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Configuring Web Application Components
The following sections describe how to configure Web Application components:
Servlets are registered and configured as a part of a Web Application. To register a servlet, you add several entries to the Web Application deployment descriptor. The first entry, under the <servlet> element, defines a name for the servlet and specifies the compiled class that executes the servlet. (Or, instead of specifying a servlet class, you can specify a JSP page.) This element also contains definitions for initialization parameters and security roles for the servlet. The second entry, under the <servlet-mapping> element, defines the URL pattern that calls this servlet.
For complete instructions on editing the Web Application deployment descriptor, see:
Servlet mapping controls how you access a servlet. The following examples demonstrate how you can use servlet mapping in your Web Application. In the examples, a set of servlet configurations and mappings (from the web.xml deployment descriptor) is followed by a table (see url-patterns and Servlet Invocation) showing the URLs used to invoke these servlets.
Listing 3-1 Servlet Mapping Example
<servlet> <servlet-name>watermelon</servlet-name> <servlet-class>myservlets.watermelon</servlet-class> </servlet>
<servlet> <servlet-name>garden</servlet-name> <servlet-class>myservlets.garden</servlet-class> </servlet>
<servlet> <servlet-name>list</servlet-name> <servlet-class>myservlets.list</servlet-class> </servlet>
<servlet> <servlet-name>kiwi</servlet-name> <servlet-class>myservlets.kiwi</servlet-class> </servlet>
<servlet-mapping> <servlet-name>watermelon</servlet-name> <url-pattern>/fruit/summer/*</url-pattern> </servlet-mapping>
<servlet-mapping> <servlet-name>garden</servlet-name> <url-pattern>/seeds/*</url-pattern> </servlet-mapping>
<servlet-mapping> <servlet-name>list</servlet-name> <url-pattern>/seedlist</url-pattern> </servlet-mapping>
<servlet-mapping> <servlet-name>kiwi</servlet-name> <url-pattern>*.abc</url-pattern> </servlet-mapping>
Servlet Initialization Parameters
You define initialization parameters for servlets in the Web Application deployment descriptor, in the <init-param> element of the <servlet> element, using <param-name> and <param-value> tags. For example:
Listing 3-2 Example of Configuring Servlet Initialization Parameters
<servlet> <servlet-name>HelloWorld2</servlet-name> <servlet-class>examples.servlets.HelloWorld2</servlet-class>
<init-param> <param-name>greeting</param-name> <param-value>Welcome</param-value> </init-param>
<init-param> <param-name>person</param-name> <param-value>WebLogic Developer</param-value> </init-param> </servlet>
For more information on editing the Web Application deployment descriptor, see Writing Web Application Deployment Descriptors.
You deploy JavaServer Pages (JSP) files by placing them in the root (or in a subdirectory below the root) of a Web Application. Additional JSP configuration parameters are defined in the <jsp-descriptor> element of the WebLogic-specific deployment descriptor, weblogic.xml. These parameters define the following functionality:
For a complete description of these parameters, see JSP Parameter Names and Values.
For instructions on editing the weblogic.xml file, see Main Steps to Create the weblogic.xml File.
You can also register a JSP as a servlet using the <servlet> tag. In this example a URL containing /main will invoke myJSPfile.jsp:
<servlet> <servlet-name>myFoo</servlet-name> <jsp-file>myJSPfile.jsp</jsp-file> </servlet>
<servlet-mapping> <servlet-name>myFoo</servlet-name> <url-pattern>/main</url-pattern> </servlet-mapping>
Registering a JSP in this manner allows you to specify the load order, initialization parameters, and security roles for a JSP, just as you would for a servlet.
Weblogic Server provides the ability to create and use custom JSP tags. Custom JSP tags are Java classes that can be called from within a JSP page. To create custom JSP tags, you place them in a tag library and define their behavior in a tag library descriptor (TLD) file. This TLD must be made available to the Web Application containing the JSP by defining it in the Web Application deployment descriptor. It is a good idea to place the TLD file in the WEB-INF directory of your Web Application, because that directory is never available publicly.
In the Web Application deployment descriptor, you define a URI pattern for the tag library. This URI pattern must match the value in the taglib directive in your JSP pages. You also define the location of the TLD. For example, if the taglib directive in the JSP page is:
<%@ taglib uri="myTaglib" prefix="taglib" %>
and the TLD is located in the WEB-INF directory of your Web Application, you would create the following entry in the Web Application deployment descriptor:
<taglib> <taglib-uri>myTaglib</taglib-uri> <tablig-location>WEB-INF/myTLD.tld</taglib-location> </taglib>
You can also deploy a tag library as a .jar file. For more information, see Deploying a JSP Tag Library as a JAR File.
