GWT-RPC method returns empty list on success - gwt

Question

I am creating a webpage having CellTable.I need to feed this table with data from hbase table.
I have written a method to retrieve data from hbase table and tested it.
But when I call that method as GWT asynchronous RPC method then rpc call succeeds but it returns nothing.In my case it returns empty list.The alert box show list's size as 0.
Following is the related code.
Please help.
greetingService.getDeviceIDData(new AsyncCallback<List<DeviceDriverBean>>(){
public void onFailure(Throwable caught) {
// Show the RPC error message to the user
System.out.println("RPC Call failed");
Window.alert("Data : RPC call failed");
}
public void onSuccess(List<DeviceDriverBean> result) {
//on success do something
Window.alert("Data : RPC call successful");
//deviceDataList.addAll(result);
Window.alert("Result size: " +result.size());
// Add a text column to show the driver name.
TextColumn<DeviceDriverBean> nameColumn = new TextColumn<DeviceDriverBean>() {
#Override
public String getValue(DeviceDriverBean object) {
Window.alert(object.getName());
return object.getName();
}
};
table.addColumn(nameColumn, "Name");
// Add a text column to show the device id
TextColumn<DeviceDriverBean> deviceidColumn = new TextColumn<DeviceDriverBean>() {
#Override
public String getValue(DeviceDriverBean object) {
return object.getDeviceId();
}
};
table.addColumn(deviceidColumn, "Device ID");
table.setRowCount(result.size(), true);
// more code here to add columns in celltable
// Push the data into the widget.
table.setRowData(0, result);
SimplePager pager = new SimplePager();
pager.setDisplay(table);
VerticalPanel vp = new VerticalPanel();
vp.add(table);
vp.add(pager);
// Add it to the root panel.
RootPanel.get("datagridContainer").add(vp);
}
});
Code to retrieve data from hbase (server side code)
public List<DeviceDriverBean> getDeviceIDData()
throws IllegalArgumentException {
List<DeviceDriverBean> deviceidList = new ArrayList<DeviceDriverBean>();
// Escape data from the client to avoid cross-site script
// vulnerabilities.
/*
* input = escapeHtml(input); userAgent = escapeHtml(userAgent);
*
* return "Hello, " + input + "!<br><br>I am running " + serverInfo +
* ".<br><br>It looks like you are using:<br>" + userAgent;
*/
try {
Configuration config = HbaseConnectionSingleton.getInstance()
.HbaseConnect();
HTable testTable = new HTable(config, "driver_details");
byte[] family = Bytes.toBytes("details");
Scan scan = new Scan();
int cnt = 0;
ResultScanner rs = testTable.getScanner(scan);
for (Result r = rs.next(); r != null; r = rs.next()) {
DeviceDriverBean deviceDriverBean = new DeviceDriverBean();
byte[] rowid = r.getRow(); // Category, Date, Sentiment
NavigableMap<byte[], byte[]> map = r.getFamilyMap(family);
Iterator<Entry<byte[], byte[]>> itrt = map.entrySet()
.iterator();
deviceDriverBean.setDeviceId(Bytes.toString(rowid));
while (itrt.hasNext()) {
Entry<byte[], byte[]> entry = itrt.next();
//cnt++;
//System.out.println("Count : " + cnt);
byte[] qual = entry.getKey();
byte[] val = entry.getValue();
if (Bytes.toString(qual).equalsIgnoreCase("account_number")) {
deviceDriverBean.setAccountNo(Bytes.toString(val));
} else if (Bytes.toString(qual).equalsIgnoreCase("make")) {
deviceDriverBean.setMake(Bytes.toString(val));
} else if (Bytes.toString(qual).equalsIgnoreCase("model")) {
deviceDriverBean.setModel(Bytes.toString(val));
} else if (Bytes.toString(qual).equalsIgnoreCase("driver_name")) {
deviceDriverBean.setName(Bytes.toString(val));
} else if (Bytes.toString(qual).equalsIgnoreCase("premium")) {
deviceDriverBean.setPremium(Bytes.toString(val));
} else if (Bytes.toString(qual).equalsIgnoreCase("year")) {
deviceDriverBean.setYear(Bytes.toString(val));
} else {
System.out.println("No match found");
}
/*
* System.out.println(Bytes.toString(rowid) + " " +
* Bytes.toString(qual) + " " + Bytes.toString(val));
*/
}
deviceidList.add(deviceDriverBean);
}
}
catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
catch (Exception e) {
// System.out.println("Message: "+e.getMessage());
e.printStackTrace();
}
return deviceidList;
}

Answer 1

Could this be lazy fetching on the server side by hbase. This means if you return the list hbase won't get a trigger to actually read the list and you will simple get an empty list. I don't know a correct solution, in the past I've seen a similar problem on GAE. This could by solved by simply asking the size of the list just before returning it to the client.

Answer 2

I don't have the exact answer, but I have an advise. In similar situation I put my own trace to check every step in my program.
On the server side before return put : System.out.println("size of table="+deviceidList.size());
You can put this trace in the loop for deviceidList;