在android中如何用Java加载解析so 在android中如何用Java加载解析

理论基础 so的加载是一种解析式装载，这与dex有一定区别，dex是先加载进行优化验证生成odex，再去解析odex文件，而so更像边解析边装载，在加载过程中主要解析是load段。
下面主要是以java层的so加载进行从源码上进行解析加载流程。
java层的so加载流程分析 System.loadLibrary入口点
在java层我们知道加载so文件是通过System.loadLibrary函数其实现的，下面就以其作为入口点进行分析它的调用关系和实现。
System.loadLibrary在的函数定义系统source\libcore\luni\src\main\java\java\lang\system.java的文件中。
下面是其函数定义实现。

//参数就是要加载的so文件名称 public static void loadLibrary(String libName) {//通过调用Runtime下面的loadLibrary函数实现//函数有两个参数，参数1是加载的so文件名，参数2 类加载器。Runtime.getRuntime().loadLibrary(libName, VMStack.getCallingClassLoader()); }

Runtime的loadLibray解析
通过上面的System.java的loadLibrary函数我们需要继续分析Runtime.java文件中的loadLibray函数的定义实现。
Runtime的loadLibrary函数在android系统中的位置是
source\libcore\luni\src\main\java\java\lang\Runtime.java文件。
下面是Runtime的 loadLibrary函数的定义实现源码。

/** Searches for and loads the given shared library using the given ClassLoader.*/void loadLibrary(String libraryName, ClassLoader loader) {if (loader != null) {//通过加载器去查找要加载的so文件名String filename = loader.findLibrary(libraryName); //查找失败if (filename == null) {// It's not necessarily true that the ClassLoader used// System.mapLibraryName, but the default setup does, and it's// misleading to say we didn't find "libMyLibrary.so" when we// actually searched for "liblibMyLibrary.so.so".throw new UnsatisfiedLinkError(loader + " couldn't find \"" +System.mapLibraryName(libraryName) + "\""); }//加载so文件名String error = doLoad(filename, loader); if (error != null) {throw new UnsatisfiedLinkError(error); }return; }String filename = System.mapLibraryName(libraryName); List candidates = new ArrayList(); String lastError = null; //循环遍历文件路径for (String directory : mLibPaths) {//文件路径和文件名进行拼接String candidate = directory + filename; candidates.add(candidate); if (IoUtils.canOpenReadOnly(candidate)) {String error = doLoad(candidate, loader); if (error == null) {return; // We successfully loaded the library. Job done.}lastError = error; }}if (lastError != null) {throw new UnsatisfiedLinkError(lastError); }throw new UnsatisfiedLinkError("Library " + libraryName + " not found; tried " + candidates); }

Runtime的doLoad解析
通过上面的Runtime的loadLibrary函数，我们看到加载so的函数是走到doLoad函数，那么我们就需要继续分析Runtime下的doload函数的定义实现。
Rutime下的doload函数在系统中的
source\libcore\luni\src\main\java\java\lang\Runtime.java文件中。
【在android中如何用Java加载解析so】下面的代码是Runtime的doload函数的定义实现。

private String doLoad(String name, ClassLoader loader) {// Android apps are forked from the zygote, so they can't have a custom LD_LIBRARY_PATH,// which means that by default an app's shared library directory isn't on LD_LIBRARY_PATH.// The PathClassLoader set up by frameworks/base knows the appropriate path, so we can load// libraries with no dependencies just fine, but an app that has multiple libraries that// depend on each other needed to load them in most-dependent-first order.// We added API to Android's dynamic linker so we can update the library path used for// the currently-running process. We pull the desired path out of the ClassLoader here// and pass it to nativeLoad so that it can call the private dynamic linker API.// We didn't just change frameworks/base to update the LD_LIBRARY_PATH once at the// beginning because multiple apks can run in the same process and third party code can// use its own BaseDexClassLoader.// We didn't just add a dlopen_with_custom_LD_LIBRARY_PATH call because we wanted any// dlopen(3) calls made from a .so's JNI_OnLoad to work too.// So, find out what the native library search path is for the ClassLoader in question...String ldLibraryPath = null; if (loader != null && loader instanceof BaseDexClassLoader) {ldLibraryPath = ((BaseDexClassLoader) loader).getLdLibraryPath(); }// nativeLoad should be synchronized so there's only one LD_LIBRARY_PATH in use regardless// of how many ClassLoaders are in the system, but dalvik doesn't support synchronized// internal natives.synchronized (this) {return nativeLoad(name, loader, ldLibraryPath); }}

总结从以上的源码实现流程分析，我们可以看出Android在java层加载so的接口是System.loadLibrary()，通过层层递进关系从而实现java层的加载so。
下图是详细的java层加载so函数的调用关系。