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Developing Web Applications, Servlets, and JSPs for WebLogic Server

# Creating and Configuring Web Applications

The following sections describe how to create and configure Web application resources.

- Directory Structure
- Main Steps to Create and Configure a Web Application
- Configuring How a Client Accesses a Web Application
- Configuring Virtual Hosts for Web Applications
- Targeting Web Applications to Virtual Hosts
- Loading Servlets, Context Listeners, and Filters
- Shared J2EE Web Application Libraries

# Directory Structure

Web applications use a standard directory structure defined in the J2EE specification. You can deploy a Web application as a collection of files that use this directory structure, known as exploded directory format, or as an archived file called a WAR file. BEA recommends that you package and deploy your exploded Web application as part of an Enterprise application. This is a BEA best practice, which allows for easier application migration, additions, and changes. Also, packaging your Web application as part of an Enterprise application allows you to take advantage of the split development directory structure, which provides a number of benefits over the traditional single directory structure.

The WEB-INF directory contains the deployment descriptors for the Web application (web.xml and weblogic.xml) and two subdirectories for storing compiled Java classes and library JAR files. These subdirectories are respectively named classes and lib. JSP taglibs are stored in the WEB-INF directory at the top level of the staging directory. The Java classes include servlets, helper classes and, if desired, precompiled JSPs.

All servlets, classes, static files, and other resources belonging to a Web application are organized under a directory hierarchy.

  `DefaultWebApp/`

  Place your static files, such as HTML files and JSP files in the directory that is the document root of your Web application. In the default installation of WebLogic Server, this directory is called `DefaultWebApp`, under user_domains/mydomain/applications.

  (To make your Web application the default Web application, you must set context-root to "/" in the weblogic.xml deployment descriptor file.)

  `DefaultWebApp/WEB-INF/web.xml`

  The Web application deployment descriptor that configures the Web application.

  `DefaultWebApp/WEB-INF/weblogic.xml`

  The WebLogic-specific deployment descriptor file that defines how named resources in the `web.xml` file are mapped to resources residing elsewhere in WebLogic Server. This file is also used to define JSP and HTTP session attributes.

  `DefaultWebApp/WEB-INF/classes`

  Contains server-side classes such as HTTP servlets and utility classes.

  `DefaultWebApp/WEB-INF/lib`

  Contains JAR files used by the Web application, including JSP tag libraries.

The entire directory, once staged, is bundled into a WAR file using the jar command. The WAR file can be deployed alone or as part of an Enterprise application (recommended) with other application components, including other Web applications, EJB components, and WebLogic Server components.

JSP pages and HTTP servlets can access all services and APIs available in WebLogic Server. These services include EJBs, database connections through Java Database Connectivity (JDBC), JavaMessaging Service (JMS), XML, and more.

## Accessing Information in WEB-INF

The `WEB-INF` directory is not part of the public document tree of the application. No file contained in the `WEB-INF` directory can be served directly to a client by the container. However, the contents of the `WEB-INF` directory are visible to servlet code using the getResource and getResourceAsStream() method calls on the ServletContext or includes/forwards using the RequestDispatcher. Hence, if the application developer needs access, from servlet code, to application specific configuration information that should not be exposed directly to the Web client, the application developer may place it under this directory.

Since requests are matched to resource mappings in a case-sensitive manner, client requests for `/WEB-INF/foo', `/WEb-iNf/foo', for example, should not result in contents of the Web application located under /WEB-INF being returned, nor any form of directory listing thereof.

## Directory Structure Example

The following is an example of a Web application directory structure, in which myWebApp/ is the staging directory:

Listing 3-1 Web Application Directory Structure

>     myWebApp/

>     	WEB-INF/

>     		web.xml

>     		weblogic.xml

>     		lib/

>     			MyLib.jar

>     		classes/

>     			MyPackage/

>     				MyServlet.class

>     	index.html

>     	index.jsp

# Main Steps to Create and Configure a Web Application

The following steps summarize the procedure for creating a Web application as part of an Enterprise application using the split development directory structure. See Creating a Split Development Directory for an Application, Building the Applications, and Deploying the Application in Developing Applications with WebLogic Server.

You may want to use developer tools included with WebLogic Server for creating and configuring Web applications. See Web Application Developer Tools.

## Step One: Create the Enterprise Application Wrapper

1. Create a directory for your root EAR file:

\src\myEAR\

2. Set your environment as follows:

- On Windows NT, execute the setWLSEnv.cmd command, located in the directory server\bin\, where server is the top-level directory in which WebLogic Server is installed.
- On UNIX, execute the setWLSEnv.sh command, located in the directory server/bin/, where server is the top-level directory in which WebLogic Server is installed and domain refers to the name of your domain.

3. Package your Enterprise application in the \src\myEAR\ directory as follows:

1. Place the Enterprise applications descriptors (`application.xml` and `weblogic-application.xml`) in the META-INF\ directory. See Enterprise Application Deployment Descriptors in Developing Applications with WebLogic Server.
2. Edit the deployment descriptors as needed to fine-tune the behavior of your Enterprise application. See Web Application Developer Tools.
3. Place the Enterprise application .jar files in:

\src\myEAR\APP-INF\lib\

## Step Two: Create the Web Application

1. Create a directory for your Web application in the root of your EAR file:

\src\myEAR\myWebApp

2. Package your Web application in the \src\myEAR\myWebApp\ directory as follows:

1. Place the Web application descriptors (web.xml and weblogic.xml) in the \src\myEAR\myWebApp\WEB-INF\ directory. See weblogic.xml Deployment Descriptor Elements.
2. Edit the deployment descriptors as needed to fine-tune the behavior of your Enterprise application. See Web Application Developer Tools.
3. Place all HTML files, JSPs, images and any other files referenced by the Web application pages in the root of the Web application:

\src\myEAR\myWebApp\images\myimage.jpg

\src\myEAR\myWebApp\login.jsp

\src\myEAR\myWebApp\index.html

4. Place your Web application Java source files (servlets, tag libs, other classes referenced by servlets or tag libs) in:

\src\myEAR\myWebApp\WEB-INF\src\

## Step Three: Creating the build.xml File

Once you have set up your directory structure, you create the build.xml file using the weblogic.BuildXMLGen utility.

