Android loads a third-party class library during runtime

Android loads a third-party class library during runtime

First, place the class library to be loaded during running to other directories of the project, such as creating a thirdlibs directory. Then use the dx command to compress the following class library and make it a dex file.

dx --dex --output=../assets/ *.jar

This will generate a classes.dexfile under assetsand compress it into a classes.zip file.

Create a class to load the class library

import java.io.File;import java.io.FileOutputStream;import java.io.FilenameFilter;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.lang.reflect.Array;import java.lang.reflect.Field;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.util.ArrayList;import java.util.Arrays;import java.util.HashSet;import java.util.List;import java.util.ListIterator;import java.util.Set;import java.util.zip.ZipFile;import android.content.Context;import android.content.pm.ApplicationInfo;import android.content.pm.PackageManager;import android.content.pm.PackageManager.NameNotFoundException;import android.content.res.AssetManager;import android.os.Build;import android.util.Log;import dalvik.system.DexFile;public class AssetsDex {static final String TAG = "AssetsDex";private static final int MAX_SUPPORTED_SDK_VERSION = 20;private static final int MIN_SDK_VERSION = 4;private static final Set
 
   installedApk = new HashSet
  
   ();private static boolean installed = false;private AssetsDex() {}public static void install(Context context) {if (installed) {return;}ensureLibs(context);Log.i(TAG, "install");if (Build.VERSION.SDK_INT < MIN_SDK_VERSION) {throw new RuntimeException("Multi dex installation failed. SDK "+ Build.VERSION.SDK_INT+ " is unsupported. Min SDK version is " + MIN_SDK_VERSION+ ".");}try {ApplicationInfo applicationInfo = getApplicationInfo(context);if (applicationInfo == null) {// Looks like running on a test Context, so just return without// patching.return;}synchronized (installedApk) {String apkPath = applicationInfo.sourceDir;if (installedApk.contains(apkPath)) {return;}installedApk.add(apkPath);if (Build.VERSION.SDK_INT > MAX_SUPPORTED_SDK_VERSION) {Log.w(TAG,"MultiDex is not guaranteed to work in SDK version "+ Build.VERSION.SDK_INT+ ": SDK version higher than "+ MAX_SUPPORTED_SDK_VERSION+ " should be backed by "+ "runtime with built-in multidex capabilty but it's not the "+ "case here: java.vm.version=\""+ System.getProperty("java.vm.version")+ "\"");}/* * The patched class loader is expected to be a descendant of * dalvik.system.BaseDexClassLoader. We modify its * dalvik.system.DexPathList pathList field to append additional * DEX file entries. */ClassLoader loader;try {loader = context.getClassLoader();} catch (RuntimeException e) {/* * Ignore those exceptions so that we don't break tests * relying on Context like a android.test.mock.MockContext * or a android.content.ContextWrapper with a null base * Context. */Log.w(TAG,"Failure while trying to obtain Context class loader. "+ "Must be running in test mode. Skip patching.",e);return;}if (loader == null) {// Note, the context class loader is null when running// Robolectric tests.Log.e(TAG,"Context class loader is null. Must be running in test mode. "+ "Skip patching.");return;}File dexDir = context.getDir("outdex", Context.MODE_PRIVATE);File[] szFiles = dexDir.listFiles(new FilenameFilter() {@Overridepublic boolean accept(File dir, String filename) {return filename.endsWith(".zip");}});List
   
     files = new ArrayList
    
     ();for (File f : szFiles) {Log.i(TAG, "load file:" + f.getName());files.add(f);}Log.i(TAG, "loader before:" + context.getClassLoader());installSecondaryDexes(loader, dexDir, files);Log.i(TAG, "loader end:" + context.getClassLoader());}} catch (Exception e) {Log.e(TAG, "Multidex installation failure", e);throw new RuntimeException("Multi dex installation failed ("+ e.getMessage() + ").");}installed = true;Log.i(TAG, "install done");}private static ApplicationInfo getApplicationInfo(Context context)throws NameNotFoundException {PackageManager pm;String packageName;try {pm = context.getPackageManager();packageName = context.getPackageName();} catch (RuntimeException e) {/* * Ignore those exceptions so that we don't break tests relying on * Context like a android.test.mock.MockContext or a * android.content.ContextWrapper with a null base Context. */Log.w(TAG,"Failure while trying to obtain ApplicationInfo from Context. "+ "Must be running in test mode. Skip patching.", e);return null;}if (pm == null || packageName == null) {// This is most likely a mock context, so just return without// patching.return null;}ApplicationInfo applicationInfo = pm.getApplicationInfo(packageName,PackageManager.GET_META_DATA);return applicationInfo;}public static void ensureLibs(Context context) {AssetManager assetManager = context.getAssets();InputStream in = null;OutputStream out = null;try {File outdex = context.getDir("outdex", Context.MODE_PRIVATE);outdex.mkdir();File dex = context.getDir("outdex", Context.MODE_PRIVATE);dex.mkdir();in = assetManager.open("classes.zip");File f = new File(dex, "classes.zip");if (f.exists() && f.length() == in.available()) {Log.i(TAG, "classes.zip no change");return;}Log.i(TAG, "classes.zip chaneged");out = new FileOutputStream(f);byte[] buffer = new byte[102400];int read;while ((read = in.read(buffer)) != -1) {out.write(buffer, 0, read);}in.close();in = null;out.flush();out.close();out = null;Log.i(TAG, "classes.zip copy over");} catch (Exception e) {e.printStackTrace();}}private static void installSecondaryDexes(ClassLoader loader, File dexDir,List
     
