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Web Technologies

4th Lecture: JSP and such

Δευτέρα, 10 Απριλίου 2023

Last Week

• HTML & CSS• TCP/IP, DNS, URL, URI• HTTP and such

http://www.htmlandcssbook.com/

URL (and many other UR*s)

• Uniform Resource Locators

Ports

• A 16-bit number that identifies a particular program on the server hardware.

• 0-1023 reserved• sys-admins control them

The apache file system

Missedlast

week

http://www.csszengarden.com/

Missed last week

Static vs Dynamic content

Static vs. dynamic content

Dynamic (deep) Web

• Dynamic pages don’t exist before the request comes in.

• It’s like making an HTML page out of air.– request comes in, – helper app “writes” the HTML, and – web server gets it back to the client.

Common Gateway Interface (CGI)

• a standard method for web servers software to delegate the generation of web pages to executable files.

• Such files are known as CGI scripts – they are programs, • often stand-alone applications, • usually written in a scripting language.

example

CGI (non-Java)

approach

Perl, C, Python, PHP, …

What’s wrong with CGI?

• Logical– Java is suppose to be the language of the internet

• Performance– Light-weight – Easy thread manipulation

• Productivity– J2EE

Servlet: prepare

• Build a directory tree

• Write the two files

Servlet: Writeimport javax.servlet.*;import javax.servlet.http.*;import java.io.*;

public class Ch1Servlet extends HttpServlet { public void doGet(HttpServletRequest request,

HttpServletResponse response) throws IOException {

PrintWriter out = response.getWriter(); java.util.Date today = new java.util.Date(); out.println(“<html> “ + “<body>” + “<h1 align=center>HF\’s Chapter1 Servlet</h1>” + “<br>” + today + “</body>” + “</html>”); }}

Save it to Servlet.java

Servlet: deploy (1)<?xml version=”1.0” encoding=”ISO-8851-1” ?><web-app xmlns=”http://java.sun.com/xml/ns/j2ee” xmlns:xsi=”http://www.w3.org/2001/XMLSchema-instance” xsi:schemaLocation=”http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd” version=”2.4”> <servlet> <servlet-name>Servlet</servlet-name> <servlet-class>Ch1Servlet</servlet-class> </servlet>

<servlet-mapping> <servlet-name>Servlet</servlet-name> <url-pattern>/Serv1</url-pattern> </servlet-mapping></web-app>

Save this deployment descriptor

(DD) to web.xml

Servlet: deploy (2)

Save your files in your file system

Servlet: deploy (3) and use

• Compile• Transfer to Tomcat’s file system• Start Tomcat• Click path in your browser

But …

• Stuff HTML as a string into java (println)?

• Why not stuff Java into HTML (or XML)?

Java Server Pages JSP

Apps developer

Web page designer

What is a Container?

What a Container offers?

• Help you to concentrate on your business logic than programming details– Communication– Lifecycle Management– Multithreading Support– Declarative Security– JSP Support

How the Container handles requests?

Back to the code (servlet.java) import javax.servlet.*;import javax.servlet.http.*;import java.io.*;

public class Ch1Servlet extends HttpServlet { public void doGet(HttpServletRequest request,

HttpServletResponse response) throws IOException {

Questions

• Where service() comes from?• How the container finds the correct servlet?• Does the URL define where exactly the servlet

is?

• Possible answers– The user gives precise URL– The container’s tool does the mapping– We store the mapping to the properties table

Three different names for a servlet

Why?

• Flexibility• Security

Map URLs top Servlet with DD

Deployment Descriptor (DD) has 2 elements

<web-app ...>

<servlet> <servlet-name>Internal name 1</servlet-name> <servlet-class>foo.Servlet1</servlet-class> </servlet> <servlet> <servlet-name>Internal name 2</servlet-name> <servlet-class>foo.Servlet2</servlet-class> </servlet>

<servlet-mapping> <servlet-name>Internal name 1</servlet-name> <url-pattern>/Public1</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>Internal name 2</servlet-name> <url-pattern>/Public2</url-pattern> </servlet-mapping>

</web-app>