Few days ago ,I was stuck in an exception that was following .

org.apache.catalina.LifecycleException:
Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/ProjectTest]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:154)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:726)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:702)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:697)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1134)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1780)
at java.util.concurrent.Executors$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.LinkageError: loader constraint violation:
loader (instance of org/apache/catalina/loader/WebappClassLoader)
 previously initiated loading for a different type with name “javax/servlet/ServletConfig”
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:760)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:455)
at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java:367)
at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:360)
at org.apache.catalina.loader.WebappClassLoader.findClass(WebappClassLoader.java:894)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1298)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1175)
at java.lang.Class.getDeclaredMethods0(Native Method)
at java.lang.Class.privateGetDeclaredMethods(Class.java:2688)
at java.lang.Class.getDeclaredMethods(Class.java:1962)
at org.apache.catalina.util.Introspection.getDeclaredMethods
(Introspection.java:127)
at org.apache.catalina.startup.WebAnnotationSet.loadMethodsAnnotation
(WebAnnotationSet.java:279)
at org.apache.catalina.startup.WebAnnotationSet.loadApplicationServletAnnotations
(WebAnnotationSet.java:141)
at org.apache.catalina.startup.WebAnnotationSet.loadApplicationAnnotations
(WebAnnotationSet.java:66)
at org.apache.catalina.startup.ContextConfig.applicationAnnotationsConfig
(ContextConfig.java:332)
at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:771)
at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:303)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent
(LifecycleSupport.java:117)
at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5058)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)

      After some goggling and R & D, I got solution .

• The jars in your WAR file contain either servlet-api.jar or javaee-api.jar.
  Do not include those, they are included in tomcat/lib and will conflict if found anywhere
  else in the class path.

It was helpful for me .