DWR Java AJAX Applications

In this chapter, we will get to the actual hands-on work. We will develop samples based on DWR, which show how to dynamically change the common user interface elements such as tables and lists as well as field completion. We also make a dynamic user interface skeleton for our samples that will hold all the samples in this book.

also read:

The section on dynamic user interfaces shows how to get started with a DWR application, and it presents a user interface skeleton that will be used to hold the tables and lists sample, and the field completion (aka. autosuggest/autocomplete) sample. Samples in the following chapter will use the same user interface skeleton, with the exception of the sample applications in Chapter 7.

The following are the sections in this chapter:

  • Creating a Dynamic User Interface—starts with creating a web project and a basis for samples mentioned in this chapter
  • Implementing Tables and Lists—shows us how to use DWR with them
  • Implementing Field Completion—has a sample for typical field completion

Creating a Dynamic User Interface

The idea behind a dynamic user interface is to have a common “framework” for all samples. We will create a new web application and then add new features to the application as we go on. The user interface will look something like the following figure:

The user interface has three main areas: the title/logo that is static, the tabs that are dynamic, and the content area that shows the actual content.

The idea behind this implementation is to use DWR functionality to generate tabs and to get content for the tab pages. The tabbed user interface is created using a CSS template from the Dynamic Drive CSS Library (http://dynamicdrive.com/style/csslibrary/item/css-tabs-menu). Tabs are read from a properties file, so it is possible to dynamically add new tabs to the web page. The following screenshot shows the user interface.

dwr-1

Creating a New Web Project

  1. First, we will create a new web project. Using the Eclipse IDE we do the following: select the menu File | New | Dynamic Web Project.
  2. This opens the New Dynamic Web Project dialog; enter the project name DWREasyAjax and click Next, and accept the defaults on all the pages till the last page, where Geronimo Deployment Plan is created as shown in the following screenshot:
    dwr-2
  3. Enter easyajax as Group Id and DWREasyAjax as Artifact Id. On clicking Finish, Eclipse creates a new web project. The following screen shot shows the generated project and the directory hierarchy.
    dwr-3
  4. Before starting to do anything else, we need to copy DWR to our web application. All DWR functionality is present in the dwr.jar file, and we just copy that to the WEB-INF | lib directory.

A couple of files are noteworthy: web.xml and geronimo-web.xml. The latter is generated for the Geronimo application server, and we can leave it as it is. Eclipse has an editor to show the contents of geronimo-web.xml when we double-clickthe file.

dwr-4

Configuring the Web Application

The context root is worth noting (visible in the screenshot above). We will need it when we test the application.

The other XML file, web.xml, is very important as we all know. This XML will hold the DWR servlet defi nition and other possible initialization parameters. The following code shows the full contents of the web.xml file that we will use:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.
sun.com/xml/ns/javaee/web-app_2_5.xsd"
id="WebApp_ID" version="2.5">
<display-name><b><i>DWR</i></b>EasyAjax</display-name>
<servlet>
<display-name><b><i>DWR</i></b> Servlet</display-name>
<servlet-name>dwr-invoker</servlet-name>
<servlet-class>
org.directwebremoting.servlet.DwrServlet
</servlet-class>
<init-param>
<param-name>debug</param-name>
<param-value>true</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>dwr-invoker</servlet-name>
<url-pattern>/dwr/*</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.htm</welcome-file>
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>
</web-app>

We hav e already seen the servlet defi nition in Chapter 3, in the section on confi guration. We use the same debug-init parameter here. Servlet mapping is the commonly used /dwr/*.

We remember that DWR cannot function without the dwr.xml configuration file. So we need to create the confi guration file. We use Eclipse to create a new XML file in the WEB-INF directory. The following is required for the user interface skeleton. It already includes the allow-element for our DWR based menu.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dwr PUBLIC
"-//GetAhead Limited//DTD Direct Web Remoting 2.0//EN"
"http://getahead.org/dwr/dwr20.dtd">
<dwr>
<allow>
<create creator="new" javascript="HorizontalMenu">
<param name="class" value="samples.HorizontalMenu" />
</create>
</allow>
</dwr>

In the allow element, there is a creator for the horizontal menu Java class that we are going to implement here. The creator that we use here is the new creator, which means that DWR will use an empty constructor to create Java objects for clients. The parameter named class holds the fully qualifi ed class name.

Developing the Web Application

Since we have already defined the name of the Java class that will be used for creating the menu, the next thing we do is implement it. The idea behind the HorizontalMenu class is that it is used to read a properties file that holds the menus that are going to be on the web page.

