Chapter 26. The javax.servlet.http Package

Cookie	Servlets 2.0
javax.servlet.http	cloneable

The Cookie class provides servlets with an easy way to read, create, and manipulate HTTP-style cookies. Cookies provide a way to store a small amount of information on the client and are typically used for session tracking or storing user-configuration information. The getCookies() method of HttpServletRequest returns an array of Cookie objects. To set a new cookie on the client, a servlet creates a new Cookie object and uses the addCookie() method of HttpServletResponse. This must be done before sending any other content, since cookies are created within the HTTP header stream. The various methods of the Cookie class allow a servlet to set and get various attributes of a Cookie object, such as its path and domain.

Hierarchy: Object-->Cookie(Cloneable)

Passed To: HttpServletResponse.addCookie()

Returned By: HttpServletRequest.getCookies()

HttpServlet	Servlets 1.0
javax.servlet.http	serializable

The abstract HttpServlet class serves as a framework for servlets that generate content for the World Wide Web using the HTTP protocol. Rather than overriding the service() method, you should override one or more of the method-specific request handlers (doGet(), doPost(), doPut(), etc.). The default service() implementation dispatches incoming requests to the appropriate methods, and so should not be overridden. The default implementations of doGet(), doPost(), doDelete(), and doPut() all return an HTTP BAD_REQUEST error, so if you want to handle one of these kinds of requests, you must override the appropriate method.

A web server calls getLastModified() in response to conditional GET requests. The default implementation returns -1. If you know when the output of your servlet last changed, you can return that time, specified in milliseconds since midnight, January 1, 1970 GMT, instead. This allows web browsers to cache your servlet's response.

Hierarchy: Object-->GenericServlet(Servlet,ServletConfig,Serializable)-->HttpServlet(Serializable)

HttpServletRequest	Servlets 1.0
javax.servlet.http

HttpServletRequest extends javax.servlet.ServletRequest and provides a number of methods that make it easy to access specific information related to an HTTP request. This includes methods for directly accessing HTTP headers: getHeader(), getIntHeader(), getDateHeader(), and getHeaderNames(). Other methods return various information about the request, including getMethod(), which returns the request method (GET, POST, etc), getPathInfo(), which returns any extra path information attached to the request, getPathTranslated(), which translates the extra path information into a filesystem path, and getServletPath(), which returns the URI pointing to the current servlet, minus any extra path information. The interface also includes the getCookies() method for retrieving cookie data and getSession() for accessing the current HttpSession object.

Hierarchy: (HttpServletRequest(ServletRequest))

Passed To: HttpServlet.{doDelete(), doGet(), doOptions(), doPost(), doPut(), doTrace(), getLastModified(), service()}, HttpUtils.getRequestURL()

HttpServletResponse	Servlets 1.0
javax.servlet.http

HttpServletResponse extends javax.servlet.ServletResponse and provides additional methods for HTTP-specific actions and a set of HTTP response code constants. The containsHeader(), setHeader(), setDateHeader(), and setIntHeader() methods allow servlets to set and update specific HTTP response headers. The addCookie() method writes a cookie, represented by a Cookie object, to the client. The sendError() and setStatus() methods allow servlets to set specific HTTP result codes, along with an optional customized error message. The encodeUrl() and encodeRedirectUrl() methods (deprecated in 2.1 in favor of encodeURL() and encodeRedirectURL()) methods support session tracking without the use of cookies. The sendRedirect() method handles an HTTP page redirect.

Hierarchy: (HttpServletResponse(ServletResponse))

Passed To: HttpServlet.{doDelete(), doGet(), doOptions(), doPost(), doPut(), doTrace(), service()}

HttpSession	Servlets 2.0
javax.servlet.http

The HttpSession interface is the core of the session tracking functionality introduced in Version 2.0 of the Servlet API. A servlet obtains an HttpSession objects from the getSession() method of HttpServletRequest. The putValue() and removeValue() methods bind Java objects to a particular session. When possible, bound objects should be (but do not need to be) serializable. getValueNames() returns a String array that contains the names of all objects bound to the session.

Passed To: HttpSessionBindingEvent.HttpSessionBindingEvent()

Returned By: HttpServletRequest.getSession(), HttpSessionBindingEvent.getSession(), HttpSessionContext.getSession()

HttpSessionBindingEvent	Servlets 2.0
javax.servlet.http	serializable event

An HttpSessionBindingEvent is passed to the appropriate method of an HttpSessionBindingListener when an object is bound to or unbound from an HttpSession. The getName() method returns the name to which the bound object has been assigned, and the getSession() method provides a reference to the session the object is being bound to.

Hierarchy: Object-->java.util.EventObject(Serializable)-->HttpSessionBindingEvent

Passed To: HttpSessionBindingListener.{valueBound(), valueUnbound()}

HttpSessionBindingListener	Servlets 2.0
javax.servlet.http	event listener

An object that implements HttpSessionBindingListener is notified with calls to valueBound() and valueUnbound() when it is bound to and unbound from an HttpSession, respectively. The valueUnbound() method is also called when a session is deleted for inactivity or at server shutdown.

Hierarchy: (HttpSessionBindingListener(java.util.EventListener))

HttpSessionContext	Servlets 2.0; Deprecated in Servlets 2.1
javax.servlet.http

HttpSessionContext provides access to all of the currently active sessions on the server. Note that this class is deprecated as of Version 2.1 of the Servlet API, due to a minor security risk whereby a servlet could expose all the session IDs in use on the server.

Returned By: HttpSession.getSessionContext()

HttpUtils	Servlets 1.0
javax.servlet.http

The HttpUtils class contains three static methods that perform useful HTTP-related tasks. getRequestURL() forms a functional approximation of the original request URL, including scheme, server name, server port, extra path information, and query string, based on an HttpServletRequest object. The parsePostData() and parseQueryString() methods parse URL-encoded form variables from an InputStream or a String. In most cases, a servlet should use the getParameter(), getParameterValues(), and getParameterNames() methods of HttpServletRequest instead.