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The Servlet API Nutshell


javax.servlet Package             javax.servlet.http Package

Interfaces:
 
Servlet ServletConfig ServletContext
ServletRequest ServletResponse SingleThreadModel

Classes:
 
GenericServlet ServletInputStream ServletOutputStream

Exceptions:
 
ServletException UnavailableException


Servlet:Interface
Defines the Life Cycle methods of a servlet: init, service and destroy methods.
It also provides methods that allows servlets to get startup information, about its server environment and also a method to provide to the server a description about the servlet.

  public abstract void destroy()
     Cleans up whatever resources are being held (e.g., memory, file handles, threads) and makes sure that any persistent state is synchronized with the servlet's current in-memory state. The servlet should be designed in such a way that all threads executing service method complete by the time destroy is called.

  public abstract ServletConfig getServletConfig()
     Returns a servlet config object, which contains any initialization parameters and startup configuration for this servlet. It is the same servlet config object passed to the init method and the init method should have stored it, so that this method could return.

public abstract String  getServletInfo()
     Returns a string containing information about the servlet, such as its author, version, and copyright.

  public abstract void init(ServletConfig) throws ServletException
     Initializes the servlet. If the initialization fails it should throw an UnavailableException and should never call System.exit() method.

public abstract void  service(ServletRequest, ServletResponse) throws ServletException , IOException
     Carries out a single request from the client. The method implements a request-response paradigm. Servlets run in multi-threaded servers. The servlet shoud be made thread-safe and synchronize access to shared resources like network connections, servlet's class and instance variables.


ServletConfig:Interface

The interface is generally implemented by services of the server in order to pass configuration information to the servlet when it gets initialized. Servlets can also implement it so as to have an eay implementation of getting the servletContext:

Here is an  implementation of  getServletContext():

public ServletContext getServletContext() {
        return getServletConfig().getServletContext();
   }

This could be replaced by:

public ServletContext getServletContext() {
        return getServletContext();
   }

GenericServlet implements the ServletConfig.

Methods:

public abstract String getInitParameter(String)
     Returns a string containing the value of the named initialization parameter of the servlet, or null if the parameter
     does not exist.

public abstract Enumeration  getInitParameterNames()
     Returns the names of the servlet's initialization parameters as an enumeration of strings, or an empty enumeration
     if there are no initialization parameters.

public abstract ServeltContext  getServletContext()
     Returns the context for the servlet.


ServletContext:Interface

The interface is implemented by the services of the server and used by the servlet to access information about its environment and also to log significant events. It is obtained by calling the getServletContext method on the ServletConfig passed on to the servlet at the time of the initialization.

Methods:

public abstract String getAttribute(String)
     Returns the value of the named attribute of the network service, or null if the attribute does not exist.

public abstract String  getMimeType(String)
     Returns the mime type of the specified file, or null if not known.

public abstract String  getRealPath(String)
     Applies alias rules to the specified virtual path and returns the corresponding real path.For example, in an HTTP
     servlet, this method would resolve the path against the HTTP service's docroot. Returns null if virtual paths are
     not supported, or if the translation could not be performed for any reason.

public abstract String   getServerInfo()
     Returns the name and version of the network service under which the servlet is running. In an HTTP server this
     value will be the same as the value of the CGI variable SERVER_SOFTWARE

public abstract Servlet getServlet(String) throw ServletException
     Returns the servlet of the specified name, or null if not found.
     This is a dangerous method to call because:

public abstract Enumeration  getServletNames()
     Returns an enumeration of the Servlet object names in this server. The enumeration always include the servlet
     itself.
     The list contains only servlets in the current namespace.
     This is a dangerous method to call for the same reason why getServlet method is dangerous to call.

public abstract Enumeration  getServlets()
     Returns an enumeration of the Servlet objects in this server. Deprecated.

public abstract void log(Exception, String)
     Write the stacktrace and the given message string to the servlet log file. The servlet log file is server specific and
      is normally an event log file.

public abstract void  log(String)
     Writes the given message string to the servlet log file.



