DWR and JQuery for AJAX Apps

11- DWR (2) and JQuery

A. Venturini

What is Ajax?

 Two components:
 Client Side (e.g. JavaScript)
 determine when to contact
server
 contact it
 display results on page

 Server side (e.g. Java, PHP)
 like normal servlet but return specifically
what is required
 maybe just OK or Fail
 maybe XML or HTML
2

What is Ajax?

 Diagram from:
http://www.codeproject.com/KB/showcase/FarPointAJAX.aspx
3
07/05/2009 3

What is DWR?
 Consists of a server-side Java libraries, a DWR
servlet, and JavaScript libraries that allow you to
write Ajax web applications
 Hides low-level XMLHttpRequest Handling
 Specifically designed with Java technology in mind
 “Easy Ajax for Java”
 Allows JavaScript code in a browser to use Java
functions running on a web server as if they were
in the browser
 That‟s why it is called “Direct remoting”

4

Why DWR?
 Without DWR, you would have to create many
Web application endpoints (servlets) that need to
be addressable via URIs
 If you have several methods in a class on the
server that you want to invoke from the browser
 Each of these methods need to be addressable via URI
 You would have to map parameters and return values to
HTML input form parameters and responses yourself
 DWR comes with some JavaScript utility functions

5

2. How DWR Works
DWR dynamically generates an AjaxService class in
Javascript to match some server-side code. This is called by
the eventHandler.
DWR then handles all the remoting details, including
converting all the parameters and return values between
Javascript and Java.
It then executes the supplied callback function (populateList)
which uses a DWR utility function to alter the web page.

6

DWR Consists of Two Main Parts
A Java Servlet running on the server
that processes requests and sends
responses back to the browser.
 uk.ltd.getahead.dwr.DWRServlet
 This servlet delegates the call to the backend class you
specify in the dwr.xml configuration file

 JavaScript
running in the browser that
sends requests and can dynamically
update the webpage.
 DWR handles XMLHttpRequest handling

7

Steps for Building DWR-based
AJAX Application

sample application on the lab
site:
modalDialogPortlet-portlet

8

GOAL: Make available remotely this class
defined server side
public class Counter {

public Counter() {
}

public String increaseCounter(int num) {
HttpSession session = WebContextFactory.get().getSession(true);
Integer counter=(Integer) session.getAttribute("COUNTER");
if(counter ==null) {
counter = new Integer(0);
}
int iValue=counter.intValue();
iValue=iValue+num;
counter=new Integer(iValue);
session.setAttribute("COUNTER",counter);
return counter.toString();
}
public String getCounter() {
HttpSession session = WebContextFactory.get().getSession(true);
Integer counter=(Integer) session.getAttribute("COUNTER");
if(counter ==null) {
counter = new Integer(0);
}
int iValue=counter.intValue();
return counter.toString();
}

}

Steps

1. Download the dwr.jar file and place it in the WEB-
INF/lib directory of your webapp
 dwr.jar contains DWR runtime code including the
DWR servlet

2. Edit web.xml in the WEB-INF directory
 add servlet and servlet mapping information

3. Create dwr.xml file in the WEB-INF directory
 You specify classes and methods DWR can create
and remote for use by client-side JavaScript code

10

Step #2 Edit web.xml in the WEB-
INF directory
<servlet>
<servlet-name>dwr-invoker</servlet-name>
<display-name>DWR Servlet</display-name>
<servlet-
class>uk.ltd.getahead.dwr.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>
11

Step#3 Create dwr.xml file in the
WEB-INF directory
 The example below creates a JavaScript class “JDate”
matching the Java class “java.util.Date”

<!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct
Web Remoting 1.0//EN"
"http://www.getahead.ltd.uk/dwr/dwr10.dtd"> <dwr>
<dwr>
<allow>
<create creator="new" javascript="Counter">
<param name="class"
value="it.unibz.awp.dwr.services.Counter"/>
</create>
</allow>
</dwr>
12

