Spring: Factory Pattern

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Simple factory:

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

public class BeanFactory {
    private static Properties env = new Properties();
    
    static{
        try {
            //Step 1: get IO Stream
            InputStream inputStream = BeanFactory.class.getResourceAsStream("/applicationContext.properties");
            //Step 2: load() method reads a property list (key and element pairs) from the input byte stream.
            env.load(inputStream);
            //Stream source doesn't belong to JVM, so it can't be handled by GC and needs to be closed mannualy
            inputStream.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    
    /*
        Way to initial an object:
            1. Constructor: UserService userService = new UserServiceImpl();
            2. Refelction: This method can loose coupling
                    Class clazz = Class.forName("com.baizhiedu.basic.UserServiceImpl");
	                UserService userService = (UserService)clazz.newInstance();
     */

    public static UserService getUserService() {
        UserService userService = null;
        try {
            Class clazz = Class.forName(env.getProperty("userService"));
            userService = (UserService) clazz.newInstance();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
        return userService;
    }

    public static UserDAO getUserDAO(){
        UserDAO userDAO = null;
        try {
            Class clazz = Class.forName(env.getProperty("userDAO"));
            userDAO = (UserDAO) clazz.newInstance();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
        return userDAO;
    }

}

applicationContext.properties:

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# Properties extends Hashtable<Object,Object>
# Map: key=String value=String
# Properties [userService = com.baizhiedu.xxx.UserServiceImpl]
# Properties.getProperty("userService")

userService = com.baizhiedu.basic.UserServiceImpl
userDAO = com.baizhiedu.basic.UserDAOImpl

General factory

There are lots of redundancy in simple factory like those exceptions in try-catch. Here introduced general factory:

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

public class BeanFactory {
    private static Properties env = new Properties();
    static{
        try {
            
            InputStream inputStream = BeanFactory.class.getResourceAsStream("/applicationContext.properties");
            env.load(inputStream);
            inputStream.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public static Object getBean(String key){
         Object ret = null;
         try {
             Class clazz = Class.forName(env.getProperty(key));
             ret = clazz.newInstance();
         } catch (Exception e) {
            e.printStackTrace();
         }
         return ret;
     }

}

General factory shares the same applicationContext.properties with simple factory.

How to use general factory:

  1. Define class
  2. Inform the factory using applicationContext.properties
  3. Get object using BeanFactroy:
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    Object ret = BeanFactory.getBean("key");