Open Source Web

DWR - Direct Web Remoting

2009-06-29T20:41:00.000-07:00

DWR stands for Direct Web Remoting. From the name it implies that Directly making remote procedure calls.

It is a technique by which interaction between

client and server takes place by marshalling objects to and fro (Java script object to Java object and vice versa).

The actual remote calls takes place using Ajax with out even user know about it.

It can call any java objects directly from Java script without having own servlet class, its inbuilt DWRServlet do your work. It has inbuilt Ajax,Object Serialization etc., and it also provides

utility scripts to format display data in the web page.

The learning curve of DWR is steep. User just have to know about using config file and using utility classes provided by DWR.

Here is one of the simple way to implment DWR.

Have these java classes in the classpath

DataManager.Java

public List getCustomers(){

List list = new ArrayList();

list.add(new Customer(1, "Bill", "Los Angeles", "000000001"));
list.add(new Customer(2, "Kumar", "Chennai", 00000000020"));
list.add(new Customer(3, "Tom", "Chicago", "000000003"));
list.add(new Customer(4, "Chian", "Kualalumpur", 000000004"));
list.add(new Customer(5, "Hong", "Singapore", "000000005"));
list.add(new Customer(6, "Jade", "Holborn", "0000000006"));

return list;

}

Customer.java

private int id; private String name; private String city; private String phone;

//have getter/setter methods for above.

DWR Configuration

Have this in claspath, preferably under WEB-INF

<!DOCTYPE dwr PUBLIC
"-//GetAhead Limited//DTD Direct Web Remoting 2.0//EN"
"http://getahead.org/dwr/dwr20.dtd">

<dwr>
<allow>
<create creator="new" javascript="JDate">
<param name="class" value="java.util.Date"/>
</create>

<create creator="new" javascript="DataManager" scope="session">
<param name="class" value="com.dwrtest.data.DataManager" />
</create>
<convert converter="bean" match="com.dwrtest.data.Customer"/>

</allow>
</dwr>

Add DWRServlet to web.xml

<servlet>
<servlet-name>dwr-invoker</servlet-name>
<display-name>DWR Servlet</display-name>
<description>DWR Servlet</description>
<servlet-lass>

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>

Testing

http://localhost:<port>/<your-webapp-context>/dwr/index.html

you should be able to see

DataManager
JDate

which is defined in dwr.xml

Clicking on DataManager will show methods defined in that. You can test methods by passing required parameters if any by clicking 'Execute' buttons.

If that works you can go to next step creating your jsp.

test.jsp

Have the below given scripts

<script type='text/javascript' src='/dwrtest/dwr/engine.js'></script>
<script type='text/javascript' src='/dwrtest/dwr/util.js'></script>
<script type='text/javascript' src='/dwrtest/dwr/interface/DataManager.js'></script>

//DataManager.jsp corresponds to the name defined in dwr.xml

function handleData(dat) {
dwr.util.addRows( "mytable",dat,[function(dat){{return dat.name}},function(dat){{return dat.city}},function(dat){{return dat.phone}}]);
dwr.util.addOptions("myselect",dat,"name","name");

}

function loadData(){
DataManager.getCustomers(handleData);

}

<table id='mytable' border="1">
</table>

Optons:<br/>

<select id='myselect'>
</select>

Output

Table :

Bill	Los Angeles	000000001
Kumar	Chennai	00000000020
Tom	Chicago	000000003
Chian	Kualalumpur	0000000004
Hong	Singapore	000000005
Jade	Holborn	0000000006

Options

Download : DWR

Reference : Documentation

Java Ajax

2009-06-25T21:08:00.001-07:00

Ajax - stands for Asynchronous Javascript and XML. With Ajax web pages interact with Server asynchronously in the background without affecting the display/behaviour of the page. It provides rich user experince comapred to old page refresh model. I uses javascript to connect server using XML Http Request.

"Ajax isn't a technology. It's really several technologies, each
flourishing in its own right, coming together in powerful new ways. Ajax
incorporates:

standards-based
presentation using XHTML and CSS;

dynamic display and interaction using the Document
Object Model;

data interchange and manipulation using XML
and XSLT;

asynchronous data retrieval using XMLHttpRequest;

and JavaScript
binding everything together."

