Configuring a Filter Configuring Filters

14-2 Developing Web Applications, Servlets, and JSPs for Oracle WebLogic Server bottom of the chain. This process continues in reverse order up through the chain of filters.

14.1.2 Uses for Filters

Filters can be useful for the following functions: ■ Implementing a logging function ■ Implementing user-written security functionality ■ Debugging ■ Encryption ■ Data compression ■ Modifying the response sent to the client. However, post processing the response can degrade the performance of your application.

14.2 Writing a Filter Class

To write a filter class, implement the javax.servlet.Filter interface see http:java.sun.comj2eetutorialapijavaxservletFilter.html . You must implement the following methods of this interface: ■ init ■ destroy ■ doFilter You use the doFilter method to examine and modify the request and response objects, perform other tasks such as logging, invoke the next filter in the chain, or block further processing. Several other methods are available on the FilterConfig object for accessing the name of the filter, the ServletContext and the filters initialization attributes. For more information see the J2EE Javadocs for javax.servlet.FilterConfig at http:java.sun.comj2eetutorialapiindex.html . To access the next item in the chain either another filter or the original resource, if that is the next item in the chain, call the FilterChain.doFilter method.

14.3 Configuring Filters

You configure filters as part of a Web application, using the applications web.xml deployment descriptor. In the deployment descriptor, you specify the filter and then map the filter to a URL pattern or to a specific servlet in the Web application. You can specify any number of filters.

14.3.1 Configuring a Filter

To configure a filter: 1. Open the web.xml deployment descriptor in a text editor or use the Administration Console. For more information, see Section 2.4, Web Application Note: The filter can modify the headers only if the response has not already been committed. Filters 14-3 Developer Tools . The web.xml file is located in the WEB-INF directory of your Web application. 2. Add a filter declaration. The filter element declares a filter, defines a name for the filter, and specifies the Java class that executes the filter. The filter element must directly follow the context-param element and directly precede the listener and servlet elements. For example: context-paramParamcontext-param filter icon small-iconMySmallIcon.gifsmall-icon large-iconMyLargeIcon.giflarge-icon icon filter-namemyFilterfilter-name display-nameMy Filterdisplay-name descriptionThis is my filterdescription filter-classexamples.myFilterClassfilter-class filter listenerListenerlistener servletServletservlet The icon, description, and display-name elements are optional. 3. Specify one or more initialization attributes inside a filter element. For example: filter icon small-iconMySmallIcon.gifsmall-icon large-iconMyLargeIcon.giflarge-icon icon filter-namemyFilterfilter-name display-nameMy Filterdisplay-name descriptionThis is my filterdescription filter-classexamples.myFilterClassfilter-class init-param param-namemyInitParamparam-name param-valuemyInitParamValueparam-value init-param filter Your Filter class can read the initialization attributes using the FilterConfig.getInitParameter or FilterConfig.getInitParameters methods. 4. Add filter mappings. The filter-mapping element specifies which filter to execute based on a URL pattern or servlet name. The filter-mapping element must immediately follow the filter elements. – To create a filter mapping using a URL pattern, specify the name of the filter and a URL pattern. URL pattern matching is performed according to the rules specified in the Servlet 2.4 Specification at http:java.sun.comproductsservletdownload.htmlspecs , in section 11.1. For example, the following filter-mapping maps myFilter to requests that contain myPattern. filter-mapping filter-namemyFilterfilter-name url-patternmyPatternurl-pattern filter-mapping 14-4 Developing Web Applications, Servlets, and JSPs for Oracle WebLogic Server – To create a filter mapping for a specific servlet, map the filter to the name of a servlet that is registered in the Web application. For example, the following code maps the myFilter filter to a servlet called myServlet: filter-mapping filter-namemyFilterfilter-name servlet-hamemyServletservlet-name filter-mapping 5. To create a chain of filters, specify multiple filter mappings. For more information, see Section 14.3.2, Configuring a Chain of Filters .