加载rocksdb实例报错：java.lang.UnsatisfiedLinkError: C:\Users\Administrator\AppData\Local\Temp\librocksdbjni3696928169151614297.dll

　　项目的缓存中用到了rocksdb，实例化时报错了：

Related cause:
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.beans.factory.config.MethodInvokingFactoryBean#1' defined in class path resource [spring-core.xml]: Cannot resolve reference to bean 'milletContext' while setting bean property 'arguments' with key [0]; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'milletContext' defined in class path resource [spring-core.xml]: Invocation of init method failed; nested exception is java.lang.UnsatisfiedLinkError: C:\Users\Administrator\AppData\Local\Temp\librocksdbjni3696928169151614297.dll: �
	at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:359)
	at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:108)
	at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveManagedList(BeanDefinitionValueResolver.java:382)
	at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:157)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1531)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1276)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:553)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483)
	at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getTypeForFactoryBean(AbstractBeanFactory.java:1508)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.getTypeForFactoryBean(AbstractAutowireCapableBeanFactory.java:816)
	at org.springframework.beans.factory.support.AbstractBeanFactory.isTypeMatch(AbstractBeanFactory.java:558)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doGetBeanNamesForType(DefaultListableBeanFactory.java:432)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanNamesForType(DefaultListableBeanFactory.java:403)
	at org.springframework.beans.factory.BeanFactoryUtils.beanNamesForTypeIncludingAncestors(BeanFactoryUtils.java:220)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1267)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1101)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1066)
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:585)
	at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:366)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1264)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:553)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483)
	at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:761)
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543)
	at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:443)
	at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:325)
	at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:107)
	at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4745)
	at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5207)
	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
	at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:752)
	at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:728)
	at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734)
	at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1144)
	at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1878)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'milletContext' defined in class path resource [spring-core.xml]: Invocation of init method failed; nested exception is java.lang.UnsatisfiedLinkError: C:\Users\Administrator\AppData\Local\Temp\librocksdbjni3696928169151614297.dll: �
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1628)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:555)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483)
	at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
	at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:351)
	... 48 more
Caused by: java.lang.UnsatisfiedLinkError: C:\Users\Administrator\AppData\Local\Temp\librocksdbjni3696928169151614297.dll: �
	at java.lang.ClassLoader$NativeLibrary.load(Native Method)
	at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1941)
	at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1824)
	at java.lang.Runtime.load0(Runtime.java:809)
	at java.lang.System.load(System.java:1086)
	at org.rocksdb.NativeLibraryLoader.loadLibraryFromJar(NativeLibraryLoader.java:78)
	at org.rocksdb.NativeLibraryLoader.loadLibrary(NativeLibraryLoader.java:56)
	at org.rocksdb.RocksDB.loadLibrary(RocksDB.java:64)
	at org.rocksdb.RocksDB.<clinit>(RocksDB.java:35)
	at org.rocksdb.Options.<clinit>(Options.java:25)
	at cn.migu.millet.common.CacheStorage.open(CacheStorage.java:31)
	at cn.migu.millet.MilletContext.init(MilletContext.java:169)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeCustomInitMethod(AbstractAutowireCapableBeanFactory.java:1758)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1695)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1624)
	... 55 more

　　问题现象：类加载失败引起的一系列后续问题：类找不到、实例加载失败、容器加载失败。

　　问题定位：代码跟踪

  public static CacheStorage open(String path) {
    try (final Options options = new Options()) {
      options.setCreateIfMissing(true);
      try {
        return new CacheStorage(RocksDB.open(options, path));
      } catch (RocksDBException e) {
        logger.error("open cache db error, path={}, e={}", path, e.getMessage());
        return null;
      }
    }
  }

public class Options extends RocksObject
    implements DBOptionsInterface<Options>, ColumnFamilyOptionsInterface<Options>,
    MutableColumnFamilyOptionsInterface<Options> {
  static {
    RocksDB.loadLibrary();
  }