ServletRequest:Interface

The Interface is used to provide data from the client to the servlet. The data includes parameter names and values, attributes, and an input stream. MIME bodies are either text or binary. If binary use getInputStream, else if text use getReader. Multipart MIME bodies are considered binary.

Methods:

public abstract String  getAttribute(String)
     Returns the value of the named attribute of the request, or null if the attribute does not exist.

public abstract String  getCharacterEncoding()
     Returns the character set encoding for the input of this request.

public abstract int  getContentLength()
     Returns the size of the request entity data, or -1 if not known.

public abstract String  getContentType()
     Returns the Internet Media Type of the request entity data, or null if not known.

public abstract ServletInputStream  getInputStream() throws IOException
     Returns an input stream for reading binary data in the request body.

public abstract String  getParameter(String)
     Returns a string containing the lone value of the specified parameter, or null if the parameter does not exist.
     For example it could return the value of the specified query String Parameter or posted form.

public abstract String  getParameterNames()
     Returns the parameter names for this request as an enumeration of strings, or an empty enumeration if there
     are no parameters or the input stream is empty. The input stream could be empty of all data had been read from
     the input Stream returned by the method getInputStream.

public abstract Enumeration getParameterValues(String)
     Returns the values of the specified parameter for the request as an array of strings, or null if the named
     parameter does not exist.

public abstract String  getProtocol()
     Returns the protocol and version of the request as a string of the form <protocol>/<major
    version>.<minor version>.

public abstract BufferedReader  getReader()
     Returns a buffered reader for reading text in the request body.

public abstract String  getRealPath(String)
     Applies alias rules to the specified virtual path and returns the corresponding real path, or null if the translation
     can not be performed for any reason.

public abstract String  getRemoteAddr()
     Returns the IP address of the agent that sent the request.

public abstract String  getRemoteHost()
     Returns the fully qualified host name of the agent that sent the request.

public abstract String  getScheme()
     Returns the scheme of the URL used in this request, for example "http", "https", or "ftp".

public abstract String  getServerName()
     Returns the host name of the server that received the request.

public abstract int  getServerPort()
     Returns the port number on which this request was received.



ServletResponse:Interface

public abstract String  getCharacterEncoding()
     Returns the character set encoding used for this MIME body.

public abstract ServletOutputStream  getOutputStream() throws IOException
     Returns an output stream for writing binary response data.

public abstract PrintWriter  getWriter() throws IOException

     Returns a print writer for writing formatted text responses.

public abstract void  setContentLength(int)
     Sets the content length for this response. Must be called before calling getWriter or getOutputStream.

public abstract void  setContentType(String)
     Sets the content type for this response. Must be called before calling getWriter or getOutputStream.



SingleThreadModel:Interface

Defines a "single" thread model for servlet execution. This empty interface allows servlet implementers to specify
how the system should handle concurrent calls to the same servlet.

If the target servlet is flagged with this interface, the servlet programmer is guaranteed that no two threads will
execute concurrently the service method of that servlet. This guarantee is ensured by maintaining a pool of servlet
instances for each such servlet, and dispatching each service call to a free servlet.

In essence, if the servlet implements this interface, the servlet will be thread safe.



GenericServlet: Abstract Class

The GenericServlet class implements the Servlet interface and, for convenience, the ServletConfig interface. Servlet
developers typically subclass GenericServlet, or its descendent HttpServlet, unless the servlet needs another class as
a parent. (If a servlet does need to subclass another class, the servlet must implement the Servlet interface directly.
This would be necessary when, for example, RMI or CORBA objects act as servlets.)

The GenericServlet class was created to make writing servlets easier. It provides simple versions of the lifecycle
methods init and destroy, and of the methods in the ServletConfig interface. It also provides a log method, from the
ServletContext interface. The servlet writer must override only the service method, which is abstract. Though not
required, the servlet implementer should also override the getServletInfo method, and will want to specialize the init
and destroy methods if expensive servlet-wide resources are to be managed.

