Java究竟怎么玩？

（源碼依舊在Jar中）

 源碼下載地址：http://code.google.com/p/loon-simple/downloads/list

老實說，延遲下載游戲資源及調用只是一種輔助手段，與游戲開發本身關系并不大，實質也無非只是文件下載及文件讀取的混用。但考慮到上周有網友問及此類問題，筆者覺得與其回郵件單獨解釋，倒不如寫篇博文看起來更具體清晰，還能令大家幫助筆者斧正刊誤，故成此文，僅供參考。 

一般來講，我們之所以會需要通過下載方式加載游戲資源，無非是出于如下幾種目的：

 1、精簡游戲體積：

     假設我做了個100MB的游戲，卻非想把它宣傳成僅有1MB的精巧程序，這時我該怎么辦呢？

    去欺騙用戶，用大量復雜的技術名詞忽悠他們說1MB和100MB等值嗎？——用戶不是傻子，至少不都是傻子，無論你的話術多么巧妙，也很難讓絕大部分人都相信1MB和100MB是一樣的。但大話已然出口，始終要想辦法解決。

     其實呢，在現有技術體系下，要搞定他們好簡單的，只需將游戲初始界面混合下載器打包成1MB的文件發布，再“騙”他們下載執行，而后——就讓他們慢慢等待系統加載剩下那99MB吧！畢竟沒人說過這個游戲不需要額外的網絡資源同步嘛……

 2、網游資源的延遲加載需要：

     目前的網絡游戲——特別是網頁游戲，為了盡可能的減少不必要的資源損耗，提高運行效率，大多數時候并不會一口氣將所有資源都加載到游戲中，而是“大而化之，分而治之”，將游戲資源構建成一個個小小的資源包，僅僅在需要時，才或同步、或異步的加載到游戲中。這也正是我們在很多網游中所見到的，當角色過屏、讀取新地圖或遭遇新怪物時，畫面會出現稍候字樣或者部分馬賽克乃至停頓的原因。

     故此，通過網絡適時地去加載需要的資源，幾乎已成為網游開發中必不可少的技巧之一。     

3、融入特殊的加密解密機制：

   我們都知道，但凡是人所做出的程序，就沒有人所不能破解掉的。但是——卻很可能發生一個人做出來的程序，另一個人數年之內無法破解的現象。而當數年之后，另一個人破解出來時，這段程序卻早已過氣，白送都沒人要了。

   因此，當你極端的不想自己游戲被反向工程——尤其是想保護Java這種極好反編譯的代碼時，通過網絡下載的另一種意義便顯現出來了。你可以將下載的jar或class乃至其它種種保存到一個不同于執行目錄的“隱秘”場所，并且無論密鑰也好，特殊結構也罷，總之變著方的將資源加密混淆，就算混淆到連你自己都不知道這是什么東西也無所謂——能解釋成字節碼就好，最大限度的增加反向難度。而當你執行完畢，再一刪了事——下次還可以再下嘛。這樣做的話，雖然不能徹底杜絕代碼被他人盜用，但，至少也可讓反向我代碼那哥們累掉層皮（^^）。

4、本地程序及資源合法性驗證：

    在大多數網絡游戲中，為了保證用戶不做出一些諸如使用外掛的“犯規”行為，是會對系統環境乃至封包數據進行合法性驗證的，而一旦發現“非法”的東西存在，則會令“違法”玩家吊線或者干脆封號以示懲罰。

    但這些驗證，主要都只針對程序“外部”，即當“犯規”對象“不是我的游戲時”才能發揮功效，但萬一“犯規”者“來自游戲本身時”或者“驗證程序認為來自游戲本身時”，則變得無能為力，這也是為什么大多數網游都“內掛”泛濫的緣故。
             
    幸運的是，Java程序由于其“天資所限”，是很難在虛擬機外部被攻破利用的，如果用Java制作網游，原則上大可不必擔心“內掛”問題——但，這也有個大前提，那就是在“內掛”運行于虛擬機之外時才行的通。