　　进入到RocksDB类，实例化rocksDB，先读取是否已加载标志位，没加载过才会去加载:

/**
   * Loads the necessary library files.
   * Calling this method twice will have no effect.
   * By default the method extracts the shared library for loading at
   * java.io.tmpdir, however, you can override this temporary location by
   * setting the environment variable ROCKSDB_SHAREDLIB_DIR.
   */
  public static void loadLibrary() {
    if (libraryLoaded.get() == LibraryState.LOADED) {
      return;
    }

    if (libraryLoaded.compareAndSet(LibraryState.NOT_LOADED,
        LibraryState.LOADING)) {
      final String tmpDir = System.getenv("ROCKSDB_SHAREDLIB_DIR");
      // loading possibly necessary libraries.
      for (final CompressionType compressionType : CompressionType.values()) {
        try {
          if (compressionType.getLibraryName() != null) {
            System.loadLibrary(compressionType.getLibraryName());
          }
        } catch (UnsatisfiedLinkError e) {
          // since it may be optional, we ignore its loading failure here.
        }
      }
      try {
        NativeLibraryLoader.getInstance().loadLibrary(tmpDir);
      } catch (IOException e) {
        libraryLoaded.set(LibraryState.NOT_LOADED);
        throw new RuntimeException("Unable to load the RocksDB shared library"
            + e);
      }

      libraryLoaded.set(LibraryState.LOADED);
      return;
    }

    while (libraryLoaded.get() == LibraryState.LOADING) {
      try {
        Thread.sleep(10);
      } catch(final InterruptedException e) {
        //ignore
      }
    }
  }

　　注意一点，临时目录是从环境变量ROCKSDB_SHAREDLIB_DIR读取的，所以可以通过设置该环境变量改变临时目录路径（日志里的C:\Users\Administrator\AppData\Local\Temp\librocksdbjni3696928169151614297.dll）。接着进入到NativeLibraryLoader看RocksDB的实例化详情：

/**
   * Firstly attempts to load the library from <i>java.library.path</i>,
   * if that fails then it falls back to extracting
   * the library from the classpath
   * {@link org.rocksdb.NativeLibraryLoader#loadLibraryFromJar(java.lang.String)}
   *
   * @param tmpDir A temporary directory to use
   *   to copy the native library to when loading from the classpath.
   *   If null, or the empty string, we rely on Java's
   *   {@link java.io.File#createTempFile(String, String)}
   *   function to provide a temporary location.
   *   The temporary file will be registered for deletion
   *   on exit.
   *
   * @throws java.io.IOException if a filesystem operation fails.
   */
  public synchronized void loadLibrary(final String tmpDir) throws IOException {
    try {
        System.loadLibrary(sharedLibraryName);
    } catch(final UnsatisfiedLinkError ule1) {
      try {
        System.loadLibrary(jniLibraryName);
      } catch(final UnsatisfiedLinkError ule2) {
        loadLibraryFromJar(tmpDir);
      }
    }
  }

  /**
   * Attempts to extract the native RocksDB library
   * from the classpath and load it
   *
   * @param tmpDir A temporary directory to use
   *   to copy the native library to. If null,
   *   or the empty string, we rely on Java's
   *   {@link java.io.File#createTempFile(String, String)}
   *   function to provide a temporary location.
   *   The temporary file will be registered for deletion
   *   on exit.
   *
   * @throws java.io.IOException if a filesystem operation fails.
   */
  void loadLibraryFromJar(final String tmpDir)
      throws IOException {
    if (!initialized) {
      System.load(loadLibraryFromJarToTemp(tmpDir).getAbsolutePath());
      initialized = true;
    }
  }

