Android对第三方类库运行时加载
首先，把需要运行时加载的类库，放到项目的其他目录，如新建一个thirdlibs的目录。然后用dx命令，对下面的类库进行压缩，做成dex文件。
dx --dex --output=../assets/ *.jar这会在assets下面生成一个classes.dex文件，压缩成classes.zip文件。
新建一个类，用来加载类库
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() {
@Override
public 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);
}
}
}
在程序初始化的地方，如Application或者启动的Activity上，用AssetsDex.install(context)，加载类库，一定要在用到类库之前就加载完毕。如果类库过大，第一次加载可能会比较慢。用这种方法的好处是：1、突破64K限制 2、Eclipse下运行速度快（需要每次打包的lib减少了）