Methods

public void  destroy()
     Destroys the servlet, cleaning up whatever resources are being held, and logs the destruction in the servlet log
     file.

public String  getInitParameter(String)
     Returns a string containing the value of the named initialization parameter, or null if the requested parameter
     does not exist.

public Enumeration  getInitParameterNames()
     Returns the names of the servlet's initialization parameters as an enumeration of strings, or an empty
     enumeration if there are no initialization parameters.

public ServletConfig  getServletConfig()
     Returns a servletConfig object containing any startup configuration information for this servlet.

public ServletContext  getServletContext()
     Returns a ServletContext object, which contains information about the network service in which the servlet is
     running.

pubic String  getServletInfo()
     Returns a string that contains information about the servlet, such as its author, version, and copyright.

public void  init(ServletConfig)
     Initializes the servlet and logs the initialization.

public void  log(String)
     Writes the class name of the servlet and the given message to the servlet log file.

public abstract void  service(ServletRequest, ServletResponse) throws ServletException, IOException
     Carries out a single request from the client.



ServletInputStream: Abstract Class

Use to read binary data from the client sent in say through HTTP POST or PUT methods. This getInputStream method of ServletRequest returns an instance of this class. The class provides a readLine method to read a line from the stream. Subclasses must provide implementation of the read method.

Methods:

public int readLine(byte[], int off, int len) throws IOException
     Starting at the specified offset, reads into the given array of bytes until all requested bytes have been read or a
     '\n' is encountered, in which case the '\n' is read into the array as well.
      Returns the actual number of bytes read, or -1 if the end of the stream is reached.



ServletOutputStream : Abstract Class

Use to write binary data as a response to the client. The getOutputStream returns an instance of this class. Subclass must implement the write method.

Methods:

All of the methods returns void and throws IOException

  print(boolean)
     Prints the boolean provided.

  print(char)
     Prints the character provided.
  print(double)

     Prints the double provided.

  print(float)
     Prints the float provided.

  print(int)
     Prints the integer provided.

  print(long)
     Prints the long provided.

  print(String)
     Prints the string provided.

  println()
     Prints a CRLF.

  println(boolean)
     Prints the boolean provided, followed by a CRLF.

  println(char)
     Prints the character provided, followed by a CRLF.

  println(double)
     Prints the double provided, followed by a CRLF.

  println(float)
     Prints the float provided, followed by a CRLF.

  println(int)
     Prints the integer provided, followed by a CRLF.

  println(long)
     Prints the long provided, followed by a CRLF.

  println(String)
     Prints the string provided, followed by a CRLF.



ServletException : Class
It is a subclass of Exception for servlets with the usual no-argument and single argument constructors.

UnavailableException :Class

This exception indicates that a servlet is unavailable. Servlets may report this exception at any time, and the network
service running the servlet should behave appropriately. There are two types of unavailability, and sophisticated
services will to deal with these differently:

     Permanent unavailability. The servlet will not be able to handle client requests until some administrative
     action is taken to correct a servlet problem. For example, the servlet might be misconfigured, or the state of
     the servlet may be corrupted. Well written servlets will log both the error and the corrective action which an
     administrator must perform to let the servlet become available.

     Temporary unavailability. The servlet can not handle requests at this moment due to a system-wide problem.
     For example, a third tier server might not be accessible, or there may be insufficient memory or disk storage
     to handle requests. The problem may be self correcting, such as those due to excessive load, or corrective
     action may need to be taken by an administrator.

Network services may safely treat both types of exceptions as "permanent", but good treatment of temporary
unavailability leads to more robust network services. Specifically, requests to the servlet might be blocked (or
otherwise deferred) for a servlet-suggested amount of time, rather than being rejected until the service itself restarts.