    而如果“內掛”運行在虛擬機之內呢？ 如果我的“內掛”是一小段插入原始游戲中的代碼呢？ 要知道，動態加載class，動態修改字節碼，早就不算什么事情了。   

    這時，就需要校驗Java程序的合法性。
     
    本來要驗證這種事情是比較耗費時間的，但如果我們善于利用每次下載資源（比較大的，比如過圖或者游戲更新），如果不單單“下載”，更同步“上行”，利用空檔同服務器校對本地Java程序的合法性及完整性，便能很大程度上避免這種無意義的校驗時間浪費。這時有缺少的文件便添加，有多余的——也就是出現不該存在的Jar或class乃至原始字節碼修改，便借機強行“咔”掉它，免得它“為禍人間”。    

5、系統升級：

     通常來說，大多數的程序是不可能一個版本用到底的，游戲也不例外，無論是功能的增加或者Bug修正都離不開系統的更新。為了避免每次升級都令用戶面臨重裝的苦惱，通過網絡下載更新資源并自動更新系統也就變得非常必要。

  如何實現：

  下面我給出一個簡單的資源延遲下載Java實現示例，分別加載我以前博文中出現的兩個示例程序，并運行其中之一。(PS:由于本例加載的資源為Jar，所以進行了動態類加載操作，當我們下載其它資源類型，比如僅包含圖片的zip壓縮文件時，下載的步驟還是一致，只不過要將操作換成讀取壓縮文件及加載壓縮文件資源而已。)

 DownloadTool.java(這是一個簡單的下載工具類，內置有下載狀態顯示及下載條繪制)

