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Android中的ClassLoader与dex文件加密实现分析

發布時間：2025/3/15 Android 22 豆豆

生活随笔收集整理的這篇文章主要介紹了 Android中的ClassLoader与dex文件加密实现分析小編覺得挺不錯的,現在分享給大家,幫大家做個參考.

Android中的ClassLoader

BaseDexClassLoader

Dex類加載器的基類，包含Dex類加載器之間通用功能的實現。

DexClassLoader

A class loader that loads classes from .jar and .apk files containing a classes.dex entry. This can be used to execute code not installed as part of an application.

一個可以從包含classes.dex實體的.jar或.apk文件中加載classes的類加載器。可以用于實現dex的動態加載、代碼熱更新等等。

This class loader requires an application-private, writable directory to cache optimized classes. Use Context.getDir(String, int) to create such a directory:

這個類加載器必須要一個app的私有、可寫目錄來緩存經過優化的classes（odex文件），使用Context.getDir(String, int)方法可以創建一個這樣的目錄。?
示例： File dexOutputDir = context.getDir(“dex”, 0);

PathClassLoader

Provides a simple ClassLoader implementation that operates on a list of files and directories in the local file system, but does not attempt to load classes from the network.?Android?uses this class for its system class loader and for its application class loader(s).

提供一個簡單的ClassLoader實現，可以操作在本地文件系統的文件列表或目錄中的classes，但不可以從網絡中加載classes。

DexClassLoader與PathClassLoader

DexClassLoader與PathClassLoader的區別就是DexClassLoader可以加載本地或者網絡的classes，而PathClassLoader只能加載本地的classes。

DexClassLoader源碼分析

以下是DexClassLoader的構造函數，源碼是來自Android2.3的系統源碼，Dex文件的加載就是在構造函數中實現的。接收3個參數dexPath、dexOutputDir、libPath、parent。

dexPath：dex文件路徑列表，多個路徑使用”:”分隔
dexOutputDir：經過優化的dex文件（odex）文件輸出目錄
libPath：動態庫路徑（將被添加到app動態庫搜索路徑列表中）
parent：這個一個ClassLoader，這個參數的主要作用是保留java中ClassLoader的委托機制（優先父類加載器加載classes，由上而下的加載機制，防止重復加載類字節碼）。

<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> /*** Creates a {@code DexClassLoader} that finds interpreted and native* code. Interpreted classes are found in a set of DEX files contained* in Jar or APK files.** The path lists are separated using the character specified by* the "path.separator" system property, which defaults to ":".** @param dexPath* the list of jar/apk files containing classes and resources* @param dexOutputDir* directory where optimized DEX files should be written* @param libPath* the list of directories containing native libraries; may be null* @param parent* the parent class loader*/public DexClassLoader(String dexPath, String dexOutputDir, String libPath,ClassLoader parent) {super(parent);if (dexPath == null || dexOutputDir == null)throw new NullPointerException();mRawDexPath = dexPath;mDexOutputPath = dexOutputDir;mRawLibPath = libPath;String[] dexPathList = mRawDexPath.split(":");int length = dexPathList.length;//System.out.println("DexClassLoader: " + dexPathList);mFiles = new File[length];mZips = new ZipFile[length];mDexs = new DexFile[length];/* open all Zip and DEX files up front */for (int i = 0; i < length; i++) {//System.out.println("My path is: " + dexPathList[i]);File pathFile = new File(dexPathList[i]);mFiles[i] = pathFile;if (pathFile.isFile()) {try {mZips[i] = new ZipFile(pathFile);} catch (IOException ioex) {// expecting IOException and ZipExceptionSystem.out.println("Failed opening '" + pathFile+ "': " + ioex);//ioex.printStackTrace();}/* we need both DEX and Zip, because dex has no resources */try {String outputName =generateOutputName(dexPathList[i], mDexOutputPath);mDexs[i] = DexFile.loadDex(dexPathList[i], outputName, 0);} catch (IOException ioex) {// might be a resource-only zipSystem.out.println("Failed loadDex '" + pathFile+ "': " + ioex);}} else {if (VERBOSE_DEBUG)System.out.println("Not found: " + pathFile.getPath());}}/** Prep for native library loading.*/String pathList = System.getProperty("java.library.path", ".");String pathSep = System.getProperty("path.separator", ":");String fileSep = System.getProperty("file.separator", "/");if (mRawLibPath != null) {if (pathList.length() > 0) {pathList += pathSep + mRawLibPath;}else {pathList = mRawLibPath;}}mLibPaths = pathList.split(pathSep);length = mLibPaths.length;// Add a '/' to the end so we don't have to do the property lookup// and concatenation later.for (int i = 0; i < length; i++) {if (!mLibPaths[i].endsWith(fileSep))mLibPaths[i] += fileSep;if (VERBOSE_DEBUG)System.out.println("Native lib path " +i+ ": " + mLibPaths[i]);}}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; 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padding: 0px 5px;">95</li><li style="box-sizing: border-box; padding: 0px 5px;">96</li><li style="box-sizing: border-box; padding: 0px 5px;">97</li></ul>

