Cis 274 intro

I
•Servlets

II
•Java Server Pages (JSP)

III
•Preparing the Dev. Enviornment

IV
•Web-App Folders and Hierarchy

V
•Writing the First Servlet

VII
•Compiling

VIII
•Deploying a Sample Servlet (Packaged & Unpackaged)

VI
•Writing the First JSP

 A servlet is a Java programming language class used to extend the
capabilities of servers that host applications accessed via a request-
response programming model

 A servlet is like any other java class

 Although servlets can respond to any type of request, they are
commonly used to extend the applications hosted by Web servers

 Use regular HTML for most of page

 Mark dynamic content with special tags

 A JSP technically gets converted to a servlet but it looks more like
PHP files where you embed the java into HTML.

 The character sequences <% and %> enclose Java expressions, which
are evaluated at run time

<%= new java.util.Date() %>

 Java Development Kit (JDK)
◦ http://www.oracle.com/technetwork/java/javase/downloads/index.html

 Apache Tomcat webserver
◦ http://tomcat.apache.org/download-70.cgi

 Set JAVA_HOME Environmental Variable
◦ Right click on “Computer” (Win 7), and click on “Properties”
◦ Click on “Advanced System Settings” on top right corner
◦ On the new window opened click on “Environment Variables”
◦ In the “System Variables” section, the upper part of the window, click on “New…”
 Variable name: JAVA_HOME
 Variable value: Path to the jdk directory (in my case C:Program FilesJavajdk1.6.0_21)
◦ Click on “OK”

 Set CATALINA_HOME Environmental Variable
◦ Right click on “Computer” (Win 7), and click on “Properties”
◦ Click on “Advanced System Settings” on top right corner
◦ On the new window opened click on “Environment Variables”
◦ In the “System Variables” section, the upper part of the window, click on “New…”
 Variable name: CATALINA_HOME
 Variable value: Path to the apache-tomcat directory (in my case D:Serversapache-tomcat-
7.0.12-windows-x86apache-tomcat-7.0.12)
◦ Click on “OK”

Note: You might need to restart your computer after adding environmental variables to
make changes to take effect

 In your browser type: localhost:8080
◦ If tomcat’s page is opened then the webserver installation was successful

 Check JAVA_HOME variable:
◦ in command prompt type: echo %JAVA_HOME%
◦ Check to see the variable value and if it is set correctly

 All the content should be placed under tomcat’s “webapps” directory

• $CATALINA_HOMEwebappshelloservlet": This directory is known as context root for the web context
"helloservlet". It contains the resources that are visible by the clients, such as HTML, CSS, Scripts and
images. These resources will be delivered to the clients as it is. You could create sub-directories such as
images, css and scripts, to further categories the resources accessible by clients.

• "$CATALINA_HOMEwebappshelloservletWEB-INF": This is a hidden directory that is used by the server.
It is NOT accessible by the clients directly (for security reason). This is where you keep your application-
specific configuration files such as "web.xml" (which we will elaborate later). It's sub-directories contain
program classes, source files, and libraries.

• "$CATALINA_HOMEwebappshelloservletWEB-INFsrc": Keep the Java program source files. It is
optional but a good practice to separate the source files and classes to facilitate deployment.

• "$CATALINA_HOMEwebappshelloservletWEB-INFclasses": Keep the Java classes (compiled from the
source codes). Classes defined in packages must be kept according to the package directory structure.

• "$CATALINA_HOMEwebappshelloservletWEB-INFlib": keep the libraries (JAR-files), which are provided
by other packages, available to this webapp only.

<HTML>
<HEAD>
<TITLE>Introductions</TITLE>
</HEAD>
<BODY>
<FORM METHOD=GET ACTION="/servlet/Hello">
If you don't mind me asking, what is your name?
<INPUT TYPE=TEXT NAME="name"><P>
<INPUT TYPE=SUBMIT>
</FORM>
</BODY>
</HTML>

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class Hello extends HttpServlet {

public void doGet(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {

res.setContentType("text/html");
PrintWriter out = res.getWriter();

String name = req.getParameter("name");
out.println("<HTML>");
out.println("<HEAD><TITLE>Hello, " + name + "</TITLE></HEAD>");
out.println("<BODY>");
out.println("Hello, " + name);
out.println("</BODY></HTML>");
}

public String getServletInfo() {
return "A servlet that knows the name of the person to whom it's" +
"saying hello";
}
}

 The web.xml file
defines each
servlet and JSP <?xml version="1.0" encoding="ISO-8859-1"?>
page within a Web
Application. <!DOCTYPE web-app
PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.2//EN"
"http://java.sun.com/j2ee/dtds/web-app_2_2.dtd">
 The file goes into
the WEB-INF <web-app>
directory <servlet>
<servlet-name>
hi
</servlet-name>
<servlet-class>
HelloWorld
</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>
hi
</servlet-name>
<url-pattern>
/hello.html
</url-pattern>
</servlet-mapping>
</web-app>

 Compile the packages:
"C:Program FilesJavajdk1.6.0_17binjavac" <Package Name>*.java -d .

 If external (outside the current working directory) classes and
libraries are used, we will need to explicitly define the CLASSPATH to
list all the directories which contain used classes and libraries
set CLASSPATH=C:libjarsclassifier.jar ;C:UserProfilingjarsprofiles.jar

 -d (directory)
◦ Set the destination directory for class files. The destination directory must
already exist.
◦ If a class is part of a package, javac puts the class file in a subdirectory
reflecting the package name, creating directories as needed.

 -classpath
◦ Set the user class path, overriding the user class path in the CLASSPATH environment
variable.
◦ If neither CLASSPATH or -classpath is specified, the user class path consists of the
current directory
java -classpath C:javaMyClasses utility.myapp.Cool

 What does the following command do?

Javac –classpath .;..classes;”D:Serversapache-
tomcat-6.0.26-windows-x86apache-tomcat-
6.0.26libservlet-api.jar” src*.java –d ./test

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class SimpleCounter extends HttpServlet {

int count = 0;

public void doGet(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
res.setContentType("text/plain");
PrintWriter out = res.getWriter();
count++;
out.println("Since loading, this servlet has been accessed " +
count + " times.");
}
}

JSP
HTML
<HTML>
<HTML>
<BODY>
<BODY>
Hello, world Hello! The time is now <%= new java.util.Date() %>
</BODY> </BODY>
</HTML> </HTML>

 Same as HTML, but just save it with .jsp extension

AUA – CoE
Apr.11, Spring 2012

1. Hashtable is synchronized, whereas HashMap is not.
1. This makes HashMap better for non-threaded applications, as
unsynchronized Objects typically perform better than synchronized ones.

2. Hashtable does not allow null keys or values. HashMap allows one null key and
any number of null values.

Cis 274 intro

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Cis 274 intro