利用泛型的基礎工廠實現MVC三層解耦

package com.gus.factory;

import java.io.FileReader;
import java.util.Properties;

public class BasicFactory {
    private static BasicFactory basicFactory = new BasicFactory();
    private static Properties properties;
    private BasicFactory(){}

    public BasicFactory getBasicFactory() {
        return basicFactory;
    }

    static {
        properties = new Properties();
        try {
            properties.load(new FileReader(BasicFactory.class.getClassLoader().getResource("config.properties").getPath()));
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }

    public <T> T getInstance(Class<T> clazz) {
        try {
            String cName = clazz.getSimpleName();
            String cImplName = properties.getProperty(cName);
            return (T)Class.forName(cImplName).newInstance();
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }

}



//在ServiceImpl中只須要這麼寫：
//CustomerDao customerDao = BasicFactory.getBasicFactory().getInstance(CustomerDao.class);

通常的實現解耦的工廠類：

package com.gus.factory;

import com.gus.dao.CustomerDao;
import java.io.FileReader;
import java.util.Properties;

//單例模式，須要對外提供方法
//這個工廠提供了dao層和service的解耦
public class CustomerDaoFactory {
    private static CustomerDaoFactory customerDaoFactory = new CustomerDaoFactory();
    private static Properties properties = null;

    private CustomerDaoFactory() {

    }

    public static CustomerDaoFactory getCustomerFactory() {
        return customerDaoFactory;
    }


    //    讀取配置文件
    static {
        properties = new Properties();
        try {
            properties.load(new FileReader(CustomerDaoFactory.class.getClassLoader().getResource("config.properties").getPath()));
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }

    public CustomerDao getCustomerDao() {
        String clazz = properties.getProperty("CustomerDao");
        try {
            return (CustomerDao) Class.forName(clazz).newInstance();
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }

}


//在service層須要這麼寫
CustomerDao customerDao = CustomerDaoFactory.getCustomerFactory().getCustomerDao();

service和dao層須要解耦，web層與service層也須要解耦，

每一個解耦都須要構建一個工廠類。

還有一種很基礎的實現方式：

public Object getInstance(String clazz) {
        clazz = properties.getProperty(clazz);
        try {
            return  Class.forName(clazz).newInstance();
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }

在service層須要這麼寫：
CustomerDao customerDao = (CustomerDao) BasicFactory.getBasicFactory().getInstance("CustomDao");
不只須要將類名變成String參數傳進去，還須要強轉一下。

因此，就用第一個吧。