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.
This class loader requires an application-private, writable directory to cache optimized classes. Use Context.getDir(String, int)
to create such a directory:
<span class="pln" style="color: rgb(0, 0, 0);"> </span><code style="line-height: 14px;"><span class="typ" style="color: rgb(102, 0, 102);">File</span><span class="pln" style="color: rgb(0, 0, 0);"> dexOutputDir </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln" style="color: rgb(0, 0, 0);"> context</span><span class="pun" style="color: rgb(102, 102, 0);">.</span><span class="pln" style="color: rgb(0, 0, 0);">getDir</span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="str" style="color: rgb(136, 0, 0);">"dex"</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="lit" style="color: rgb(0, 102, 102);">0</span><span class="pun" style="color: rgb(102, 102, 0);">);</span><span class="pln" style="color: rgb(0, 0, 0);"> </span></code>
Do not cache optimized classes on external storage. External storage does not provide access controls necessary to protect your application from code injection attacks.
Creates a DexClassLoader
that finds interpreted and native code. Interpreted classes are found in a set of DEX files contained in Jar or APK files.
创建一个DexClassLoader用来找出指定的类和本地代码(c/c++代码)。用来解释执行在DEX文件中的class文件。
路径的分隔符使用通过System的属性 path.separator
获得 :
.
String separeater = System.getProperty("path.separtor");
dexPath | 需要装载的APK或者Jar文件的路径。包含多个路径用File.pathSeparator间隔开 ,在Android上默认是 ":" |
---|---|
optimizedDirectory | 优化后的dex文件存放目录,不能为null |
libraryPath | 目标类中使用的C/C++库的列表,每个目录用File.pathSeparator间隔开 ; 可以为 null |
parent | 该类装载器的父装载器,一般用当前执行类的装载器 |
下面是代码部分,代码参考自《Android内核剖析》(作者柯元旦,这本书不错,推荐阅读):
@SuppressLint("NewApi") private void useDexClassLoader(){ //创建一个意图,用来找到指定的apk Intent intent = new Intent("com.suchangli.android.plugin", null); //获得包管理器 PackageManager pm = getPackageManager(); List<ResolveInfo> resolveinfoes = pm.queryIntentActivities(intent, 0); //获得指定的activity的信息 ActivityInfo actInfo = resolveinfoes.get(0).activityInfo; //获得包名 String pacageName = actInfo.packageName; //获得apk的目录或者jar的目录 String apkPath = actInfo.applicationInfo.sourceDir; //dex解压后的目录,注意,这个用宿主程序的目录,android中只允许程序读取写自己 //目录下的文件 String dexOutputDir = getApplicationInfo().dataDir; //native代码的目录 String libPath = actInfo.applicationInfo.nativeLibraryDir; //创建类加载器,把dex加载到虚拟机中 DexClassLoader calssLoader = new DexClassLoader(apkPath, dexOutputDir, libPath, this.getClass().getClassLoader()); //利用反射调用插件包内的类的方法 try { Class<?> clazz = calssLoader.loadClass(pacageName+".Plugin1"); Object obj = clazz.newInstance(); Class[] param = new Class[2]; param[0] = Integer.TYPE; param[1] = Integer.TYPE; Method method = clazz.getMethod("function1", param); Integer ret = (Integer)method.invoke(obj, 1,12); Log.i("Host", "return result is " + ret); } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (InstantiationException e) { e.printStackTrace(); } catch (IllegalAccessException e) { e.printStackTrace(); } catch (NoSuchMethodException e) { e.printStackTrace(); } catch (IllegalArgumentException e) { e.printStackTrace(); } catch (InvocationTargetException e) { e.printStackTrace(); } }
Plugin1.apk中的一个类:
package com.suchangli.plugin1; public class Plugin1 { public int function1(int a, int b){ return a+b; } }