SpringBean注入属性的四种方式

一.setter注入

二.构造器注入

三.注解注入

三种方式的代码都在一块，在类上面的注解，是使用注解形式
public interface UserDAO {
    public void insert();
}

//@Repository("userDAO")
public class UserDAOImpl implements UserDAO{
    public UserDAOImpl(){
        System.out.println(this + "已创建");
    }
    public void insert() {
        System.out.println(this + ":正在调用UserDAOImpl.insert()");
    }
}

//@Service("userService")
public class UserService {
//    @Resource(name="userDAO")
    private UserDAO userDAO;

    public UserService() {
        System.out.println(this + "已创建");
    }

    //通过构造函数注入
    public UserService(UserDAO userDAO) {
        this.userDAO = userDAO;
        System.out.println(this + ":正在调用构造函数注入，UserService(" + userDAO + ")");
    }

    //通过Setter方法注入
    public void setUserDAO(UserDAO userDAO) {
        this.userDAO = userDAO;
        System.out.println(this + ":正在调用Setter方法注入，setUserDAO(" + userDAO + ")");
    }

    public void createUser(){
        System.out.println(this + ":正在调用UserService.createUser()");
        userDAO.insert();
    }

setter和构造器注入的配置文件代码

配置文件名为injection.xml
<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">
    <bean id="userDAO" class="com.imooc.spring.injection.UserDAOImpl"/>
    <bean id="userService" class="com.imooc.spring.injection.UserService">
        <property name="userDAO" ref="userDAO"/>//这是setter注入配置的代码块
        <constructor-arg name="userDAO" ref="userDAO"/>//这是构造器注入代码块
    </bean>-->
</beans>

 注解注入的配置文件

配置文件名为injection.xml
<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">
    <context:component-scan base-package="com.imooc.spring"/>
</beans>

//运行文件
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class InjectionRunner {
    public static void main(String[] args) {
        ApplicationContext ctx = new ClassPathXmlApplicationContext("classpath:injection.xml");
        UserService userService = (UserService)ctx.getBean("userService");
        userService.createUser();
    }
}

四.JavaConfig注入

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class AppConfig {
    @Bean(name="userDAO")
    public UserDAO userDAO(){
        return new UserDAOImpl();
    }

    @Bean(name="userService")
    public UserService userService(){
        UserService userService = new UserService();
        userService.setUserDAO(this.userDAO());
        return userService;
    }
}