="byName">  
              <property name="name" value="张三"/>  
          </bean>  
        
          <bean id="teacher" class="test.Teacher">  
              <property name="name" value="李四"/>  
          </bean>  
        
      </beans>  

      这里我并没有显式为Student对象注入Teacher属性，而是使用autowired="byName"代替，这样一来Spring会帮我们处理这些细节，将名字是teacher的组件注入到Student对象中。
       
      • 基于注解的自动装配

      其实上面已经应用过了，这里再提一下@Resource和@Autowired的区别。@Resource默认是使用byName进行装配，@Autowired默认使用byType进行装配。
      
      

       

      @Component("teacher")  
      public class Teacher {  
        
          @Value("李四")  
          private String name;  
        
          public String getName() {  
              return name;  
          }  
        
          public void setName(String name) {  
              this.name = name;  
          }  
      }  
      
       
      @Component("student")  
      public class Student {  
        
          @Value("张三")  
          private String name;  
        
          @Resource  
          private Teacher teacher;  
        
          public String getName() {  
              return name;  
          }  
        
          public void setName(String name) {  
              this.name = name;  
          }  
        
          public Teacher getTeacher() {  
              return teacher;  
          }  
        
          public void setTeacher(Teacher teacher) {  
              this.teacher = teacher;  
          }  
      }  

      
      
      

      三、如何进行选择？

      <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">          
      
      
      <property name="driverClassName" value="com.mysql.jdbc.Driver"/>  
              <property name="url" value="jdbc:mysql://localhost:3306/study"/>  
              <property name="username" value="账号"/>  
              <property name="password" value="密码"/>  
      </bean>  
      
      
      自动装配：一般我使用基于注解的自动装配。同样也是为了减少XML配置文件的“篇幅”。