javax.script support on Appengine

[Faisal Iqbal]

Dears,

I am having issue in running javax.script when deployed on Google Appengine. Please note local DEV environment is working just fine. I am pasting a hello world servlet below which has issue.

Thanks in advance.
Faisal Iqbal

********************************************************************************************************************************************************************************
import java.io.IOException;
import javax.servlet.http.*;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import javax.script.ScriptEngine;

@SuppressWarnings("serial")
public class MyScriptServlet extends HttpServlet {
    public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        resp.setContentType("text/plain");
         // create a script engine manager
        ScriptEngineManager factory = new ScriptEngineManager();
        // create a JavaScript engine
        ScriptEngine engine = factory.getEngineByName("JavaScript");
        // evaluate JavaScript code from String
        try {
            engine.put("rs", resp);
            engine.eval("rs.getWriter().println('This is from script')");
        } catch (ScriptException e) {
            resp.getWriter().println("Exception Catched");
            e.printStackTrace();
        }
        resp.getWriter().println("Hello, Faisal Iqbal");
    }
}
************************************************************************************************************************************************************

[Vinny P]

On Sun, Dec 1, 2013 at 10:43 AM, Faisal Iqbal <faisal...@gmail.com> wrote:

I am having issue in running javax.script when deployed on Google Appengine. Please note local DEV environment is working just fine. I am pasting a hello world servlet below which has issue.

Can you post the contents of the exception message and the full stack trace of the exception? They'll be written into logging, which you can access by going to the Logs page in the admin console.

-----------------

-Vinny P

Technology & Media Advisor

Chicago, IL

App Engine Code Samples: http://www.learntogoogleit.com

[Randy Balaban]

I am having a similar issue where I always get a 0 value returned when I try to use the ScriptEngine eval. By using Logger, I was able to determine that there are NullPointerExceptions being generated. After further inspection, it appears that GAE doesn't always return a valid script engine (if ever), because it throws an exception when you try to use it.

My code looks like:

public double myEval(String JsFormulaStr ) {
    double solutionValue = 0;
    ScriptEngineManager mgr = new ScriptEngineManager();
    ScriptEngine eng = mgr.getEngineByName("JavaScript");
    if(eng == null) {  // Added this block of code to prevent java.lang.NullPointerException...
        log.severe("Unable to get Script Engine." );
        return 0;
    }
    try {
        Object jsResults = eng.eval(JsFormulaStr);
        solutionValue = Double.parseDouble(jsResults.toString());
        return solutionValue;
    } catch(Exception e) {
        log.severe("[ERROR] in getCalculatedSolution_FromJS_ToDouble()::\n\t" +
                "Formula String is: " + JsFormulaStr + "\n\t" + e);
        return 0;
    }     
}

Everything works fine if I run it locally as a WebApp (Both in Eclipse & Netbeans. And within Tomcat & Glassfish 4.0).

Some of the strings which I tried to eval:

• 62.0 / 100
• 0.0 * 352.0
• (0 - 428) * 1000
• (0 - 597) * 1000
• 73.0 / 100

NOTE: The 0's or 0.0's are from other evaluations which have failed in previous calls. Since this function returns 0 on error.

According to Google's JRE Class Whitelist the ScriptEngineManager and ScriptEngine classes are allowed. So I don't understand why it isn't working as expected.

Any suggestions?

Thanks in advance,

Randy

[Randy Balaban]

I deployed the app to Amazon's Elastic Beanstalk server with no issues at all. :(

-Randy

[Faisal Iqbal]

Thanks Vinny for your response. I moved to groovy after that. Can you please review stack trace below.

1. java.lang.NullPointerException
   	at asbaat.MyScriptServlet.doGet(MyScriptServlet.java:18)
   	at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
   	at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
   	at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
   	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
   	at com.google.apphosting.utils.servlet.ParseBlobUploadFilter.doFilter(ParseBlobUploadFilter.java:125)
   	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
   	at com.google.apphosting.runtime.jetty.SaveSessionFilter.doFilter(SaveSessionFilter.java:35)
   	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
   	at com.google.apphosting.utils.servlet.JdbcMySqlConnectionCleanupFilter.doFilter(JdbcMySqlConnectionCleanupFilter.java:60)
   	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
   	at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
   	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
   	at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
   	at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
   	at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
   	at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
   	at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
   	at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.handle(AppVersionHandlerMap.java:254)
   	at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
   	at org.mortbay.jetty.Server.handle(Server.java:326)
   	at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
   	at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
   	at com.google.apphosting.runtime.jetty.RpcRequestParser.parseAvailable(RpcRequestParser.java:76)
   	at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
   	at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:146)
   	at com.google.apphosting.runtime.JavaRuntime$RequestRunnable.run(JavaRuntime.java:446)
   	at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:437)
   	at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:444)
   	at com.google.tracing.CurrentContext.runInContext(CurrentContext.java:188)
   	at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:308)
   	at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:300)
   	at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:441)
   	at com.google.apphosting.runtime.ThreadGroupPool$PoolEntry.run(ThreadGroupPool.java:251)
   	at java.lang.Thread.run(Thread.java:724)
   

2. C 2014-06-14 08:04:24.114

   Uncaught exception from servlet
   java.lang.NullPointerException
   	at asbaat.MyScriptServlet.doGet(MyScriptServlet.java:18)
   	at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
   	at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
   	at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
   	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
   	at com.google.apphosting.utils.servlet.ParseBlobUploadFilter.doFilter(ParseBlobUploadFilter.java:125)
   	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
   	at com.google.apphosting.runtime.jetty.SaveSessionFilter.doFilter(SaveSessionFilter.java:35)
   	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
   	at com.google.apphosting.utils.servlet.JdbcMySqlConnectionCleanupFilter.doFilter(JdbcMySqlConnectionCleanupFilter.java:60)
   	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
   	at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
   	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
   	at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
   	at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
   	at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
   	at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
   	at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
   	at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.handle(AppVersionHandlerMap.java:254)
   	at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
   	at org.mortbay.jetty.Server.handle(Server.java:326)
   	at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
   	at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
   	at com.google.apphosting.runtime.jetty.RpcRequestParser.parseAvailable(RpcRequestParser.java:76)
   	at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
   	at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:146)
   	at com.google.apphosting.runtime.JavaRuntime$RequestRunnable.run(JavaRuntime.java:446)
   	at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:437)
   	at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:444)
   	at com.google.tracing.CurrentContext.runInContext(CurrentContext.java:188)
   	at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:308)
   	at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:300)
   	at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:441)
   	at com.google.apphosting.runtime.ThreadGroupPool$PoolEntry.run(ThreadGroupPool.java:251)
   	at java.lang.Thread.run(Thread.java:724)
   

[Faisal Iqbal]

I believe google have not implemented any ScriptEngine. As ScriptEngine engine = factory.getEngineByName("

JavaScript") always return null...

[poke]

Yes , sure it return null .

You need to using rhino to use javascript in appengine .

[Vinny P]

On Sat, Jun 14, 2014 at 12:06 PM, Faisal Iqbal <faisal...@gmail.com> wrote:

I believe google have not implemented any ScriptEngine. As ScriptEngine engine = factory.getEngineByName("

JavaScript") always return null...

You have to package the Rhino JARs and use the APIs directly. See an example here:

http://stackoverflow.com/a/19828128

[Faisal Iqbal]

Hello Vinny, Thanks a lot for your response. I will check and will update
 the post

[Randy Balaban]

This post has a deleted post.  I believe it was mine.  Does anyone have a copy of what I typed?