  File loadLibraryFromJarToTemp(final String tmpDir)
          throws IOException {
    final File temp;
    if (tmpDir == null || tmpDir.isEmpty()) {
      temp = File.createTempFile(tempFilePrefix, tempFileSuffix);
    } else {
      temp = new File(tmpDir, jniLibraryFileName);
      if (temp.exists() && !temp.delete()) {
        throw new RuntimeException("File: " + temp.getAbsolutePath()
            + " already exists and cannot be removed.");
      }
      if (!temp.createNewFile()) {
        throw new RuntimeException("File: " + temp.getAbsolutePath()
            + " could not be created.");
      }
    }

    if (!temp.exists()) {
      throw new RuntimeException("File " + temp.getAbsolutePath() + " does not exist.");
    } else {
      temp.deleteOnExit();
    }

    // attempt to copy the library from the Jar file to the temp destination
    try (final InputStream is = getClass().getClassLoader().
      getResourceAsStream(jniLibraryFileName)) {
      if (is == null) {
        throw new RuntimeException(jniLibraryFileName + " was not found inside JAR.");
      } else {
        Files.copy(is, temp.toPath(), StandardCopyOption.REPLACE_EXISTING);
      }
    }

    return temp;
  }

　　先从sharedLibraryName（rocksdbjni）实例化，再从jniLibraryName（rocksdbjni-win64）实例化，最后从临时目录实例化。第一步是从JDK环境变量（即java.library.path，本机是D:\Dev\Java\jdk1.8.0_102\jre\bin）加载rocksdbjni，失败再从类路径加载rocksdbjni-win64，最后从本地临时目录加载librocksdbjni-win64.dll。这三部曲是rocksDB实例化的精髓。而最后一步是最复杂的，需要创建一个临时文件，然后从rocksdbjni这个jar包中把librocksdbjni-win64.dll复制到本地C:\Users\Administrator\AppData\Local\Temp\librocksdbjni3696928169151614297.dll，最后用org.rocksdb.NativeLibraryLoader这个类加载器来加载librocksdbjni3696928169151614297.dll得到rocksdb的实例，然后把这个DLL文件加入到加载类库中，后续容器重复加载时无需再次复制DLL文件。

　　上面的三部曲都需要利用java.lang包的工具来进行类加载，用的到类有System、Runtime和ClassLoader：

    /**
     * Loads the native library specified by the filename argument.  The filename
     * argument must be an absolute path name.
     *
     * If the filename argument, when stripped of any platform-specific library
     * prefix, path, and file extension, indicates a library whose name is,
     * for example, L, and a native library called L is statically linked
     * with the VM, then the JNI_OnLoad_L function exported by the library
     * is invoked rather than attempting to load a dynamic library.
     * A filename matching the argument does not have to exist in the
     * file system.
     * See the JNI Specification for more details.
     *
     * Otherwise, the filename argument is mapped to a native library image in
     * an implementation-dependent manner.
     *
     * <p>
     * The call <code>System.load(name)</code> is effectively equivalent
     * to the call:
     * <blockquote><pre>
     * Runtime.getRuntime().load(name)
     * </pre></blockquote>
     *
     * @param      filename   the file to load.
     * @exception  SecurityException  if a security manager exists and its
     *             <code>checkLink</code> method doesn't allow
     *             loading of the specified dynamic library
     * @exception  UnsatisfiedLinkError  if either the filename is not an
     *             absolute path name, the native library is not statically
     *             linked with the VM, or the library cannot be mapped to
     *             a native library image by the host system.
     * @exception  NullPointerException if <code>filename</code> is
     *             <code>null</code>
     * @see        java.lang.Runtime#load(java.lang.String)
     * @see        java.lang.SecurityManager#checkLink(java.lang.String)
     */
    @CallerSensitive
    public static void load(String filename) {
        Runtime.getRuntime().load0(Reflection.getCallerClass(), filename);
    }