We add properties to a file named dwrapplication.properties, and we create it in the same samples-package as the HorizontalMenu-class. The properties file for the menu items is as follows:

menu.1=Tables and lists,TablesAndLists
menu.2=Field completion,FieldCompletion

The syntax for the menu property is that it contains two elements separated by a comma. The fi rst element is the name of the menu item. This is visible to user. The second is the name of HTML template file that will hold the page content of the menu item. The class contains just one method, which is used from JavaScript and via DWR to retrieve the menu items. The full class implementation is shown here:

package samples;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import java.util.Properties;
import java.util.Vector;
public class HorizontalMenu {
public HorizontalMenu() {
}
public List<String> getMenuItems() throws IOException {
List<String> menuItems = new Vector<String>();
InputStream is = this.getClass().getClassLoader().
getResourceAsStream(
"samples/dwrapplication.properties");
Properties appProps = new Properties();
appProps.load(is);
is.close();
for (int menuCount = 1; true; menuCount++) {
String menuItem = appProps.getProperty("menu." + menuCount);
if (menuItem == null) {
break;
}
menuItems.add(menuItem);
}
return menuItems;
}
}

The implementation is straightforward. The getMenuItems() method loads properties using the ClassLoader.getResourceAsStream() method, which searches the class path for the specified resource. Then, after loading properties, a for loop is used to loop through menu items and then a List of String-objects is returned to the client. The client is the JavaScript callback function that we will see later. DWR automatically converts the List of String objects to JavaScript arrays, so we don’t have to worry about that.

Testing the Web Application

We hav en’t completed any client-side code now, but let’s test the code anyway. Testing uses the Geronimo test environment.

1.The Project context menu has the Run As menu that we use to test the application as shown in the following screenshot:
dwr-5
2.Run on Server opens a wizard to defi ne a new server runtime. The following screenshot shows that the Geronimo test environment has already been set up, and we just click Finish to run the application. If the test environment is not set up, we can manually defi ne a new one in this dialog:
dwr-6
3.After we click Finish, Eclipse starts the Geronimo test environment and our application with it. When the server starts, the Console tab in Eclipse informs us that it’s been started.
dwr-7

The Servers tab shows that the server is started and all the code has been synchronized, that is, the code is the most recent (Synchronization happens whenever we save changes on some deployed file.) The Servers tab also has a list of deployed applications under the server. Just the one application that we are testing here is visible in the Servers tab.
dwr-8

Now comes the interesting part—what are we going to test if we haven’t really implemented anything? If we take a look at the web.xml file, we will fi nd that we have defi ned one initialization parameter. The Debug parameter is true, which means that DWR generates test pages for our remoted Java classes. We just point the browser (Firefox in our case) to the URL  ttp://127.0.0.1:8080/DWREasyAjax/dwr and the following page opens up:
dwr-9
This page w ill show a list of all the classes that we allow to be remoted. When we click the class name, a test page opens as in the following screenshot:
dwr-10
This is an interesting page. We see all the allowed methods, in this case, all public class methods since we didn’t specifi cally include or exclude anything. The most important ones are the script elements, which we need to include in our HTML pages. DWR does not automatically know what we want in our web pages, so we must add the script includes in each page where we are using DWR and a
remoted functionality.

Then there is the possibility of testing remoted methods. When we test our own method, getMenuItems(), we see a response in an alert box:

dwr-11

The array in the alert box in the screenshot is the JavaScript array that DWR returns from our method.

Developing Web Pages

The next step is to add the web pages. Note that we can leave the test environment running. Whenever we change the application code, it is automatically published to test the environment, so we don’t need to stop and start the server each time we make some changes and want to test the application.

The CSS style sheet is from the Dynamic Drive CSS Library. The file is named styles.css, and it is in the WebContent directory in Eclipse IDE. The CSS code is as shown:

/*URL: http://www.dynamicdrive.com/style/ */
.basictab{
padding: 3px 0;
margin-left: 0;
font: bold 12px Verdana;
border-bottom: 1px solid gray;
list-style-type: none;
text-align: left; /*set to left, center, or right to align the menu as
desired*/
}
.basictab li{
display: inline;
margin: 0;
}
.basictab li a{
text-decoration: none;
padding: 3px 7px;
margin-right: 3px;
border: 1px solid gray;
border-bottom: none;
background-color: #f6ffd5;
color: #2d2b2b;
}
.basictab li a:visited{
color: #2d2b2b;
}
.basictab li a:hover{
background-color: #DBFF6C;
color: black;
}
.basictab li a:active{
color: black;
}
.basictab li.selected a{ /*selected tab effect*/
position: relative;
top: 1px;
padding-top: 4px;
background-color: #DBFF6C;
color: black;
}

This CSS is shown for the sake of completion, and we will not go into details of CSS style sheets. It is suffi cient to say that CSS provides an excellent method to create websites with good presentation.

The next step is the actual web page. We create an index.jsp page, in the WebContent directory, which will have the menu and also the JavaScript functions for our samples. It should be noted that although all JavaScript code is added to a single JSP page here in this sample, in “real” projects it would probably be more useful to create a separate file for JavaScript functions and include the JavaScript file in the HTML/JSP page using a code snippet such as this:

<script type="text/javascript" src="myjavascriptcode/ HorizontalMenu.js">// <![CDATA[

We will add JavaScript functions later for each sample. The following is the JSP code
that shows the menu using the remoted HorizontalMenu class.

