Question

I am coding in GWT 2.3 using Eclipse. While I have had coding experience, it has been limited to client-side. My current project involves creating a mapping program, which takes a list of points from an Excel sheet and places them on a predefined image. Now, I have my servlet and my client code connected, and I already have some idea how to read the Excel file.

My current problem: I get the following error when I load my application on Firefox using Development Mode:

Something other than an int was returned from JSNI method ‘@com.google.gwt.user.client.rpc.impl.ClientSerializationStreamReader::readInt()‘: JS value of type undefined, expected int

Development Mode’s console doesn’t give me any errors when I run, those it does tell me there is a [WARN] with two things I’m not using (images which I misnamed, but do not load ever).

Currently, my code is as follows:

In my Floor.java client side code:

 MyServiceAsync service = (MyServiceAsync) GWT.create(MyService.class);
    AsyncCallback<String> callback = new AsyncCallback<String>() {

        public void onFailure(Throwable caught) {
            printerModel.setText("FAILED");
            String details = caught.getMessage();
            printerModel.setText(details);
        }
        @Override
        public void onSuccess(String result) {
            //I purposefully have this as an empty method so I could figure out the error

        }
    };

    service.readFile("PrinterList.xls", callback);

In my MyService.java:

>public String readFile(String s);

In `MyServiceImpl.java`:

>public String readFile(String s) {

        // TODO Auto-generated method stub
        try {
           } catch (Exception e) {
        }
        return "foo";
    }

My AsyncCallback type is String, which seems to be causing the error. The method my client code calls returns a single String at this point, “fubar” (for simplicity). I thought that Strings were automatically serializable, but I am not sure. So, how do I get this error to go away? And how do I make the server code serialized?

Answer 1

What the exception says is basically this:

Client was trying to read an object from the data stream. Based on the signature of called method (or some other hint) the stream reader was expecting an int but found undefined instead.

As for the serializability of String, your assumption is correct. They are serializable without any effort on your part.

Without looking at the code and/or exception trace, it’s difficult to say anything more.

---

EDIT:

Your code seems fine to me. Is there a chance that you are mixing GWT versions? That is you compiled your GWT application with 2.3, but the server classpath contains an older GWT jar (or vice versa). Take a look at:

1. Project GWT version settings. Project-> Properties -> Google -> Web Toolkit. Which version of GWT is selected there?
2. Compare the GWT settings with Project -> Properties -> Java Build Path -> Libraries. How many GWT related jars do you see there? Which version? Are there more than one gwt-servlet-x.y.jar?