Constructors:

  UnavailableException(int, Servlet, String)
     Constructs a new exception with the specified descriptive message, indicating that the servlet is temporarily
     unavailable and giving an estimate of how long it will be unavailable in seconds.
  UnavailableException(Servlet, String)
     Constructs a new exception with the specified descriptive message, indicating that the servlet is permanently
     unavailable.

Methods:

public Servlet getServlet()
     Returns the servlet that is reporting its unavailability.

public int getUnavailableSeconds()
     Returns the amount of time the servlet expects to be temporarily unavailable.

public boolean   isPermanent()
     Returns true if the servlet is "permanently" unavailable, indicating that the service administrator must take
     some corrective action to make the servlet be usable.



javax.servlet.http Package

Interfaces:
 
HttpServletRequest HttpServletResponse HttpSession
HttpSessionBindingListener HttpSessionContext

Classes:
 
Cookie HttpServlet
HttpSessionBindingEvent HttpUtils

HttpServletRequest : Interface

This Interface extends the ServletRequest Interface. The interface allows HTTP-protocol specific header information to be accessed from the service method of the servlet.

Methods:

public abstract String  getAuthType()
     Gets the authentication scheme of this request.

public abstract Cookies[]  getCookies()
     Gets the array of cookies found in this request.

public abstract long  getDateHeader(String)
     Gets the value of the requested date header field of this request. The case of the header name is ignored. If the
     value cannot be converted to a Date then an IllegalArgumentException is thrown.

public abstract String  getHeader(String)
     Gets the value of the requested header field of this request. The case of the header name is ignored.

public abstract Enumeration  getHeaderNames()
     Gets the header names for this request.

public abstract int  getIntHeader(String)
     Gets the value of the specified integer header field of this request. Throws a NumberFormatException if the
     value cannot be converted to an integer. The case of the Header name is ignored.

public abstract String  getMethod()
     Gets the HTTP method (for example, GET, POST, PUT) with which this request was made.

public abstract String  getPathInfo()
     Gets any optional extra path information following the servlet path of this request's URI, but immediately
     preceding its query string.

public abstract String  getPathTranslated()
     Gets any optional extra path information following the servlet path of this request's URI, but immediately
     preceding its query string, and translates it to a real path.

public abstract String   getQueryString()
     Gets any query string that is part of the HTTP request URL.

public abstract String  getRemoteUser()
     Gets the name of the user making this request.

public abstract String  getRequestedSessionId()
     Gets the session id specified with this request. This returned ID may be different from the one send in with the
      request if the sent in one is the ID of an invalid session in which case a new session ic created the new ID is
      returned.

public abstract String  getRequestURI()
     Gets, from the first line of the HTTP request, the part of this request's URI that is to the left of any query
     string. For example,

           First line of HTTP request                                         Return from getRequestURI
           POST /some/path.html HTTP/1.1                                        /some/path.html
           GET http://foo.bar/a.html HTTP/1.0                                     http://foo.bar/a.html
           HEAD /xyz?a=b HTTP/1.1                                                /xyz

     To reconstruct a URL with a URL scheme and host, use the method
     javax.servlet.http.HttpUtils.getRequestURL, which returns a StringBuffer.

public abstract String  getServletPath()
     Gets the part of this request's URI that refers to the servlet being invoked.

public abstract HttpSession  getSession(boolean)
     Gets the current valid session associated with this request, if create is false or, if necessary, creates a new
     session for the request, if create is true.

public abstract boolean  isRequestedSessionIdFromCookie()
     Checks whether the session id specified by this request came in as a cookie.

public abstract boolean  isRequestedSessionIdFromUrl()
     Checks whether the session id specified by this request came in as part of the URL.

public abstract boolean  isRequestedSessionIdValid()
     Checks whether this request is associated with a session that is valid in the current session context.



HttpServletResponse: Interface

The interface defines all the status codes of HTTP-protocol as static fields.
The class is used to manipulate header of the response to the client.