<%@ page lan guage="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-
1">
<link href="styles.css" rel="stylesheet" type="text/css"/>
<script type='text/javascript' src='/DWREasyAjax/dwr/engine.js'></
script>
<script type='text/javascript' src='/DWREasyAjax/dwr/util.js'></
script>
<script type='text/javascript' src='/DWREasyAjax/dwr/interface/
HorizontalMenu.js'></script>
<title>DWR samples</title>
<script type="text/javascript">
function loadMenuItems()
{
HorizontalMenu.getMenuItems(setMenuItems);
}
function getContent(contentId)
{
AppContent.getContent(contentId,setContent);
}
function menuItemFormatter(item)
{
elements=item.split(',');
return '<li><a href="#" onclick="getContent(\''+elements[1]+'\
');return false;">'+elements[0]+'</a></li>';
}
function setMenuItems(menuItems)
{
menu=dwr.util.byId("dwrMenu");
menuItemsHtml='';
for(var i=0;i<menuItems.length;i++)
{
menuItemsHtml=menuItemsHtml+menuItemFormatter(menuItems[i]);
}
menu.innerHTML=menuItemsHtml;
}
function setContent(htmlArray)
{
var contentFunctions='';
var scriptToBeEvaled='';
var contentHtml='';
for(var i=0;i<htmlArray.length;i++)
{
var html=htmlArray[i];
if(html.toLowerCase().indexOf('<script')>-1)
{
if(html.indexOf('TO BE EVALED')>-1)
{
scriptToBeEvaled=html.substring(html.indexOf('>')+1,
html.indexOf('</'));
}
else
{
eval(html.substring(html.indexOf('>')+1,html.indexOf('</')));
contentFunctions+=html;
}
}
else
{
contentHtml+=html;
}
}
conte ntScriptArea=dwr.util.byId("contentAreaFunctions");
contentScriptArea.innerHTML=contentFunctions;
contentArea=dwr.util.byId("contentArea");
contentArea.innerHTML=contentHtml;
if(scriptToBeEvaled!='')
{
eval(scriptToBeEvaled);
}
}
</script>
</head>
<body onload="loadMenuItems()">
<h1>DWR Easy Java Ajax Applications</h1>
<ul class="basictab" id="dwrMenu">
</ul>
<div id="contentAreaFunctions">
</div>
<div id="contentArea">
</div>
</body>
</html>

This JSP is our user interface. The HTML is just normal HTML with a head element and a body element. The head includes reference to a style sheet and to DWR JavaScript files, engine.js, util.js, and our own HorizontalMenu.js. The util.js file is optional, but as it contains very useful functions, it could be included in all the web pages where we use the functions in util.js.

The body elem ent has a contentArea place holder for the content pages just below the menu. It also contains the content area for JavaScript functions for a particular content.The body element onload-event executes the loadMenuItems() function when the page is loaded. The loadMenuItems()function calls the remoted method of the HorizontalMenu Java class. The parameter of the HorizontalMenu.getMenuItem()JavaScript function is the callback function that is called by DWR when the Java method has been executed and it returns menu items.

The setMenuItems()function is a callback function for the loadMenuItems() function mentioned in the previous paragraph. While loading menu items, the Horizontal.getMenuItems()remoted method returns menu items as a List of Strings as a parameter to the setMenuItems() function. The menu items are formatted using the menuItemFormatter() helper function.

The menuItemFormatter()function creates li elements of menu texts. Menus are formatted as links, (a href) and they have an onclick event that has a function call to the getContent-function, which in turn calls the AppContent.getContent() function. The AppContent is a remoted Java class, which we haven’t implemented yet, and its purpose is to read the HTML from a file based on the menu item that the user
clicked. Implementation of AppContent and the content pages are described in the next section.

The setContent() function sets the HTML content to the content area and also evaluates JavaScript options that are within the content to be inserted in the content area (this is not used very much, but it is there for those who need it).

Our dynamic user interface looks like this:

Note the Fireb ug window at the bottom of the browser screen. The Firebug console in the screenshot shows one POST request to our HorizontalMenu.getMenuItems() method. Other Firebug features are extremely useful during development work, and we fi nd it useful that Firebug has been enabled throughout the development work.

Callback Functions

We saw our first callback function as a parameter in the HorizontalMenu.getMenuItems(setMenuItems) function, and since callbacks are an important concept in DWR, it would be good to discuss a little more about them now that we have seen their fi rst usage.

Callbacks are used to operate on the data that was returned from a remoted method. As DWR and AJAX are asynchronous, typical return values in RPCs (Remote Procedure Calls), as in Java calls, do not work. DWR hides the details of calling the callback functions and handles everything internally from the moment we return a value from the remoted Java method to receiving the returned value to the callback function.

Two methods are recommended while using callback functions.

We have already seen the fi rst method in the HorizontalMenu.getMenuItems (setMenuItems) function call. Remember that there are no parameters in the getMenuItems()Java method, but in the JavaScript call, we added the callback function name at the end of the parameter list. If the Java method has parameters, then the JavaScript call is similar to CountryDB.getCountries(selectedLetters,setCountryRows), where selectedLetters is the input parameter for the Java method and setCountryRows is the name of the callback function (we see the implementation later on).

The second method to use callbacks is a meta-data object in the remote JavaScript call. An example (a full implementation is shown later in this chapter) is shown here:

CountryDB.saveCountryNotes(ccode,newNotes, {
callback:function(newNotes)
{
//function body here
}
});

Here, the function is anonymous and its implementation is included in the JavaScript call to the remoted Java method. One advantage here is that it is easy to read the code, and the the code is executed immediately after we get the return value from the Java method. The other advantage is that we can add extra options to the call. Extra options include timeout and error handler as shown in the following example:

CountryDB.saveCountryNotes(ccode,newNotes, {
callback:function(newNotes)
{
//function body here
},
timeout:10000,
errorHandler:function(errorMsg) { alert(errorMsg);}
});

It is also possible to add a callback function to those Java methods that do not return a value. Adding a callback to methods with no return values would be useful in getting a notifi cation when a remote call has been completed.

