com.google.gwt.sample.hello.client.HelloJsonp.java Source code

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Here is the source code for com.google.gwt.sample.hello.client.HelloJsonp.java

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/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package com.google.gwt.sample.hello.client;

import com.google.gwt.core.client.GWT;
import com.google.gwt.core.client.JavaScriptObject;
import com.google.gwt.json.client.JSONArray;
import com.google.gwt.json.client.JSONObject;
import com.google.gwt.json.client.JSONString;
import com.google.gwt.json.client.JSONValue;
import java.util.Set;

/*
 * JSON Services Example from http://www.gwtapps.com/?p=42
 * GWT Tutorial: How to Read Web Services Client-Side with JSONP
 * 
http://www.geonames.org/postalCodeLookupJSON?
postalcode=94566&country=US&callback=abcd    
    
abcd({"postalcodes":
        [{"adminName2":"Alameda","adminCode2":"001",
          "postalcode":"94566","adminCode1":"CA",
          "countryCode":"US","lng":-121.8755,
          "placeName":"Pleasanton","lat":37.665804,
          "adminName1":"California"}]}); 
              
 * The JSONP example below is modified from
http://www.gwtsite.com/how-to-access-web-services-with-gwt/ 
 * The same example is also in the book "Google Web Toolkit by Ryan Dewsbury 
 * and published by Prentice Hall 2008", on page 338.
 * 
 * Note abcd function name is used as the callback function, 
 * and abcd_script id tag  as the injected javascript element. 
 * 
 * The function decodeJson is from the JSON sample of gwt sdk.
 */

/**
 *
 * @author gwt user
 */
public class HelloJsonp implements HelloJsonRequestHandler {

    private StringBuilder str = new StringBuilder(); /* response decoding */
    private int indent = 0;

    private void prefix() {
        StringBuilder bdr = new StringBuilder();
        for (int i = 0; i < indent; i++)
            bdr.append(" ");
        str.append(bdr.toString());
    }

    private void decodeJson(JSONValue jv) {
        JSONArray jsonArray;
        JSONObject jsonObject;
        JSONString jsonString;

        if ((jsonArray = jv.isArray()) != null) {
            str.append(" [[ \n");
            indent += 4;
            prefix();
            for (int i = 0; i < jsonArray.size(); ++i) {
                str.append("[" + Integer.toString(i) + "]=(");
                decodeJson(jsonArray.get(i));
                str.append(")\n");
                prefix();
            }
            str.append("\n");
            indent -= 4;
            prefix();
            str.append(" ]] \n");
            prefix();
        } else if ((jsonObject = jv.isObject()) != null) {
            Set<String> keys = jsonObject.keySet();
            str.append(" {{ \n");
            indent += 4;
            prefix();
            for (String key : keys) {
                str.append("{" + key + "}=(");
                decodeJson(jsonObject.get(key));
                str.append(")\n");
                prefix();
            }
            str.append("\n");
            indent -= 4;
            prefix();
            str.append(" }} \n");
            prefix();
        } else if ((jsonString = jv.isString()) != null) {
            // Use stringValue instead of toString() because we don't want escaping
            str.append("\"" + jsonString.stringValue() + "\"\n");
            prefix();
        } else {
            // JSONBoolean, JSONNumber, and JSONNull work well with toString().
            str.append(jv.toString() + "\n");
            prefix();
        }
    }

    @Override
    public void onRequestComplete(JavaScriptObject json) {
        GWT.log(json.toString(), null);
        str.append("Return:\n");

        JSONObject jo = new JSONObject(json);
        decodeJson(jo);

        Hello.callback(str.toString());
        removeScript();
    }

    public static void get() {
        String url = "http://www.geonames.org/postalCodeLookupJSON?" + "postalcode=94566&country=US&callback=abcd";
        HelloJsonp.get(url, "abcd", new HelloJsonp());
    }

    public static void get(String url, HelloJsonRequestHandler handler) {
        String callbackName = "JSONCallback" + handler.hashCode();
        get(url + callbackName, callbackName, handler);
    }

    public static void get(String url, String callbackName, HelloJsonRequestHandler handler) {
        createCallbackFunction(handler, callbackName);
        addScript(url);
    }

    public static native void addScript(String url) /*-{
                                                    var scr = document.createElement("script");
                                                    scr.setAttribute("language", "JavaScript");
                                                    scr.setAttribute("src", url);
                                                    scr.setAttribute("id", "abcd_script");
                                                    document.getElementsByTagName("body")[0].appendChild(scr);
                                                    }-*/;

    public static native void removeScript() /*-{
                                             var scr = document.getElementById("abcd_script");
                                             document.getElementsByTagName("body")[0].removeChild(scr);
                                             delete src;
                                             }-*/;

    private native static void createCallbackFunction(HelloJsonRequestHandler obj, String callbackName)/*-{
                                                                                                       tmpcallback = function(j) {
                                                                                                       obj.@com.google.gwt.sample.hello.client.HelloJsonp::onRequestComplete(Lcom/google/gwt/core/client/JavaScriptObject;)(j);
                                                                                                       };
                                                                                                       eval( "window." + callbackName + "=tmpcallback" );
                                                                                                       }-*/;

    /*
    obj.@com.google.gwt.sample.hello.client.HelloJsonRequestHandler::onRequestComplete(Lcom/google/gwt/core/client/JavaScriptObject;)(j);
     */
}

/* Further notes: 
 * 
 * --------------------------------------------------------
 * Hello.java: 
 * 
public class Hello implements EntryPoint {
    
  public void onModuleLoad() {
Button b = new Button("Click me", new ClickHandler() {
  public void onClick(ClickEvent event) {
    //Window.alert("Hello, AJAX");
      HelloJsonp.get();
  }
});
    
RootPanel.get().add(b);
  }
      
  public static void callback(String m) {
Window.alert("Hello, AJAX\n" + m);
  }
}
 * 
 * --------------------------------------------------------
 * HelloJsonRequestHandler.java:
 * 
public interface HelloJsonRequestHandler {
public void onRequestComplete( JavaScriptObject json );
}
 * 
 * --------------------------------------------------------
 * Hello.gwt.xml: add this: 
 * 
    <inherits name='com.google.gwt.json.JSON'/>
 * 
 * --------------------------------------------------------
 * build.xml: modify the location:
 * 
  <property name="gwt.sdk" location="../../gwt-linux-1.7.1" />
 * 
 * --------------------------------------------------------
 * build.xml: add these it will be slow but prints more errors:
 * 
  <!-- Additional arguments like -style PRETTY or -logLevel DEBUG -->
  <arg value="-style"/>
  <arg value="DETAILED"/>
  <arg value="-logLevel"/>
  <arg value="DEBUG"/>
 * 
 */