CS441

CURRENT TOPICS IN PROGRAMMING LANGUAGES

LECTURE 5_1

George Koutsogiannakis/ Summer 2011

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Web Servers

• Large and complex piece of software that interact with a client software such as a Browser via the http protocol.

• A web server receives a http request and sends a http response.

• The job of the web server is to translate the http request and find and execute the requested resource. It sends a response back to the client that sent the request in the form of http response packet(s)

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Web Server resources• Web server resources vary i.e– HTML or DHTML or XML script files. They should be

transferred to the client for interpretation.– Java Applets. They should be transferred to the client

for interpretation.– Java servlets. They get executed by the server and the

results are converted into http response data sent to the client.

– Java Server Pages. Partial execution by the server (the java code part) and the results including any HTML script are sent to the client in the form of http respnse packets.

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Web Server resources

• Java script files.– The Server side java script is interpreted by the

server and the results are sent to the client in the form of http response packets.

– Client side java script files are sent ton the client for interpretation.

– Java Beans. Executed by the server.– Other resources such as Active Server pages,

Visual basic, PHP, C# etc.

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Common Web Servers

• Which of the listed can be used depends on the particular web server. Some support Microsoft type of resources whereas others support Java type of resources.

• Some common Web Servers are:– Apache: Open Source maintained by Apache Software

Foundation. – IIS (Internet Information Services): Microsoft’ s Web Server.– Tomcat: Open Source, maintained by Apache Software

Foundation. Supports Java resources. Not as powerful as Apache web server. Can be used in low volume web climates.

– Java System Web Server, Zeus and others.

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Execution Environment for resources

• In order for certain resources to be executed by the web server an environment is needed (called engine or container).

• For example:– To execute java servlet programs a servlet container is

needed.– To interpret Java Server Pages code a jsp container is

needed.• Tomcat has both of the above two containers

(engines).

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Deployment

• A web site can consist of one or more of the resources mentioned.

• The combination of the resources used to build the web site is called the “Application”.

• The application needs to be installed on the web server. The process of installing it on the web server is called “Deployment”.

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Deployment on Tomcat

• Normally a web application should be developed outside Tomcat.

• The applications have to be deployed in a specific directory of Tomcat called “webapps”.

• Tomcat is normally installed (Windows O.S.) in the path i.e:

C:\Program Files\Apache Software Foundation\Apache Tomcat 6.0.18

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Tomcat Directories

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Tomcat Directories

• Clicking on the webapps directory displays the applications’ names that are deployed i.e

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Web Apps

• For example the folder: MyWebSite is a web application whose name is MyWebSite• The name of the web application in the

webapps directory is referred to as the “context-root” of the web application.

• The root context needs to be typed in the http link (URL) on the client side (i.e the browser) in order to make a connection to this specific application on the web server.

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Calling The web application

• To connect to Tomcat one needs the IP address of the web server.

• In our case since the client and the web server are collocated on the same machine the IP address is called “localhost”.

• Besides the IP addres the software port that the web server uses on your machine to listen for requests, has to be listed in the url.

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Calling The web application• The default software for Windows based web servers is

8080. That port can be changed if it conflicts with another application on your machine.

• Tomcat is installed as a service in Windows. That means that every time you boot up your computer Tomcat starts automatically and it listens for requests to come in.

• If for some reason Tomcat is not working, you can start the service by going to the Administrative Tools of the Control Panel and clicking on Services. You will see the option to either start or stop any of the services including Tomcat.

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Calling The web application

• Tomcat ha sits own default web application that can be called from a Browser by using the URL:

http://localhost:8080/• You will see the Tomcats default page that

gives you information about using Tomcat and also provides links on the left side for various types of information.

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Tomcat’ s Administration

• When you installed Tomcat on your computer you were asked to provide a password for the administrator. Make sure that you remember the password!

• Clicking on the Tomcat Manager link will transfer you to a login page for the administrator.

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Tomcat’ s Administration

• As an administrator you will be able to:– Observe the status of the various applications.– Deploy new applications.

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Deployment

• The easiest way to deploy an application is via a war file.

• If you are creating a war file the deployment procedure will automatically create the proper folders and names within webapps directory of Tomcat.

• A web application should be developed in your directory structure in some folder not in the path of Tomcat’s installation (IT SHOULD BE OUTSIDE OF Program Files directory).

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Deployment

• The first step in creating a web application is creating this structure.

• The following table contains a sample web application, named "MyWebSite".

• Each one of these directories should be created from the <SERVER_ROOT> of the servlet container.

• An example of a <SERVER_ROOT>, using Tomcat, would be Program Files/Apache Software Foundation/Tomcat6.8/webapps.

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Deployment• The Web Application Directory Structure

1) webapps/MyWebSite

This is the root directory (root context) of the web application. All JSP, .class and XHTML files are stored here.

2) webapps/MyWebSite/WEB-INF

This directory contains all resources related to the application that are not in the document root of the application. The file web.xml (deployment descriptor) resides here. No files contained in this directory can be served directly to a client.

