Stanford POS tagger doesn't work in servlet

Question

I am trying to use Stanford POS Tagger in Java servlet. I created Dynamic Web Page project in J2EE and included build path of jar files by following this tutorial. http://www.galalaly.me/index.php/2011/05/tagging-text-with-stanford-pos-tagger-in-java-applications/

If I create a separate java file, I am able to get POS Tagger working as shown below.

public static String tagger(String sample) throws IOException, ClassNotFoundException {

 // Initialize the tagger
 MaxentTagger tagger = new MaxentTagger("models/english-left3words-distsim.tagger");

 // The tagged string
 String tagged = tagger.tagString(sample);

 // Output the result
 return tagged;
 }

public static void main(String[] args){
    try {
        System.out.println(tagger("This is a sample."));
    } catch (ClassNotFoundException | IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

Which means POS tagger works in main method of simple Java class which I named Taggers.java. But when I try to instantiate the object of Tagger.java class in servlet, I can't get it working. The following code is a servlet in which I am trying to instantiate the object of Tagger.java.

/**
 * @see HttpServlet#service(HttpServletRequest request, HttpServletResponse response)
 */
protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException  {
    PrintWriter out = response.getWriter(); 
    try {
        out.println(Tagger.tagger("This is a sample sentence."));
    } catch (ClassNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

When I run the above servlet on tomcat-8, it shows following exceptions.

SEVERE: Servlet.service() for servlet [com.exp.pkg.ExpServlet] in context with path [/webProj1] threw exception [Servlet execution threw an exception] with root cause java.lang.ClassNotFoundException: edu.stanford.nlp.tagger.maxent.MaxentTagger at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1305) at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1157) at com.exp.pkg.Tagger.tagger(Tagger.java:17) at com.exp.pkg.ExpServlet.service(ExpServlet.java:34) at javax.servlet.http.HttpServlet.service(HttpServlet.java:725) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:516) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1086) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:659) at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:223) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1558) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1515) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Unknown Source)

After I set classpath=".;..;C:\Users\Faisal\workspace_EE\webProj1\tagger\english-left3words-distsim.ta‌gger;C:\stanford-postagger-2015-01-29\stanford-postagger-2015-01-30\stanford-post‌agger;C:\apache-tomcat-8\apache-tomcat-8.0.20\lib\servlet-api"

The stack trace is as follows:

SEVERE: Servlet.service() for servlet [com.exp.pkg.ExpServlet] in context with path [/webProj1] threw exception edu.stanford.nlp.io.RuntimeIOException: Unrecoverable error while loading a tagger model at edu.stanford.nlp.tagger.maxent.MaxentTagger.readModelAndInit(MaxentTagger.java:769) at edu.stanford.nlp.tagger.maxent.MaxentTagger.(MaxentTagger.java:297) at edu.stanford.nlp.tagger.maxent.MaxentTagger.(MaxentTagger.java:262) at com.exp.pkg.Tagger.tagger(Tagger.java:17) at com.exp.pkg.ExpServlet.service(ExpServlet.java:34) at javax.servlet.http.HttpServlet.service(HttpServlet.java:725) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:516) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1086) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:659) at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:223) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1558) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1515) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Unknown Source) Caused by: java.io.IOException: Unable to resolve "tagger/english-bidirectional-distsim.tagger" as either class path, filename or URL at edu.stanford.nlp.io.IOUtils.getInputStreamFromURLOrClasspathOrFileSystem(IOUtils.java:463) at edu.stanford.nlp.tagger.maxent.MaxentTagger.readModelAndInit(MaxentTagger.java:764) ... 27 more

It looks like the CoreNLP classes are not on your classpath. Is this the case? — Jon Gauthier
classpath is explained on stanford's website nlp.stanford.edu/software/pos-tagger-faq.shtml#api. Following the info on this link, I updated my classpath env. variable which looks like ".;..;C:\Users\Faisal\workspace_EE\webProj1\tagger\english-left3words-distsim.tagger;C:\stanford-postagger-2015-01-29\stanford-postagger-2015-01-30\stanford-postagger;C:\apache-tomcat-8\apache-tomcat-8.0.20\lib\servlet-api". This time error is little different such as "edu.stanford.nlp.io.RuntimeIOException: Unrecoverable error while loading a tagger model" — Faisal
I have just posted the entire stack trace after setting classpath. — Faisal

Jon Gauthier Jon Gauthier · Accepted Answer · 2015-03-16T16:49:28

You need to make sure your classpath is correct.

From your updated post, it looks like you don't have the right model path on your classpath. You shouldn't add the .tagger file directly to your classpath; add the directory which contains the tagger folder. If your file setup looks like this:

C:\mystuff
    tagger\
        english-left3words-distsim.tagger
        english-bidirectional-distsim.tagger

then you should put the directory C:\mystuff on your classpath.

Stanford POS tagger doesn't work in servlet

2 Answers