Ajax is also a key component of Web 2.0

XML Http Request(XHR)

To show how Ajax works Here is the simple code that parses an .xml file located in server and display it is web page

states.xml

<?xml version="1.0" encoding="UTF-8"?>

<Items>

<Option value="CA">California</Option>

<Option value="IL">Illinois</Option>

</Items>

Server side code say AjaxTestServlet

try{

javax.xml.parsers.DocumentBuilderFactory dbf = javax.xml.parsers.DocumentBuilderFactory.newInstance();

dbf.setValidating(false);

javax.xml.parsers.DocumentBuilder parser = dbf.newDocumentBuilder();

String file = request.getParameter("file");

org.w3c.dom.Document doc = parser.parse("http://localhost/<appcontext>/"+file);

org.w3c.dom.NodeList nList = doc.getElementsByTagName("Option");

int len = doc.getElementsByTagName("Option").getLength();

StringBuffer buff = new StringBuffer();

buff.append("<?xml version='1.0' encoding='UTF-8' ?><items>");

String attrib = "";

String val = "";

for(int i=0;i<len;i++){

attrib = nList.item(i).getAttributes().getNamedItem("value").getNodeValue();

val = nList.item(i).getChildNodes().item(0).getNodeValue();

buff.append("<option value='"+attrib+"'>"+val+"</option>");

}

buff.append("</items>");

response.setContentType("text/xml");

response.setHeader("Cache-Control","no-cache");

response.getWriter().write(buff.toString());

}catch(Exception e){

e.printStackTrace();

}

Client Side say test.html

create xhr object
var xmlHttp;

function createXMLHttpRequest() {

if(window.ActiveXObject) {

xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");

} else if(window.XMLHttpRequest) {

// Firefox, Opera 8.0+, Safari

xmlHttp = new XMLHttpRequest();

}

}

response handler

function handleServerResponse() {

var elements ;

var elemSize ;

var server_response = "";

if(xmlHttp.readyState == 4) { // the state when the request has completed

if (xmlHttp.status == 200) { // the status code returned from the server

elements = xmlHttp.responseXML.getElementsByTagName("option");

elemSize = elements.length;

for(var i=0;i<elemSize;i++) {

server_response = server_response+elements[i].getAttribute("value")+" : "+elements[i].firstChild.data+"<br>";

}

}else{

server_response='No Data';

}

}

document.getElementById("mydiv").innerHTML = "<table><tr><td>"+server_response+"</td></tr></table>";

}

request handler

function doProcess(fileName){

createXMLHttpRequest();

xmlHttp.open("GET", "testAjaxProcess.jsp");

xmlHttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded");

xmlHttp.send("file="+fileName);

xmlHttp.onreadystatechange = handleServerResponse;

return false;

}

html code

<a href="#" onclick="javascript:doProcess('states.xml')">STATES</a>
<div id="mydiv"> </div>

Output :

CA : California
IL : Illinois

There are many open source frameworks availabe to implement Ajax. But I would suggest to start with raw code to know working of actual objects

Java Paging and Sorting

2009-06-25T21:05:00.000-07:00

Paging and Sorting in jsp can be done in easy steps using Display Tags java library.

The display tag library is an open source suite of custom tags that
provide high-level web presentation patterns which will work in an MVC
model. The library provides a significant amount of functionality while
still being easy to use.

Here is the simple steps to implements

Customer.java

int id;
String name;
String city;
String phone;

DisplayTagAction.java (Struts Action)

execute(.....){
List list = new ArrayList(); list.add(new Customer(1, "Bill", "Los Angeles", "000000001"));
list.add(new Customer(2, "Kum", "Chennai", "00000000020"));
list.add(new Customer(3, "Tom", "Chicago", "000000003"));
list.add(new Customer(4, "Chian", "Kualalumpur", "0000000004"));
list.add(new Customer(5, "Hong", "Singapore", "000000005"));

list.add(new Customer(6, "Jade", "Holborn", "0000000006"));
request.setAttribute( "test", list );
//...forward to customers.jsp
}

customers.jsp

<display:table cellspacing="4" name="test" export="xls" pagesize="2" requestURI="/displayTag.do" defaultorder="ascending" >
<display:column class="" property="name" sortable="true" title="Name"/>
<display:column property="city" title="City" sortable="true"/>
<display:column property="phone" title="Phone"/>
</display:table>

result will look like:

6 items found,
displaying 1 to 3.[First/Prev] 1,
2 [Next/Last]

Name	City	Phone
Bill	Los Angeles	000000001
Kum	Chennai	00000000020
Tom	Chicago	000000003

Display tags java library can be used for many other purposes like Subtotalling(using column grouping), Exporting data to CSV,Excel,XML,PDF,RTF, etc.,

Resouce :
Download : displaytag library

Tag reference

User guide

Java 5 Language Features

2009-06-25T21:00:00.000-07:00

a5features.html

The Java 2 Platform Standard Edition Development Kit 5.0 (JDK 5.0) is a feature release of the Java platform. It contains new features and enhancements in many functional areas.

