在android中怎么用Java加载解析so

本篇文章为大家展示了在android中怎么用Java加载解析so，内容简明扼要并且容易理解，绝对能使你眼前一亮，通过这篇文章的详细介绍希望你能有所收获。

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。

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);        }    }

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。

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