Afterword

Our first sample is ready, and it is also the basis for the following samples. We also looked at how applications are tested in the Eclipse environment.

Using DWR, we can look at JavaScript code on the browser and Java code on the server as one. It may take a while to get used to it, but it will change the way we develop web applications. Logically, there is no longer a client and a server but just a single run time platform that happens to be physically separate. But in practice, of course, applications using DWR, JavaScript on the client and Java in the server, are using the typical client-server interaction. This should be remembered when writing applications in the logically single run-time platform.

Implementing Tables and Lists

The first actual sample is very common in applications: tables and lists. In this sample, the table is populated using the DWR utility functions, and a remoted Java class. The sample code also shows how DWR is used to do inline table editing. When a table cell is double-clicked, an edit box opens, and it is used to save new cell data. The sample will have country data in a CSV file: country Name, Long Name,
two-letter Code, Capital, and user-defi ned Notes. The user interface for the table sample appears as shown in the following screenshot:

Server Code for Tables and Lists

T he fi rst thing to do is to get the country data. Country data is in a CSV file (named countries.csv and located in the samples Java package). The following is an excerpt of the content of the CSV file (data is from http://www.state.gov ).

Short-form name,Long-form name,FIPS Code,Capital
Afghanistan,Islamic Republic of Afghanistan,AF,Kabul
Albania,Republic of Albania,AL,Tirana
Algeria,People's Democratic Republic of Algeria,AG,Algiers
Andorra,Principality of Andorra,AN,Andorra la Vella
Angola,Republic of Angola,AO,Luanda
Antigua and Barbuda,(no long-form name),AC,Saint John's
Argentina,Argentine Republic,AR,Buenos Aires
Armenia,Republic of Armenia,AM,Yerevan

The CSV file is read each time a client requests country data. Although this is not very effi cient, it is good enough here. Other alternatives include an in-memory cache or a real database such as Apache Derby or IBM DB2. As an example, we have created a CountryDB class that is used to read and write the country CSV. We also have another class, DBUtils, which has some helper methods. The DBUtils code is as follows:

package samples;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.List;
import java.util.Vector;
public class DBUtils {
private String fileName=null;
public void initFileDB(String fileName)
{
this.fileName=fileName;
// copy csv file to bin-directory, for easy
// file access
File countriesFile = new File(fileName);
if (!countriesFile.exists()) {
try {
List<String> countries = getCSVStrings(null);
PrintWriter pw;
pw = new PrintWriter(new FileWriter(countriesFile));
for (String country : countries) {
pw.println(country);
}
pw.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
protected List<String> getCSVStrings(String letter) {
List<String> csvData = new Vector<String>();
try {
File csvFile = new File(fileName);
BufferedReader br = null;
if(csvFile.exists())
{
br=new BufferedReader(new FileReader(csvFile));
}
else
{
InputStream is = this.getClass().getClassLoader()
.getResourceAsStream("samples/"+fileName);
br=new BufferedReader(new InputStreamReader(is));
br.readLine();
}
for (String line = br.readLine(); line != null; line =
br.readLine()) {
if (letter == null|| (letter != null &amp;&amp; line.startsWith(letter))) {
csvData.add(line);
}
}
br.close();
} catch (IOException ioe) {
ioe.printStackTrace();
}
return csvData;
}
}

The DBUtils class is a straightforward utility class that returns CSV content as a List of Strings. It also copies the original CSV file to the runtime directory of any application server we might be running. This may not be the best practice, but it makes it easier to manipulate the CSV file, and we always have the original CSV file untouched if and when we need to go back to the original version. The code for CountryDB is given here:

package samples;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.List;
import java.util.Vector;
public class CountryDB {
private DBUtils dbUtils = new DBUtils();
private String fileName = "countries.csv";
public CountryDB() {
dbUtils.initFileDB(fileName);
}
public String[] getCountryData(String ccode) {
List<String> countries = dbUtils.getCSVStrings(null);
for (String country : countries) {
if (country.indexOf("," + ccode + ",") > -1) {
return country.split(",");
}
}
return new String[0];
}
public List<List<String>> getCountries(String startLetter) {
List<List<String>> allCountryData = new Vector<List<String>>();
List<String> countryData = dbUtils.getCSVStrings(startLetter);
for (String country : countryData) {
String[] data = country.split(",");
allCountryData.add(Arrays.asList(data));
}
return allCountryData;
}
public String[] saveCountryNotes(String ccode, String notes) {
List<String> countries = dbUtils.getCSVStrings(null);
try {
PrintWriter pw = new PrintWriter(new FileWriter(fileName));
for (String country : countries) {
if (country.indexOf("," + ccode + ",") > -1) {
if (country.split(",").length == 4) {
// no existing notes
country = country + "," + notes;
} else {
if (notes.length() == 0) {
country = country.substring(0, country
.lastIndexOf(","));
} else {
country = country.substring(0, country
.lastIndexOf(","))
+ "," + notes;
}
}
}
pw.println(country);
}
pw.close();
} catch (IOException ioe) {
ioe.printStackTrace();
}
String[] rv = new String[2];
rv[0] = ccode;
rv[1] = notes;
return rv;
}
}

The CountryDB class is a remoted class. The getCountryData() method returns country data as an array of strings based on the country code. The getCountries()method returns all the countries that start with the specified parameter, and saveCountryNotes() saves user added notes to the country specified by the country code.