The major Language feature enhancements are

Generics

Autoboxing/Unboxing

Enhanced for Loop

Typesafe Enums

Varargs

Static Import

Generics

Generics adds compile-time type safety to the Collections Framework and eliminates casting.

List list = new ArrayList();

list.add(new String("Test")); // store any object type

To get the data you will do

String s = (String)list.get(0); // Need explicit casting

In Java 5, we can define the datatype for what we are going to store by using generics so that explicit casting is not required.

List<String> list = new ArrayList<String>(); // here we have mentioned which datatype we are going to store.

list.add(new String(""));

If you add any other datatype to the above list object it will give compile time error

list.add(new Integer(1)); // will give compile time error.

Getting the data out
String s = list.get(0); // No explicit casting required

Autoboxing/Unboxing

It elminates monotonous routine work/overhead to convert values of primitive types to objects of the corresponding wrapper classes

and Wrappr classes to primitive data types.

double d = 100.50;

Double doubleObj = new Double(i); to Wrapper class. Explicity convertion.

double dConverted = doubleObj.doubleValue(); // to primitive data type. Explicit convertion.

In Java 5, We can convert it like this

Double doubleObj = d; //Auto boxing(primitive type to Wrapper class).

double dConverted = doubleObj // Auto Unboxing(wrapper class to primitive data type).

Enhanced for Loop

Iterating Collections with for loop (using ; ; format)was bit ugly and time consuming which involves getting the object from collection, Cast to the object's data type. It is uglier with nested loops.
List list = new ArrayList();

Person person1 = new Person();

person1.setFirstName("1First");

person1.setLastName("1Last");
list.add(person1);

Person person2 = new Person();

person2.setFirstName("2First");

person21.setLastName("2Last");

list.add(person2);

for(int i=0;i<list.size();i++)
{

Person person = (Person)list.get(i);

System.out.prinln("FirstName : "+person.getFirstName()+" Last Name : "+person.getLastName());
}

In Java 5, we can write the same code as

List<Person> persons = new ArrayList<Person>();
list.add(person1)
;
list.add(person2)

for(Person person : persons)
{

System.out.prinln("FirstName : "+person.getFirstName()+" Last Name : "+person.getLastName());

}

TypeSafe
Enums

Typesafe enums defined as set of symbolic names and values.

Previous to Java 5 any enums defined and used as below

final int MONDAY = 1;
final int TUESDAY = 2;

calculateNextDay(MONDAY)

It has following disadvantages

It is 'Not TypeSafe' - we can pass any int value in above method as calculateNextDay(2)
It has 'No namespage' - first monday can be defined as 'FIRST_MONDAY' a String prefix need to be added to identify.
It has 'No informative representation' when we print that variable. In this case, printing MONDY will print 1.
It has 'Constants need to be Compiled' when the constant value changes, we need to compile the class for the changes to take effect

with Java 5
enum DAYS{MONDAY,TUESDAY}

System.out.prinln(DAYS.MONDAY);// will print MONDAY

values (returns array of enums) and valueOf (returns value of enum for the passed in value) are the most useful method

public enum OfficeHours {

INTIME(8,30),OUTTIME(5,30),LUNCHTIME(12,30);

OfficeHours(int h,int m){

this.hh = h;

this.mm=m;

}

private int hh;

private int mm;

public int getHour() { return this.hh; }

public int getMins() { return this.mm; }

}

for(OfficeHours oHrs : OfficeHours.values()){

System.out.println(oHrs+" is "+oHrs.getHour()+" : "+oHrs.getMins());

}

The detailed explaination for Enum is availabe here

VarArgs

Before Java 5 when a set of values need to be passed to an method We should put the values in array or any collection and then pass it to a method

In Java 5 we can pass set of values in varargs format

Syntax is Datatype... name i.,e Object... arg

public static void extract(String... x){

for(String m : x){

System.out.println("The month is "+m);

}

extract("Jan","Feb","March")

more details

Static Import

with static impor we can access static members without having qualified(means without using classname)

import static org.apache.commons.lang.time.DateUtils.*; // all the static memebers can be accessed with out using class name DateUtils

System.out.println("Milliseconds per hour : "+MILLIS_PER_HOUR);// instead of DateUtils.MILLIS_PER_HOUR

References : Java 5 Features