Spring自动装配之方法、构造器位置的自动注入操作

@Target ({ElementType.CONSTRUCTOR, ElementType.METHOD, ElementType.PARAMETER, ElementType.FIELD, ElementType.ANNOTATION_TYPE})

@Retention (RetentionPolicy.RUNTIME)

@Documented

public @interface Autowired {

  /**

   * Declares whether the annotated dependency is required.

   * <p>Defaults to {@code true}.

   */

  boolean required() default true ;

}

@Autowired //定义在构造器方法上

public UserService(UserDao userDao) {

  this .userDao = userDao;

}

// 定义在构造器参数上

public UserService( @Autowired UserDao userDao) {

  this .userDao = userDao;

}

@Autowired //定义在set方法上

public void setUserDao(UserDao userDao) {

  this .userDao = userDao;

}

package com.yibai.spring.annotation.main.config;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.context.annotation.Bean;

import org.springframework.stereotype.Service;

import com.yibai.spring.annotation.service.UserDao;

import com.yibai.spring.annotation.service.UserService;

//@ComponentScan("com.yibai.spring.annotation.service")

@Service

public class MainConfigForAutowired {

  // Spring自动从IOC容器中找出UserDao作为方法参数传入，这里@Autowired可有可无

  @Bean

  public UserService userService( @Autowired UserDao userDao) {

   UserService userService = new UserService();

   userService.setUserDao(userDao);

   return userService;

  }

  @Bean

  public UserDao userDao() {

   return new UserDao();

  }

}

package com.yibai.spring.annotation.service;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.beans.factory.annotation.Qualifier;

import org.springframework.stereotype.Service;

import lombok.Getter;

@Getter

@Service

public class UserService {

  @Qualifier (value = "userDao" )

  @Autowired (required = true )

  private UserDao userDao;

  public void setUserDao(UserDao userDao) {

   this .userDao = userDao;

  }

}

package com.yibai.spring.annotation.service;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.beans.factory.annotation.Qualifier;

import org.springframework.stereotype.Service;

import lombok.Getter;

@Getter

@Service

public class UserService {

  @Qualifier (value = "userDao" )

  @Autowired (required = true )

  private UserDao userDao;

  public UserService() {

   //@Autowired定义在字段或者set方式上，在构造器上无法获取到依赖的组件

   System.out.println(userDao); // null

  }

  public void setUserDao(UserDao userDao) {

   this .userDao = userDao;

  }

}

@Autowired (required = false )

@Qualifier ( "bookDao2" )

private BookDao bookDao;

@Resource (name = "bookDao3" )

private BookDao bookDao;

<!--    inject 注解    -->

< dependency >

     < groupId >javax.inject</ groupId >

     < artifactId >javax.inject</ artifactId >

     < version >1</ version >

</ dependency >

@Inject

private BookDao bookDao;

@Component

public class Boss {

     private Car car;

     public Car getCar() {

         return car;

     }

     @Autowired

     public void setCar(Car car) {

         this .car = car;

     }

}

@Autowired

public Boss(Car car) {

     this .car = car;

}

public Boss( @Autowired Car car) {

     this .car = car;

}

@Bean

public Boss boss( @Autowired Car car) {

     return new Boss();

}

public class Red implements ApplicationContextAware {

     private ApplicationContext context;

     @Override

     public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {

         this .context = applicationContext;

     }

}

@Override

@Nullable

public Object postProcessBeforeInitialization( final Object bean, String beanName) throws BeansException {

  AccessControlContext acc = null ;

  if (System.getSecurityManager() != null && (bean instanceof ApplicationContextAware)) {

   acc = this .applicationContext.getBeanFactory().getAccessControlContext();

  }

  if (acc != null ) {

   AccessController.doPrivileged((PrivilegedAction<Object>) () -> {

    invokeAwareInterfaces(bean);

    return null ;

   }, acc);

  }

  else {

   invokeAwareInterfaces(bean);

  }

  return bean;

}

if (bean instanceof ApplicationContextAware) {

  ((ApplicationContextAware) bean).setApplicationContext( this .applicationContext);

}