after upgrading to latest version of eclipse **Helios 3.6**, **M2E 1.0** , **WTP 3.2.5**
and trying to run my maven project which uses **JSF 2.1.3** and **Spring 3** on **tomcat 7**, i am getting the following exception:

```
java.lang.ClassNotFoundException: javax.servlet.jsp.el.ImplicitObjectELResolver$ImplicitObjects$4
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1678)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1523)
    at org.apache.catalina.startup.ContextConfig.checkHandlesTypes(ContextConfig.java:2006)
    at org.apache.catalina.startup.ContextConfig.processAnnotationsStream(ContextConfig.java:1969)
    at org.apache.catalina.startup.ContextConfig.processAnnotationsJar(ContextConfig.java:1858)
    at org.apache.catalina.startup.ContextConfig.processAnnotationsUrl(ContextConfig.java:1826)
    at org.apache.catalina.startup.ContextConfig.processAnnotations(ContextConfig.java:1812)
    at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1306)
    at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:896)
    at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:322)
    at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
    at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5103)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:148)
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1033)
    at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:774)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:148)
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1033)
    at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:291)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:148)
    at org.apache.catalina.core.StandardService.startInternal(StandardService.java:443)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:148)
    at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:727)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:148)
    at org.apache.catalina.startup.Catalina.start(Catalina.java:621)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:322)
    at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:450)

java.lang.LinkageError: loader constraint violation: when resolving interface method "javax.servlet.jsp.JspApplicationContext.getExpressionFactory()Ljavax/el/ExpressionFactory;" the class loader (instance of org/apache/catalina/loader/WebappClassLoader) of the current class, com/sun/faces/config/ConfigureListener, and the class loader (instance of org/apache/catalina/loader/StandardClassLoader) for resolved class, javax/servlet/jsp/JspApplicationContext, have different Class objects for the type javax/el/ExpressionFactory used in the signature
    at com.sun.faces.config.ConfigureListener.registerELResolverAndListenerWithJsp(ConfigureListener.java:693)
    at com.sun.faces.config.ConfigureListener.contextInitialized(ConfigureListener.java:243)
    at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4723)
    at org.apache.catalina.core.StandardContext$1.call(StandardContext.java:5226)
    at org.apache.catalina.core.StandardContext$1.call(StandardContext.java:5221)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
    at java.util.concurrent.FutureTask.run(FutureTask.java:138)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:662)
Dec 17, 2011 4:56:04 PM org.apache.catalina.core.StandardContext listenerStart
SEVERE: Exception sending context initialized event to listener instance of class com.sun.faces.config.ConfigureListener
java.lang.RuntimeException: java.lang.LinkageError: loader constraint violation: when resolving interface method "javax.servlet.jsp.JspApplicationContext.getExpressionFactory()Ljavax/el/ExpressionFactory;" the class loader (instance of org/apache/catalina/loader/WebappClassLoader) of the current class, com/sun/faces/config/ConfigureListener, and the class loader (instance of org/apache/catalina/loader/StandardClassLoader) for resolved class, javax/servlet/jsp/JspApplicationContext, have different Class objects for the type javax/el/ExpressionFactory used in the signature
    at com.sun.faces.config.ConfigureListener.contextInitialized(ConfigureListener.java:292)
    at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4723)
    at org.apache.catalina.core.StandardContext$1.call(StandardContext.java:5226)
    at org.apache.catalina.core.StandardContext$1.call(StandardContext.java:5221)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
    at java.util.concurrent.FutureTask.run(FutureTask.java:138)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.LinkageError: loader constraint violation: when resolving interface method "javax.servlet.jsp.JspApplicationContext.getExpressionFactory()Ljavax/el/ExpressionFactory;" the class loader (instance of org/apache/catalina/loader/WebappClassLoader) of the current class, com/sun/faces/config/ConfigureListener, and the class loader (instance of org/apache/catalina/loader/StandardClassLoader) for resolved class, javax/servlet/jsp/JspApplicationContext, have different Class objects for the type javax/el/ExpressionFactory used in the signature
    at com.sun.faces.config.ConfigureListener.registerELResolverAndListenerWithJsp(ConfigureListener.java:693)
    at com.sun.faces.config.ConfigureListener.contextInitialized(ConfigureListener.java:243)
    ... 8 more

```

following is my configuration for maven:

```
<dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>3.0.1</version>
        <scope>provided</scope>
       </dependency>

        <dependency>
         <groupId>com.sun.faces</groupId>
         <artifactId>jsf-api</artifactId>
         <version>2.1.3</version>
        </dependency>

        <dependency>
         <groupId>com.sun.faces</groupId>
         <artifactId>jsf-impl</artifactId>
         <version>2.1.3</version>
        </dependency>

        <dependency>
          <groupId>jstl</groupId>
          <artifactId>jstl</artifactId>
          <version>1.2</version>
        </dependency>

```

am i missing a jar file, or using an incompatible version of a jar ?

please advise, thanks.

**UPDATE:** what i get so far is that i get the application to run fine by removing the following dependencies from pom file:

```
<dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>javax.servlet.jsp-api</artifactId>
            <version>2.2.1</version>
           <scope>provided</scope>
          </dependency>

          <dependency>
           <groupId>javax.el</groupId>
            <artifactId>javax.el-api</artifactId>
           <version>2.2.2</version>
           <scope>provided</scope>
          </dependency>

```

i think that they were conflicting with the jars provided by the container.

**WHAT I NEED TO KNOW:**

1- Do i have to add the dependencies: `javax.servlet.jsp-api` , `javax.el-api` to my pom file as provided or i don't need to add them at all ?

2- If i have to add those two dependencies, then how should i add them properly in a way that they will not conflict with tomcat jars, meaning what version, and should i mark the dependency as provided or not ?

and the important question if i have to add them, why i have to do that, what is the importance of adding them since they are provided by the container, what i understand so far, is that i need to add the `javax.servlet-api` dependency and mark it as provided since i am using **servlets** in some classes.
['https://Stackoverflow.com/questions/8545687', 'https://Stackoverflow.com', 'https://Stackoverflow.com/users/429377/']
You should add these dependencies only if you require them in your code meaning that they are required to compile your code. If you don't use JSP or EL classes in your code, you can remove the dependencies. So you can test if you need the dependencies by just removing them. If your code still compiles, you don't need them. :)

If you need them, you should definitely add them as `provided` dependencies because the classes are provided by Tomcat during runtime. Just make sure that the versions of the dependencies match the versions provided by Tomcat. Then you won't have any problems. Provided dependencies are just used to compile your code but they are not packaged into the resulting WAR file, which is OK, because Tomcat provides them.
I had a similar problem: I was able to run a project in one computer, but in another one, I was obtaining the ClassNotFoundException described in the question.

The only difference between the 2 environments was the version of the tomcat server: 7.0.26 in the working computer and 7.0.16 in the other one. I installed the same version in both computers (7.0.26) and it solved the issue.

I hope this answer could be useful to someone.