出自：csdn bootcool
壓縮數(shù)據(jù)
怎樣壓縮不以文件為基礎(chǔ)的數(shù)據(jù)


12月7日, 2002

Q: 本周,我回答了兩個(gè)使用Java進(jìn)行數(shù)據(jù)壓縮的問(wèn)題.

第一個(gè)問(wèn)題是: 我怎樣才能壓縮那些不在文件中的數(shù)據(jù).

第二個(gè)問(wèn)題是: 我以極大的熱情閱讀了Todd Sundsted的"壓縮你的數(shù)據(jù),從而提高你的網(wǎng)絡(luò)應(yīng)用程序的性能",但是讀完后我卻有點(diǎn)失望.當(dāng)我讀到文章標(biāo)題時(shí)我很高興.我想我總算找到了解決問(wèn)題的辦法了.

在我們的公司,我們?cè)噲D提高一個(gè)組織數(shù)據(jù)的RMI應(yīng)用程序的性能.服務(wù)器端進(jìn)行了絕大部分的處理和優(yōu)化.我們花了一年半的時(shí)間去提高性能,但是現(xiàn)在看來(lái)瓶頸在于數(shù)據(jù)的傳輸上.在一天的任何時(shí)間內(nèi),我們都有可能在客戶和服務(wù)器之間傳送成千上萬(wàn)的數(shù)據(jù).

一種可能的解決辦法,我建議我們能夠在把數(shù)據(jù)返回給客戶端時(shí)先壓縮這些數(shù)據(jù),這在Todd的文章中已經(jīng)說(shuō)得很清楚了.但是,文章中的例子卻是壓縮文件,而不是我們所需要的----對(duì)數(shù)據(jù)進(jìn)行壓縮.

在RMI中的實(shí)現(xiàn)中,我們先從數(shù)據(jù)庫(kù)取得數(shù)據(jù),再把數(shù)據(jù)放入一個(gè)列表中,接著把這個(gè)列表返回給客戶端,最后再把它們插入JTable中.我想在把數(shù)據(jù)返回給客戶時(shí),首先把列表中的數(shù)據(jù)壓縮,然后在客戶端解壓縮,最后把數(shù)據(jù)插入到表格中.

這樣的想法可行嗎?

A:最近我收到了一些關(guān)于Todd的文章的疑問(wèn).很多讀者看起來(lái)對(duì)文章中的舉例很疑惑.因?yàn)槲恼轮械睦邮且晕募嚎s為核心的.

首先回答第一個(gè)問(wèn)題,當(dāng)你使用ZipInputStream 和 ZipOutputStream 并沒(méi)有強(qiáng)制你必須使用文件.唯一要注意的是你必須把數(shù)據(jù)轉(zhuǎn)換為字節(jié)數(shù)組的形式.

第二個(gè)問(wèn)題比較棘手.在網(wǎng)絡(luò)中,以RMI方式通信就需要作一些調(diào)整了.為了在傳送數(shù)據(jù)之前就讓RMI進(jìn)行數(shù)據(jù)壓縮,你必須創(chuàng)建一個(gè)能夠壓縮數(shù)據(jù)的新的套接字.然后,當(dāng)你創(chuàng)建了一個(gè)套接字后,你得告訴RMI使用這一套接字.

以下是創(chuàng)建一個(gè)RMI形式的套接字的簡(jiǎn)要步驟:

1:選擇或者創(chuàng)建一個(gè)新的套接字.(可以參看SUN'S的"創(chuàng)建一個(gè)典型的套接字").

2:創(chuàng)建一個(gè)服務(wù)器端的套接字.

3:創(chuàng)建一個(gè)RMIClientSocketFactory

4:創(chuàng)建一個(gè)RMIServerSocketFactory

5:創(chuàng)建一個(gè)繼承了UnicastRemoteObjec的遠(yuǎn)程對(duì)象,從而使用新的factories.

根據(jù)這一大致的想法,我們來(lái)看每一步如何具體的實(shí)現(xiàn).