In order to use CountryDB, the following script element must be added to the index.jsp file together with other JavaScript elements.

<script type='text/javascript' src='/DWREasyAjax/dwr/interface/
CountryDB.js'></script>

There is one other Java class that we need to create and remote. That is the AppContent class that was already present in the JavaScript functions of the home page. The AppContent class is responsible for reading the content of the HTML file and parses the possible JavaScript function out of it, so it can become usable by the existing JavaScript functions in index.jsp file.

package samples;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import java.util.Vector;
public class AppContent {
public AppContent()
{
}
public List<String> getContent(String contentId)
{
InputStream is = this.getClass().getClassLoader().
getResourceAsStream(
"samples/"+contentId+".html");
String content=streamToString(is);
List<String> contentList=new Vector<String>();
//Javascript within script tag will be extracted and sent
separately to client
for(String script=getScript(content);!script.equals("");script=g
etScript(content))
{
contentList.add(script);
content=removeScript(content);
}
//content list will have all the javascript
//functions, last element is executed last
//and all other before html content
if(contentList.size()>1)
{
contentList.add(contentList.size()-1, content);
}
else
{
contentList.add(content);
}
return contentList;
}
public List<String> getLetters()
{
List<String> letters=new Vector<String>();
char[] l=new char[1];
for(int i=65;i<91;i++)
{
l[0]=(char)i;
letters.add(new String(l));
}
return letters;
}
public String removeScript(String html)
{
//removes first script element
int sIndex=html.toLowerCase().indexOf("<script ");
if(sIndex==-1)
{
return html;
}
int eIndex=html.toLowerCase().indexOf("</script>")+9;
return html.substring(0, sIndex)+html.substring(eIndex);
}
public String getScript(String html)
{
//returns first script element
int sIndex=html.toLowerCase().indexOf("<script ");
if(sIndex==-1)
{
return "";
}
int eIndex=html.toLowerCase().indexOf("</script>")+9;
return html.substring(sIndex, eIndex);
}
public String streamToString(InputStream is)
{
String content="";
try
{
ByteArrayOutputStream baos=new ByteArrayOutputStream();
for(int b=is.read();b!=-1;b=is.read())
{
baos.write(b);
}
content=baos.toString();
}
catch(IOException ioe)
{
content=ioe.toString();
}
return content;
}
}

The getContent() method reads the HTML code from a file based on the contentId. ContentId was specified in the dwrapplication.properties file, and the HTML is just contentId plus the extension .html in the package directory. There is also a getLetters() method that simply lists letters from A to Z and returns a list of letters to the browser.

If we test the application now, we will get an error as shown in the following screenshot:

We know why the AppContent is not defi ned error occurs, so lets fi x it by adding AppContent to the allow element in the dwr.xml file. We also add CountryDB to the allow element. The fi rst thing we do is to add required elements to the dwr.xml file. We add the following creators within the allow element in the dwr.xml file.

<create creator="new" javascript="AppContent">
<param name="class" value="samples.AppContent" />
<include method="getContent" />
<include method="getLetters" />
</create>
<create creator="new" javascript="CountryDB">
<param name="class" value="samples.CountryDB" />
<include method="getCountries" />
<include method="saveCountryNotes" />
<include method="getCountryData" />
</create>

We explicitly define the methods we are remoting using the include elements. This is a good practice, as we don’t accidentally allow access to any methods that are not meant to be remoted.

Client Code for Tables and Lists

We also need to add a JavaScript interface to the index.jsp page. Add the following with the rest of the scripts in the index.jsp file.

<script type='text/javascript' src='/DWREasyAjax/dwr/interface/
AppContent.js'></script>

Be fore testing, we need the sample HTML for the content area. The following HTML is in the TablesAndLists.html file under the samples directory:

<h2>Countries</h2>
Show countries starting with
<select id="letters" onchange="selectLetter(this);return false;"> </
select><br/>
Doubleclick "Notes"-cell to add notes to country.

<table border="1">
<thead>
<tr>
<th>Name</th>
<th>Long name</th>
<th>Code</th>
<th>Capital</th>
<th>Notes</th>
</tr>
</thead>
<tbody id="countryData">
</tbody>
</table>
<script type='text/javascript'>
//TO BE EVALED
AppContent.getLetters(addLetters);
</script>

The script element at the end is extracted by our Java class, and it is then evaluated by the browser when the client-side JavaScript receives the HTML. There is the select element, and its onchange event calls the selectLetter()JavaScript function. We will implement the selectLetter() function shortly.

