Lecture6
- 1. Server-side Web Programming Lecture 6: Java Servlets and the web.xml Configuration File
- 2. Configuration Files Each webapp has a web.xml file In WEB-INF subdirectory Defines: Mapping from servlet names to servlet files Global constants Default error pages Security roles…
- 3. The web.xml file Complex (and finicky) XML If buggy, application will not load Errors displayed in Tomcat window when started NetBeans provides interface to manipulate its values
- 4. The web.xml file Internally, still XML Can view and edit at XML tab Basic form of XML: <tag>text</tag> or <tag/> Tags must be properly balanced and nested Must have a root tag <webapp>
- 5. Welcome Page Properties Page shown at webapp startup Default: index.jsp Can change to a new welcome file
- 6. New Welcome Page Will go to that page when webapp started Note change in web.xml
- 7. Servlet Mapping Web.xml links referrer page to be linked with actual servlet class Mapping from a name to a java class Allows servlet code to be changed without having to rewrite other pages Important since name of class = name of file in Java Mapping from a url pattern to a servlet name Allows servlets to be “hidden” from user Referring file that invokes servlet url pattern used in FORM ACTION web.xml url pattern name name servlet class Java servlet class with actual code
- 8. Servlet Mapping No such file – this is just a url pattern that will refer to an actual servlet via web.xml Added to the url patterns that map to this servlet
- 9. Servlet Mapping Note that the url pattern appears in the browser Code in web.xml that does the servlet mapping
- 10. Initial Parameters Global constants stored in web.xml Better than “hardwiring” values directly into the code Easier for nonprogrammer to modify Form like parameter: name/value Example: “price per unit” in widget site Note that such information is usually in a database However, the name of the database is often an initial parameter! web.xml pricePerUnit=9.95 Java servlet class that needs widget cost
- 11. Initial Parameters Configuration level Specific to single servlet Context level General to all server pages/servlets overall application context … context-level parameters SomeServlet ‘s configuration configuration-level parameters SomeServlet object AnotherServlet ‘s configuration configuration-level parameters AnothereServlet object
- 12. Configuration Parameters Can create in servlet tab
- 13. Configuration Parameters Form of xml tag
- 14. Configuration Parameters Accessing from servlet: Get the servlet configuration ServletConfig config = getServletConfig(); Get the value corresponding to the name of the parameter String value = config.getInitParameter(“ name ");
- 15. Context Parameters Can create in general tab
- 16. Context Parameters Form of xml tag
- 17. Configuration Parameters Accessing from servlet: Get the servlet configuration ServletConfig config = getServletConfig(); Get the webapp context from the configuration ServletContext context = config.getServletContext(); Get the value corresponding to the name of the parameter String value = context.getInitParameter(“ name "); Accessing from a JSP: String value = application.getInitParameter(“ name "); Built-in object in JSP (like “request”)