smartGWT ListGrid JSON issue - json

Question

I have created a REST API at URL: http://localhost:8888/rest/contacts with this JSON output:
{
"contact": {
"address": [
{
"city":"Shanghai",
"street":"Long Hua Street"
},
{
"city":"Shanghai",
"street":"Dong Quan Street"
}
],
"id": "huangyim",
"name": "Huang Yi Ming"
}
}
I want to print only the id value in a smartGWT ListGrid.
public class ExampleEntry implements EntryPoint {
#Override
public void onModuleLoad() {
DataSource dataSource = new DataSource();
dataSource.setDataFormat(DSDataFormat.JSON);
dataSource.setDataURL("http://localhost:8888/rest/contacts");
dataSource.setRecordXPath("/contact");
DataSourceTextField field = new DataSourceTextField("id", "id");
dataSource.addField(field);
final ListGrid grid = new ListGrid();
grid.setDataSource(dataSource);
grid.setAutoFetchData(true);
grid.draw();
}
}
But it is throwing the following exception:
15:33:12.766 [ERROR] [jerseyexample] 15:33:12.747:XRP2:WARN:RPCManager:xmlHttpRequest.getAllResponseHeaders() returned null
com.smartgwt.client.core.JsObject$SGWT_WARN: 15:33:12.747:XRP2:WARN:RPCManager:xmlHttpRequest.getAllResponseHeaders() returned null
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:105)
at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessages(BrowserChannelServer.java:293)
at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:547)
at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:364)
at java.lang.Thread.run(Unknown Source)
I tried searching google to find a fix but that did not help. Please let me know if anyone knows a solution for this issue.

Answer 1

You just need to change the data url, instead of using an absolute path use a relative one.
change
dataSource.setDataURL("http://localhost:8888/rest/contacts");
to
dataSource.setDataURL("rest/contacts");
This is also neccesary when you'll have to deploy it to a remote server.
I recommend you use a RestDataSource instead of a plain DataSource, it has been designed specificaly for REST services, as you've said you use.
Using a RestDataSource is as simple as using DataSource.
#Override
public void onModuleLoad() {
RestDataSource dataSource = new RestDataSource();
dataSource.setDataFormat(DSDataFormat.JSON);
dataSource.setDataURL("rest/contacts");
dataSource.setRecordXPath("/contact");
DataSourceTextField field = new DataSourceTextField("id", "id");
dataSource.addField(field);
OperationBinding get=new OperationBinding();
get.setOperationType(DSOperationType.FETCH);
dataSource.setOperationBindings(get);
final ListGrid grid = new ListGrid();
grid.setDataSource(dataSource);
grid.setAutoFetchData(true);
grid.draw();
}
You can map each OperationBinding with each http method (GET, POST PUT, DELETE) or whatever suits your REST API.
Cheers!

Answer 2

You can put directly Xpath in the field you want to map
RecordXPath can be specified directly on the DataSource for a simple read-only DataSource only capable of "fetch" operations.
field.setRecordXPath("contact")