步驟1: 創(chuàng)建ZipSocket

由于要進(jìn)行Zip壓縮,我們重新創(chuàng)建這樣的套接字

mport java.io.InputStream;

import java.io.OutputStream;

import java.util.zip.ZipInputStream;

import java.util.zip.ZipOutputStream;

import java.net.Socket;

public class ZipSocket extends Socket {



private InputStream in;

private OutputStream out;



public ZipSocket() { super(); }



public ZipSocket(String host, int port)

throws IOException {

super(host, port);

}



public InputStream getInputStream()

throws IOException {

if (in == null) {

in = new ZipInputStream(super.getInputStream());

}

return in;

}



public OutputStream getOutputStream()

throws IOException {

if (out == null) {

out = new ZipOutputStream(super.getOutputStream());

}

return out;

}



public synchronized void close() throws IOException {

OutputStream o = getOutputStream();

o.flush();

super.close();

}

}





步驟2: 創(chuàng)建ZipServerSocket



import java.net.ServerSocket;

import java.net.Socket;

import java.io.IOException;



public class ZipServerSocket extends ServerSocket

{

public ZipServerSocket(int port) throws IOException {

super(port);

}



public Socket accept() throws IOException {

Socket socket = new ZipSocket();

implAccept(socket);

return socket;

}

}





步驟3:創(chuàng)建ZipClientSocketFactory

客戶端的factory的創(chuàng)建必須遵循以下的形式:



import java.io.IOException;

import java.io.Serializable;

import java.net.Socket;

import java.rmi.server.RMIClientSocketFactory;



public class ZipClientSocketFactory

implements RMIClientSocketFactory, Serializable {

public Socket createSocket(String host, int port)

throws IOException {

ZipSocket socket = new ZipSocket(host, port);

return socket;

}

}



步驟4:創(chuàng)建ZipServerSocketFactory



import java.io.IOException;

import java.io.Serializable;

import java.net.ServerSocket;

import java.rmi.server.RMIServerSocketFactory;



public class ZipServerSocketFactory

implements RMIServerSocketFactory, Serializable {



public ServerSocket createServerSocket(int port)

throws IOException {

ZipServerSocket server = new ZipServerSocket(port);

return server;

}

}



步驟5: 創(chuàng)建一個(gè)繼承了UnicastRemoteObjec的遠(yuǎn)程對(duì)象,從而使用新的factories.

public class YourRMIObject extends UnicastRemoteObject {



public YourRemoteObject( int port ) {

super( port, new ZipClientSocketFactory(), new ZipServerSocketFactory() );

}



// 剩下的是你自己的程序?qū)崿F(xiàn)



}



現(xiàn)在你的通信數(shù)據(jù)得到了壓縮.





關(guān)于作者:

Tony Sintes 是一個(gè)獨(dú)立咨詢?nèi)?同時(shí)也是First Class Consulting, Inc. 的創(chuàng)始人.這一咨詢公司主要致力與對(duì)各個(gè)不同的企業(yè)系統(tǒng)進(jìn)行量身定制和培訓(xùn) . 業(yè)余時(shí)間,Tony 是一個(gè)積極的自由作家,同時(shí)也是Sams出版的<<21天學(xué)通面向?qū)ο缶幊?gt;>的作者 (Sams, 2001; ISBN: 0672321092).



資源:

To download the source code that accompanies this article, go to:

http://www.javaworld.com/javaworld/javaqa/2001-12/ziprmi/01-qa-1207-ziprmi.zip



"Zip Your Data and Improve the Performance of Your Network-Based Applications,"
Todd Sundsted (JavaWorld, November 1998):

http://www.javaworld.com/javaworld/jw-11-1998/jw-11-howto.html



"Creating a Custom RMI Socket Factory," (Sun Microsystems, 1999):

http://java.sun.com/products/jdk/1.2/docs/guide/rmi/rmisocketfactory.doc.html



"Creating a Custom Socket Type," (Sun Microsystems, 1999):

http://java.sun.com/products/jdk/1.2/docs/guide/rmi/sockettype.doc.html



Be sure to check out Tony's suggested reading list at:

http://www.firstclassconsulting.net/reading.html



For more RMI stories, visit the RMI / RMI-IIOP section of JavaWorld's Topical Index:

http://www.javaworld.com/channel_content/jw-rmi-index.shtml



Want more? See the Java Q&A Index for the full Q&A catalog:

http://www.javaworld.com/columns/jw-qna-index.shtml



For over 100 insightful Java tips from some of the best minds in the business,
visit JavaWorld's Java Tips Index:

http://www.javaworld.com/columns/jw-tips-index.shtml



Learn the basics of client-side Java in our Java Beginner discussion.
Core topics include the Java language, the Java Virtual Machine, APIs, and development tools:

http://forums.idg.net/webx?50@@.ee6b804



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譯者:我覺(jué)得這篇文章很有實(shí)用性,并且告訴了我們一種在網(wǎng)絡(luò)通信時(shí)進(jìn)行數(shù)據(jù)壓縮的一個(gè)可行的解決辦法.所以把它翻譯出來(lái),希望大家都能學(xué)到這一方法.這篇文章翻譯起來(lái)比較簡(jiǎn)單.但是由于水平有限,如果不對(duì)的地方懇請(qǐng)大家指正. bootcool@263.net.