Test and Deploy the Portlet

13

Javascript class automatically created
by DWR
<script type="text/javascript"
src="/modalDialogPortlet-
portlet/dwr/interface/Counter.js"></script>

It creates dynamically a javascript class as a proxy
of the methods exposed server side:
1) Counter.increaseCounter(value, yourCallback)
2) Counter.getCounter(anotherCallback)

the HTML is:

Counter is: <span id="counter" class="reply">""</span>
<br/>
increase the counter by: <input class="itext" size="10"
value="1" id="p00" title="Will be converted to: int" type="text">
<input class="ibutton"
onclick='Counter.increaseCounter(objectEval($("p00").value),
getCounterCallback);' value="Execute" type="button">
<br/>

When the button is pressed:

1) the javascript calls the
Counter.increaseCounter(objectEval($("p00").val
ue), getCounterCallback)
2) the increaseCounter is called on the server side
3) then getCounterCallback is called

And the callback is:

function getCounterCallback(data) {
Counter.getCounter(function(data)
{dwr.util.setValue("counter", data,
{ escapeHtml:false }
);
});
}

When the callback is called it gets the updated
version of the counter (another Ajax call) and
update the edit box

Types of Converters
 A converter converts data between the client and
the server
 Types of converters provided by DWR
 Basic Converters
 Bean and Object Converters
 Enum Converters
 Collection Converter
 DOM Objects
 Servlet Objects (HttpServletRequest, HttpSession, etc.)
 While you can create your own converters this is
rarely needed

19

Basic Converters
 Handle
 Boolean, byte, short, int, long, float, double, char, java.lang.Boolean,
java.lang. byte, java.lang.Short, java.lang.Integer, java.lang.Long,
java.lang.Float, java.lang.Double, java.lang.Character,
java.math.BigInteger, java.math.BigDecimal and java.lang.String

 No need to have a <convert> element in the
<allow>section in dwr.xml to use them.
 They are enabled by default

 A Date Converter converts data between a
JavaScript date and a java.util.Date, java.sql.Date,
java.sql.Times, or, java.sql. Timestamp

20

1. Bean and Object Converters
 The Bean converter converts Plain Old Java
Objects (POJOs) into JavaScript Associative arrays
and back again.
 The Object converter is similar except that it works
on object members directly rather than through
getters and setters.
 You can enable the bean converter for a single
class using the following:
<convert converter="bean"
match="your.full.package.BeanName"/>
 To allow conversion of any class in the given
package, or sub package:
<convert converter="bean" match="your.full.package.*"/>

21

 DWR will convert Javascript objects (aka maps, aka
associative arrays) into Java beans or Java objects.
public class Remoted {
public void setPerson(Person p) {
// ...
}
}

public class Person {
public void setName(String name) { ... }
public void setAge(int age) { ... }
// ...
}

 If Remoted was configured as a Creator, and Person is
convertible using the Bean Converter, then you can call the
Java code as follows:
var p = { name:"Fred", age:21 };
22
Remoted.setPerson(p);

 Restricting Property Conversions
Just as you have exclude and include for creators to instruct DWR to
exclude methods, there is a similar system for Bean Converters :
<convert converter="bean" match="com.example.Fred">
<param name="exclude" value="property1, property2"/>
</convert>
 This will ensure that DWR does not call
fred.getProperty1() and fred.getProperty2.
 Alternatively if you prefer to white-list rather than black-list
you can do the following:
<convert converter="bean" match="com.example.Fred">
<param name="include" value="property1, property2"/>
</convert>
 Good security design commonly involves white-listing rather
than black-listing.

23

1. Enum Converters

Converts Java5 Enums into JavaScript strings and back
again. Not enabled by default.

