/* * Copyright 2006 Google Inc. *  * Licensed under the Apache License, Version 2.0 (the "License"); you may not * use this file except in compliance with the License. You may obtain a copy of * the License at *  * http://www.apache.org/licenses/LICENSE-2.0 *  * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the * License for the specific language governing permissions and limitations under * the License. */package com.google.gwt.sample.json.client;import com.google.gwt.json.client.JSONArray;import com.google.gwt.json.client.JSONException;import com.google.gwt.json.client.JSONObject;import com.google.gwt.json.client.JSONParser;import com.google.gwt.json.client.JSONString;import com.google.gwt.json.client.JSONValue;import com.google.gwt.user.client.HTTPRequest;import com.google.gwt.user.client.ResponseTextHandler;import com.google.gwt.user.client.Window;import com.google.gwt.user.client.ui.Button;import com.google.gwt.user.client.ui.ClickListener;import com.google.gwt.user.client.ui.RootPanel;import com.google.gwt.user.client.ui.Tree;import com.google.gwt.user.client.ui.TreeItem;import com.google.gwt.user.client.ui.Widget;import java.util.Iterator;import java.util.Set;/** * Class that acts as a client to a JSON service. Currently, this client just * requests a text which contains a JSON encoding of a search result set from * yahoo. We use a text file to demonstrate how the pieces work without tripping * on cross-site scripting issues. *  * If you would like to make this a more dynamic example, you can associate a * servlet with this example and simply have it hit the yahoo service and return * the results. */public class JSON {  /**   * Class for handling the response text associated with a request for a JSON   * object.   *    */  private class JSONResponseTextHandler implements ResponseTextHandler {    public void onCompletion(String responseText) {      try {        JSONValue jsonValue = JSONParser.parse(responseText);        displayJSONObject(jsonValue);      } catch (JSONException e) {        displayError(responseText);      }      searchButton.setText(SEARCH_BUTTON_DEFAULT_TEXT);    }  }  /*   * Class for handling the fetch button's click event.   */  private class SearchButtonClickListener implements ClickListener {    public void onClick(Widget sender) {      jsonTree.setVisible(false);      doFetchURL();    }  }  /*   * Default URL to use to fetch JSON objects. Note that the contents of this   * JSON result were as a result of requesting the following URL:   *    * http://api.search.yahoo.com/ImageSearchService/V1/imageSearch?appid=YahooDemo&query=potato&results=2&output=json   *    */  private static final String DEFAULT_SEARCH_URL = "search-results.js";  /*   * Text displayed on the fetch button when we are in a default state.   */  private static final String SEARCH_BUTTON_DEFAULT_TEXT = "Search";  /*   * Text displayed on the fetch button when we are waiting for a JSON reply.   */  private static final String SEARCH_BUTTON_WAITING_TEXT = "Waiting for JSON Response...";  private Tree jsonTree = new Tree();  private Button searchButton = new Button();  /**   * Entry point for this simple application. Currently, we build the   * application's form and wait for events.   */  public void onModuleLoad() {    initializeMainForm();  }  /*   * Add the object presented by the JSONValue as a children to the requested   * TreeItem.   */  private void addChildren(TreeItem treeItem, JSONValue jsonValue) {    JSONArray jsonArray;    JSONObject jsonObject;    JSONString jsonString;    if ((jsonArray = jsonValue.isArray()) != null) {      for (int i = 0; i < jsonArray.size(); ++i) {        TreeItem child = treeItem.addItem(getChildText("["            + Integer.toString(i) + "]"));        addChildren(child, jsonArray.get(i));      }    } else if ((jsonObject = jsonValue.isObject()) != null) {      Set keys = jsonObject.keySet();      for (Iterator iter = keys.iterator(); iter.hasNext();) {        String key = (String) iter.next();        TreeItem child = treeItem.addItem(getChildText(key));        addChildren(child, jsonObject.get(key));      }    } else if ((jsonString = jsonValue.isString()) != null) {      // Use stringValue instead of toString() because we don't want escaping      treeItem.addItem(jsonString.stringValue());    } else {      // JSONBoolean, JSONNumber, and JSONNull work well with toString().      treeItem.addItem(getChildText(jsonValue.toString()));    }  }  private void displayError(String responseText) {    jsonTree.removeItems();    jsonTree.setVisible(true);    TreeItem treeItem = jsonTree.addItem("Failed to parse JSON response");    treeItem.addItem(responseText);    treeItem.setStyleName("JSON-JSONResponseObject");    treeItem.setState(true);  }  /*   * Update the treeview of a JSON object.   */  private void displayJSONObject(JSONValue jsonValue) {    jsonTree.removeItems();    jsonTree.setVisible(true);    TreeItem treeItem = jsonTree.addItem("JSON Response");    addChildren(treeItem, jsonValue);    treeItem.setStyleName("JSON-JSONResponseObject");    treeItem.setState(true);  }  /*   * Fetch the requested URL.   */  private void doFetchURL() {    searchButton.setText(SEARCH_BUTTON_WAITING_TEXT);    if (!HTTPRequest.asyncGet(DEFAULT_SEARCH_URL, new JSONResponseTextHandler())) {      // Reset the caption.      //      searchButton.setText(SEARCH_BUTTON_DEFAULT_TEXT);    }  }  /*   * Causes the text of child elements to wrap.   */  private String getChildText(String text) {    return "<span style='white-space:normal'>" + text + "</span>";  }  /**   * Initialize the main form's layout and content.   */  private void initializeMainForm() {    searchButton.setStyleName("JSON-SearchButton");    searchButton.setText(SEARCH_BUTTON_DEFAULT_TEXT);    searchButton.addClickListener(new SearchButtonClickListener());    // Find out where the host page wants the button.    //    RootPanel searchButtonSlot = RootPanel.get("search");    if (searchButtonSlot == null) {      Window.alert("Please define a container element whose id is 'search'");      return;    }    // Find out where the host page wants the tree view.    //    RootPanel treeViewSlot = RootPanel.get("tree");    if (treeViewSlot == null) {      Window.alert("Please define a container element whose id is 'tree'");      return;    }    // Add both widgets.    //    searchButtonSlot.add(searchButton);    treeViewSlot.add(jsonTree);  }}