我已经在aws ec2 linux实例上安装了jdk 1.8和tomcat 8.5。我使用url和uploded war访问tomcat，但它显示500内部服务器错误。我尝试了一切，但是每当我检查tomcat的日志时，都会出现以下问题：
org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/examples]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:167)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:754)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:730)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1141)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1875)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NullPointerException
at org.apache.tomcat.util.scan.StandardJarScanner.process(StandardJarScanner.java:373)
at org.apache.tomcat.util.scan.StandardJarScanner.scan(StandardJarScanner.java:191)
at org.apache.catalina.startup.ContextConfig.processJarsForWebFragments(ContextConfig.java:1888)
at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1116)
at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:765)
at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:299)
at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:94)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5113)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
... 10 more
03-Aug-2018 08:51:34.991 SEVERE [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Error deploying web application directory [/var/lib/tomca$
java.lang.IllegalStateException: ContainerBase.addChild: start: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHos$
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:758)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:730)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1141)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1875)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/examples]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:167)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:754)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:730)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1141)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1875)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NullPointerException
at org.apache.tomcat.util.scan.StandardJarScanner.process(StandardJarScanner.java:373)
at org.apache.tomcat.util.scan.StandardJarScanner.scan(StandardJarScanner.java:191)
at org.apache.catalina.startup.ContextConfig.processJarsForWebFragments(ContextConfig.java:1888)
at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1116)
at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:765)
at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:299)
at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:94)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5113)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
... 10 more
03-Aug-2018 08:56:27.181 SEVERE [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Error deploying web application directory [/var/lib/tomca$
java.lang.IllegalStateException: ContainerBase.addChild: start: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHos$
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:758)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:730)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1141)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1875)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)