CODEWITHSUNDEEP
javagwtservletsrequestresponse
Saurabh Saxena
Saurabh Saxena

Reputation: 3205

how to run actual java in the backend of gwt web application

For a specific requirement in my project, I want to retrieve JSON response from a web service api.

I am tried a java code in a simple Java project which is running fine.

String message = null;
HttpClient httpclient = new DefaultHttpClient(); 
JSONParser parser = new JSONParser();

String url = "working - url";
HttpResponse response = null;
response = httpclient.execute(new HttpGet(url));

JSONObject json_data = null;
json_data = (JSONObject)parser.parse(EntityUtils.toString(response.getEntity()));
JSONArray results = (JSONArray)json_data.get("result");
for (Object queid : results) {
    message = message.concat((String) ((JSONObject)queid).get("id"));
    message = message.concat("\t");
    message = message.concat((String) ((JSONObject)queid).get("owner"));
    message = message.concat("\n");
}

If I try to run this code in a GWT application servlet, I am getting several errors om compilation.

[ERROR] Line 16: No source code is available for type org.apache.http.client.ClientProtocolException; did you forget to inherit a required module?
[ERROR] Line 16: No source code is available for type org.apache.http.ParseException; did you forget to inherit a required module?
[ERROR] Line 16: No source code is available for type org.json.simple.parser.ParseException; did you forget to inherit a required module?

I have added the required jars using the project build path ->add external jars. But still I am facing the same problem. I have tried attaching the source to the jars but still the problem is same.

What possibly could be done in this case? Can I run actual java in the backend of my GWT application

Edit #1:

This code is written in my GWT servlet. I have tried using adding throws clause to the method in my servlet and applying try/catch block as well. But I am still getting these errors.

Edit #2:

I have got following errors in my console log after applying try/catch block.

Mar 10, 2012 1:16:28 PM com.google.appengine.tools.development.ApiProxyLocalImpl log
SEVERE: javax.servlet.ServletContext log: Exception while dispatching incoming RPC call
com.google.gwt.user.server.rpc.UnexpectedException: Service method 'public abstract java.lang.String com.google.detracker.client.DeService.getJSONRespnse()' threw an unexpected exception: java.lang.NoClassDefFoundError: javax.net.ssl.KeyManagerFactory is a restricted class. Please see the Google  App Engine developer's guide for more details.
    at com.google.gwt.user.server.rpc.RPC.encodeResponseForFailure(RPC.java:385)
    at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:588)
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:208)
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:248)
    at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:62)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    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$CachedChain.doFilter(ServletHandler.java:1166)
    at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:35)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:58)
    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 com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:122)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.tools.development.BackendServersFilter.doFilter(BackendServersFilter.java:97)
    at org.mortbay.jetty.servlet.ServletHandler$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.utils.jetty.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:70)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:351)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:938)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:755)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)
Caused by: java.lang.NoClassDefFoundError: javax.net.ssl.KeyManagerFactory is a restricted class. Please see the Google  App Engine developer's guide for more details.
    at com.google.appengine.tools.development.agent.runtime.Runtime.reject(Runtime.java:51)
    at org.apache.http.conn.ssl.SSLSocketFactory.createSSLContext(SSLSocketFactory.java:184)
    at org.apache.http.conn.ssl.SSLSocketFactory.createDefaultSSLContext(SSLSocketFactory.java:209)
    at org.apache.http.conn.ssl.SSLSocketFactory.<init>(SSLSocketFactory.java:333)
    at org.apache.http.conn.ssl.SSLSocketFactory.getSocketFactory(SSLSocketFactory.java:165)
    at org.apache.http.impl.conn.SchemeRegistryFactory.createDefault(SchemeRegistryFactory.java:45)
    at org.apache.http.impl.client.AbstractHttpClient.createClientConnectionManager(AbstractHttpClient.java:294)
    at org.apache.http.impl.client.AbstractHttpClient.getConnectionManager(AbstractHttpClient.java:445)
    at org.apache.http.impl.client.AbstractHttpClient.createHttpContext(AbstractHttpClient.java:274)
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:797)
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:754)
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:732)
    at com.google.detracker.server.DeServiceImpl.getJSONRespnse(DeServiceImpl.java:32)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.google.appengine.tools.development.agent.runtime.Runtime.invoke(Runtime.java:100)
    at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:569)
    ... 34 more

Mar 10, 2012 1:16:28 PM com.google.appengine.tools.development.LocalResourceFileServlet doGet

Upvotes: 1

Views: 1463

Answers (4)

Adel Boutros
Adel Boutros

Reputation: 10285

If you pay attention, The error is about an Exception class. This means your code is returning an exception which you are not handling. type org.apache.http.client.ClientProtocolException

Try surronding your code with try catch block and see what you get in the dev console.

Try {
    String message = null;
    HttpClient httpclient = new DefaultHttpClient(); 
    JSONParser parser = new JSONParser();

    String url = "working - url";
    HttpResponse response = null;
    response = httpclient.execute(new HttpGet(url));

    JSONObject json_data = null;
    json_data = (JSONObject)parser.parse(EntityUtils.toString(response.getEntity()));
    JSONArray results = (JSONArray)json_data.get("result");
    for (Object queid : results) {
        message = message.concat((String) ((JSONObject)queid).get("id"));
        message = message.concat("\t");
        message = message.concat((String) ((JSONObject)queid).get("owner"));
        message = message.concat("\n");
    }
} catch (Exception e) {
    e.printStack();
}

Explanation:

Some more explanation for all those who want it. In your code, you do not handle the exceptions with try catch blocks. Thus, when an exception is raised, the server will send it back to the client but most of the exceptions are NOT serializable, so they cannot be transported back to the client and this is why you get the mentioned error.

Upvotes: 1

Hilbrand Bouwkamp
Hilbrand Bouwkamp

Reputation: 13519

Yes you can, but the error message suggest you have somewhere in your client side code imported a class that uses those server side external jars.

Edit: Based the answer of Adel Boutros I guess you have added throws to your GWT service interfaces for the classes that generate these errors? You can only throw exceptions that are also available to the client, so catch them on the server and rethrow a new exception that is available in the client.

Upvotes: 0

dldnh
dldnh

Reputation: 8951

use RequestBuilder

http://code.google.com/webtoolkit/doc/latest/tutorial/JSON.html

Upvotes: 1

Eric C.
Eric C.

Reputation: 3368

If those librabries can actually be used in GWT, you have to add lines in your application.gwt.xml file to inherit the modules.

Example with library smartgwt:

<?xml version="1.0" encoding="UTF-8"?>

<!-- Inherit the core Web Toolkit stuff.                        -->
<inherits name='com.google.gwt.user.User'/>

<!-- Other module inherits                                      -->
<inherits name="com.smartgwt.SmartGwt"/>

<!-- Specify the app entry point class.                         -->
<entry-point class='blablabla'/>

<!-- Specify the paths for translatable code                    -->
<source path='client'/>
<source path='shared'/>

Upvotes: -1

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