JavaScript functions are added in the index.jsp file, and within the head element. Functions could be in separate JavaScript files, but the embedded script is just fine here.

function selectLetter(selectElement)
{
var selectedIndex = selectElement.selectedIndex;
var selectedLetter= selectElement.options[selectedIndex ].value;
CountryDB.getCountries(selectedLetter,setCountryRows);
}
function addLetters(letters)
{
dwr.util.addOptions('letters',['letter...']);
dwr.util.addOptions('letters',letters);
}
function setCountryRows(countryData)
{
var cellFuncs = [
function(data) { return data[0]; },
function(data) { return data[1]; },
function(data) { return data[2]; },
function(data) { return data[3]; },
function(data) { return data[4]; }
];
dwr.util.removeAllRows('countryData');
dwr.util.addRows( 'countryData',countryData,cellFuncs, {
cellCreator:function(options) {
var td = document.createElement("td");
if(options.cellNum==4)
{
var notes=options.rowData[4];
if(notes==undefined)
{
notes=' ';// + options.rowData[2]+'notes';
}
var ccode=options.rowData[2];
var divId=ccode+'_Notes';
var tdId=divId+'Cell';
td.setAttribute('id',tdId);
var html=getNotesHtml(ccode,notes);
td.innerHTML=html;
options.data=html;
}
return td;
},
escapeHtml:false
});
}
function getNotesHtml(ccode,notes)
{
var divId=ccode+'_Notes';
return "<div onDblClick=
\"editCountryNotes('"+divId+"','"+ccode+"');\" id=
\""+divId+"\">"+notes+"</div>";
}
function editCountryNotes(id,ccode)
{
var notesElement=dwr.util.byId(id);
var tdId=id+'Cell';
var notes=notesElement.innerHTML;
if(notes==' ')
{
notes='';
}
var editBox='<input id="'+ccode+'NotesEditBox" type=
"text" value="'+notes+'"/><br/>';
editBox+="<input type='button' id='"+ccode+"SaveNotesButton'
value='Save' onclick='saveCountryNotes(\""+ccode+"\");'/>";
editBox+="<input type='button' id='"+ccode+"CancelNotesButton'
value='Cancel' onclick='cancelEditNotes
(\""+ccode+"\");'/>";
tdElement=dwr.util.byId(tdId);
tdElement.innerHTML=editBox;
dwr.util.byId(ccode+'NotesEditBox').focus();
}
function cancelEditNotes(ccode)
{
var countryData=CountryDB.getCountryData(ccode, {
callback:function(data)
{
var notes=data[4];
if(notes==undefined)
{
notes=' ';
}
var html=getNotesHtml(ccode,notes);
var tdId=ccode+'_NotesCell';
var td=dwr.util.byId(tdId);
td.innerHTML=html;
}
});
}
function saveCountryNotes(ccode)
{
var editBox=dwr.util.byId(ccode+'NotesEditBox');
var newNotes=editBox.value;
CountryDB.saveCountryNotes(ccode,newNotes, {
callback:function(newNotes)
{
var ccode=newNotes[0];
var notes=newNotes[1];
var notesHtml=getNotesHtml(ccode,notes);
var td=dwr.util.byId(ccode+"_NotesCell");
td.innerHTML=notesHtml;
}
});
}

There are lots of functions for table samples, and we go through each one of them. The fi rst is the selectLetter()function. This function gets the selected letter from the select element and calls the CountryDB.getCountries() remoted Java method. The callback function is setCountryRows. This function receives the return value from the Java getCountries() method, that is List<List>, a List of Lists of Strings.
The second function is addLetters(letters), and it is a callback function for theAppContent.getLetters() method, which simply returns letters from A to Z. The addLetters() function uses the DWR utility functions to populate the letter list. Th en there is a callback function for the CountryDB.getCountries() method. The parameter for the function is an array of countries that begin with a specified letter.
Each array element has a format: Name, Long name, (country code) Code, Capital, Notes. The purpose of this function is to populate the table with country data; and let’s see how it is done. The variable, cellFuncs, holds functions for retrieving data for each cell in a column. The parameter named data is an array of country data that was returned from the Java class.

The table is populated using the DWR utility function, addRows(). The cellFuncs variable is used to get the correct data for the table cell. The cellCreator function is used to create custom HTML for the table cell. Default implementation generates just a td element, but our custom implementation generates the td-element with the div placeholder for user notes.

The getNotesHtml() function is used to generate the div element with the event listener for double-click.

The editCountryNotes() function is called when the table cell is double-clicked. The function creates input fi elds for editing notes with the Save and Cancel buttons. The cancelEditNotes() and saveCountryNotes()functions cancel the editing of new notes, or saves them by calling the CountryDB.saveCountryNotes() Java method.

The following screenshot shows what the sample looks like with the populated table:

Now that we have added necessary functions to the web page we can test the application.

Testing Tables and Lists

The application should be ready for testing if we have had the test environment running during development. Eclipse automatically deploys our new code to the server whenever something changes. So we can go right away to the test page http://127.0.0.1:8080/DWREasyAjax. On clicking Tables and lists we can see the page we have developed. By selecting some letter, for example “I” we get a list of all the countries that start with letter “I” (as shown in the previous screenshot).

