Question

I’m coding a servlet in GWT and I don’t really understand what’s happening with the data variable declared as global in the function. Maybe it’s a more general Java issue related with using variables into dynamic function declarations but I can’t find an answer to this.

This is my code:

private AbstractDataTable fetchDataFromServer() {

    final DataTable data = DataTable.create();
    System.out.println("1 Table has " + data.getNumberOfColumns() + " columns");
    System.out.println("1 Table has " + data.getNumberOfRows() + " rows");

    try {

        RequestBuilder rb = new RequestBuilder(RequestBuilder.GET, "/mongo.json");

        rb.setCallback(new RequestCallback() {
            @Override
            public void onResponseReceived(Request request, Response response) {
                JSONValue value = JSONParser.parse(response.getText());
                JSONObject productsObj = value.isObject();          
                JSONArray radiation = productsObj.get("ShortWave_Rad").isArray();

                if (radiation != null) {

                    data.addColumn(ColumnType.NUMBER, "Horizon");
                    data.addColumn(ColumnType.NUMBER, "Value");

                    System.out.println("Values " + radiation.size());

                    for (int i=0; i<=radiation.size()-1; i++) {

                        JSONObject productObj = radiation.get(i).isObject();
                        data.addRows(radiation.size());
                        data.setValue(i, 0, productObj.get("horizon").isNumber().doubleValue());
                        data.setValue(i, 1, productObj.get("value").isNumber().doubleValue());      
                    }

                    System.out.println("2 Table has " + data.getNumberOfColumns() + " columns");
                    System.out.println("2 Table has " + data.getNumberOfRows() + " rows");      

                }
            }
            @Override
            public void onError(Request request, Throwable exception) {
                Window.alert("Error occurred" + exception.getMessage());
            }
        });
        rb.send();

    } 
    catch (RequestException e) {
        Window.alert("Error occurred" + e.getMessage());
    }

    System.out.println("3 Table has " + data.getNumberOfColumns() + " columns");
    System.out.println("3 Table has " + data.getNumberOfRows() + " rows");

    return data;
}

And this is the output I get:

1 Table has 0 colums

1 Table has 0 rows

2 Table has 2 colums

2 Table has 10 rows

3 Table has 0 colums

3 Table has 0 rows

Where did the contents of data went after the onResponseReceived declaration used it?

Many thanks for your help.

Answer 1

Your onResponseReceived is invoked after a asynchronous call response. It is very much likely that statements below are executed before it receives the response.

System.out.println("3Table has colums " + data.getNumberOfColumns());
System.out.println("3Table has rows " + data.getNumberOfRows());

Use some status flag to to check the status of call back before printing the size in the end.