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Assembling and Configuring Web Applications

Configuring Web Application Components

The following sections describe how to configure Web Application components:

- Configuring Servlets

- Configuring JSP

- Configuring JSP Tag Libraries

- Configuring Welcome Pages

- Setting Up a Default Servlet

- Customizing HTTP Error Responses

- Using CGI with WebLogic Server

- Serving Resources from the CLASSPATH with the ClasspathServlet

- Configuring Resources in a Web Application

- Referencing EJBs in a Web Application

- Determining the Encoding of an HTTP Request

- Mapping IANA Character Sets to Java Character Sets

Configuring Servlets

Servlets are defined as a part of a Web Application in several entries in 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:

- Step 9: Deploy Servlets

- Step 10: Map a servlet to a URL

Servlet Mapping

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>

Table 3-1 url-patterns and Servlet Invocation

URL | Servlet Invoked
--- | ---
http://host:port/mywebapp/fruit/summer/index.html | watermelon
http://host:port/mywebapp/fruit/summer/index.abc | watermelon
http://host:port/mywebapp/seedlist | list
http://host:port/mywebapp/seedlist/index.html | The default servlet, if configured, or an HTTP 404 File Not Found error message. If the mapping for the list servlet had been /seedlist*, the list servlet would be invoked.
http://host:port/mywebapp/seedlist/pear.abc | kiwi If the mapping for the list servlet had been /seedlist*, the list servlet would be invoked.
http://host:port/mywebapp/seeds | garden
http://host:port/mywebapp/seeds/index.html | garden
http://host:port/mywebapp/index.abc | kiwi

Servlet Initialization Parameters

You define initialization parameters for servlets in the Web Application deployment descriptor, web.xml, 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 in web.xml

>     <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

Configuring JSP

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:

- Options for the JSP compiler

- Debugging

- How often WebLogic Server checks for updated JSPs that need to be recompiled

- Character encoding

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.

Configuring JSP Tag Libraries

Weblogic Server lets you create and use custom JSP tags. Custom JSP tags are Java classes you can call 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. You make this TLD 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:

- Using Custom WebLogic JSP Tags.

- Using WebLogic JSP Form Validation Tags.

Configuring Welcome Pages

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:

1. index.html

2. index.htm

3. index.jsp

For more information, see How WebLogic Server Resolves HTTP Requests.

Setting Up a Default Servlet

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:

1. Define your servlet as described in Configuring Servlets.

2. Map your default servlet with a url-pattern of "/". This causes your default servlet to respond to all types of files except for those with extensions of *.htm or *.html, which are internally mapped to the FileServlet.

   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.

3. If you still want the FileServlet to serve files with other extensions:

   1. Define a servlet and give it a <servlet-name>, for example myFileServlet.

   2. Define the <servlet-class> as weblogic.servlet.FileServlet.

   3. Using the <servlet-mapping> element, map file extensions to the myFileServlet (in addition to the mappings for your default servlet). For example, if you want the myFileServlet to serve gif files, map *.gif to the myFileServlet.

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 serve 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.

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.

Configuring WebLogic Server to Use CGI

To configure CGI in WebLogic Server:

1. Declare the CGIServlet in your Web Application by using the <servlet> and <servlet-mapping> elements. The class name for the CGIServlet is weblogic.servlet.CGIServlet. You do not need to package this class in your Web Application.

2. Register the following initialization parameters for the CGIServlet by defining the following <init-param> elements:

     cgiDir

     The path to the directory containing your CGI scripts. You can specify multiple directories, separated by a ";" (Windows) or a ":" (Unix). If you do not specify cgiDir, the directory defaults to a directory named cgi-bin under the Web Application root.

     useByteStream

     The alternate to using the default Char streams for data transfer, this parameter, which is case sensitive, will allow the use of images in the CGI servlet without distortion.

     extension mapping

     Maps a file extension to the interpreter or executable that runs the script. If the script does not require an executable, this initialization parameter may be omitted.

     The <param-name> for extension mappings must begin with an asterisk followed by a dot, followed by the file extension, for example, *.pl.

     The <param-value> contains the path to the interpreter or executable that runs the script. You can create multiple mappings by creating a separate <init-param> element for each mapping.

