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       JNI_OnLoad是在加载so的时候调用的，也就是System.loadLibrary("test")时候调用的。具体调用步骤如下：

System.loadLibrary(libName)->Runtime.loadLibrary(libName,classLoader)->Runtime.doLoad(libName,loader)->Runtime.nativeLoad(name,loader,ldLibraryPath)->JavaVMExt.loadNativieLibrary:(JavaVMExt* vm=Runtime::Current()->GetJavaVM(); vm->LoadNativieLibrary(filename,classloader,detail))->jni_internal.cc::LoadNativieLibrary->dlopen,dlsym->JNI_OnLoad。

以上给出了调用顺序，具体代码可以根据类名或方法名看出。有兴趣的可以自己查看下源码。

在Runtime.loadLibrary中，会在多个多个路径下寻找对应的so，只要找到了就会去加载，加载成功就会返回。对应代码如下：

Runtime.java

/*     * Searches for and loads the given shared library using the given ClassLoader.     */    void loadLibrary(String libraryName, ClassLoader loader) {        if (loader != null) {            String filename = loader.findLibrary(libraryName);            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) + "\"");            }            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;        for (String directory : mLibPaths) {            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);    }
     
    

/**     * Holds the library paths, used for native library lookup.     */    private final String[] mLibPaths = initLibPaths();    private static String[] initLibPaths() {        String javaLibraryPath = System.getProperty("java.library.path");        if (javaLibraryPath == null) {            return EmptyArray.STRING;        }        String[] paths = javaLibraryPath.split(":");        // Add a '/' to the end of each directory so we don't have to do it every time.        for (int i = 0; i < paths.length; ++i) {            if (!paths[i].endsWith("/")) {                paths[i] += "/";            }        }        return paths;    }