For more information on creating custom JSP tag libraries, see Programming JSP Tag Extensions.
WebLogic Server also includes several custom JSP tags that you can use in your applications. These tags perform caching, facilitate query parameter-based flow control, and facilitate iterations over sets of objects. For more information, see:
WebLogic Server allows you to set a page that is served by default if the requested URL is a directory. This feature can make your site easier to use, because the user can type a URL without giving a specific filename.
Welcome pages are defined at the Web Application level. If your server is hosting multiple Web Applications, you need to define welcome pages separately for each Web Application.
To define Welcome pages, edit the Web Application deployment descriptor, web.xml. For more information, see Step 13: Define welcome pages
If you do not define Welcome Pages, WebLogic Server looks for the following files in the following order and serves the first one it finds:
For more information, see How WebLogic Server Resolves HTTP Requests.
Each Web Application has a default servlet. This default servlet can be a servlet that you specify, or, if you do not specify a default servlet, WebLogic Server uses an internal servlet called the FileServlet as the default servlet. For more information on the FileServlet, see How WebLogic Server Resolves HTTP Requests.
You can register any servlet as the default servlet. Writing your own default servlet allows you to use your own logic to decide how to handle a request that falls back to the default servlet.
Setting up a default servlet replaces the FileServlet and should be done carefully because the FileServlet is used to serve most files, such as text files, HTML file, image files, and more. If you expect your default servlet to serve such files, you will need to write that functionality into your default servlet.
To set up a user-defined default servlet:
If you also want your default servlet to respond to files ending in *.htm or *.html, then you must map those extensions to your default servlet, in addition to mapping "/". For instructions on mapping servlets, see Configuring Servlets.
Note: The FileServlet includes the SERVLET_PATH when determining the source filename if docHome is not specified. As a result, it is possible to explicitly server only files from specific directories by mapping the FileServlet to /dir/*, etc.
Customizing HTTP Error Responses
You can configure WebLogic Server to respond with your own custom Web pages or other HTTP resources when particular HTTP errors or Java exceptions occur, instead of responding with the standard WebLogic Server error response pages.
You define custom error pages in the <error-page> element of the Web Application deployment descriptor (web.xml). For more information on error pages, see error-page Element.
Using CGI with WebLogic Server
WebLogic Server provides functionality to support your legacy Common Gateway Interface (CGI) scripts. For new projects, we suggest you use HTTP servlets or JavaServer Pages.
WebLogic Server supports all CGI scripts through an internal WebLogic servlet called the CGIServlet. To use CGI, register the CGIServlet in the Web Application deployment descriptor (see Sample Web Application Deployment Descriptor Entries for Registering the CGIServlet). For more information, see Configuring Servlets.
Note: It is important to note that a CGI script cannot be served by CGIServlet if the script filename does not have an extension. Filename extensions are required.
Configuring WebLogic Server to use CGI
To configure CGI in WebLogic Server:
Listing 3-3 Sample Web Application Deployment Descriptor Entries for Registering the CGIServlet
<servlet> <servlet-name>CGIServlet</servlet-name> <servlet-class>weblogic.servlet.CGIServlet</servlet-class> <init-param> <param-name>cgiDir</param-name> <param-value> /bea/wlserver6.0/config/mydomain/applications/myWebApp/cgi-bin </param-value> </init-param>
<init-param> <param-name>*.pl</param-name> <param-value>/bin/perl.exe</param-value> </init-param> </servlet>
...
<servlet-mapping> <servlet-name>CGIServlet</servlet-name> <url-pattern>/cgi-bin/*</url-pattern> </servlet-mapping>
The URL used to request a perl script must follow the pattern:
http://host:port/myWebApp/cgi-bin/myscript.pl
Where
Serving Resources from the CLASSPATH with the ClasspathServlet
If you need to serve classes or other resources from the system CLASSPATH, or from the WEB-INF/classes directory of a Web Application, you can use a special servlet called the ClasspathServlet. The ClasspathServlet is useful for applications that use applets or RMI clients and require access to server-side classes. The ClasspathServlet is implicitly registered and available from any application.