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>

Requesting a CGI Script

The URL used to request a perl script must follow the pattern:

>     http://host:port/myWebApp/cgi-bin/myscript.pl

Where

  host:port

  Is the host name and port number of WebLogic Server.

  myWebApp

  is the name of your Web Application.

  cgi-bin

  is the url-pattern name mapped to the CGIServlet.

  myscript.pl

  is the name of the Perl script that is located in the directory specified by the cgiDir initialization parameter.

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.

There are two ways that you can use the ClasspathServlet:

- To serve a resource from the system CLASSPATH, call the resource with a URL such as:

  >     http://server:port/classes/my/resource/myClass.class

- To serve a resource from the WEB-INF/classes directory of a Web Application, call the resource with a URL such as:

  >     http://server:port/myWebApp/classes/my/resource/myClass.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

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 Resources in a Web Application

The resources that you use in a Web Application are generally deployed externally to the application. JDBC Datasources can optionally be deployed within the scope of the Web Application as part of an EAR file.

Prior to WebLogic Server 7.0, JDBC DataSources were always deployed externally to the Web Application. To use external resources in the Web Application, you resolve the JNDI resource name that the application uses with the global JNDI resource name using the web.xml and weblogic.xml deployment descriptors. See Configuring External Resources for more information.

WebLogic Server 7.0 enables you deploy JDBC DataSources as part of the Web Application EAR file by configuring those resources in the weblogic-application.xml deployment descriptor. Resources deployed as part of the EAR file are referred to as application-scoped resources. These resources remain private to the Web Application, and application components can access the resource names directly from the local JNDI tree at java:comp/env. See Configuring Application-Scoped Resources for more information.

Configuring External Resources

When accessing external resources (resources not deployed with the application EAR file) such as a DataSource from a Web Application via Java Naming and Directory Interface (JNDI), you can map the JNDI name you look up in your code to the actual JNDI name as bound in the global 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:

1. Enter the resource name in the deployment descriptor as you use it in your code, the Java type, and the security authorization type. For instructions on making deployment descriptor entries, see Step 16: Reference external resources.

2. Map the resource name to the JNDI name. For instructions on making deployment descriptor entries, see Step 3 Map resources to JNDI.

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 an External 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>

Configuring Application-Scoped Resources

WebLogic Server binds application-scoped resource names to the application's local JNDI tree. The Web Application code accesses these resources by looking up the actual JNDI resource name relative to java:comp/env.

If your Web Application uses only application-scoped resources, you do not need to enter global JNDI resources names in the weblogic.xml deployment descriptor, as described in Configuring External Resources. (In fact, you can omit weblogic.xml entirely if you do not require any other features of that deployment descriptor.)

To configure application-scoped resources:

1. Enter the resource definition in the weblogic-application.xml deployment descriptor. See weblogic-application.xml Deployment Descriptor Elements in Developing WebLogic Server Applications for more information.

2. Ensure that Web Application code uses the same JNDI name specified in weblogic-application.xml, and that it references the name relative to the local JNDI tree at java:comp/env.

   Note: If Web Application code uses a different JNDI name to reference the resource, you must treat the resource as external and configure the weblogic.xml deployment descriptor as describe in the next section.

Listing 3-5 Example of Using an External DataSource

>     Servlet code:
>     javax.sql.DataSource ds = (javax.sql.DataSource) ctx.lookup
>                                ("java:comp/env/myDataSource");

>     weblogic-application.xml entries:

>     <weblogic-application>
>        <data-source-name>myDataSource</data-source-name>
>     </weblogic-application>

Referencing EJBs in a Web Application

EJBs that you use in a Web Application can be deployed either externally to the application, or deployed within the scope of the Web Application as part of an EAR file. The procedures for referencing an EJB differ depending on whether the EJB is external or application-scoped.

Referencing External EJBs

Web Applications can access EJBs that are deployed as part of a different application (a different EAR file) by using an external reference. The EJB being referenced exports a name to the global JNDI tree in its weblogic-ejb-jar.xml deployment descriptor. An EJB reference in the Web Application module can be linked to this global JNDI name by adding an <ejb-reference-description> element to its weblogic.xml 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 external EJB for use in a Web Application:

1. Enter the EJB reference name you use to look up the EJB in your code, the Java class name, and the class name of the home and remote interfaces of the EJB in the <ejb-ref> element of the Web Application deployment descriptor. For instructions on making deployment descriptor entries, see Step 21: Reference Enterprise JavaBean (EJB) resources

2. Map the reference name in <ejb-reference-description> element of the WebLogic-specific deployment descriptor, weblogic.xml, to the JNDI name defined in the weblogic-ejb-jar.xml file. For instructions on making deployment descriptor entries, see Step 3 Map resources to JNDI.

