Android热补丁动态修复实践，腾讯&字节&网易&华为Android面试题分享

apply plugin: ‘com.android.application’
task(‘processWithJavassist’) << {
String classPath = file(‘build/intermediates/classes/debug’)// 项目编译class所在目录
com.devilwwj.patch.PatchClass.process(classPath, project(‘:hackdex’).buildDir.absolutePath + “/intermediates/classes/debug”) // 第二个参数是hackdex的class所在目录
}
android {
compileSdkVersion 23
buildToolsVersion “23.0.1”
defaultConfig {
applicationId “com.devilwwj.hotfixdemo”
minSdkVersion 14
targetSdkVersion 23
versionCode 1
versionName “1.0”
}
buildTypes {
debug {
minifyEnabled false
proguardFiles getDefaultProguardFile(‘proguard-android.txt’), ‘proguard-rules.pro’
}
release {
minifyEnabled false
proguardFiles getDefaultProguardFile(‘proguard-android.txt’), ‘proguard-rules.pro’
}
}
applicationVariants.all { variant ->
variant.dex.dependsOn << processWithJavassist // 在执行dx命令之前将代码打入到class中
}
}
dependencies {
compile fileTree(dir: ‘libs’, include: [‘*.jar’])
testCompile ‘junit:junit:4.12’
compile ‘com.android.support:appcompat-v7:23.1.1’
compile ‘com.android.support:design:23.1.1’
compile project(‘:hotfixlib’)
}
这时候我们run项目，反编译build/output/apk下的app-debug.apk文件，你就可以看到代码已经成功植入了。
mac下的反编译工具：
https://sourceforge.net/projects/jadx/?source=typ_redirect
反编译的结果如下图：
其实你也可以直接在项目中看：
创建hotfixlib模块，并关联到项目中
这差不多是最后一步了，也是最核心的一步，提供将heck_dex.jar动态插入到dexElements的方法。
核心代码：
package com.devilwwj.hotfixlib;
import android.annotation.TargetApi;
import android.content.Context;
import java.io.File;
import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import dalvik.system.DexClassLoader;
import dalvik.system.PathClassLoader;
/**
• com.devilwwj.hotfixlib
• Created by devilwwj on 16/3/9.
*/
public final class HotFix {
public static void patch(Context context, String patchDexFile, String patchClassName) {
if (patchDexFile != null && new File(patchDexFile).exists()) {
try {
if (hasLexClassLoader()) {
injectAliyunOs(context, patchDexFile, patchClassName);
} else if (hasDexClassLoader()) {
injectAboveEqualApiLevel14(context, patchDexFile, patchClassName);
} else {
injectBelowApiLevel14(context, patchDexFile, patchClassName);
}
} catch (Throwable th) {
}
}
}
private static boolean hasLexClassLoader() {
try {
Class.forName(“dalvik.system.LexClassLoader”);
return true;
} catch (ClassNotFoundException e) {
e.printStackTrace();
return false;
}
}
private static boolean hasDexClassLoader() {
try {
Class.forName(“dalvik.system.BaseDexClassLoader”);
return true;
} catch (ClassNotFoundException e) {
e.printStackTrace();
return false;
}
}
private static void injectAliyunOs(Context context, String patchDexFile, String patchClassName) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException, NoSuchFieldException {
PathClassLoader obj = (PathClassLoader) context.getClassLoader();
String replaceAll = new File(patchDexFile).getName().replaceAll(“\.[a-zA-Z0-9]+”, “.lex”);
Class cls = Class.forName(“dalvik.system.LexClassLoader”);
Object newInstance = cls.getConstructor(new Class[]{String.class, String.class, String.class, ClassLoader.class}).newInstance(
new Object[]{context.getDir(“dex”, 0).getAbsolutePath()
• File.separator + replaceAll, context.getDir(“dex”, 0).getAbsolutePath(), patchDexFile, obj});
cls.getMethod(“loadClass”, new Class[]{String.class}).invoke(newInstance, new Object[]{patchClassName});
setField(obj, PathClassLoader.class, “mPaths”, appendArray(getField(obj, PathClassLoader.class, “mPaths”), getField(newInstance, cls, “mRawDexPath”)));
setField(obj, PathClassLoader.class, “mFiles”, combineArray(getField(obj, PathClassLoader.class, “mFiles”), getField(newInstance, cls, “mFiles”)));
setField(obj, PathClassLoader.class, “mZips”, combineArray(getField(obj, PathClassLoader.class, “mZips”), getField(newInstance, cls, “mZips”)));