You can enable the Enum Converter for a single class using
the following:
<convert converter="enum" match="your.full.package.EnumName"/>

Setting up JavaScript variables
public class Remoted {
public void setStatus(Status p) {
// ...
}
}

enum Status {
PASS,
FAIL,
}
24

2. Enum Converter

 If Remoted was configured as a Creator, and Status is
convertible using the EnumConverter, then you can call the
Java code from JavaScript as follows:

Remoted.setStatus("PASS");

If no match is found in the given enum, then an exception
will be thrown.

25

DOM Objects

 DWR automatically converts DOM trees from
DOM, DOM4J, JDOM and XOM.

 You simply return a Document, Element or Node
from any of the above and DWR will
automatically convert it into a browser DOM
object.

26

1. Creators
 The create element in your dwr.xml file has the
following structure.
<allow>
<create creator="..." javascript="..." scope="...">
<param name="..." value="..."/>
<auth method="..." role="..."/>
<exclude method="..."/>
<include method="..."/>
</create>
...
</allow>
Most of these elements are optional. All you really
need is to specify a creator and a JavaScript name.
The creator attribute is required – it specifies which
creator will be used.
The javascript attribute gives your newly created
object a name in the browser. 28

2. Creators
 The scope attribute is optional. It defaults to “page”. The
other options are “application”, “session”, and “request”.
 The param attribute is used by the various creators for
specific bits of configuration. For example the 'new' creator
needs to be told what type of object to call 'new' on.
 The include and exclude elements allow a creator to
restrict access to class methods. A Creator should specify
EITHER a list of include elements (which implies that the
default policy is denial) OR a list of exclude elements
(which implies that the default policy is to allow access).
 For example to deny access to all methods in some class
except for the setHourlyPay() method you should put the
following into your dwr.xml
<create creator="new" javascript="Fred">
<param name="class" value="com.example.Fred"/>
<auth method="setHourlyPay" role="admin"/>
</create>
29

3. Creators

 The new creator is declared by default by DWR as follows: <creator
id="new" class="uk.ltd.getahead.dwr.create.NewCreator"/>. It creates an
instance of a class using the default constructor.
 You allow DWR to use the new creator to create and remote your beans as
follows:
<allow>
<create creator="new" javascript=“Date">
<param name="class" value="java.util.Date"/>
</create>
...
</allow>

 This remotes java.util.Date to Javascript and gives it the name Date so in
Javascript when you call Date.toString(reply) then a new java.util.Date will
be constructed using the default constructor, then the toString() method
will be called, and the data returned to the javascript reply function (in
this case the current date in string form).

30

Creators and Converters Summary
 Creators create objects that live on the server
and have their methods remoted
 Converters convert parameters and return types
 Created objects do things while converted objects
carry data
var r=Remote.method (param, callback)

creator converter

31

Utility Functions

32

1. Utility Functions
 The util.js contains utility functions to help you
update your web pages with JavaScript data
 You can even use it outside of DWR because it does
not depend on DWR to function
 Some of the available utility functions are:
 $(id)
 getValue, getValues, setValue, setValues
 addRows and removeAllRows

33

2. Utility Functions
 $(id) is the same as
 Document.getElementById(id) in DOM API
 DWRUtil.getValue(id) get the value(s) out of the
HTML elements
 DWRUtil.setValue(id, value) finds the element
with the id in the first parameter and alters its
contents to the second parameter

34

What is jQuery?
 A framework for Client Side JavaScript.
 Frameworks provide useful alternatives for
common programming tasks, creating
functionality which may not be available or
cumbersome to use within a language.
 An open source project, maintained by a group of
developers, with a very active support base and
thorough, well written documentation.
 Adopted by Liferay as javascript framework

What jQuery is not…

 A substitute for knowing JavaScript
 jQuery is extraordinarily useful, but you should
still know how JavaScript works and how to
use it correctly. This means more than
Googling a tutorial and calling yourself an
expert.
 A solve all
 There is still plenty of functionality built into
JavaScript that should be utilized! Don‟t turn
every project into a quest to „jQuery-ize‟ the
problem, use jQuery where it makes sense.
Create solutions in environments where they
belong.

What is available with jQuery?