   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.

Referencing Application-Scoped EJBs

Within an application, WebLogic Server binds any EJBs referenced by other application components to the environments associated with those referencing components. These resources are accessed at runtime through a JNDI name lookup relative to java:comp/env.

The following is an example of an application deployment descriptor (application.xml) for an application containing an EJB and a Web Application. (The XML header is not included for brevity.)

Listing 3-6 Example Deployment Descriptor

>       <application>

>          <display-name>MyApp</display-name>

>          <module>

>             <web>

>                <web-uri>myapp.war</web-uri>

>                <context-root>myapp</context-root>

>             </web>

>          </module>

>          <module>

>             <ejb>ejb1.jar</ejb>

>          </module>

>       </application>

To allow the code in the Web application to use an EBJ in ejb1.jar, the Web application deployment descriptor (web.xml) must include an <ejb-ref> stanza that contains an <ejb-link> referencing the JAR file and the name of the EJB that is being called.

The format of the <ejb-link> entry must be as follows:

>     filename#ejbname

where filename is the name of the JAR file, relative to the Web application, and ejbname is the EJB within that JAR file. The <ejb-link> element should look like the following:

>     <ejb-link>../ejb1.jar#myejb</ejb-link>

Note that since the JAR path is relative to the WAR file, it begins with "../". Also, if the ejbname is unique across the application, the JAR path may be dropped. As a result, your entry may look like the following:

>     <ejb-link>myejb</ejb-link>

The <ejb-link> element is a sub-element of an <ejb-ref> element contained in the Web application's web.xml descriptor. The <ejb-ref> element should look like the following:

Listing 3-7 <ejb-ref> Element

>      <web-app>

>        ...

>        <ejb-ref>

>           <ejb-ref-name>ejb1</ejb-ref-name>

>           <ejb-ref-type>Session</ejb-ref-type>

>           <home>mypackage.ejb1.MyHome</home>

>           <remote>mypackage.ejb1.MyRemote</remote>

>           <ejb-link>../ejb1.jar#myejb</ejb-link>

>        </ejb-ref>

>        ...

>      </web-app>

The name referenced in the <ejb-link> (in this example, myejb) corresponds to the <ejb-name> element of the referenced EJB's descriptor. As a result, the deployment descriptor (ejb-jar.xml) of the EJB module that this <ejb-ref> is referencing should have an entry an entry similar to the following:

Listing 3-8

>      <ejb-jar>

>        ...

>        <enterprise-beans>

>           <session>

>              <ejb-name>myejb</ejb-name>

>              <home>mypackage.ejb1.MyHome</home>

>              <remote>mypackage.ejb1.MyRemote</remote>

>              <ejb-class>mypackage.ejb1.MyBean</ejb-class>

>              <session-type>Stateless</session-type>

>              <transaction-type>Container</transaction-type>

>           </session>

>        </enterprise-beans>

>        ...

>      </ejb-jar>

Notice the <ejb-name> element is set to myejb.

Note: For more instructions on creating deployment descriptor entries, see Step 21: Reference Enterprise JavaBean (EJB) resources.

At runtime, the Web Application code looks up the EJB's JNDI name relative to java:/comp/env. The following is an example of the servlet code:

>     MyHome home = (MyHome)ctx.lookup("java:/comp/env/ejb1");

The name used in this example (ejb1) is the <ejb-ref-name> defined in the <ejb-ref> element of the web.xml segment above.

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:

- For a POST operation, you can set the encoding in the HTML <form> tag. For example, this form tag sets SJIS as the character set for the content:

  >     <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.

- Because all Web clients do not transmit the information after the semicolon in the above example, you can set the codeset to be used for requests by using the <input-charset> element in the WebLogic-specific deployment descriptor, weblogic.xml. The <java-charset-name> element defines the encoding used to convert data when the URL of the request contains the path specified with the <resource-path> element.

  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 from 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>