setField(obj, PathClassLoader.class, “mLexs”, combineArray(getField(obj, PathClassLoader.class, “mLexs”), getField(newInstance, cls, “mDexs”)));
}
@TargetApi(14)
private static void injectBelowApiLevel14(Context context, String str, String str2) throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
PathClassLoader obj = (PathClassLoader) context.getClassLoader();
DexClassLoader dexClassLoader = new DexClassLoader(str, context.getDir(“dex”, 0).getAbsolutePath(), str, context.getClassLoader());
dexClassLoader.loadClass(str2);
setField(obj, PathClassLoader.class, “mPaths”,
appendArray(getField(obj, PathClassLoader.class, “mPaths”), getField(dexClassLoader, DexClassLoader.class, “mRawDexPath”)));
setField(obj, PathClassLoader.class, “mFiles”,
combineArray(getField(obj, PathClassLoader.class, “mFiles”), getField(dexClassLoader, DexClassLoader.class, “mFiles”)));
setField(obj, PathClassLoader.class, “mZips”,
combineArray(getField(obj, PathClassLoader.class, “mZips”), getField(dexClassLoader, DexClassLoader.class, “mZips”)));
setField(obj, PathClassLoader.class, “mDexs”,
combineArray(getField(obj, PathClassLoader.class, “mDexs”), getField(dexClassLoader, DexClassLoader.class, “mDexs”)));
obj.loadClass(str2);
}
/**
• 将dex注入dexElements数组中
• @param context
• @param str
• @param str2
• @throws ClassNotFoundException
• @throws NoSuchFieldException
• @throws IllegalAccessException
*/
private static void injectAboveEqualApiLevel14(Context context, String str, String str2) throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
PathClassLoader pathClassLoader = (PathClassLoader) context.getClassLoader();
Object a = combineArray(getDexElements(getPathList(pathClassLoader)), getDexElements(getPathList(new DexClassLoader(str, context.getDir(“dex”, 0).getAbsolutePath(), str, context.getClassLoader()))));
Object a2 = getPathList(pathClassLoader);
setField(a2, a2.getClass(), “dexElements”, a);
pathClassLoader.loadClass(str2);
}
/**
• 通过PathClassLoader拿到pathList
• @param obj
• @return
• @throws ClassNotFoundException
• @throws NoSuchFieldException
• @throws IllegalAccessException
*/
private static Object getPathList(Object obj) throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
return getField(obj, Class.forName(“dalvik.system.BaseDexClassLoader”), “pathList”);
}
/**
• 通过pathList取得dexElements对象
• @param obj
• @return
• @throws NoSuchFieldException
• @throws IllegalAccessException
*/
private static Object getDexElements(Object obj) throws NoSuchFieldException, IllegalAccessException {
return getField(obj, obj.getClass(), “dexElements”);
}
/**
• 通过反射拿到指定对象
• @param obj
• @param cls
• @param str
• @return
• @throws NoSuchFieldException
• @throws IllegalAccessException
*/
private static Object getField(Object obj, Class cls, String str) throws NoSuchFieldException, IllegalAccessException {
Field declaredField = cls.getDeclaredField(str);
declaredField.setAccessible(true);
return declaredField.get(obj);
}
/**
• 通过反射设置属性
• @param obj
• @param cls
• @param str
• @param obj2
• @throws NoSuchFieldException
• @throws IllegalAccessException
*/
private static void setField(Object obj, Class cls, String str, Object obj2) throws NoSuchFieldException, IllegalAccessException {
Field declaredField = cls.getDeclaredField(str);
declaredField.setAccessible(true);
declaredField.set(obj, obj2);
}
/**
• 合并数组
• @param obj
• @param obj2
• @return
*/
private static Object combineArray(Object obj, Object obj2) {
Class componentType = obj2.getClass().getComponentType();
int length = Array.getLength(obj2);
int length2 = Array.getLength(obj) + length;
Object newInstance = Array.newInstance(componentType, length2);
for (int i = 0; i < length2; i++) {
if (i < length) {
Array.set(newInstance, i, Array.get(obj2, i));
} else {
Array.set(newInstance, i, Array.get(obj, i - length));
}
}
return newInstance;
}
/**
• 添加到数组
• @param obj
• @param obj2