       files) throws IllegalArgumentException,IllegalAccessException, NoSuchFieldException,InvocationTargetException, NoSuchMethodException, IOException {if (!files.isEmpty()) {if (Build.VERSION.SDK_INT >= 19) {V19.install(loader, files, dexDir);} else if (Build.VERSION.SDK_INT >= 14) {V14.install(loader, files, dexDir);} else {V4.install(loader, files);}}}/** * Locates a given field anywhere in the class inheritance hierarchy. * * @param instance *            an object to search the field into. * @param name *            field name * @return a field object * @throws NoSuchFieldException *             if the field cannot be located */private static Field findField(Object instance, String name)throws NoSuchFieldException {for (Class
       clazz = instance.getClass(); clazz != null; clazz = clazz.getSuperclass()) {try {Field field = clazz.getDeclaredField(name);if (!field.isAccessible()) {field.setAccessible(true);}return field;} catch (NoSuchFieldException e) {// ignore and search next}}throw new NoSuchFieldException("Field " + name + " not found in "+ instance.getClass());}/** * Locates a given method anywhere in the class inheritance hierarchy. * * @param instance *            an object to search the method into. * @param name *            method name * @param parameterTypes *            method parameter types * @return a method object * @throws NoSuchMethodException *             if the method cannot be located */private static Method findMethod(Object instance, String name,Class
      ... parameterTypes) throws NoSuchMethodException {for (Class
       clazz = instance.getClass(); clazz != null; clazz = clazz.getSuperclass()) {try {Method method = clazz.getDeclaredMethod(name, parameterTypes);if (!method.isAccessible()) {method.setAccessible(true);}return method;} catch (NoSuchMethodException e) {// ignore and search next}}throw new NoSuchMethodException("Method " + name + " with parameters "+ Arrays.asList(parameterTypes) + " not found in "+ instance.getClass());}/** * Replace the value of a field containing a non null array, by a new array * containing the elements of the original array plus the elements of * extraElements. *  * @param instance *            the instance whose field is to be modified. * @param fieldName *            the field to modify. * @param extraElements *            elements to append at the end of the array. */private static void expandFieldArray(Object instance, String fieldName,Object[] extraElements) throws NoSuchFieldException,IllegalArgumentException, IllegalAccessException {Field jlrField = findField(instance, fieldName);Object[] original = (Object[]) jlrField.get(instance);Object[] combined = (Object[]) Array.newInstance(original.getClass().getComponentType(), original.length + extraElements.length);System.arraycopy(original, 0, combined, 0, original.length);System.arraycopy(extraElements, 0, combined, original.length,extraElements.length);Log.i(TAG, "install 4");jlrField.set(instance, combined);Log.i(TAG, "install 5");}/** * Installer for platform versions 19. */private static final class V19 {private static void install(ClassLoader loader,List
      
        additionalClassPathEntries, File optimizedDirectory)throws IllegalArgumentException, IllegalAccessException,NoSuchFieldException, InvocationTargetException,NoSuchMethodException {/* * The patched class loader is expected to be a descendant of * dalvik.system.BaseDexClassLoader. We modify its * dalvik.system.DexPathList pathList field to append additional DEX * file entries. */Log.i(TAG, "install 1");Field pathListField = findField(loader, "pathList");Object dexPathList = pathListField.get(loader);Log.i(TAG, "install 2");ArrayList
       
         suppressedExceptions = new ArrayList
        
         ();expandFieldArray(dexPathList,"dexElements",makeDexElements(dexPathList, new ArrayList
         