以上代碼大概可以總結為以下幾個步驟：?
1. super(parent)，調用父類構造函數，關聯父類ClassLoader。?
2. 對dexPath進行分割，得到dex文件路徑列表dexPathList。?
3. 迭代dexPathList，調用DexFile的靜態方法loadDex加載dex文件。?
4. 通過System.getProperty(“java.library.path”, “.”)獲取app動態庫搜索路徑列表，并把libPath添加其后。

使用DexClassLoader加載dex文件

把jar轉換為dex

關于dex的詳細解釋可以參考這篇文章?
http://blog.csdn.net/androidsecurity/article/details/9428861

1.首先我編寫了一個Test類，注意我這里讓Test繼承自Date，并導出為jar2dex.jar

dex2jar里一個腳本d2j-jar2dex可以將jar轉換為dex

dex2jar github地址：https://github.com/pxb1988/dex2jar

dex2jar下載地址：http://yun.baidu.com/s/1bnAkIb9

2.把jar拷貝到dexjar解壓目錄下執行命令：d2j-jar2dex xxx.jar -o xxx.dex（把xxx.jar轉換為xxx.dex）?

實現dex文件的加密解密

dex文件的加密解密算法使用C/C++實現，使用NDK編譯成動態庫，通過jni調用加密解密算法對dex文件實現加密、解密。

以下是java層中加密、解密算法的接口

解密dex文件實現（注意：這里的解密實現是比較簡單的，實際應用中應該做代碼混淆或放到C/C++中實現，而且注意解密文件的保護）

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">package linchaolong.utils;import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import android.util.Log;/*** Dex文件保護工具類* * @author linchaolong**/ public class DexProtector {private static final int BUFF_SIZE = 1024*1024;private static final String TAG = "DexProtector";/*** 解密Dex文件* * @param in 加密文件輸入流* @param outFile 輸出解密文件* @return 是否解密成功*/public static boolean decryptDex(InputStream in, File outFile){// 加密dex文件所在目錄File outDir = outFile.getParentFile();// 如果目錄不存在則創建if (!outDir.exists() && outDir.isDirectory()) {outDir.mkdirs();}try {if (outFile.exists()) {outFile.delete();}FileOutputStream out = new FileOutputStream(outFile);byte[] buff = new byte[BUFF_SIZE];int len = 0;while((len = in.read(buff)) != -1){// 調用native方法解密dex文件數據byte[] decryptBuff = DataProtector.decrypt(buff, len);out.write(decryptBuff, 0, len);}// 釋放資源in.close();out.close();return true;} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}return false;}public static boolean decryptDex(File encryptFile, File outFile){if (!encryptFile.exists()) {Log.e(TAG, "加密文件 '" + encryptFile.getPath() + " ''不存在");return false;}try {return decryptDex(new FileInputStream(encryptFile), outFile);} catch (FileNotFoundException e) {e.printStackTrace();}return false;}} </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; 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padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; padding: 0px 5px;">84</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; 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padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; 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padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; padding: 0px 5px;">84</li></ul>

實現dex文件的動態加載

1.新建一個Application，并重寫onCreate方法，用于在應用啟動的時候解密并加載dex文件。

我這里把加密的test.dex放到了assets目錄下，并命名為encrypt.dex?

以下是Application的源碼：

<code class="language-java hljs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">package linchaolong.dexproctor;import java.util.Date; import linchaolong.utils.DataProtector; import linchaolong.utils.DexProtector; import android.app.Application; import android.content.res.AssetManager; import android.util.Log; import dalvik.system.DexClassLoader;public class DexApplicatoin extends Application{private static final String TAG = "DexApplicatoin";@Overridepublic void onCreate() {testDexLoader();super.onCreate();}/*** 動態加載dex實現*/private void testDexLoader() {try {// 解密dex文件的File對象File decryptFile = new File(getDir("dex",MODE_PRIVATE), "test.dex");// 經過優化的dex輸出目錄File odexDir = getDir("odex_dir", MODE_PRIVATE);try {// 讀取assets目錄下的encrypt.dex并解密InputStream encryptDexIn = getAssets().open("encrypt.dex");DexProtector.decryptDex(encryptDexIn, decryptFile);} catch (IOException e1) {e1.printStackTrace();return;}// 創建類加載器，加載解密后的dex文件ClassLoader dexClassLoader = new DexClassLoader(decryptFile.getPath(), odexDir.getPath(), null, getClassLoader());// 加載Test類String className = "linchaolong.jar2dex.test.Test";Class<?> testClass = dexClassLoader.loadClass(className);if (testClass == null) {Log.e(TAG,"ClassNotFoundException : can not found class " + className);}else{try {// 創建Test對象，Test繼承自Date，這里用Date引用Test對象Date testObj = (Date) testClass.newInstance();if (testObj == null) {Log.e(TAG,"testObj is null ");}else{// 調用Test對象的toStirng方法Log.e("Test", "testObj.toString() = " + testObj.toString()); }}catch(Exception e) {e.printStackTrace();}}} catch (ClassNotFoundException e) {e.printStackTrace();}}} </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; 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padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li></ul>

2.在AndroidManifest.xml中配置Application。?

運行結果：?
?
最終打印結果與Test中toString方法實現一致，表示dex解密并加載成功了

項目地址：https://coding.net/u/linchaolong/p/DexProtector/git

原文地址：?http://blog.csdn.net/linchaolong/article/details/46960091

總結

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