Web Application Deployment
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This document provides an overview of key concepts for deploying web applications in Java, including: 1) Session tracking is provided by the HttpSession object returned by the getSession() method, which can store attributes. 2) A web application typically includes HTML, images, servlets, source code, libraries and other resources. 3) The server is responsible for mapping URLs to the location of a web application based on a specific prefix. 4) The standard structure for a web application includes the /WEB-INF directory for private resources and configuration files.
Web Application Deployment
- 1. Web Application Deployment COMP 118 Spring 2003
- 2. Help from Java Session tracking is provided by Java servlet API. HttpSession object Returned by getSession method of request. Can store info in session object as named attributes. setAttribute, getAttribute Other methods to configure session timeout, get information about session, etc. Uses cookies.
- 3. Example 3 Same as example 2, but uses built in Java session support.
- 4. Example 3 discussion What happens is cookies are disabled? Can use URL rewriting, but need to let servlet encode URL’s with session id. Use encodeURL method of request object Does rewrites URL with session id embedded as additional parameter is cookies are turned off. Returns URL unchanged if cookies turned on.
- 5. Java Servlet API Documentation on Java Servlet API A good book. Java Servlet Programming by Jason Hunter, published by O’Reilly Unfortunately, pretty expensive.
- 6. Web Application Deployment Typically a web application is comprised of: HTML pages Data Images Servlets Source code Libraries Other resources A servlet is a component of a web application.
- 7. Separating server from web app. Person running the web server and person writing a web application running on that web server may not be the same. Example: a web hosting company runs a web server which “hosts” the sites of several other companies for a fee. What could be problematic about this? Need to isolate customers. Web app developer shouldn’t need to know anything about web server’s installation.
- 8. Standardizing deployment Server products (like Tomcat) have support for setting up resources and isolating one web application from another. Old days: different servers each did things their own way. Now: there is a standard (Servlet 2.4) that defines exactly how a web application is organized and how a server maps requests to it. Note: our version of Tomcat implements 2.3
- 9. Mapping to a web app. The server is responsible for mapping URL’s that start with a specific prefix to the location of a web application. This is the “root” of the web application. In Tomcat, this is done with a configuration file. We have defined a single web application that maps to each of your class directories.
- 10. Web app structure There is a specific organization of the files within a web application that you need to adhere to. /WEB-INF Private resources of a web application that can not be directly served to a client. /WEB-INF/web.xml Deployment descriptor that configures the web application.
- 11. Web app structure /WEB-INF/classes Class files for servlets Directory structure needs to reflect package names. /WEB-INF/lib Libraries (jar) files that may be needed by servlets
- 12. Common code Many web applications may need access to common libraries and classes. Servlet API XML processing libraries Email processing libraries These are put in the server’s root /common/classes /common/lib
- 13. COMP 118 Setup Server: wwwj.cs.unc.edu:8080 To compile correctly, be sure to: setenv JAVA_HOME /usr/java1.2 setenv CLASSPATH /opt/jakarta-4.1.18/common/lib/servlet.jar:.
- 14. web.xml This file contains important configuration information needed to make servlets work. For a servlet to function properly, you need to add a “servlet definition” and a “servlet mapping” for each servlet. /servlet/class_name used to be a shortcut Supposed to work, but doesn’t seem to in the new version. The order of things in web.xml is important. We will put in a template which you can modify.
- 15. Defining Servlets <servlet> <servlet-name>Name</servlet-name> <servlet-class>servlet.class</servlet-class> </servlet>
- 16. Servlet Mapping This determines what URL’s get mapped to the servlet. <servlet-mapping> <servlet-name>Name</servlet-name> <url-pattern>/path</url-pattern> </servlet-mapping>
- 18. Administrivia Examples from class will be put up on the web site. First programming assignment will be put up on the web site by the weekend. Make a home page (index.html) and put it at the top of your class directory. Put a picture and your name on it. Write and deploy a “hello world” servlet to test your environment.
- 19. Initialization Parameters Can use web.xml to provide initialization parameters to a web application. Within servlet definition: <init-param> <param-name>name</param-name> <param-value>value</param-value> </init-param> Example reading book info from file.
- 20. Debugging Our server is set up to log error messages to a file in WEB-INF/logs
- 21. Multithread Issues There is one instance of each servlet deployed which handles every request to that servlet. But, each request is handled in its own thread. When will this cause problems? Problematic if the servlet updates non-local variables (i.e., persistent state). What is the solution? Use Java’s synchronization mechanisms Example using forms to add new books.
- 22. Redirection and Errors Servlet can redirect request sendRedirect() Servlet can generate an error page. sendError() Status codes in documentation for HttpServletResponse
- 23. Generating Your Own Error Pages Server puts together error page to report errors to users. You can configure your web application in order to generate your own error pages. <error-page> <error-code> 400 </error-code> <location> /400.html </location> </error-page>