Important Static Fields:

SC_CONTINUE(100), SC_OK(200), SC_ACCEPTED(202), SC_NO_CONTENT(204), SC_MOVED_PERMANENTLY(301), SC_MOVED_TEMPORARILY(302), SC_BAD_REQUEST(400), SC_UNAUTHORIZED(401), SC_FORBIDDEN(403), SC_NOT_FOUND(404), SC_PROXY_AUTHENTICATION_REQUIRED(407), SC_CONFLICT(409), SC_GONE(410), SC_CONTENT_LENGTH(411), SC_UNSUPPORTED_MEDIA_TYPE(415), SC_INTERNAL_SERVER_ERROR(500), SC_SERVICE_UNAVAILABLE(503), SC_HTTP_VERSION_NOT_SUPPORTED(505) etc

Methods:

public abstract void  addCookie(Cookie)
     Adds the specified cookie to the response.

public abstract boolean containsHeader(String)
     Checks whether the response message header has a field with the specified name.

public abstract void encodeRedirectUrl(String)
     Encodes the specified URL for use in the sendRedirect method or, if encoding is not needed, returns the
     URL unchanged.  The implementation has logic to determine whether to encode or not. The logic is different
     from that of encodeURL method.

     URLs used in sendRedirect must have been encoded using this method.

public abstract void  encodeUrl(String)
     Encodes the specified URL by including the session ID in it, or, if encoding is not needed, returns the URL
     unchanged. The implementation should include logic to determine whether encoding is required or not. For
     example if the browser supports cookies and sever can set cookies to the client browser, then encoding is
     not needed.

     All URLs emitted from the servlet must go through this method, otherwise URL rewriting cannot be done if the
     browser does not support cookies.

public abstract void  sendError(int) throws IOException
     Sends an error response to the client using the specified status code and a default message.

public abstract void  sendError(int, String) throws IOException
     Sends an error response to the client using the specified status code and descriptive message. The message is
     sent as the body of an html page with a default header.

public abstract void  sendRedirect(String URL) throws IOException
     Sends a temporary redirect response to the client using the specified redirect location URL. The URL must
     be absolute (for example, https://hostname/path/file.html). Relative URLs are not permitted here. The URL must
     be encoded using the encodeRedirectURL method to include the session ID.

public abstract void  setDateHeader(String, long)
     Adds a field to the response header with the given name and date-valued field.

public abstract void  setHeader(String, String)
     Adds a field to the response header with the given name and value.

public abstract void  setIntHeader(String, int)
     Adds a field to the response header with the given name and integer value.

public abstract void  setStatus(int)
     Sets the status code for this response when there is no error.

public abstract void  setStatus(int, String)
     Sets the return status code and message for this response when there is no error. The message is sent as the
     body of a html page to the client.  The page has a default header.



HttpSession: Interface

Session is an interface that is used to maintain state and user identity across multiple page requests. The session is stored with the server.
A server considers a session to be new until it is joined by a client. The isNew method returns true under the following conditions:

If the isNew method returns true the server may direct to a welcome page welcomeURL where the user might have to enter some required informatin.

If the objects stored in the session implements the HttpSessionBindingListener then the object will be notified when it is bounded or unbounded from the session.

Methods:

 All  methods throws an IllegalArgumentException if the method is invoked when the session has been invalidated.

public abstract long  getCreationTime()
     Returns the time at which this session representation was created, in milliseconds since midnight, January 1, 1970
     UTC.

public abstract String  getId()
     Returns the identifier assigned to this session. The session ID is a unique string created and maintained by the
    HttpSessionContext.

public abstract long  getLastAccessedTime()
     Returns the last time the client sent a request carrying the identifier assigned to the session. Application level
    operation  like getting and putting objects into the object does not count as accessing.

public abstract HttpSesionContext  getSessionContext()
     Returns the context in which this session is bound.