    /**
     * Loads the native library specified by the filename argument.  The filename
     * argument must be an absolute path name.
     * (for example
     * <code>Runtime.getRuntime().load("/home/avh/lib/libX11.so");</code>).
     *
     * If the filename argument, when stripped of any platform-specific library
     * prefix, path, and file extension, indicates a library whose name is,
     * for example, L, and a native library called L is statically linked
     * with the VM, then the JNI_OnLoad_L function exported by the library
     * is invoked rather than attempting to load a dynamic library.
     * A filename matching the argument does not have to exist in the file
     * system. See the JNI Specification for more details.
     *
     * Otherwise, the filename argument is mapped to a native library image in
     * an implementation-dependent manner.
     * <p>
     * First, if there is a security manager, its <code>checkLink</code>
     * method is called with the <code>filename</code> as its argument.
     * This may result in a security exception.
     * <p>
     * This is similar to the method {@link #loadLibrary(String)}, but it
     * accepts a general file name as an argument rather than just a library
     * name, allowing any file of native code to be loaded.
     * <p>
     * The method {@link System#load(String)} is the conventional and
     * convenient means of invoking this method.
     *
     * @param      filename   the file to load.
     * @exception  SecurityException  if a security manager exists and its
     *             <code>checkLink</code> method doesn't allow
     *             loading of the specified dynamic library
     * @exception  UnsatisfiedLinkError  if either the filename is not an
     *             absolute path name, the native library is not statically
     *             linked with the VM, or the library cannot be mapped to
     *             a native library image by the host system.
     * @exception  NullPointerException if <code>filename</code> is
     *             <code>null</code>
     * @see        java.lang.Runtime#getRuntime()
     * @see        java.lang.SecurityException
     * @see        java.lang.SecurityManager#checkLink(java.lang.String)
     */
    @CallerSensitive
    public void load(String filename) {
        load0(Reflection.getCallerClass(), filename);
    }

    synchronized void load0(Class<?> fromClass, String filename) {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkLink(filename);
        }
        if (!(new File(filename).isAbsolute())) {
            throw new UnsatisfiedLinkError(
                "Expecting an absolute path of the library: " + filename);
        }
        ClassLoader.loadLibrary(fromClass, filename, true);
    }

    // Invoked in the java.lang.Runtime class to implement load and loadLibrary.
    static void loadLibrary(Class<?> fromClass, String name,
                            boolean isAbsolute) {
        ClassLoader loader =
            (fromClass == null) ? null : fromClass.getClassLoader();
        if (sys_paths == null) {
            usr_paths = initializePath("java.library.path");
            sys_paths = initializePath("sun.boot.library.path");
        }
        if (isAbsolute) {
            if (loadLibrary0(fromClass, new File(name))) {
                return;
            }
            throw new UnsatisfiedLinkError("Can't load library: " + name);
        }
        if (loader != null) {
            String libfilename = loader.findLibrary(name);
            if (libfilename != null) {
                File libfile = new File(libfilename);
                if (!libfile.isAbsolute()) {
                    throw new UnsatisfiedLinkError(
    "ClassLoader.findLibrary failed to return an absolute path: " + libfilename);
                }
                if (loadLibrary0(fromClass, libfile)) {
                    return;
                }
                throw new UnsatisfiedLinkError("Can't load " + libfilename);
            }
        }
        for (int i = 0 ; i < sys_paths.length ; i++) {
            File libfile = new File(sys_paths[i], System.mapLibraryName(name));
            if (loadLibrary0(fromClass, libfile)) {
                return;
            }
            libfile = ClassLoaderHelper.mapAlternativeName(libfile);
            if (libfile != null && loadLibrary0(fromClass, libfile)) {
                return;
            }
        }
        if (loader != null) {
            for (int i = 0 ; i < usr_paths.length ; i++) {
                File libfile = new File(usr_paths[i],
                                        System.mapLibraryName(name));
                if (loadLibrary0(fromClass, libfile)) {
                    return;
                }
                libfile = ClassLoaderHelper.mapAlternativeName(libfile);
                if (libfile != null && loadLibrary0(fromClass, libfile)) {
                    return;
                }
            }
        }
        // Oops, it failed
        throw new UnsatisfiedLinkError("no " + name + " in java.library.path");
    }