The general form for invoking the ClasspathServlet is:
http://server:port[/<context-path>]/classes[/<app>@[<webapp.]]/ <package>.<classname>>.class
where
There are two ways that you can use the ClasspathServlet:
http://server:port/classes/weblogic/myClass.class
http://server:port/classes/myApp@myWebApp/examples/servlets/myC lass.class
In this case, the resource is located in the following directory, relative to the root of the Web Application:
WEB-INF/classes/my/resource/myClass.class
disableStrictCheck relaxes the restriction of the download file type. When disableStrictCheck is set to false, ClasspathServlet only allows downloads of .class files, .war files, .jar files, .ear files, .rar files and .mf files.
To access an applet or another similar file, set disableStrictCheck to true.
Warning: Since the ClasspathServlet serves any resource located in the system CLASSPATH, do not place resources that should not be publicly available in the system CLASSPATH.
Configuring External Resources in a Web Application
When accessing external resources, such as a DataSource from a Web Application via JNDI, you can map the JNDI name you look up in your code to the actual JNDI name as bound in the JNDI tree. This mapping is made using both the web.xml and weblogic.xml deployment descriptors and allows you to change these resources without changing your application code. You provide a name that is used in your Java code, the name of the resource as bound in the JNDI tree, and the Java type of the resource, and you indicate whether security for the resource is handled programmatically by the servlet or from the credentials associated with the HTTP request.
To configure external resources:
This example assumes that you have defined a data source called accountDataSource. For more information, see JDBC Data Sources.
Listing 3-4 Example of Using a DataSource
Servlet code:
javax.sql.DataSource ds = (javax.sql.DataSource) ctx.lookup
("myDataSource");
web.xml entries:
<resource-ref> . . . <res-ref-name>myDataSource</res-ref-name> <res-type>javax.sql.DataSource</res-type> <res-auth>CONTAINER</res-auth> . . . </resource-ref>
weblogic.xml entries:
<resource-description> <res-ref-name>myDataSource</res-ref-name> <jndi-name>accountDataSource</jndi-name> </resource-description>
Referencing EJBs in a Web Application
You can reference EJBs in a Web Application by giving them a name in the Web Application deployment descriptor that is mapped to the JNDI name for the EJB that is defined in the weblogic-ejb-jar.xml file deployment descriptor. This procedure provides a level of indirection between the Web Application and an EJB and is useful if you are using third-party EJBs or Web Applications and cannot modify the code to directly call an EJB. In most situations, you can call the EJB directly without using this indirection. For more information, see Invoking Deployed EJBs.
To reference an EJB for use in a Web Application:
If the Web Application is part of an Enterprise Application Archive (.ear file), you can reference an EJB by the name used in the .ear with the <ejb-link> element.
Determining the Encoding of an HTTP Request
WebLogic Server needs to convert character data contained in an HTTP request from its native encoding to the Unicode encoding used by the Java servlet API. In order to perform this conversion, WebLogic Server needs to know which codeset was used to encode the request.
There are two ways you can define the codeset:
<form action="http://some.host.com/myWebApp/foo/index.html"> <input type="application/x-www-form-urlencoded; charset=SJIS"> </form>
When the form is read by WebLogic Server, it processes the data using the SJIS character set.
For example:
<input-charset> <resource-path>/foo/*</resource-path> <java-charset-name>SJIS</java-charset-name> </input-charset>
This method works for both GET and POST operations.
For more information on the Web Application deployment descriptor, see Writing the WebLogic-Specific Deployment Descriptor (weblogic.xml).
Mapping IANA Character Sets to Java Character Sets
The names assigned by the Internet Assigned Numbers Authority (IANA) to describe character sets are sometimes different than the names used by Java. Because all HTTP communication uses the IANA character set names and these names are not always the same, WebLogic Server internally maps IANA character set names to Java character set names and can usually determine the correct mapping. However, you can resolve any ambiguities by explicitly mapping an IANA character set to the name of a Java character set.
To map a IANA character set to a Java character set the character set names in the <charset-mapping> element of the WebLogic-specific deployment descriptor, weblogic.xml. Define the IANA character set name in the <iana-charset-name> element and the Java character set name in the <java-charset-name> element. For example:
<charset-mapping> <iana-charset-name>Shift-JIS</iana-charset-name> <java-charset-name>SJIS</java-charset-name> </charset-mapping>
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