Servlet API packages

The Servlet API is a specification published by the Java Software division of Sun Microsystems. It outlines classes, methods, and behaviors required by Java Servlets and servers that support Java Servlets. JRun Version 4.0 supports the Java Servlet Specification Version 2.3.

The Servlet API includes the following packages:

javax.servlet
javax.servlet.http

JRun ships with full online Servlet API documentation, located in jrun_root/docs/api. You can also access the latest API documentation from http://java.sun.com/products/servlet.

javax.servlet

The javax.servlet package contains interfaces, classes, and exceptions that apply to all servlets, as the following tables explain.

javax.servlet interfaces

The following table describes the interfaces in javax.servlet:

Interface

Description

RequestDispatcher

Defines an object that forwards processing of a request to another servlet, JSP, or HTML file. Also lets you include the output of another servlet in the response.

Servlet

Defines methods to initialize a servlet instance, process a request, and destroy a servlet instance. The GenericServlet class implements this interface.

ServletConfig

Defines an object that passes information to the servlet's init method. Contains name/value pairs, the servlet's name, and a reference to the web application's ServletContext object.

ServletContext

Defines methods that a servlet uses to access information about the servlet container. Also includes application init parameters. There is one ServletContext per web application per virtual machine.

ServletRequest

Defines an object that encapsulates client request information. Each instance includes name/value pairs, attributes, and an input stream.

ServletResponse

Defines an object that encapsulates information returned to the client. You can send binary data or character data.

SingleThreadModel

Defines an object that ensures that each servlet instance executes only one request at a time. For more information on this interface, see the servlet API JavaDoc.

Interface	Description
RequestDispatcher	Defines an object that forwards processing of a request to another servlet, JSP, or HTML file. Also lets you include the output of another servlet in the response.
Servlet	Defines methods to initialize a servlet instance, process a request, and destroy a servlet instance. The `GenericServlet` class implements this interface.
ServletConfig	Defines an object that passes information to the servlet's `init` method. Contains name/value pairs, the servlet's name, and a reference to the web application's `ServletContext` object.
ServletContext	Defines methods that a servlet uses to access information about the servlet container. Also includes application init parameters. There is one `ServletContext` per web application per virtual machine.
ServletRequest	Defines an object that encapsulates client request information. Each instance includes name/value pairs, attributes, and an input stream.
ServletResponse	Defines an object that encapsulates information returned to the client. You can send binary data or character data.
SingleThreadModel	Defines an object that ensures that each servlet instance executes only one request at a time. For more information on this interface, see the servlet API JavaDoc.

javax.servlet classes

The following table describes the classes in javax.servlet:

Class

Description

GenericServlet

Protocol-independent servlet. You typically use HttpServlet instead of this class.

ServletInputStream

Stream for reading binary data from a client request. You typically do not use this class.

ServletOutputStream

Stream for sending binary data to a client. You typically do not use this class.

Class	Description
GenericServlet	Protocol-independent servlet. You typically use `HttpServlet` instead of this class.
ServletInputStream	Stream for reading binary data from a client request. You typically do not use this class.
ServletOutputStream	Stream for sending binary data to a client. You typically do not use this class.

javax.servlet exceptions

The following table describes the exceptions in javax.servlet:

Exception

Description

ServletException

Indicates problems in a servlet.

UnavailableException

Indicates that a servlet is unavailable. You can use this exception to indicate either temporary or permanent unavailability.

Exception	Description
ServletException	Indicates problems in a servlet.
UnavailableException	Indicates that a servlet is unavailable. You can use this exception to indicate either temporary or permanent unavailability.

javax.servlet.http

The javax.servlet.http package contains interfaces and classes that apply to servlets requiring HTTP functionality, as the following tables explain.

javax.servlet.http interfaces

The following table describes the interfaces in javax.servlet.http:

Interface

Description

HttpServletRequest

Extends ServletRequest for HTTP servlets. Use this object to access cookies, attributes, and other information for the request.

HttpServletResponse

Extends ServletResponse for HTTP servlets. Use this object to send a response to the browser.

HttpSession

Contains user information that persists across page requests. Sessions are keyed by session ID, which is maintained either in cookies or by URL parameters.

HttpSessionBinding Listener

Notifies objects when they are bound or unbound from a session. Use this interface to initialize and clean up session-specific resources.

Interface	Description
HttpServletRequest	Extends `ServletRequest` for HTTP servlets. Use this object to access cookies, attributes, and other information for the request.
HttpServletResponse	Extends `ServletResponse` for HTTP servlets. Use this object to send a response to the browser.
HttpSession	Contains user information that persists across page requests. Sessions are keyed by session ID, which is maintained either in cookies or by URL parameters.
HttpSessionBinding Listener	Notifies objects when they are bound or unbound from a session. Use this interface to initialize and clean up session-specific resources.

javax.servlet.http classes

The following table describes the classes in javax.servlet.http:

Class

Description

Cookie

Lets servlets create, read, and modify client cookies. Read cookies using the HttpServletRequest object. Set cookies using the HttpServletResponse object.

HttpServlet

Abstract class that you extend to create HTTP servlets. Use this class for all web-oriented servlets.

HttpSessionBindingEvent

Contains two methods, getName and getSession.

Passed to objects that implement the HttpSessionBindingListener interface when they are bound or unbound from a session.

HttpUtils

Contains useful utility methods. Methods include getRequestURL, parsePostData, and parseQueryString.

Class	Description
Cookie	Lets servlets create, read, and modify client cookies. Read cookies using the `HttpServletRequest` object. Set cookies using the `HttpServletResponse` object.
HttpServlet	Abstract class that you extend to create HTTP servlets. Use this class for all web-oriented servlets.
HttpSessionBindingEvent	Contains two methods, `getName` and `getSession`. Passed to objects that implement the `HttpSessionBindingListener` interface when they are bound or unbound from a session.
HttpUtils	Contains useful utility methods. Methods include `getRequestURL`, `parsePostData`, and `parseQueryString`.

Programmer's Guide
Servlet Programming Techniques