Programming WebLogic HTTP Servlets
The following sections provide an overview of administration and configuration tasks for WebLogic HTTP servlets. For a complete discussion of servlet administration and configuration see Configuring Servlets.
Consistent with the Java 2 Enterprise Edition standard, HTTP servlets are deployed as part of a Web Application. A Web Application is a grouping of application components, such as servlet classes, JavaServer Pages (JSP), static HTML pages, images, and utility classes.
In a Web Application the components are deployed using a standard directory structure. This directory structure can be archived into a file called a
.war file and then deployed on WebLogic Server. Information about the resources and operating parameters of a Web Application are defined using two deployment descriptors, which are packaged with the Web Application.
The first deployment descriptor,
web.xml, is defined in the Servlet 2.3 specification from Sun Microsystems and provides a standardized format that describes the Web Application. The second deployment descriptor,
weblogic.xml, is a WebLogic-specific deployment descriptor that maps resources defined in the
web.xml file to resources available in WebLogic Server, defines JSP behavior, and defines HTTP session parameters.
init()method of the servlet is executed when WebLogic Server starts
For a complete discussion of creating the
web.xml file, see Deployment Descriptors.
For a complete discussion of creating the
weblogic.xml file, see Writing Web Application Deployment Descriptors.
WebLogic Server provides the user with the ability to implement a URL matching utility which does not conform to the J2EE rules for matching. The utility must be configured in the weblogic.xml deployment descriptor rather than the web.xml deployment descriptor used for the configuration of the default implementation of URLMatchMap.
The included SimpleApacheURLMatchMap utility is not J2EE specific. It can be configured in the weblogic.xml deployment descriptor file and allows the user to specify Apache style pattern matching rather than the default URL pattern matching provided in the web.xml deployment descriptor.
Security for servlets is defined in the context of the Web Application containing the servlet. Security can be handled by WebLogic Server, or it can be incorporated programmatically into your servlet classes.
For more information see Securing WebLogic Resourcessecwlres/index.html.
The BASIC and FORM techniques call into a security role that contains user and password information. You can use a default role provided with WebLogic Server, or a variety of existing roles, including roles for Windows NT, UNIX, RDBMS, and user-defined roles. For more information about security roles, see Security Fundamentals.
You can restrict access to servlets and other resources in a Web Application by using security constraints. Security constraints are defined in the Web Application deployment descriptor (
web.xml). There are three basic types of security constraints:
Roles can be mapped to a principal. Specific resources can be constrained by matching a URL pattern to a resource in a Web Application. You can also use Secure Sockets Layer (SSL) as a security constraint.
For more information see the javax.servlet API.
WEB-INF/classesdirectory of your Web Application.
init()method of the servlet is called. All servlets are reloaded when a modified servlet class is discovered due to the possibility that there are interdependencies among the servlet classes.
You can set the interval (in seconds) at which WebLogic Server checks the time stamp with the
Servlet Reload attribute. This attribute is set on the
Descriptor tab of your Web Application, in the Administration Console. If you set this attribute to zero, WebLogic Server checks the time stamp on every request, which can be useful while developing and testing servlets but is needlessly time consuming in a production environment. If this attribute is set to
-1, WebLogic Server does not check for modified servlets.
Clustering servlets provides failover and load balancing benefits. To deploy a servlet in a WebLogic Server cluster, deploy the Web Application containing the servlet on all servers in the cluster. For instructions, see Deploying Applications to a Cluster in Using WebLogic Server Clusters.
For information on requirements for clustering servlets, and to understand the connection and failover processes for requests that are routed to clustered servlets, see Replication and Failover for Servlets and JSPs in Using WebLogic Server Clusters.
Note: Automatic failover for servlets requires that the servlet session state be replicated in memory. For instructions, see Configure In-Memory HTTP Replication in Using WebLogic Server Clusters.
For information on the load balancing support that a WebLogic Server cluster provides for servlets, and for related planning and configuration considerations for architects and administrators, see Load Balancing for Servlets and JSPs in Using WebLogic Server Clusters.