Chapter 4: Core Web Technologies

Contents - Chapter 1 Exchanging information over the Internet HTTP, HTML URI, URI Web server, web browser Web services for supporting remote clients Applets Common Gateway Interface (CGI) Servlets Application servers Middleware for Web applications J2EE Web technologies for application integration Middleware extensions Firewalls and tunneling

Before and after the web Early protocols, applications Telnet: to log in to a remote machine SMTP: Simple Mail Transfer Protocol FTP: File Transfer Protocol Archie: FTP to create a distributed file system Gopher: GUI for publishing and accessing text files over the Internet Web technologies Web server Web browser HTTP: HyperText Transfer Protocol HTML: HyperText Markup Language URI: Uniform Resource Identifier URL: Uniform Resource Locator

wide area network (Internet) Proxy HTTP tunnel firewall firewall HTTP client HTTP proxy HTTP gateway HTTP server wide area network (Internet) Acts as a server and client Caching Block undesired sites Log usage Bypass blocks Scan outgoing traffic

wide area network (Internet) Gateway HTTP tunnel firewall firewall HTTP client HTTP proxy HTTP gateway HTTP server wide area network (Internet) Acts as an intermediary for a server Keeps machines anonymous Controls access to the network Performs load-balancing, authentication, decryption

wide area network (Internet) Firewall HTTP tunnel firewall firewall HTTP client HTTP proxy HTTP gateway HTTP server wide area network (Internet) Blocks unauthorized access, permits authorized communications permit / deny / encrypt / decrypt / proxy all computer traffic between different security domains

wide area network (Internet) Tunnel HTTP tunnel firewall firewall HTTP client HTTP proxy HTTP gateway HTTP server wide area network (Internet) Acts as a blind relay between two connections Encapsulate protocols within HTTP or SSH (Secure Shell) to get through what the firewall would prevent

Secure Socket Layer (SSL) HTTPS client HTTPS server application layer network layer Secure Sockets Layer (SSL) TCP/IP Normally HTTP traffic is not encrypted, it can be “sniffed” SSL uses public key encryption HTTPS: HyperText Transfer Protocol over Secure sockets layer HTTP “cookies” are used to store data on the client machine

A 3-tier architecture on the web client client HTTP server HTTP client wide area network (Internet) middleware “Let’s put an ATM” in every home” Business-to-consumer (B2C) interaction The web browser is a universal client server (resource manager) Copyright Springer Verlag Berlin Heidelberg 2004

Applets firewall wide area network (Internet) middleware Web server client applet java virtual machine browser wide area network (Internet) HTTP is a document exchange protocol, it’s static Applets are downloadable programs The server sends the appropriate program each time The web browser becomes a universal client Code must be small for rapid transfer middleware server (resource manager) Copyright Springer Verlag Berlin Heidelberg 2004

Common Gateway Interface HTTP GET request Web server browser firewall client CGI program wide area network (Internet) middleware The CGI program is on the server and it has a URL When the URL is accessed, the CGI program is executed and its output is saved as an HTML document This saved document is returned to the web browser which then displays it It is possible to pass parameters to CGI programs server (resource manager) Copyright Springer Verlag Berlin Heidelberg 2004

Servlets firewall HTTP GET request wide area network (Internet) Web server Java server process HTTP GET request firewall browser Java thread client Similar to CGI, but “lightweight” Run as Java threads Saves the cost of context switching Memory efficient Can be stateless wide area network (Internet) middleware server (resource manager) Copyright Springer Verlag Berlin Heidelberg 2004

Application servers CHAPTER 2 FIGURE 2 -section 1.2 firewall other protocols client other servers (email, SOAP,..) Web server browser HTTP firewall presentation layer It’s a middleware platform that provides support for Web access Covers both the application logic and the presentation layer Prepares, dynamically generates, manages document wide area network (Internet) application logic layer connection to resource mgmt layer CHAPTER 2 FIGURE 2 -section 1.2 application server resource management layer Copyright Springer Verlag Berlin Heidelberg 2004

J2EE – main components support for communication and presentation Servlets JavaServer Pages (JSP) Java API for XML Processing (JAXP) JavaMail support for communication and presentation Java Authentication and Authorization Service (JAAS) Enterprise Java Beans (EJB) Java transaction API (JTA) support for the application integration Java Message Service (JMS) Java Naming and Directory Interface (JNDI) Java DataBase Connectivity (JDBC) Java 2 Connector Architecture (J2CA) support for access to resource managers Copyright Springer Verlag Berlin Heidelberg 2004

presentation layer application logic layer EJB EJB EJB (load balancing, pooling, caching, transaction, persistence,…) services EJB container (management and security) administration JNDI JMS JDBC J2CA resource adapter J2CA resource adapter other adapters application server DBMS applications enterprise system 1 enterprise system 2 enterprise system n Copyright Springer Verlag Berlin Heidelberg 2004

application logic layer client servers for other connections (e.g., WAP) E-mail server Web server multidevice content delivery (load balancing, pooling, caching,…) services Servlets JSPs XML support Web services support (management and security) administration personalization logic presentation layer application logic layer connection to resource mgmt layer application server resource management layer Copyright Springer Verlag Berlin Heidelberg 2004

Possible ways to connect client client middleware wide area network (Internet) middleware server (resource manager) server (resource manager) Copyright Springer Verlag Berlin Heidelberg 2004

Direct integration of middleware platforms client client middleware middleware remote-middleware protocol remote-middleware protocol WAN communication protocol wide area network (Internet) WAN communication protocol server (resource manager) server (resource manager) Copyright Springer Verlag Berlin Heidelberg 2004

wide area network (Internet) HTTP tunnel firewall firewall client Web server Web server client wide area network (Internet) middleware middleware remote-middleware protocol remote-middleware protocol WAN communication protocol WAN communication protocol server (resource manager) server (resource manager) Copyright Springer Verlag Berlin Heidelberg 2004

Summary Decades of accumulated knowledge on multi-tier architectures Use the same technology over the Internet The client can be on A Local Area Network (LAN) Over the Internet Architectural implications and design constraints from using the Web are important