          (additionalClassPathEntries), optimizedDirectory,suppressedExceptions));Log.i(TAG, "install 3");if (suppressedExceptions.size() > 0) {for (IOException e : suppressedExceptions) {Log.w(TAG, "Exception in makeDexElement", e);}Field suppressedExceptionsField = findField(loader,"dexElementsSuppressedExceptions");IOException[] dexElementsSuppressedExceptions = (IOException[]) suppressedExceptionsField.get(loader);if (dexElementsSuppressedExceptions == null) {dexElementsSuppressedExceptions = suppressedExceptions.toArray(new IOException[suppressedExceptions.size()]);} else {IOException[] combined = new IOException[suppressedExceptions.size() + dexElementsSuppressedExceptions.length];suppressedExceptions.toArray(combined);System.arraycopy(dexElementsSuppressedExceptions, 0,combined, suppressedExceptions.size(),dexElementsSuppressedExceptions.length);dexElementsSuppressedExceptions = combined;}suppressedExceptionsField.set(loader,dexElementsSuppressedExceptions);}}/** * A wrapper around * {@code private static final dalvik.system.DexPathList#makeDexElements} * . */private static Object[] makeDexElements(Object dexPathList,ArrayList
          
            files, File optimizedDirectory,ArrayList
           
             suppressedExceptions)throws IllegalAccessException, InvocationTargetException,NoSuchMethodException {Log.i(TAG, "install 9");Method makeDexElements = findMethod(dexPathList, "makeDexElements",ArrayList.class, File.class, ArrayList.class);return (Object[]) makeDexElements.invoke(dexPathList, files,optimizedDirectory, suppressedExceptions);}}/** * Installer for platform versions 14, 15, 16, 17 and 18. */private static final class V14 {private static void install(ClassLoader loader,List
            
              additionalClassPathEntries, File optimizedDirectory)throws IllegalArgumentException, IllegalAccessException,NoSuchFieldException, InvocationTargetException,NoSuchMethodException {/* * The patched class loader is expected to be a descendant of * dalvik.system.BaseDexClassLoader. We modify its * dalvik.system.DexPathList pathList field to append additional DEX * file entries. */Field pathListField = findField(loader, "pathList");Object dexPathList = pathListField.get(loader);expandFieldArray(dexPathList,"dexElements",makeDexElements(dexPathList, new ArrayList
             
              (additionalClassPathEntries), optimizedDirectory));}/** * A wrapper around * {@code private static final dalvik.system.DexPathList#makeDexElements} * . */private static Object[] makeDexElements(Object dexPathList,ArrayList
              
                files, File optimizedDirectory)throws IllegalAccessException, InvocationTargetException,NoSuchMethodException {Method makeDexElements = findMethod(dexPathList, "makeDexElements",ArrayList.class, File.class);return (Object[]) makeDexElements.invoke(dexPathList, files,optimizedDirectory);}}/** * Installer for platform versions 4 to 13. */private static final class V4 {private static void install(ClassLoader loader,List
               
                 additionalClassPathEntries)throws IllegalArgumentException, IllegalAccessException,NoSuchFieldException, IOException {/* * The patched class loader is expected to be a descendant of * dalvik.system.DexClassLoader. We modify its fields mPaths, * mFiles, mZips and mDexs to append additional DEX file entries. */int extraSize = additionalClassPathEntries.size();Field pathField = findField(loader, "path");StringBuilder path = new StringBuilder((String) pathField.get(loader));String[] extraPaths = new String[extraSize];File[] extraFiles = new File[extraSize];ZipFile[] extraZips = new ZipFile[extraSize];DexFile[] extraDexs = new DexFile[extraSize];for (ListIterator
                
                  iterator = additionalClassPathEntries.listIterator(); iterator.hasNext();) {File additionalEntry = iterator.next();String entryPath = additionalEntry.getAbsolutePath();path.append(':').append(entryPath);int index = iterator.previousIndex();extraPaths[index] = entryPath;extraFiles[index] = additionalEntry;extraZips[index] = new ZipFile(additionalEntry);extraDexs[index] = DexFile.loadDex(entryPath, entryPath+ ".dex", 0);}pathField.set(loader, path.toString());expandFieldArray(loader, "mPaths", extraPaths);expandFieldArray(loader, "mFiles", extraFiles);expandFieldArray(loader, "mZips", extraZips);expandFieldArray(loader, "mDexs", extraDexs);}}}
                
               
              
             
            
           
          
         
        
       
      
     
    
   
  
 

In the place where the program is initialized, such as Application or started Activity, use AssetsDex. install (context) to load the class library, which must be loaded before the class library is used. If the library is too large, loading for the first time may be slow. The advantage of this method is: 1. Break through the 64 K limit. 2. The running speed in Eclipse is fast (the lib package needs to be reduced each time)