## Step Four: Execute the Split Development Directory Structure Ant Tasks

1. Execute the wlcompile Ant task to invoke the javac compiler. This compiles your Web application Java components into an output directory: /build/myEAR/WEB-INF/classes.
2. Execute wlappc Ant task to invoke the appc compiler. This compiles any JSPs and container-specific EJB classes for deployment.
3. Execute the wldeploy Ant task to deploy your Web application as part of an archived or exploded EAR to WebLogic Server.
4. If this is a production environment (rather than development), execute the wlpackage Ant task to package your Web application as part of an archived or exploded EAR.

Note: The wlpackage Ant task places compiled versions of your Java source files in the build directory. For example: /build/myEAR/myWebApp/classes.

# Configuring How a Client Accesses a Web Application

You construct the URL that a client uses to access a Web application using the following pattern:

http://`hoststring`/`ContextPath`/`servletPath`/`pathInfo`

Where

  `hoststring`

  is either a host name that is mapped to a virtual host or `hostname:portNumber`.

  `ContextPath`

  is the name of your Web application.

  `servletPath`

  is a servlet that is mapped to the `servletPath`.

  `pathInfo`

  is the remaining portion of the URL, typically a file name.

If you are using virtual hosting, you can substitute the virtual host name for the `hoststring` portion of the URL.

# Configuring Virtual Hosts for Web Applications

WebLogic Server supports two methods for configuring virtual hosts for Web applications:

- channel based
- host based

## Configuring a Channel-based Virtual Host

The following is an example of how to configure a channel-based virtual host:

>     <VirtualHost Name="channel1vh" NetworkAccessPoint="Channel1" Targets="myserver"/>

>     <VirtualHost Name="channel2vh" NetworkAccessPoint="Channel2" Targets="myserver"/>

Where Channel1 and Channel2 are the names of NetworkAccessPoint configured in the config.xml file. NetworkAccessPoint represents the dedicated server channel name for which the virtual host serves HTTP requests. If the NetworkAccessPoint for a given HTTP request does not match the NetworkAccessPoint of any virtual host, the incoming HOST header is matched with the VirtualHostNames in order to resolve the correct virtual host. If an incoming request does not match a virtual host, the request will be served by the default Web server.

## Configuring a Host-based Virtual Host

The following is an example of how to configure a host-based virtual host:

>     <VirtualHost Name="cokevh" Targets="myserver" VirtualHostNames="coke"/>

>     <VirtualHost Name="pepsivh" Targets="myserver" VirtualHostNames="pepsi"/>

# Targeting Web Applications to Virtual Hosts

A Web application component can be targeted to servers and virtual hosts using the WebLogic Administration Console.

If you are migrating from previous versions of WebLogic Server, note that in the config.xml file, all Web application targets must be specified in the targets attribute. The targets attribute has replaced the virtual hosts attribute and a virtual host cannot have the same name as a server or cluster in the same domain. The following is an example of how to target a Web application to a virtual host:

>     <AppDeployment name="test-app" Sourcepath="/myapps/test-app.ear">
>        <SubDeployment Name="test-webapp1.war" Targets="virutalhost-1"/>
>        <SubDeployment Name="test-webapp2.war" Targets="virtualhost-2"/>
>        ...
>     </AppDeployment>

# Loading Servlets, Context Listeners, and Filters

Servlets, Context Listeners, and Filters are loaded and destroyed in the following order:

Order of loading:

1. Context Listeners
2. Filters
3. Servlets

Order of destruction:

1. Servlets
2. Filters
3. Context Listeners

Servlets and filters are loaded in the same order they are defined in the `web.xml` file and unloaded in reverse order. Context listeners are loaded in the following order:

1. All context listeners in the `web.xml` file in the order as specified in the file
2. Packaged JAR files containing tag library descriptors
3. Tag library descriptors in the WEB-INF directory

# Shared J2EE Web Application Libraries

A J2EE Web application library is a standalone Web application module registered with the J2EE application container upon deployment. Using WebLogic Server 9.1, multiple Web applications can easily share a single Web application module or collection of modules.

A Web application may reference one or more Web application libraries, but cannot reference other library types (EJBs, EAR files, plain JAR files).

Web application libraries are Web application modules deployed as libraries. They are referenced from the `weblogic.xml` file using the same syntax that is used to reference application libraries in the `weblogic-application.xml` file, except that the `<context-root>` element is ignored.

At deployment time, the classpath of each referenced library is appended to the Web application's classpath. Therefore, the search for all resources and classes occurs first in the original Web application and then in the referenced library.

The deployment tools, appc, wlcompile, and BuildXMLGen support libraries at the Web application level in the same way they support libraries at the application level. For more information about shared J2EE libraries and their deployment, see Creating Shared J2EE Libraries and Optional Packages in Developing Applications with WebLogic Server.