实战学习设计模式之Decorator装饰模式

     这里先借鉴一下Jdon中关于装饰器模式的一个解释：

装饰模式:Decorator常被翻译成"装饰",我觉得翻译成"油漆工"更形象点,油漆工(decorator)是用来刷油漆的,那么被刷油漆的对象我们称decoratee.这两种实体在Decorator模式中是必须的.

Decorator定义 :
动态给一个对象添加一些额外的职责,就象在墙上刷油漆.使用Decorator模式相比用生成子类方式达到功能的扩充显得更为灵活.

为什么使用Decorator ?
我们通常可以使用继承来实现功能的拓展,如果这些需要拓展的功能的种类很繁多,那么势必生成很多子类,增加系统的复杂性,同时,使用继承实现功能拓展,我们必须可预见这些拓展功能,这些功能是编译时就确定了,是静态的.

使用Decorator的理由是:这些功能需要由用户动态决定加入的方式和时机.Decorator提供了"即插即用"的方法,在运行期间决定何时增加何种功能.

    我觉得其实也就是相当于我们实际生活中的包装的概念。这里来看一个实例，我们知道在使用Hibernate的时候对于创建SessionFactory的话只要一次就够了，这时候我们就可以对SessionFactory进行一个简单的包装来实现这样的目的：

package cn.jcenterhome.util;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Map;
import java.util.Properties;
import org.hibernate.Session;
import org.hibernate.cfg.Configuration;
public class SessionFactory {
	private static String CONFIG_FILE_LOCATION = "/hibernate.cfg.xml";
	private static org.hibernate.SessionFactory sessionFactory;
	public static synchronized void buildSessionFactory() throws SQLException {
		if (sessionFactory == null) {
			Map<String, String> jchConfig = JavaCenterHome.jchConfig;
			String dbHost = jchConfig.get("dbHost");
			String dbPort = jchConfig.get("dbPort");
			String dbName = jchConfig.get("dbName");
			String dbUser = jchConfig.get("dbUser");
			String dbPw = jchConfig.get("dbPw");
			String dbCharset = jchConfig.get("dbCharset");
			if (connect(dbHost, dbPort, dbName, dbUser, dbPw, dbCharset)) {
				Properties extraProperties = new Properties();
				extraProperties.setProperty("hibernate.connection.url", "jdbc:mysql://" + dbHost + ":"
						+ dbPort + "/" + dbName + "?zeroDateTimeBehavior=convertToNull");
				extraProperties.setProperty("hibernate.connection.username", dbUser);
				extraProperties.setProperty("hibernate.connection.password", dbPw);
				extraProperties.setProperty("hibernate.connection.characterEncoding", dbCharset);
				extraProperties.setProperty("hibernate.connection.characterSetResults", dbCharset);
				Configuration configuration = new Configuration();
				configuration = configuration.configure(CONFIG_FILE_LOCATION);
				configuration = configuration.addProperties(extraProperties);
				sessionFactory = configuration.buildSessionFactory();
			}
		}
	}
	public static Session getSession() throws SQLException {
		if (sessionFactory == null) {
			buildSessionFactory();
		}
		return sessionFactory.getCurrentSession();
	}
	public static void rebuildSessionFactory() throws SQLException {
		sessionFactory = null;
		buildSessionFactory();
	}
	public static org.hibernate.SessionFactory getSessionFactory() {
		return sessionFactory;
	}
	private static boolean connect(String dbHost, String dbPort, String dbName, String dbUser, String dbPw,
			String dbCharset) throws SQLException {
		try {
			Class.forName("com.mysql.jdbc.Driver");
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
		Connection conn = DriverManager.getConnection("jdbc:mysql://" + dbHost + ":" + dbPort + "/" + dbName
				+ "?useUnicode=true&characterEncoding=" + dbCharset, dbUser, dbPw);
		if (conn != null) {
			if (!conn.isClosed()) {
				conn.close();
				conn = null;
			}
			return true;
		}
		return false;
	}
}

 上面只是一个简单的应用，但是思想就是这样了，我觉得学习设计模式思想很重要，不是说一定要用设计模式来写代码，但是用了设计模式以后确实简单多了。对接口重新包装，对类重新包装，不仅可以重新包装自己写的接口，还可以重新包装我们所有的jar中的接口，目的就一个:使得功能更加完善，更好用。

   一句话：以后如果实现功能的拓展我们就可以考虑是否采用用Decorator模式。

package cn.jcenterhome.util;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Map;
import java.util.Properties;
import org.hibernate.Session;
import org.hibernate.cfg.Configuration;
public class SessionFactory {
	private static String CONFIG_FILE_LOCATION = "/hibernate.cfg.xml";
	private static org.hibernate.SessionFactory sessionFactory;
	public static synchronized void buildSessionFactory() throws SQLException {
		if (sessionFactory == null) {
			Map<String, String> jchConfig = JavaCenterHome.jchConfig;
			String dbHost = jchConfig.get("dbHost");
			String dbPort = jchConfig.get("dbPort");
			String dbName = jchConfig.get("dbName");
			String dbUser = jchConfig.get("dbUser");
			String dbPw = jchConfig.get("dbPw");
			String dbCharset = jchConfig.get("dbCharset");
			if (connect(dbHost, dbPort, dbName, dbUser, dbPw, dbCharset)) {
				Properties extraProperties = new Properties();
				extraProperties.setProperty("hibernate.connection.url", "jdbc:mysql://" + dbHost + ":"
						+ dbPort + "/" + dbName + "?zeroDateTimeBehavior=convertToNull");
				extraProperties.setProperty("hibernate.connection.username", dbUser);
				extraProperties.setProperty("hibernate.connection.password", dbPw);
				extraProperties.setProperty("hibernate.connection.characterEncoding", dbCharset);
				extraProperties.setProperty("hibernate.connection.characterSetResults", dbCharset);
				Configuration configuration = new Configuration();
				configuration = configuration.configure(CONFIG_FILE_LOCATION);
				configuration = configuration.addProperties(extraProperties);
				sessionFactory = configuration.buildSessionFactory();
			}
		}
	}
	public static Session getSession() throws SQLException {
		if (sessionFactory == null) {
			buildSessionFactory();
		}
		return sessionFactory.getCurrentSession();
	}
	public static void rebuildSessionFactory() throws SQLException {
		sessionFactory = null;
		buildSessionFactory();
	}
	public static org.hibernate.SessionFactory getSessionFactory() {
		return sessionFactory;
	}
	private static boolean connect(String dbHost, String dbPort, String dbName, String dbUser, String dbPw,
			String dbCharset) throws SQLException {
		try {
			Class.forName("com.mysql.jdbc.Driver");
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
		Connection conn = DriverManager.getConnection("jdbc:mysql://" + dbHost + ":" + dbPort + "/" + dbName
				+ "?useUnicode=true&characterEncoding=" + dbCharset, dbUser, dbPw);
		if (conn != null) {
			if (!conn.isClosed()) {
				conn.close();
				conn = null;
			}
			return true;
		}
		return false;
	}
}

你不说，我还真没看内容，好像是外观。。。