Arun Gupta, Miles to go ...

TOTD #5: Loading data from beans in jMaki widgets

The jMaki tutorial from SWDP explained the different approaches to load your own data into a jMaki widget. The jMaki widget models have formalized since then and so the code there no longer works. This TOTD explains how a combo box widget in a JSP page gets it data from a bean.

This TOTD uses NetBeans IDE configured with jMaki plugin and GlassFish.

1. Create a new Web application project using NetBeans IDE, enable "jMaki Framework" and use all the defaults. Choose GlassFish as the "Server".
2. In the default generated "index.jsp" page, drag-and-drop "Dojo Combobox" in the "Main Content Area".
3. Replace the generated code with the following fragment
   
   <jsp:useBean id="itemBean" scope="session" class="server.ItemValueBean" />
<a:widget name="dojo.combobox" value="${itemBean.value}"/>

jsp:useBean tag instantiates the bean "server.ItemValueBean" in session scope. a:widget tag uses ${itemBean.value} expression to load the data by invoking getValue() method from the bean.
4. Add a new class to the project and name it "ItemValueBean" in the package "server". Replace the entire generated code with the following:
   
   package server;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

   public class ItemValueBean {
  public String getValue() {
    JSONArray value = new JSONArray();
    for (int i=0; i<2; i++) {
      try {
        JSONObject item = new JSONObject();
        item.put("name", "name" + i);
        item.put("label", "label" + i);
        value.put(item);
      } catch (JSONException ex) {
        ex.printStackTrace();
      }
    }

    try {
      return jsonArrayToString(value, null);
    } catch (JSONException ex) {
      ex.printStackTrace();
    }

    return null;
  }

  /**
  * Converts a JSON Object to an Object Literal
  *
  */
  public String jsonToObjectLibertal(JSONObject jo, StringBuffer buff) throws JSONException {
    if (buff == null)
      buff = new StringBuffer("{");
    else
      buff.append("{");
    JSONArray names = jo.names();
    for (int l=0; (names != null) && l < names.length(); l++) {
      String key = names.getString(l);
      String value = null;
      if (jo.optJSONObject(key) != null) {
        value = key + ":";
        buff.append(value);
        jsonToObjectLibertal(jo.optJSONObject(key), buff);
      } else if (jo.optJSONArray(key) != null) {
        value = key + ":";
        buff.append(value);
        jsonArrayToString(jo.optJSONArray(key), buff);
      } else if (jo.optLong(key, -1) != -1) {
        value = key + ":" + jo.get(key) + "";
        buff.append(value);
      } else if (jo.optDouble(key, -1) != -1) {
        value = key + ":" + jo.get(key) + "";
        buff.append(value);
      } else if (jo.opt(key) != null) {
        Object obj = jo.opt(key);
        if (obj instanceof Boolean) {
          value = key + ":" + jo.getBoolean(key) + "";
        } else {
          value = key + ":" + "'" + jo.get(key) + "'";
        }
        buff.append(value);
      }
      if (l < names.length() -1) buff.append(",");
    }
    buff.append("}");
    return buff.toString();
  }
 
  public String jsonArrayToString(JSONArray ja, StringBuffer buff) throws JSONException {
    if (buff == null)
      buff = new StringBuffer("[");
    else
      buff.append("[");

    for (int key=0; (ja != null) && key < ja.length(); key++) {
      String value = null;
      if (ja.optJSONObject(key) != null){
        jsonToObjectLibertal(ja.optJSONObject(key), buff);
      } else if (ja.optJSONArray(key) != null) {
        jsonArrayToString(ja.optJSONArray(key), buff);
      } else if (ja.optLong(key, -1) != -1) {
        value = ja.get(key) + "";
        buff.append(value);
      } else if (ja.optDouble(key, -1) != -1) {
        value = ja.get(key) + "";
        buff.append(value);
      } else if (ja.optBoolean(key)) {
        value = ja.getBoolean(key) + "";
        buff.append(value);
      } else if (ja.opt(key) != null) {
        Object obj = ja.opt(key);
        if (obj instanceof Boolean) {
          value = ja.getBoolean(key) + "";
        } else {
          value = "'" + ja.get(key) + "'";
        }
        buff.append(value);
      }
      if (key < ja.length() -1) buff.append(",");
    }
    buff.append("]");
    return buff.toString();
  }
}

The getValue methods contains the logic to generate the business data. In this case, the method generates the data model expected by ComboBox using JSON APIs. This data can very well be generated by creating a Persistence Unit and querying a database using JPA or any other mechanism.
   
   The jsonToObjectLibertal and jsonArrayToString methods were originally posted here. These two methods are required because the JSON parser does not allow you to create object literals but only JSON objects. By default these contain key : value pairs where the keys are enclosed in double quotes which does not match with the expected data model.

5. Deploy and Run the application. The browser windows shows the default page with a drop-down list box. The expanded list box shows the items that are added to the combo box.
   
   
    

Another way to populate jMaki widgets with your data (using JPA) is explained here.

Please leave suggestions on other TOTD that you'd like to see. A complete archive is available here.

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Posted by Arun Gupta in web2.0  |  Comments[10]