动态加载.apk、.jar和.dex文件而且路径不受限制
4.1之后的版本中,不允许直接加载外部jar包
final File dexOutputPath =new File(Environment.getExternalStorageDirectory().toString()
+ File.separator + "dextest/Demojar-dex.jar");
File dir = this.getDir("out-dex", 0);
DexClassLoader cl = new DexClassLoader(dexOutputPath.getAbsolutePath(),
dir.getAbsolutePath(), null, getClassLoader());