Now we can add notes to countries. We can double-click any table cell under Notes. For example, if we want to enter notes to Iceland, we double-click the Notes cell in Iceland’s table row, and we get the edit box for the notes as shown in the following screenshot:

The edit box is a simple text input fi eld. We didn’t use any forms. Saving and canceling editing is done using JavaScript and DWR. If we press Cancel, we get the original notes from the CountryDB Java class using DWR and saving also uses DWR to save data. CountryDB.saveCountryNotes() takes the country code and the notes that the user entered in the edit box and saves them to the CSV file. When notes are available, the application will show them in the country table together with other country information as shown in the following screenshot:

Afterword

The sample in this section uses DWR features to get data for the table and list from the server. We developed the application so that most of the application logic is written in JavaScript and Java beans that are remoted. In principle, the application logic can be thought of as being fully browser based, with some extensions in the server.

Implementing Field Completion

Nowadays, field completion is typical of many web pages. A typical use case is getting a stock quote, and field completion shows matching symbols as users type letters. Many Internet sites use this feature.

Our sample here is a simple license text fi nder. We enter the license name in the input text fi eld, and we use DWR to show the license names that start with the typed text. A list of possible completions is shown below the input fi eld. The following is a screenshot of the field completion in action:

Selected license content is shown in an iframe element from http://www.opensource.org.

Server Code for Field Completion

We will re-use some of the classes we developed in the last section. AppContent is used to load the sample page, and the DBUtils class is used in the LicenseDB class. The LicenseDB class is shown here:

package samples;
import java.util.List;
import java.util.Vector;
public class LicenseDB{
private DBUtils dbUtils=new DBUtils();
public LicenseDB()
{
dbUtils.initFileDB("licenses.csv");
}
public List<String> getLicensesStartingWith(String startLetters)
{
List<String> list=new Vector<String>();
List<String> licenses=dbUtils.getCSVStrings(startLetters);
for(String license : licenses)
{
list.add(license.split(",")[0]);
}
return list;
}
public String getLicenseContentUrl(String licenseName)
{
List<String> licenses=dbUtils.getCSVStrings(licenseName);
if(licenses.size()>0)
{
return licenses.get(0).split(",")[1];
}
return "";
}
}

The getLicenseStartingWith()method goes through the license names and returns valid license names and their URLs. Similar to the data in the previous section, license data is in a CSV file named licenses.csv in the package directory. The following is an excerpt of the file content:

Academic Free License, http://opensource.org/licenses/afl-3.0.php
Adaptive Public License, http://opensource.org/licenses/apl1.0.php
Apache Software License, http://opensource.org/licenses/apachepl-1.1.php
Apache License, http://opensource.org/licenses/apache2.0.php
Apple Public Source License, http://opensource.org/licenses/apsl-2.0.php
Artistic license, http://opensource.org/licenses/artisticlicense-
1.0.php

There are quite a few open-source licenses. Some are more popular than others (like the Apache Software License) and some cannot be re-used (like the IBM Public License).

We want to remote the LicenseDB class, so we add the following to the dwr.xml file.

<create creator="new" javascript="LicenseDB">
<param name="class" value="samples.LicenseDB"/>
<include method="getLicensesStartingWith"/>
<include method="getLicenseContentUrl"/>
</create>

Client Code for Field Completion

The following script element will go in the index.jsp page.

<script type='text/javascript' src='/DWREasyAjax/dwr/interface/LicenseDB.js'></script>

The HTML for the field completion is as follows:

Field completion

Enter Open Source license name to see it’s contents.

<input type="text" id="licenseNameEditBox" value="" onkeyup="showPopup
Menu()" size="40"/>
<input type="button" id="showLicenseTextButton" value="Show license
text" onclick="showLicenseText()"/>
<div id="completionMenuPopup"></div>
<div id="licenseContent"></div>

The input element, where we enter the license name, listens to the onkeyup event which calls the showPopupMenu() JavaScript function. Clicking the Input button calls the showLicenseText() function (the JavaScript functions are explained shortly). Finally, the two div elements are place holders for the pop-up menu and the iframe element that shows license content.

For the pop-up box functionality, we use existing code and modify it for our purpose (many thanks to http://www.jtricks.com). The following is the popup.js file, which is located under the WebContent | js directory.

jtricks.com/javascript/window/box.html
*
* Modified by Sami Salkosuo.
*/
// Moves the box object to be directly beneath an object.
function move_box(an, box)
{
var cleft = 0;
var ctop = 0;
var obj = an;
while (obj.offsetParent)
{
cleft += obj.offsetLeft;
ctop += obj.offsetTop;
obj = obj.offsetParent;
}
box.style.left = cleft + 'px';
ctop += an.offsetHeight + 8;
// Handle Internet Explorer body margins,
// which affect normal document, but not
// absolute-positioned stuff.
if (document.body.currentStyle &amp;&amp;
document.body.currentStyle['marginTop'])
{
ctop += parseInt(
document.body.currentStyle['marginTop']);
}
box.style.top = ctop + 'px';
}
var popupMenuInitialised=false;
// Shows a box if it wasn't shown yet or is hidden
// or hides it if it is currently shown
function show_box(html, width, height, borderStyle,id)
{
// Create box object through DOM
var boxdiv = document.getElementById(id);
boxdiv.style.display='block';
if(popupMenuInitialised==false)
{
//boxdiv = document.createElement('div');
boxdiv.setAttribute('id', id);
boxdiv.style.display = 'block';
boxdiv.style.position = 'absolute';
boxdiv.style.width = width + 'px';
boxdiv.style.height = height + 'px';
boxdiv.style.border = borderStyle;
boxdiv.style.textAlign = 'right';
boxdiv.style.padding = '4px';
boxdiv.style.background = '#FFFFFF';
boxdiv.style.zIndex='99';
popupMenuInitialised=true;
//document.body.appendChild(boxdiv);
}
var contentId=id+'Content';
var contents = document.getElementById(contentId);
if(contents==null)
{
contents = document.createElement('div');
contents.setAttribute('id', id+'Content');
contents.style.textAlign= 'left';
boxdiv.contents = contents;
boxdiv.appendChild(contents);
}
move_box(html, boxdiv);
contents.innerHTML= html;
return false;
}
function hide_box(id)
{
document.getElementById(id).style.display='none';
var boxdiv = document.getElementById(id+'Content');
if(boxdiv!=null)
{
boxdiv.parentNode.removeChild(boxdiv);
}
return false;
}
//--></script>

