The Google Web Toolkit GWT
offers native already has a relatively easy way usable- Data from servers in
- JSON format to pick . Here is a little comparison to be made with the possibilities offered by GXT and Ext GWT .
- is important in particular the question of how simple JSON data are connected to widgets, since we have relatively many types of data sets to be processed, but in a more or less identical masks. The question of how the data is then sent back to the server plays no role here first. Test Preparations: Static JSON files
be made to simplify the implementation of the JSON data in GWT using static files available. In my Google about the plugin have created the Eclipse project
/ was- folder that contains GWT version 1.6 are a complete Web application. For the static JSON files there just created a subdirectory, let's call him
- model / . example file:
contents of the file: 
[ {id: 123, name: degree 1, 
},
]
This file may Jetty Server that is started in Ecplise, are available on http://localhost:8080/modell/abschluss.json
(or under the configured port).
JSON with GWT
This works only a very brief sketch like this, the detailed description can be found in this
GWT 1.6 Page
:
Creating
JSON source (we have)
stub class , Which implements create JSNI methods to directly access the contents of the JSON structure. Instances of the stub class generated by a JSNI method that essentially
eval ()calls (note the safety instructions!)
-
- generating a representation, z. As a Grid .
-
Important: Do not
The URL to the JSON file
GWT.getModuleBaseURL ()
be preceded by as shown in the GWT tutorial. It extends an indication of this type:
-
private static final String JSON_URL = "/ model / abschluss.json";
implementation of an asynchronous
request builder
call, the JSON data collected and processed .
experience
The implementation of the stub class can mean annoying repetition of work, if appropriate on the server side already are (bean) classes. Here, however, can not achieve Reuse
Once you have the stub classes, the rest of the implementation relatively easy, apart from the usual 'hardship' of the representation with the relatively primitive GWT widgets
-
- com.google.gwt.core.client.EntryPoint import;
com.google import. gwt.core.client.JsArray;
import com.google.gwt.event.dom.client.ClickEvent; import com.google.gwt.event.dom.client.ClickHandler;
Source
package com.chb.gxt2m3.client;
import com.google.gwt.http.client.Request;
com.google import. gwt.http.client.RequestCallback;
import com.google.gwt.http.client.RequestException;
import com.google.gwt.http.client.Response;
import com.google.gwt.user.client.ui. Button;
com.google.gwt.user.client.ui.Grid import, import
com.google.gwt.user.client.ui.HTML;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.RootPanel;
public class GXTTest implements EntryPoint {public void
onModuleLoad () {
btLaden Button = new Button ("Load");
RootPanel.get ("buttons") add (btLaden).
btLaden.addClickHandler (new click handler () {public void onClick
(click event) {
refreshAbschluesse ();}
});
} private static final String
JSON_URL_ABS = "/ model / abschluesse.json";
private void refreshAbschluesse () {
RootPanel.get ("display") clear ();.
RootPanel.get (" display "). add (
new Label (" financial statements are loaded of "+ JSON_URL_ABS));
request builder builder builder = new request (RequestBuilder.GET,
JSON_URL_ABS);
try {
builder.sendRequest (null, new request callback () {public void onError
(Request request, Throwable exception) {
display error ("JSON call could not be executed");}
public void onResponseReceived (Request request, Response response
) {
if (200 == response.getStatusCode ()) {
ClearError ();
abschluesseZeigen (asArrayOfAbsData (response.getText ()));} else {
display error ("Failed to call JSON (
response.getStatusText + () + ")");}
}
});} catch
(request Exception e) {
display error ("access to JSON failed");}
} private void abschluesseZeigen (JsArray
abs) {
RootPanel.get ("display") . clear ();
if (abs == null
Name "));
for (int idx = 0; idx \u0026lt;abs.length (), idx + +) {a = data
statements abs.get (idx);
agrid.setWidget (idx + 1, 0, new Label ("" +
a.getId ()));
agrid.setWidget (idx + 1, 1, new Label (a.getKuerzel ()));
agrid.setWidget (idx + 1, 2, new Label ("" + a.getName
()));}}
} private void clear error () {
RootPanel.get ("errorMsg") clear ();.
}
private void display error (String error) {
clear error ();
if (error = null)
RootPanel.get ("errorMsg") add (new Label (error));.
}
private final native JsArray
asArrayOfAbsData (String json) / *- {return
eval (json);}
}-*/;
JSON with GXT
A strength GXT (whose version 2 is available today as Milestone 3) are certainly the great widgets and Databinding ways through which changes the underlying data model to sign in all parts of the application can be. Unfortunately in the demo page only
Grid example with an XML source
. Anything but a search shows that there is a
JsonReader
. One can transfer the sample also.
One problem is the structure of the JSON file. Apparently, nested styles are not possible, at least you can understand this thread in the ExtJS Forum
be so.
There are, however, a different example:
http://extjs.net/forum/showthread.php?t=71978
use in my GWT 1.6 application, both the client-server-side code as well as the same business model classes. These classes are, however, in another Eclipse project and are therefore not simply in my with the Google plugin Eclipse GWT project creator available. To ensure that everything runs smoothly following configurations are required: 
to enforce. But I think unfortunately no way. Therefore had to proceed as follows: 
org.xy.smod