package org.loon.game.simple.download; import java.awt.Color; import java.awt.Font; import java.awt.FontMetrics; import java.awt.Graphics; import java.awt.Image; import java.awt.Rectangle; import java.io.File; import java.io.InputStream; import java.io.RandomAccessFile; import java.net.HttpURLConnection; import java.net.MalformedURLException; import java.net.URL; /** * Copyright 2008 - 2009 * * Licensed under the Apache License, Version 2.0 (the "License"); you may not * use this file except in compliance with the License. You may obtain a copy of * the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the * License for the specific language governing permissions and limitations under * the License. * * @project loonframework * @author chenpeng * @email：ceponline@yahoo.com.cn * @version 0.1 */ public class DownloadTool implements Runnable { final static private Font font = new Font("黑體", 0, 14); private Rectangle rectangle; final static private Image barImage = GraphicsUtils .loadImage("image/bar.png"); final static private int MAX_BUFFER_SIZE = 2048; final static private int DOWNLOADING = 0; final static private int PAUSED = 1; final static private int COMPLETE = 2; final static private int CANCELLED = 3; final static private int ERROR = 4; private Image backgroundBarImage; private Image progressBarImage; private Image dialogBarImage; private URL url; private int size; private int downloaded; private int contentLength; private int status; private DownloadListen listen; private String downloadName; /** * 創建進度條提示框 * * @param object * @param w * @param h * @param filtrate * @return */ private static Image createDialog(Image object, int w, int h, boolean filtrate) { Image barImage = null; if (filtrate) { barImage = GraphicsUtils.drawClipImage(object, 249, 30, 1, 57); barImage = GraphicsUtils.transBlackColor(barImage); } else { barImage = GraphicsUtils.drawClipImage(object, 249, 27, 0, 0); } Image imageLeft = GraphicsUtils.drawClipImage(barImage, 8, 27, 0, 0); Image imageRight = GraphicsUtils.drawClipImage(barImage, 8, 27, 241, 0); Image ImageCenter = GraphicsUtils .drawClipImage(barImage, 233, 27, 8, 0); ImageCenter = GraphicsUtils.getResize(ImageCenter, w, h); Graphics cg = ImageCenter.getGraphics(); cg.drawImage(imageLeft, 0, 0, null); cg.drawImage(imageRight, w - 8, 0, null); cg.dispose(); return ImageCenter; } /** * 構造函數，加載指定url * * @param url */ public DownloadTool(String url) { this.size = -1; this.downloaded = 0; this.status = DOWNLOADING; try { this.url = new URL(url); } catch (MalformedURLException e) { throw new RuntimeException(e); } } public DownloadTool(URL url) { this.url = url; this.size = -1; this.downloaded = 0; this.status = DOWNLOADING; } /** * 設定進度條所在方位 * * @param x * @param y * @param w * @param h */ public void setRectangle(int x, int y, int w, int h) { setRectangle(new Rectangle(x, y, w, h)); } /** * 設定進度條所在方位 * * @param rectangle */ public void setRectangle(Rectangle rectangle) { this.backgroundBarImage = GraphicsUtils.drawClipImage(barImage, 249, 27, 0, 0); this.backgroundBarImage = createDialog(backgroundBarImage, rectangle.width - 21, rectangle.height - 2, false); // this.progressBarImage = GraphicsUtils.drawClipImage(barImage, 27, 27, // 28, 28); // this.progressBarImage = GraphicsUtils.drawClipImage(barImage, 27, 27, // 56, 28); this.progressBarImage = GraphicsUtils.drawClipImage(barImage, 27, 27, 0, 28); this.dialogBarImage = createDialog(barImage, rectangle.width, rectangle.height, true); this.rectangle = rectangle; } /** * 返回當前url地址 * * @return */ public String getUrl() { return url.toString(); } /** * 返回當前下載文件總長度 * * @return */ public int getSize() { return size; } /** * 返回當前下載已完成長度 * * @return */ public int getLevel() { return downloaded; } /** * 返回當前進度 * * @return */ public int getProgress() { return (int) ((double) downloaded / (double) size * 100); } public int getStatus() { return status; } public void pause() { status = PAUSED; } public void resume() { status = DOWNLOADING; download(listen); } public void cancel() { status = CANCELLED; } private void error() { status = ERROR; } public int getContentLength() { return contentLength; } public void download(DownloadListen listen) { this.listen = listen; Thread thread = new Thread(this); thread.start(); } private String getFileName(URL url) { String fileName = url.getFile(); return fileName.substring(fileName.lastIndexOf('/') + 1); } public String getFileName() { return getFileName(url); } public boolean isExists() { return new File(getFileName()).exists(); } public String getDownloadName() { return downloadName; } public void setDownloadName(String downloadName) { this.downloadName = downloadName; } /** * 進行文件下載并顯示進度 */ public void run() { if (!isExists()) { RandomAccessFile file = null; InputStream stream = null; try { HttpURLConnection connection = (HttpURLConnection) url .openConnection(); connection.setRequestProperty("Range", "bytes=" + downloaded + "-"); connection.connect(); if (connection.getResponseCode() / 100 != 2) { error(); } contentLength = connection.getContentLength(); if (contentLength < 1) { error(); } if (size == -1) { size = contentLength; } file = new RandomAccessFile(getFileName(url), "rw"); file.seek(downloaded); stream = connection.getInputStream(); while (status == DOWNLOADING) { byte buffer[]; if (size - downloaded > MAX_BUFFER_SIZE) { buffer = new byte[MAX_BUFFER_SIZE]; } else { buffer = new byte[size - downloaded]; } int read = stream.read(buffer); if (read == -1) { break; } file.write(buffer, 0, read); downloaded += read; listen.updateScreen(); } if (status == DOWNLOADING) { status = COMPLETE; listen.call(); } } catch (Exception e) { error(); } finally { if (file != null) { try { file.close(); file = null; } catch (Exception e) { } } if (stream != null) { try { stream.close(); stream = null; } catch (Exception e) { } } } } else { status = COMPLETE; listen.call(); } } /** * 繪制下載進度 * * @param g */ public synchronized void draw(Graphics g) { int progress = getProgress(); double ratio = (double) ((double) getLevel() / (double) getSize()); int offset = (int) (rectangle.width * ratio); g.drawImage(backgroundBarImage, rectangle.x + 19, rectangle.y, null); g.drawImage(progressBarImage, rectangle.x + 1, rectangle.y, offset + 20, rectangle.height - 2, null); g.drawImage(dialogBarImage, rectangle.x, rectangle.y, null); g.setFont(font); String mes = (getDownloadName() + ",已完成進度 : " + progress + " %") .intern(); FontMetrics fm = g.getFontMetrics(); int w = fm.stringWidth(mes); int h = fm.getHeight() + 2; g.setColor(Color.white); GraphicsUtils.setRenderingHints(g); g.drawString(mes, (rectangle.x + rectangle.width) / 2 - w / 2, rectangle.y + h); } }

