我想从http post获取数据，所以在servlet中我实现了如下dopost

package PostHandler;

import java.io.IOException;
import java.util.Enumeration;
import java.util.Properties;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import kafka.producer.ProducerConfig;
import kafka.javaapi.producer.ProducerData;

@WebServlet(description = "This is to handle the posted data on HTTP", urlPatterns = { "/ClsPostHandler" })
public class ClsPostHandler extends HttpServlet 
{
protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException 
      {
            final kafka.javaapi.producer.Producer<Integer, String> producer;
            final Properties props = new Properties();
            props.put("serializer.class", "kafka.serializer.StringEncoder");
            props.put("zk.connect", "localhost:2181");
            producer = new kafka.javaapi.producer.Producer<Integer, String>(
                    new ProducerConfig(props));
            String messageStr = new String("Testing to publish on testing topic");
            producer.send(new ProducerData<Integer, String>("testing",
                    messageStr));
    }
}

它会引发如下运行时错误：

Jul 26, 2013 11:57:08 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [PostHandler.ClsPostHandler] in context with path [/JavaRest] threw exception [Servlet execution threw an exception] with root cause
java.lang.NoClassDefFoundError: kafka/javaapi/producer/Producer
    at PostHandler.ClsPostHandler.doPost(ClsPostHandler.java:105)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:462)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:562)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:395)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:250)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:188)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:166)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1146)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:679)

出了什么问题，有人能帮我理解吗？
提前谢谢你的时间。
更新：下面是我的 .classpath 文件内容

<?xml version="1.0" encoding="UTF-8"?>
<classpath>
    <classpathentry kind="src" path="src"/>
    <classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/java-6-openjdk-amd64">
        <attributes>
            <attribute name="owner.project.facets" value="java"/>
        </attributes>
    </classpathentry>
    <classpathentry kind="con" path="org.eclipse.jst.server.core.container/org.eclipse.jst.server.tomcat.runtimeTarget/Apache Tomcat v7.0">
        <attributes>
            <attribute name="owner.project.facets" value="jst.web"/>
        </attributes>
    </classpathentry>
    <classpathentry kind="con" path="org.eclipse.jst.j2ee.internal.web.container"/>
    <classpathentry kind="con" path="org.eclipse.jst.j2ee.internal.module.container"/>
    <classpathentry kind="lib" path="/usr/local/kafka/kafka-0.7.2-incubating-src/lib_managed/scala_2.8.0/compile/apache-rat-0.8.jar"/>
    <classpathentry kind="lib" path="/usr/local/kafka/kafka-0.7.2-incubating-src/lib_managed/scala_2.8.0/compile/apache-rat-core-0.8.jar"/>
    <classpathentry kind="lib" path="/usr/local/kafka/kafka-0.7.2-incubating-src/lib_managed/scala_2.8.0/compile/apache-rat-tasks-0.8.jar"/>
    <classpathentry kind="lib" path="/usr/local/kafka/kafka-0.7.2-incubating-src/lib_managed/scala_2.8.0/compile/commons-cli-1.2.jar"/>
    <classpathentry kind="lib" path="/usr/local/kafka/kafka-0.7.2-incubating-src/lib_managed/scala_2.8.0/compile/commons-collections-3.2.jar"/>
    <classpathentry kind="lib" path="/usr/local/kafka/kafka-0.7.2-incubating-src/lib_managed/scala_2.8.0/compile/commons-compress-1.0.jar"/>
    <classpathentry kind="lib" path="/usr/local/kafka/kafka-0.7.2-incubating-src/lib_managed/scala_2.8.0/compile/commons-io-1.4.jar"/>
    <classpathentry kind="lib" path="/usr/local/kafka/kafka-0.7.2-incubating-src/lib_managed/scala_2.8.0/compile/commons-lang-2.1.jar"/>
    <classpathentry kind="lib" path="/usr/local/kafka/kafka-0.7.2-incubating-src/core/lib_managed/scala_2.8.0/compile/zookeeper-3.3.4.jar"/>
    <classpathentry kind="lib" path="/usr/local/kafka/kafka-0.7.2-incubating-src/core/lib_managed/scala_2.8.0/compile/zkclient-0.1.jar"/>
    <classpathentry kind="lib" path="/usr/local/kafka/kafka-0.7.2-incubating-src/core/lib_managed/scala_2.8.0/compile/snappy-java-1.0.4.1.jar"/>
    <classpathentry kind="lib" path="/usr/local/kafka/kafka-0.7.2-incubating-src/core/lib_managed/scala_2.8.0/compile/log4j-1.2.15.jar"/>
    <classpathentry kind="lib" path="/usr/local/kafka/kafka-0.7.2-incubating-src/core/lib_managed/scala_2.8.0/compile/jopt-simple-3.2.jar"/>
    <classpathentry kind="lib" path="/usr/local/kafka/kafka-0.7.2-incubating-src/core/target/scala_2.8.0/kafka-0.7.2.jar"/>
    <classpathentry kind="lib" path="/usr/local/scala-2.9.1.final/lib/jline.jar"/>
    <classpathentry kind="lib" path="/usr/local/scala-2.9.1.final/lib/scala-library.jar"/>
    <classpathentry kind="output" path="build/classes"/>
</classpath>