Spring学习之——工厂模式

工厂模式

作用：由工厂来进行创建对象，同时到达了解耦合的效果

耦合：代码被硬编码在了程序中，后期维护的代技大。

例子1（自己创建一个BeanFactory）

1. pom.xml

<dependencies>
        <!-- Spring常用依赖 -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>5.1.8.RELEASE</version>
        </dependency>
</dependencies>

2.DAO

/**
 * 持久层实现类
 */
public class UserDaoImpl implements UserDao {

    @Override
    public void addUser(){
        System.out.println("insert into tb_user......");
    }
}

3.Service

/**
 * 业务层实现类
 */
public class UserServiceImpl implements UserService {
    //此处有依赖关系是service和BeanFactory
    private UserDao userDao = (UserDao)BeanFactory.getBean("userDao");

    public void addUser(){
        userDao.addUser();
    }
}

4.BeanFactory

public class BeanFactory {

    //定义一个容器，用于存放对象
    private static Map<String, Object> beans = new HashMap<>();

    /**
     * 加载配置文件
     */
    static {
        try {
            //2、读取配置文件
            //不能使用：web工程发布后没有src目录
            //InputStream is = new FileInputStream("src/bean.properties");
            InputStream is = 
            BeanFactory_v3.class.getClassLoader()
                .getResourceAsStream("bean.properties");

            //3、通过反射创建对象,把对象存到容器中
            Properties prop = new Properties();
            prop.load(is);
            Set<Map.Entry<Object, Object>> entrySet = prop.entrySet();
            for (Map.Entry<Object, Object> entry : entrySet) {
                String key = entry.getKey().toString();
                String beanName = entry.getValue().toString();
                Object value = Class.forName(beanName).newInstance();
                beans.put(key, value);
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * 4、在使用的时候，直接从工厂拿
     * @param beanName
     * @return
     */
    public static Object getBean(String beanName) {
        try {
            return beans.get(beanName);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

5.测试

/**
 * 模拟表现层
 */
public class Client {
    public static void main(String[] args) {
        //1.通过自己定义工厂的方法获取对象
        UserDao userDao = (UserDao) BeanFactory.getBean("userDao");
        System.out.println(userDao);

        UserService userService = (UserService) BeanFactory.getBean("userService");
        System.out.println(userService);
        userService.addUser();
    }
}

例子2（由Spring的工厂创建——IOC）

1. pom.xml

<dependencies>
        <!-- Spring常用依赖 -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>5.1.8.RELEASE</version>
        </dependency>
</dependencies>

2.DAO

/**
 * 持久层实现类
 */
public class UserDaoImpl implements UserDao {

    @Override
    public void addUser(){
        System.out.println("insert into tb_user......");
    }
}

3.Service

/**
 * 业务层实现类
 */
public class UserServiceImpl implements UserService {
    //此处有依赖关系
    private UserDao userDao = new UserDaoImpl();

    public void addUser(){
        userDao.addUser();
    }
}

4.applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--1、注意：要导入schema约束-->
<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">
    
    <!--
		2、把对象交给spring来创建
       		id：给对象在容器中提供一个唯一标识。用于获取对象	
		   	class：指定类的全限定类名。用于反射创建对象。默认情况下调用无参构造函数
	-->
    <bean id="userDao" class="com.by.dao.UserDaoImpl"></bean>
    <bean id="userService" class="com.by.service.UserServiceImpl"></bean>
</beans>

5.测试

/**
 * 模拟表现层
 */
public class Client {
    public static void main(String[] args) {
        //1.使用ApplicationContext接口，就是在获取spring容器
        ApplicationContext ac = new 
            ClassPathXmlApplicationContext("applicationContext.xml");
        //2.根据bean的id获取对象
        UserDao userDao = (UserDao) ac.getBean("userDao");
        System.out.println(userDao);

        UserService userService = (UserService) ac.getBean("userService");
        System.out.println(userService);
        userService.addUser();
    }
}