DownloadCanvas.java(下載條及背景顯示用畫布)

package org.loon.game.simple.download; import java.awt.Canvas; import java.awt.Graphics; import java.awt.Image; import java.awt.Rectangle; import java.awt.Toolkit; import java.awt.Window; import java.awt.image.BufferStrategy; import java.util.ArrayList; import java.util.List; /** * Copyright 2008 - 2009 * * Licensed under the Apache License, Version 2.0 (the "License"); you may not * use this file except in compliance with the License. You may obtain a copy of * the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the * License for the specific language governing permissions and limitations under * the License. * * @project loonframework * @author chenpeng * @email：ceponline@yahoo.com.cn * @version 0.1 */ public class DownloadCanvas extends Canvas implements DownloadListen { /** * */ private static final long serialVersionUID = 1L; private DownloadTool progress; private Graphics canvasGraphics = null; private BufferStrategy bufferStrategy; private Image backgroundImage = GraphicsUtils .loadImage("image/background.jpg"); private boolean initFlag; private Window window; final static List downloadList = new ArrayList(2); /** * 預定下載的文件 */ static { DownloadTool download1 = new DownloadTool( "http://loon-simple.googlecode.com/files/Java25DSimple.jar"); download1.setDownloadName("下載Java2.5D八法行走示例中"); DownloadTool download2 = new DownloadTool( "http://greenvm.googlecode.com/files/LocalOS_src.rar"); download2.setDownloadName("下載Java外掛入門示例中"); downloadList.add(download1); downloadList.add(download2); } public void call() { if (downloadList.size() == 0) { window.setVisible(false); window.dispose(); JarLoaderUtils.callJarMain("Java25DSimple.jar"); } else { progress = (DownloadTool) downloadList.remove(0); progress.setRectangle(rectangle); progress.download(this); } } final Rectangle rectangle; public void createBufferGraphics() { createBufferStrategy(2); bufferStrategy = getBufferStrategy(); } public DownloadCanvas(Window window, int width, int height) { int pw = 600; int ph = 27; this.rectangle = new Rectangle(width / 2 - pw / 2, height / 2 - ph / 2, pw, ph); this.window = window; this.call(); } public synchronized void updateScreen() { canvasGraphics = bufferStrategy.getDrawGraphics(); if (!initFlag) { canvasGraphics.drawImage(backgroundImage, 0, 0, null); initFlag = true; } else { progress.draw(canvasGraphics); } bufferStrategy.show(); canvasGraphics.dispose(); Toolkit.getDefaultToolkit().sync(); Thread.yield(); } }

Main.java(主類，用以啟動此下載示例)

package org.loon.game.simple.download; import java.awt.Color; import java.awt.Dimension; import java.awt.Frame; import java.awt.event.WindowAdapter; import java.awt.event.WindowEvent; /** * Copyright 2008 - 2009 * * Licensed under the Apache License, Version 2.0 (the "License"); you may not * use this file except in compliance with the License. You may obtain a copy of * the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the * License for the specific language governing permissions and limitations under * the License. * * @project loonframework * @author chenpeng * @email：ceponline@yahoo.com.cn * @version 0.1 */ public class Main extends Frame { /** * */ private static final long serialVersionUID = 1L; public Main(String titleName, int width, int height) { this.setTitle(titleName); this.setBackground(Color.black); this.setPreferredSize(new Dimension(width + 5, height + 25)); this.requestFocus(); this.addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent e) { System.exit(0); } }); DownloadCanvas progress = new DownloadCanvas(this,width,height); this.add(progress); this.pack(); progress.createBufferGraphics(); this.setResizable(false); this.setLocationRelativeTo(null); this.setIgnoreRepaint(true); this.setVisible(true); } public static void main(String[] args) { java.awt.EventQueue.invokeLater(new Runnable() { public void run() { new Main("下載游戲數據", 640, 480); } }); } }

  程序執行效果如下圖所示：

 下載完畢后后將自動加載并執行下載的Java2.5D行走示例，畫面如下圖：

  （源碼依舊在Jar中）

 源碼下載地址：http://code.google.com/p/loon-simple/downloads/list