读书笔记_java设计模式深入研究 第十一章 装饰器模式 Decorator

1，装饰器模式利用包含代替继承，动态的给一个对象添加一些额外的功能。如下图UML，右侧采用装饰模式后实现。

2，装饰器角色描述：

     -1，抽象构建角色（Component）：接口，封装了将要实现的方法，如ILogger。

    -2，具体构建角色（ConcreteComponent）：多个类，实现了抽象构建接口。

    -3，装饰角色（Decorator）：抽象类，该类实现Component接口，同时引用对应接口的实例。

    -4，具体装饰角色：对具体过程完成装饰。

3，具体代码如下：

package pattern.chp11.decorator.logger;
 
/**
 *  类描述：日志接口
 * 
 *  @author:  Jing
 *  @version  $Id: Exp$ 
 *
 *  History:  Jan 5, 2015 2:27:01 PM   Jing   Created.
 *           
 */
public interface ILogger {
	/**
	 * 
	 * 方法说明：记录日志模式
	 *
	 * Author：       Jing                
	 * Create Date：   Jan 5, 2015 2:27:27 PM
	 *
	 * @param msg
	 * @return void
	 */
	void log(String msg);
}

 
package pattern.chp11.decorator.logger;
 
import java.io.DataOutputStream;
import java.io.FileOutputStream;
 
/**
 *  类描述：文件LOG
 * 
 *  @author:  Jing
 *  @version  $Id: Exp$ 
 *
 *  History:  Jan 5, 2015 2:28:40 PM   Jing   Created.
 *           
 */
public class FileLogger implements ILogger {
	
	
	public void log(String msg) {
		
		DataOutputStream dos = null;
		try {
			dos = new DataOutputStream(new FileOutputStream("c:/log.txt", true));
			dos.writeBytes(msg + "\r\n");
			dos.flush();
			dos.close();
		} catch (Exception e) {
			
			e.printStackTrace();
		}
	}
 
}

package pattern.chp11.decorator.logger;
 
/**
 *  类描述：Console日志
 * 
 *  @author:  Jing
 *  @version  $Id: Exp$ 
 *
 *  History:  Jan 5, 2015 2:27:54 PM   Jing   Created.
 *           
 */
public class ConsoleLog implements ILogger {
 
	public void log(String msg) {
		
		System.out.println("Console Log!");
	}
 
}

package pattern.chp11.decorator.logger;
 
/**
 *  类描述：装饰器
 * 
 *  @author:  Jing
 *  @version  $Id: Exp$ 
 *
 *  History:  Jan 5, 2015 2:46:34 PM   Jing   Created.
 *           
 */
public abstract class Decorator implements ILogger {
	
	protected ILogger logger;
 
	public Decorator(ILogger logger) {
		this.logger = logger;
	}
}

package pattern.chp11.decorator.logger;
 
/**
 * 类描述：信息大写日志
 * 
 * @author: Jing
 * @version $Id: Exp$
 * 
 * History: Jan 5, 2015 2:48:31 PM Jing Created.
 * 
 */
public class UpLogger extends Decorator {
 
	public UpLogger(ILogger logger) {
		super(logger);
	}
 
	public void log(String msg) {
 
		msg = msg.toUpperCase();
		logger.log(msg);
	}
 
}

package pattern.chp11.decorator.logger;
 
/**
 * 类描述：XML格式化数据
 * 
 * @author: Jing
 * @version $Id: Exp$
 * 
 * History: Jan 5, 2015 2:49:36 PM Jing Created.
 * 
 */
public class XMLLogger extends Decorator {
 
	public XMLLogger(ILogger logger) {
		super(logger);
	}
 
	public void log(String msg) {
 
		String s = "<msg>" + msg + "</msg>\r\n";
		logger.log(s);
	}
	
}

 
package pattern.chp11.decorator.logger;
 
/**
 *  类描述：
 * 
 *  @author:  Jing
 *  @version  $Id: Exp$ 
 *
 *  History:  Jan 5, 2015 2:51:22 PM   Jing   Created.
 *           
 */
public class MainTest {
 
	public static void main(String[] args) {
		
		ILogger fileLog = new FileLogger();//文件日志
		XMLLogger log = new XMLLogger(fileLog);
		log.log("asdasdsad");
	}
}

4，JDK中的装饰器。

        JDK中装饰器使用最广的是IO输入输出流部分。查看对应源码。

        -1，接口 java.lang.Readable

public int read(java.nio.CharBuffer cb) throws IOException;    

-2，类 java.io.Reader

成员变量：protected Object lock 用来实现同步。初始化时，指向当前对象。

  protected Reader() {
    this.lock = this;
    }

-3，java.io.BufferedReader

成员变量：private Reader in;含有一个对Reader类的引用。

private char cb[]; 缓存区

方法：read

    public int read() throws IOException {
	synchronized (lock) {
	    ensureOpen();
	    for (;;) {
		if (nextChar >= nChars) {
		    fill();
		    if (nextChar >= nChars)
			return -1;
		}
		if (skipLF) {
		    skipLF = false;
		    if (cb[nextChar] == '\n') {
			nextChar++;
			continue;
		    }
		}
		return cb[nextChar++];
	    }
	}
    }

-4,java.io.LineNumberReader

    继承BufferedReader

LineNumberReader extends BufferedReader

    按行读取对应文件信息。

    public int read() throws IOException {
	synchronized (lock) {
	    int c = super.read();
	    if (skipLF) {
		if (c == '\n')
		    c = super.read();
		skipLF = false;
	    }
	    switch (c) {
	    case '\r':
		skipLF = true;
	    case '\n':		/* Fall through */
		lineNumber++;
		return '\n';
	    }
	    return c;
	}
    }

-5，FileReader：实现对文件的读取

public class FileReader extends InputStreamReader

/**
	 * Creates a new <tt>FileReader</tt>, given the name of the file to read
	 * from.
	 * 
	 * @param fileName
	 *            the name of the file to read from
	 * @exception FileNotFoundException
	 *                if the named file does not exist, is a directory rather
	 *                than a regular file, or for some other reason cannot be
	 *                opened for reading.
	 */
	public FileReader(String fileName) throws FileNotFoundException {
		super(new FileInputStream(fileName));
	}
 
	/**
	 * Creates a new <tt>FileReader</tt>, given the <tt>File</tt> to read
	 * from.
	 * 
	 * @param file
	 *            the <tt>File</tt> to read from
	 * @exception FileNotFoundException
	 *                if the file does not exist, is a directory rather than a
	 *                regular file, or for some other reason cannot be opened
	 *                for reading.
	 */
	public FileReader(File file) throws FileNotFoundException {
		super(new FileInputStream(file));
	}
 
	/**
	 * Creates a new <tt>FileReader</tt>, given the <tt>FileDescriptor</tt>
	 * to read from.
	 * 
	 * @param fd
	 *            the FileDescriptor to read from
	 */
	public FileReader(FileDescriptor fd) {
		super(new FileInputStream(fd));
	}

可以看到IO流完全按照装饰模式来实现。