package com.example.ui;

import com.example.factory.BeanFactory;
import com.example.service.IAccountService;
import com.example.service.impl.AccountServiceImpl;

/**
 * 模擬一個表現層，用於呼叫業務層
 */
public class Client {
    public static void main(String[] args) {
        //IAccountService as=new AccountServiceImpl();
 

        IAccountService as= (IAccountService) BeanFactory.getBean("accountService");
        as.saveAccount();
    }
}

package com.example.factory;

import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

/**
 * 一個建立Bean物件的工廠
 *
 * Bean：在計算機英語中，有可重用元件的含義。
 * JavaBean：用java語言編寫的可重用元件。
 *
 *              javabean > 實體類
 *
 * 他就是建立我們的service和dao物件的
 *
 * 第一個：需要一個配置檔案來配置我們的service和dao
 *      配置的內容：唯一標識=全限定類名（key=value）
 * 第二個：通過讀取配置檔案中的內容，反射建立物件
 *
 * 我的配置檔案可以是xml，也可以是properties
 
 
*/
public class BeanFactory {
    //定義一個properties物件
    private static Properties props;
    //使用靜態程式碼塊為Properties物件賦值
    static{
        //例項化物件
        props=new Properties();
        //獲取properties物件的流物件
        InputStream in= BeanFactory.class.getClassLoader().getResourceAsStream("Bean.properties");
        
 
try {
            props.load(in);
        } catch (IOException e) {
            throw new ExceptionInInitializerError("初始化properties失敗");
        }
    }

    /**
     * 根據bean的名稱獲取bean物件
     * @param beanName
     * @return
     */
    public static Object getBean(String beanName){
        Object bean = null;
        String beanPath = props.getProperty(beanName);
        System.out.println(beanPath);
        try {
            bean=Class.forName(beanPath).newInstance();
        } catch (InstantiationException|IllegalAccessException|ClassNotFoundException e) {
            e.printStackTrace();
        }
        return bean;
    }
}

package com.example.service;

/**
 * 賬戶業務層介面
 */
public interface IAccountService {

    /**
     * 模擬儲存賬戶
     */
    void saveAccount();
}

package com.example.service.impl;

import com.example.factory.BeanFactory;
import com.example.service.IAccountService;
import com.example.dao.IAccountDao;
import com.example.dao.impl.AccountDaoImpl;

/**
 * 賬戶的業務層實現類
 */
public class AccountServiceImpl implements IAccountService {

    //private IAccountDao accountDao=new AccountDaoImpl();
    private IAccountDao accountDao= (IAccountDao) BeanFactory.getBean("accountDao");

    @Override
    public void saveAccount() {
        accountDao.saveAccount();
    }
}

package com.example.dao;

/**
 * 賬戶的持久層介面
 */
public interface IAccountDao {

    /**
     * 模擬儲存賬戶
     */
    void saveAccount();
}

package com.example.dao.impl;

import com.example.dao.IAccountDao;

/**
 * 賬戶的持久層實現類
 */
public class AccountDaoImpl implements IAccountDao {
    @Override
    public void saveAccount(){
        System.out.println("儲存了賬戶");
    }
}

#Bean.properties
accountService=com.example.service.impl.AccountServiceImpl
accountDao=com.example.dao.impl.AccountDaoImpl

<!--pom.xm-->
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>learn</artifactId>
    <version>1.0-SNAPSHOT</version>

    <packaging>jar</packaging>


    <dependencies>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <version>1.4.200</version>
        </dependency>
    </dependencies>

    <repositories>
        <repository>
            <id>alimaven</id>
            <name>aliyun maven</name>
            <url>http://maven.aliyun.com/nexus/content/groups/public/</url>
            <releases>
                <enabled>true</enabled>
            </releases>
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </repository>
    </repositories>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>14</java.version>
        <maven.compiler.source>14</maven.compiler.source>
        <maven.compiler.target>14</maven.compiler.target>
        <encoding>UTF-8</encoding>
    </properties>
</project>