    private static boolean loadLibrary0(Class<?> fromClass, final File file) {
        // Check to see if we're attempting to access a static library
        String name = findBuiltinLib(file.getName());
        boolean isBuiltin = (name != null);
        if (!isBuiltin) {
            boolean exists = AccessController.doPrivileged(
                new PrivilegedAction<Object>() {
                    public Object run() {
                        return file.exists() ? Boolean.TRUE : null;
                    }})
                != null;
            if (!exists) {
                return false;
            }
            try {
                name = file.getCanonicalPath();
            } catch (IOException e) {
                return false;
            }
        }
        ClassLoader loader =
            (fromClass == null) ? null : fromClass.getClassLoader();
        Vector<NativeLibrary> libs =
            loader != null ? loader.nativeLibraries : systemNativeLibraries;
        synchronized (libs) {
            int size = libs.size();
            for (int i = 0; i < size; i++) {
                NativeLibrary lib = libs.elementAt(i);
                if (name.equals(lib.name)) {
                    return true;
                }
            }

            synchronized (loadedLibraryNames) {
                if (loadedLibraryNames.contains(name)) {
                    throw new UnsatisfiedLinkError
                        ("Native Library " +
                         name +
                         " already loaded in another classloader");
                }
                /* If the library is being loaded (must be by the same thread,
                 * because Runtime.load and Runtime.loadLibrary are
                 * synchronous). The reason is can occur is that the JNI_OnLoad
                 * function can cause another loadLibrary invocation.
                 *
                 * Thus we can use a static stack to hold the list of libraries
                 * we are loading.
                 *
                 * If there is a pending load operation for the library, we
                 * immediately return success; otherwise, we raise
                 * UnsatisfiedLinkError.
                 */
                int n = nativeLibraryContext.size();
                for (int i = 0; i < n; i++) {
                    NativeLibrary lib = nativeLibraryContext.elementAt(i);
                    if (name.equals(lib.name)) {
                        if (loader == lib.fromClass.getClassLoader()) {
                            return true;
                        } else {
                            throw new UnsatisfiedLinkError
                                ("Native Library " +
                                 name +
                                 " is being loaded in another classloader");
                        }
                    }
                }
                NativeLibrary lib = new NativeLibrary(fromClass, name, isBuiltin);
                nativeLibraryContext.push(lib);
                try {
                    lib.load(name, isBuiltin);
                } finally {
                    nativeLibraryContext.pop();
                }
                if (lib.loaded) {
                    loadedLibraryNames.addElement(name);
                    libs.addElement(lib);
                    return true;
                }
                return false;
            }
        }
    }

　　这里拿三部曲最后一部举例说明下：参数fromClass就是调用System.load方法所在的类，这里是rocksDB的加载库类org.rocksdb.NativeLibraryLoader，另一个参数File就是C:\Users\Administrator\AppData\Local\Temp\librocksdbjni3696928169151614297.dll，从NativeLibraryLoader类加载librocksdbjni5581206381055061043.dll后，把这个DLL文件放入loadedLibraryNames这个Vector，后续重复加载直接从该Vector取，无需再从rocksdbjni的jar包中复制DLL文件。

　　跟踪到这里，问题代码已经浮出水面：

lib.load(name, isBuiltin);

　　这个load方法是ClassLoader类的内部类NativeLibrary的原生方法，动态链接库加载就是从这里进入DLL文件里具体加载方法的

native void load(String name, boolean isBuiltin);

　　从这个load出来就是UnsatisfiedLinkError。所以问题的焦点转移到了DLL文件本身，用Dependency Walker打开一看，有错误提示：

Error: Modules with different CPU types were found.

　　继续跟进，发现其中一个文件叫IEShims.dll显示是X86，而我本机是X64的。替换该文件，Dependency Walker不再报错，但跑代码发现依然报错。

　　问题解决：捕获rockdbs异常，记录日志，跳过，继续启动加载spring容器。该DLL的加载涉及太多因素，无法一一排查，只能吃掉异常来规避，rocksdb加载失败对主业务无太大影响。