3) webapps/MyWebSite/WEB-INF/classes

This directory is where servlet .class files and other utility classes are located.

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Deployment4) webapps/MyWebSite/WEB-INF/lib

This directory contains Java Archive files that the web application depends upon. For example, this is where you would place a JAR file that contained a JDBC driver.

As you look over the contents of the web application's directory structure, you will notice that web applications allow for classes to be stored in both the /WEB-INF/classes and /WEB-INF/lib directories. Of these two, the class loader will load classes from the /classes directory first followed by the JARs in the /lib directory. If you have duplicate classes in both the /classes and /lib directories, the classes in the /classes directory will be used.

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Deployment Descriptor File web.xml

• The Web application deployment descriptor file web.xml is very important and improper formatting of it can cause your application not to be deployed!

• It describes configuration information for the entire web application. For our application the location of the web.xml file is

• in the /<SERVER_ROOT>/MyWebSite /WEB-INF/ directory.

• The information inside in in terms of “elements”. We are going to discuss that more when we talk about servlets.

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Deployment Descriptor File web.xml

• The information that is contained in the deployment descriptor includes the following elements:

• * ServletContext Init Parameters• * Localized Content• * Session Configuration• * Servlet / JSP Definitions• * Servlet / JSP Mappings• * Mime Type Mappings• * Welcome File list• * Error Pages• * Security

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Deploying the web site MyWebSite

• Suppose we have a folder named MyWebSite and inside the folder we have the resources needed for the application to run on the web server.

• For example we have the folder in the path:C:\CS441\examples\ServletandApplet\MyWebSite

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Deploying the web site MyWebSite

• Inside the folder MyWebSite we have placed the needed resources following the folder names that needed in a Tomcat webapp:

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Deploying the web site MyWebSite

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Deploying the web site MyWebSite-Inside WEB-INF folder

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Deploying the web site MyWebSite• Packaging a Web application using WAR files

• Now that we know what a web application is, we can package it for deployment. The standard method for packaging web applications is to use a Web Archive file (WAR). You can create a WAR file by using Java's archiving tool jar.

• An example of this would be to change to the root directory of your web application and type the following command:

• >jar cvf MyWebSite.war . (Notice that dot after war and space) (open DOS command window at the level where your folder MyWebSite (inside the folder) exists and use the jar command).

• This command will produce an archive file named MyWebSite.war that will contain your entire web application.

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Deploying the web site MyWebSite

• Login as an administrator in the Manager site of Tomcat ( From Tomcat’s Home Page link to Manager)

• In the Tomcat Web Application Manager page scroll down to “War File To Deploy” part.

• Browse to where your war file is located in your directory structure and then press deploy.

• A O.K. message and an entry onto the list of deployed webapps means successful deployment.

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Deploying the web site MyWebSite

• Change to the root directory of your web application. In this case the root directory would be TOMCAT_HOME/webapps/MyWebSite/

• You should be able to see the war file and the web app called for instance MyWebSite.

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URL for your application

• Open your Browser and type the URL:http://localhost:8080/MyWebSite/index.htmlWhere index.html is the resource that needs to be

called first as an example (or the name of any other resource that needs to be called first, depending of course on the application).

• Notice that failure to deploy is a possibility. Make sure that you double check the structure of the folders of your web app and more importantly the web.xml file.

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Undeploy

• If the web site does not work :– In the manager page of Tomcat where web apps

status is indicated click “undeploy” in the row where the name of the web app appears.

– Make corrections and repeat the deploy procedure after you have created a new war file.

– Follow the same procedure every time a change is needed in the web app.

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Deploy Certified Applet

• Create a new webapp folder (new context-root name) somewhere in your directory structure (not in Tomcat’s directory structure and NOT in Program Files for Windows).

• Proceed through steps to create the certificate and import it into cacerts keystore.

• Create the jar file of all the .class files of the Applet.• Create the signed version of the jar file.

– Make sure that you use the alias and the passwords when the keytool command was used for the certificate.

– Note: Do not copy certificates from one machine to another unless you re import the pasted certificate into the new machine’s cacerts keystore.

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Deploy Certified Applet

• Delete the unsigned version of the jar file. • Place the signed jar file in the WEB-INF/lib folder.• Change the html file with applet tag to include the

applet tag attribute : archive=“NameofyourSignedJarFile.jar”

• Create the war file with the same name as the context-root (you must be in the webapp folder where your html file is located).

• Deploy the web file.

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Deploy Certified Applet

• Test your web site by opening an instance of the browser and typing the proper URL for the new web site.

• A message may be shown asking you to agree to run the certified applet.

• Test the functionality of the File menu. This time the exit menu item and the menu items that have to do with opening files should work!

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Deploy Certified Applet

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Study

• Text: Web Based Application Development pages 35-39.

• Tomcat’s documentation that came with the download.

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