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:UsersAdministratorAppDataLocalTemplibrocksdbjni3696928169151614297.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:UsersAdministratorAppDataLocalTemplibrocksdbjni3696928169151614297.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$1.getObject(AbstractBeanFactory.java:306)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:351)
... 48 more
Caused by: java.lang.UnsatisfiedLinkError: C:UsersAdministratorAppDataLocalTemplibrocksdbjni3696928169151614297.dll: �
at java.lang.ClassLoader$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:UsersAdministratorAppDataLocalTemplibrocksdbjni3696928169151614297.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:DevJavajdk1.8.0_102jrein）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:UsersAdministratorAppDataLocalTemplibrocksdbjni3696928169151614297.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:UsersAdministratorAppDataLocalTemplibrocksdbjni3696928169151614297.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。