我一直致力于构建一个基于 SAML 2.0 的自定义单点登录 Apache Tomcat 阀门。在这个 Tomcat 阀门的初始化过程中，在某些服务器启动运行时（在每次服务器启动期间不经常发生），我在 Tomcat 日志中遇到了以下异常：
05-Feb-2016 00:35:08.643 SEVERE [localhost-startStop-1] org.apache.catalina.session.StandardManager.startInternal Exception loading sessions from persistent storage
javax.xml.parsers.FactoryConfigurationError: Provider for class javax.xml.parsers.DocumentBuilderFactory cannot be created
at javax.xml.parsers.FactoryFinder.findServiceProvider(FactoryFinder.java:311)
at javax.xml.parsers.FactoryFinder.find(FactoryFinder.java:267)
at javax.xml.parsers.DocumentBuilderFactory.newInstance(DocumentBuilderFactory.java:120)
at org.opensaml.xml.parse.BasicParserPool.initializePool(BasicParserPool.java:505)
at org.opensaml.xml.parse.BasicParserPool.<init>(BasicParserPool.java:141)
at org.opensaml.xml.XMLConfigurator.<init>(XMLConfigurator.java:88)
at org.opensaml.xml.XMLConfigurator.<init>(XMLConfigurator.java:74)
at org.opensaml.DefaultBootstrap.initializeXMLTooling(DefaultBootstrap.java:220)
at org.opensaml.DefaultBootstrap.initializeXMLTooling(DefaultBootstrap.java:207)
at org.opensaml.DefaultBootstrap.bootstrap(DefaultBootstrap.java:100)
at org.wso2.appserver.webapp.security.sso.saml.SAMLSSOUtils.doBootstrap(SAMLSSOUtils.java:175)
at org.wso2.appserver.webapp.security.sso.saml.SAMLSSOUtils.<clinit>(SAMLSSOUtils.java:113)
at org.wso2.appserver.webapp.security.sso.bean.LoggedInSession$SAML2SSO.readObject(LoggedInSession.java:189)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1017)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1900)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1801)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2000)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1924)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1801)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:371)
at org.apache.catalina.session.StandardSession.doReadObject(StandardSession.java:1629)
at org.apache.catalina.session.StandardSession.readObjectData(StandardSession.java:1092)
at org.apache.catalina.session.StandardManager.doLoad(StandardManager.java:261)
at org.apache.catalina.session.StandardManager.load(StandardManager.java:180)
at org.apache.catalina.session.StandardManager.startInternal(StandardManager.java:460)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5198)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:725)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:701)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:717)
at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:945)
at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1798)
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: java.lang.RuntimeException: Provider for class javax.xml.parsers.DocumentBuilderFactory cannot be created
at javax.xml.parsers.FactoryFinder.findServiceProvider(FactoryFinder.java:308)
... 43 more
Caused by: java.util.ServiceConfigurationError: javax.xml.parsers.DocumentBuilderFactory: Provider org.apache.xerces.jaxp.DocumentBuilderFactoryImpl not found
at java.util.ServiceLoader.fail(ServiceLoader.java:239)
at java.util.ServiceLoader.access$300(ServiceLoader.java:185)
at java.util.ServiceLoader$LazyIterator.nextService(ServiceLoader.java:372)
at java.util.ServiceLoader$LazyIterator.next(ServiceLoader.java:404)
at java.util.ServiceLoader$1.next(ServiceLoader.java:480)
at javax.xml.parsers.FactoryFinder$1.run(FactoryFinder.java:294)
at java.security.AccessController.doPrivileged(Native Method)
at javax.xml.parsers.FactoryFinder.findServiceProvider(FactoryFinder.java:289)
... 43 more
05-Feb-2016 00:35:08.650 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployWAR Deployment of web application archive /home/chiranga/WSO2-Internship-Projects/wso2-products/product-as/distribution/target/application-server-6.0.0/webapps/bar-app.war has finished in 1,119 ms
05-Feb-2016 00:35:08.651 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployWAR Deploying web application archive /home/chiranga/WSO2-Internship-Projects/wso2-products/product-as/distribution/target/application-server-6.0.0/webapps/sample.war
05-Feb-2016 00:35:09.615 INFO [localhost-startStop-1] org.apache.jasper.servlet.TldScanner.scanJars At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.
05-Feb-2016 00:35:09.625 SEVERE [localhost-startStop-1] org.apache.catalina.session.StandardManager.startInternal Exception loading sessions from persistent storage
java.lang.NoClassDefFoundError: Could not initialize class org.wso2.appserver.webapp.security.sso.saml.SAMLSSOUtils
at org.wso2.appserver.webapp.security.sso.bean.LoggedInSession$SAML2SSO.readObject(LoggedInSession.java:189)
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:497)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1017)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1900)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1801)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2000)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1924)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1801)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:371)
at org.apache.catalina.session.StandardSession.doReadObject(StandardSession.java:1629)
at org.apache.catalina.session.StandardSession.readObjectData(StandardSession.java:1092)
at org.apache.catalina.session.StandardManager.doLoad(StandardManager.java:261)
at org.apache.catalina.session.StandardManager.load(StandardManager.java:180)
at org.apache.catalina.session.StandardManager.startInternal(StandardManager.java:460)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5198)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:725)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:701)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:717)
at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:945)
at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1798)
at java.util.concurrent.Executors$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)
我浏览了几个建议使用以下依赖项的论坛：
<dependency>
<groupId>xerces</groupId>
<artifactId>xercesImpl</artifactId>
</dependency>
正如建议的那样，这确实解决了以前经常发生的问题，但是我看到在服务器启动期间有时会抛出上述异常。
而且我在 Tomcat lib 文件夹中也有上面提到的 DocumentBuilderFactory.class。
我是否遗漏了我应该在我的代码中包含的东西，或者这是一个与性能相关的问题？非常感谢任何帮助。