IOC容器Bean对象管理有纯配置文件方式、注解方式、配置类+注解方式,本文讨论的是配置类+注解方式即Java Config的方式管理IOC容器的Bean对象,此种方式没有xml文件配置,使用配置类+注解实现,常用的注解如下:
- @Configuration 作用在配置类上,功能相当于spring的applicationContext.xml文件
- @Bean 作用在方法上,方法返回值对象放入IOC容器,bean id=方法名
- @ComponentScan(basePackages = "com.text") 功能相当于applicationContext.xml中的扫描包配置
示例代码如下:
配置类SpringConfig:
java
package com.text.config;
import com.text.controller.StudentController;
import com.text.service.StudentService;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@Configuration //配置类,相当于spring的applicationContext.xml文件
@ComponentScan(basePackages = "com.text") //相当于applicationContext.xml中的扫描包配置
public class SpringConfig {
@Bean //方法返回的studentController对象放入IOC容器,bean id=方法名
public StudentController studentController(StudentService studentService) {
StudentController controller = new StudentController();
controller.setStudentService(studentService);
return controller;
}
}
组件类:
java
package com.text.dao.impl;
import com.text.dao.StudentDao;
import org.springframework.stereotype.Repository;
@Repository
public class StudentDaoImpl implements StudentDao {
}
java
package com.text.service.impl;
import com.text.dao.StudentDao;
import com.text.service.StudentService;
import org.springframework.stereotype.Service;
import javax.annotation.Resource;
@Service
public class StudentServiceImpl implements StudentService {
@Resource
private StudentDao studentDao;
public StudentDao getStudentDao() {
return studentDao;
}
public void setStudentDao(StudentDao studentDao) {
this.studentDao = studentDao;
}
}
java
package com.text.controller;
import com.text.service.StudentService;
public class StudentController {
private StudentService studentService;
public StudentService getStudentService() {
return studentService;
}
public void setStudentService(StudentService studentService) {
this.studentService = studentService;
}
}
测试类:
java
package com.text;
import com.text.config.SpringConfig;
import com.text.controller.StudentController;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class Application {
public static void main(String[] args) {
//创建基于注解的Spring应用上下文,以纯Java注解的方式来替代XML配置文件来创建和管理Spring容器上下文。
ApplicationContext context = new AnnotationConfigApplicationContext(SpringConfig.class);
String[] beanDefinitionNames = context.getBeanDefinitionNames();
for(String beanName:beanDefinitionNames) {
System.out.println(beanName + ":" + context.getBean(beanName));
}
StudentController studentController = (StudentController)context.getBean("studentController");
System.out.println(studentController);
System.out.println(studentController.getStudentService());
/**
* 输出:
* springConfig:com.text.config.SpringConfig$$EnhancerBySpringCGLIB$$5adc8a5@23282c25
* studentDaoImpl:com.text.dao.impl.StudentDaoImpl@7920ba90
* studentServiceImpl:com.text.service.impl.StudentServiceImpl@6b419da
* studentController:com.text.controller.StudentController@3b2da18f
* com.text.controller.StudentController@3b2da18f
* com.text.service.impl.StudentServiceImpl@6b419da
*/
}
}
运行结果分析:
- @ComponentScan(basePackages = "com.text") 说明com.text包项下的通过注解标识的StudentDaoImpl、StudentServiceImpl 对象已被实例化并放入了IOC容器中
- @Configuration标识的SpringConfig类在IOC容器启动时也被对象实例化出来-springConfig
- @Bean标识的方法,其返回值对象也会被放入IOC容器中,bean id为方法名;方法参数的注入从IOC容器中寻找id为studentService的对象(系统只有id=studentServiceImpl的对象),找不到则按照StudentService类型寻找,找到StudentService类型的studentServiceImpl,注入到方法参数中,进而赋值到studentController 的属性studentService
- 从运行结果可以看出,上述实例的对象都是单例,打印出的对象地址都相同