使用工厂模式解耦

AccountDao接口：

package com.qublog.dao;

//账户的持久层接口
public interface AccountDao {

    //模拟保存账户
    void saveAccount();
}

AccountDaoImpl类：

package com.qublog.dao.impl;

import com.qublog.dao.AccountDao;

//账户的持久层实现类
public class AccountDaoImpl implements AccountDao {

    public void saveAccount() {
        System.out.println("保存了账户");
    }
}

AccountService接口：

package com.qublog.service;

//账户业务层接口
public interface AccountService {
    //模拟保存账户
    void saveAccount();
}

AccountServiceImpl类：

package com.qublog.service.impl;

import com.qublog.dao.AccountDao;
import com.qublog.factory.BeanFactory;
import com.qublog.service.AccountService;

//账户的业务层实现类
public class AccountServiceImpl implements AccountService {

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

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

bean.properties

accountService=com.qublog.service.impl.AccountServiceImpl
accountDao=com.qublog.dao.impl.AccountDaoImpl

BeanFactory类：

package com.qublog.factory;

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

//一个创建Bean对象的工厂
//Bean：在计算机英语中有可重用组件的含义。
//JavaBean：用java编写的可重用组件
//JavaBean != 实体类
//它就是创建我们的service和dao对象的。
//1.需要一个配置文件来配置我们的service和dao
//配置内容：唯一标志=全限定类名（key=value）
//2.通过读取配置文件中配置的内容，反射创建对象
//
//配置文件可以是xml或properties
public class BeanFactory {
    //定义一个Properties对象
    private static Properties props;

    //使用静态代码块为Properties对象赋值
    static {
        try {
            //实例化对象
            props = new Properties();
            //获取properties文件的流对象
            InputStream in = BeanFactory.class.getClassLoader().getResourceAsStream("bean.properties");
            props.load(in);
        } catch (Exception e) {
            throw new ExceptionInInitializerError("初始化properties失败");
        }
    }

    //根据bean名称获取bean对象
    public static Object getBean(String beanName) {
        Object bean = null;
        try {
            String beanPath = props.getProperty(beanName);
            bean = Class.forName(beanPath).newInstance();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return bean;
    }
}

Client类：

package com.qublog.ui;

import com.qublog.factory.BeanFactory;
import com.qublog.service.AccountService;
import com.qublog.service.impl.AccountServiceImpl;

//模拟一个表现层，用于调用业务层
public class Client {
    public static void main(String[] args) {
        //AccountService accountService = new AccountServiceImpl();
        AccountService accountService = (AccountService) BeanFactory.getBean("accountService");
        accountService.saveAccount();
    }
}