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Look-up Tables: One more LookupTableJsonServlet

18 March 2009

Author: Restamon Posted under Code

Now that we’ve given it some thought, it’s time to make the necessary changes to the LookupTableJsonServlet. The current version of the servlet produces valid Javascript code that looks something like this:

[{label: "Test #1", value: "test1"},
{label: "Test #2", value: "test2"}]

… which is simply a JSON object in the form of an array, or list, of objects with a label property and a value property. The new approach that I have decided to take will produce a “map” of such objects, keyed by context. Such a map will look more like this in Javascript Object Notation:

{global: [{label: "Data Type", value: "dataType"}],
testonly: [{label: "Test #1", value: "test1"},
{label: "Test #2", value: "test2"}]}

We will still allow the possibility of passing a specific context as a parameter in the URL, which will still limit the results to just the tables in the identified context, but the format of the resulting output will remain the same. It will simply be a map that contains only one element. This way, any code written to utilize the output of this servlet will work, whether a context parameter has been provided or not.

The changes required to implement this approach did not turn out to be all that extensive, and the final result now looks like this:

package org.restafarian.core.servlets.impl;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.lang.StringUtils;
import org.restafarian.core.beans.LookupTable;
import org.restafarian.core.service.LookupTableManager;
import org.restafarian.core.servlets.JavascriptServletBase;

/**
 * <p>This servlet handles LookupTables.</p>
 */
public class LookupTableJsonServlet extends JavascriptServletBase {
  private static final long serialVersionUID = 1;
  private LookupTableManager lookupTableManager;

  /**
   * <p>The Servlet "doGet()" method.</p>
   *
   * @param req the <code>HttpServletRequest</code> object
   * @param res the <code>HttpServletResponse</code> object
   * @throws ServletException
   * @throws IOException
   */
  public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException,
         IOException {
    // log request, if enabled
    if (log.isDebugEnabled()) {
      String message = "Processing GET request.";
      if (req.getQueryString() != null && req.getQueryString().length() > 0) {
        message += "; query string=" + req.getQueryString();
      }
      log.debug(message);
    }

    sendOptionList(req, res);
  }

  /**
   * <p>Handles a query request for a list of LookupTables.</p>
   *
   * @param req the <code>HttpServletRequest</code> object
   * @param res the <code>HttpServletResponse</code> object
   */
  private void sendOptionList(HttpServletRequest req, HttpServletResponse res) throws IOException {
    List<LookupTable> list = null;
    String context = req.getParameter("context");
    if (StringUtils.isNotEmpty(context)) {
      list = lookupTableManager.findByContext(context);
    } else {
      list = lookupTableManager.findAll();
    }

    if (list != null && list.size() > 0) {
      PrintWriter pw = res.getWriter();
      pw.println(lookupTableListToJson(list, req));
    } else {
      sendError(req, res, 404, "The requested resource was not found on this server.");
    }
  }

  /**
   * <p>Converts a list of LookupTableEntries to JSON.</p>
   *
   * @param list the list of LookupTableEntries
   * @param req the <code>HttpServletRequest</code> object
   * @return the list of LookupTableEntries in JSON format
   */
  private static String lookupTableListToJson(List<LookupTable> list, HttpServletRequest req) {
    StringBuffer buffer = new StringBuffer();

    String var = req.getParameter("var");
    if (StringUtils.isNotEmpty(var)) {
      buffer.append("var ");
      buffer.append(var);
      buffer.append(" = ");
    }
    buffer.append("{");
    if (list != null && list.size() > 0) {
      Map<String,Map<String,String>> contexts = new TreeMap<String,Map<String,String>>();
      Iterator<LookupTable> i = list.iterator();
      while (i.hasNext()) {
        LookupTable lookupTable = i.next();
        String context = lookupTable.getContext();
        Map<String,String> contextMap = contexts.get(context);
        if (contextMap == null) {
          contextMap = new TreeMap<String,String>();
          contexts.put(context, contextMap);
        }
        contextMap.put(lookupTable.getDisplayName(), lookupTable.getTableName());
      }
      String separator = "";
      Iterator<String> j = contexts.keySet().iterator();
      while (j.hasNext()) {
        String context = j.next();
        buffer.append(separator);
        buffer.append(context);
        buffer.append(": [");
        Map<String,String> contextMap = contexts.get(context);
        String tableSeparator = "";
        Iterator<String> k = contextMap.keySet().iterator();
        while (k.hasNext()) {
          String label = k.next();
          buffer.append(tableSeparator);
          buffer.append("{label: \"");
          buffer.append(label);
          buffer.append("\", value: \"");
          buffer.append(contextMap.get(label));
          buffer.append("\"}");
          tableSeparator = ",\n";
        }
        buffer.append("]");
        separator = ",\n";
      }
    }
    buffer.append("}");
    if (StringUtils.isNotEmpty(var)) {
      buffer.append(";");
    }

    return buffer.toString();
  }

  /**
   * <p>Sets the LookupTableManager.</p>
   *
   * @param lookupTableManager the LookupTableManager
   */
  public void setLookupTableManager(LookupTableManager lookupTableManager) {
    this.lookupTableManager = lookupTableManager;
  }
}

Now that that’s out of the way, we can get back to client side of things and get started on that example table definition update page.