 Cross browser  JavaScript
support and animation
detection  Hundreds of
 AJAX functions plugins for pre-
 CSS functions built user
interfaces,
 DOM manipulation
advanced
 DOM transversal animations, form
 Attribute validation, etc
manipulation  Expandable
 Event detection functionality using
and handling custom plugins
 Small foot print

jQuery Syntax

$.func(…);
or
$(selector).func1(…).func2(…).funcN(…);

jQuery Object, can be used instead of jQuery (in liferay
$
should be used always JQuery)
selector
Selector syntax, many different selectors allowed
func
Chainable, most functions return a jQuery object
(…)
Function parameters

The jQuery/$ Object

 Represented by both $ and jQuery
 To use jQuery only, use jQuery.noConflict(),
for other frameworks that use $
 By default, represents the jQuery object. When
combined with a selector, can represent multiple
DOM Elements, see next slide.
 Used with all jQuery functions.

jQuery Selectors
 $( html )  $( expr, context )
Create DOM elements on- This function accepts a
the-fly from the provided string containing a CSS or
String of raw HTML. basic XPath selector which
is then used to match a set
of elements. Default
 $( elems ) context is document. Used
Wrap jQuery functionality most often for DOM
around single or multiple transversal.
DOM Elements.
 Selectors will return a
 $( fn ) jQuery object, which can
contain one or more
A shorthand for elements, or contain no
$(document).ready(), elements at all.
allowing you to bind a
function to be executed
when the DOM document
has finished loading.

jQuery Selector Examples
 $( html )
 $(„<p><a href=“index.html”>Click here!</a></p>‟)

 $ ( elems )
 $(document), $(window), $(this)

 $(document.getElementsByTagName(“p”))

 $ ( fn )
 $(function() { alert(“Hello, World!”) });

 $ ( expr, context )
 $(“p”), $(“form”), $(“input”)

jQuery Functions

 Attached to the jQuery object or chained off of a
selector statement.
 Most functions return the jQuery object they
were originally passed, so you can perform many
actions in a single line.
 The same function can perform an entirely
different action based on the number and type of
parameters.

jQuery Usage Example

$(“li:odd”).prepend(„<span>Changed</span>‟).css({background:“red”});

<ul> <ul> <ul>
<li> <li> <li style=“background:red;”>
First item <span>Changed</span> <span>Changed</span>
</li> First item First item
<li> </li> </li>
Second item <li> <li>
</li> Second item Second item
<li> </li> </li>
Third item <li> <li style=“background:red;”>
</li> <span>Changed</span> <span>Changed</span>
</ul> Third item Third item
</li> </li>
</ul> </ul>

jQuery Usage Example

$(“div:hidden”).find(“.foo”).empty().text(“Changed”).end().show();

<div> <div> <div>
<span class=“foo”> <span class=“foo”> <span class=“foo”>
Some text Some text Some text
</span> </span> </span>
</div> </div> </div>
<div style=“display:none”> <div style=“display:none”> <div style=“display:none”>
<span> <span> <span>
More text More text More text
Goodbye cruel world. Goodbye cruel world. </span>
</span> </span> </div>
</div> </div>

<div> <div> <div>
Some text Some text Some text
<div style=“display:none”> <div style=“display:none”> <div style=“display:block”>
<span> <span> <span>
More text More text More text
Changed Changed Changed

Example JQuery (from the
modalDialogPortlet-portlet)

The HTML
<script type="text/javascript"
src="/html/js/jquery/ui.tabs.js"></script>

<div id="tabsExamples">
<ul>
<li><a href="#tabexample1"><span>TAB1</span></a></li>
<li><a href="#tabexample2"><span>TAB2</span></a></li>
</ul>
</div>
<div id="tabexample1">hello, I am TAB 1</div>
<div id="tabexample2">And I am TAB 2</div>

The Javascript

jQuery(document).ready(function(){
jQuery("#tabsExamples > ul").tabs();
});

DWR and JQuery for AJAX Apps

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