Functions in the popup.js file are used as menu options directly below the edit box.

The show_box()function takes the following arguments: HTML code for the pop-up, position of the pop-up window, and the “parent” element (to which the pop-up box is related). The function then creates a pop-up window using DOM. The move_box()function is used to move the pop-up window to its correct place under the edit box and the hide_box()function hides the pop-up window by removing the pop-up window from the DOM tree.

In order to use functions in popup.js, we need to add the following script-element to the index.jsp file:

<script type='text/javascript' src='js/popup.js'></script>

Our own JavaScript code for the field completion is in the index.jsp file. The following are the JavaScript functions, and an explanation follows the code:

function showPopupMenu()
{
var licenseNameEditBox=dwr.util.byId('licenseNameEditBox');
var startLetters=licenseNameEditBox.value;
LicenseDB.getLicensesStartingWith(startLetters, {
callback:function(licenses)
{
var html="";
if(licenses.length==0)
{
return;
}
if(licenses.length==1)
{
hidePopupMenu();
licenseNameEditBox.value=licenses[0];
}
else
{
for (index in licenses)
{
var licenseName=licenses[index];//.split(",")[0];
licenseName=licenseName.replace(/\"/g,""");
html+="<div style=\"border:1px solid #777777;
margin-bottom:5;\" onclick=
\"completeEditBox('"+licenseName+"');
\">"+licenseName+"</div>";
}
show_box(html, 200, 270, '1px solid','completionMenuPopup');
}
}
});
}
function hidePopupMenu()
{
hide_box('completionMenuPopup');
}
function completeEditBox(licenseName)
{
var licenseNameEditBox=dwr.util.byId('licenseNameEditBox');
licenseNameEditBox.value=licenseName;
hidePopupMenu();
dwr.util.byId('showLicenseTextButton').focus();
}
function showLicenseText()
{
var licenseNameEditBox=dwr.util.byId('licenseNameEditBox');
licenseName=licenseNameEditBox.value;
LicenseDB.getLicenseContentUrl(licenseName,{
callback:function(licenseUrl)
{
var html='<iframe src="'+licenseUrl+'" width="100%"
height="600"></iframe>';
var content=dwr.util.byId('licenseContent');
content.style.zIndex="1";
content.innerHTML=html;
}
});
}

The showPopupMenu() function is called each time a user enters a letter in the input box. The function gets the value of the input field and calls the LicenseDB. getLicensesStartingWith() method. The callback function is specified in the function parameters. The callback function gets all the licenses that match the parameter, and based on the length of the parameter (which is an array), it either shows a pop-up box with all the matching license names, or, if the array length is one, hides the pop-up box and inserts the full license name in the text fi eld. In the pop up box, the license names are wrapped within the div element that has an onclick event listener that calls the completeEditBox() function.

The hidePopupMenu()function just closes the pop-up menu and the competeEditBox() function inserts the clicked license text in the input box
and moves the focus to the button. The showLicenseText() function is called when we click the Show license text button. The function calls the LicenseDB.
getLicenseContentUrl() method and the callback function creates an iframe element to show the license content directly from http://www.opensource.org, as shown in the following screenshot:

Afterword

Field completion improves user experience in web pages and the sample code in this section showed one way of doing it using DWR.

It should be noted that the sample for field completion presented here is only for demonstration purposes.

Summary

This chapter provided samples for a couple of common tasks that are used in web development: tables and lists, field completion, and even a generic frame, called a dynamic user interface, for our sample code. Both the tables and lists sample and the field completion sample had a very simple CSV-based “database” that holds the data for our purposes, and both had a remoted method that DWR uses to get the data from the server and show it in the client.

We also saw some good examples of HTML, CSS, and JavaScript. In fact, without knowledge of JavaScript it would be diffi cult to write web applications. Many years ago, as some of you may remember, JavaScript was a dirty word in web development and no self-respecting developer would touch JavaScript. But change is a part of life, and in this case, change has been for the better. JavaScript and Java work very well together with the DWR in between.

also read:

The next chapter continues with the user interface part, and shows a couple more samples, including a map scrolling functionality, similar to what is found in the popular Google Maps website.

Comments

comments

Speak Your Mind

*

Close
Please support the site
By clicking any of these buttons you help our site to get better