public abstract Object  getValue(String)
     Returns the object bound to the given name in the session's application layer data. Returns null if there is no binding.

public abstract String[]  getValueNames()
     Returns an array of the names of all the application layer data objects bound into the session.

public abstract void  invalidate()
     Causes this representation of the session to be invalidated and removed from its context.

public abstract boolean  isNew()
     A session is considered to be "new" if it has been created by the server, but the client has not yet acknowledged
     joining the session. If the client does not allows cookies to be set and the server allows only cookies-based clients,
     the call to HttpServletRequest.getSession() is always going to return a "new" session.

public abstract void   putValue(String, Object)
     Binds the specified object into the session's application layer data with the given name. If the object implements the
     HttpSessionBindingListener then the valueBound() method will be invoked.

public abstract void  removeValue(String)
     Removes the object bound to the given name in the session's application layer data. Does nothing if there is no
     object  bound to the given name. If the object implements HttpSessionBindingListener then its valueUnbound()
     method is called.



HttpSessionBindingListener: Interface
When an object that implements this interface is put into a session by calling the HttpSession.putValue() method, the valueBound() method of the object is called. Similary valueUnbound() is called when the HttpSession.removeValue() method is called.

Methods:

public abstract void  valueBound(HttpSessionBindingEvent)
     Notifies the listener that it is being bound into a session.

public abstract void  valueUnbound(HttpSessionBindingEvent)
     Notifies the listener that it is being unbound from a session.



HttpSessionContext: Interface
The interface allows the servlet to get all the ids of the sessions and their names listed with its server. The HttpSessionContext can be obtined by a servlet using the getSessionContext() method of  HttpSession.

Methods:

public abstract Enumeration  getIds()
     Returns an enumeration of all of the session IDs in this context.

public abstract HttpSession  getSession(String)
     Returns the session bound to the specified session ID.



Cookie : Class

Cookie allows user agents (say web browser) to save some state associated with a user's web browsing. It can store information  like user preferences, low-level security information etc.

Cookies are names and has a single value. It can have other attributes like comments, user, path and domain of hosts, maximum age, and version.

Cookies are set by the server through the cookies added to the servlet response using javax.servlet.http.HttpServletResponse.addCookie method. User agents are expected to support 20 cookies per host, with each cookie of 4 KB.

Cookies are sent in from the clients to those servers who set them by using the HTTP request. This can be extracted by using javax.servlet.http.HttpServletRequest.getCookies() method.

Constructor:
Cookie(String name, String value)
Defines a cookie with an initial name/value pair.

Methods:

public Object  clone()
     Returns a copy of this object.

public String  getComment()
     Returns the comment describing the purpose of this cookie, or null if no such comment has been defined.

public String  getDomain()
     Returns the domain of this cookie.

public int  getMaxAge()
     Returns the maximum specified age of the cookie. If it was not set it returns a negative value which is the default in
     setMaxAge method.

public String  getName()
     Returns the name of the cookie. Once the cookie has been set, the name may not be changed.

public String  getPath()
     Returns the prefix of all URLs for which this cookie is targetted.

public boolean  getSecure()
     Returns the value of the 'secure' flag.

public String  getValue()
     Returns the value of the cookie.

public int  getVersion()
     Returns the version of the cookie.

public void  setComment(String)
     If a user agent (web browser) presents this cookie to a user, the cookie's purpose will be described using this
     comment.

public void  setDomain(String)
     This cookie should be presented only to hosts satisfying this domain name pattern. In www.foo.com, .foo.com is the
     domain. If the domain has been set to .foo.com then host in that DNS zone (i.e www.foo.com and not a.b.foo.com)
     could see the cookie. By default only host that set the cookie can access the cookie.

public void  setMaxAge(int)
     Sets the maximum age of the cookie in seconds. A negative value indicates the default: when user agent exits the
    cookie is destroyed. A zero value mean delete the cookie.

public void  setPath(String)
     This cookie should be presented only with requests beginning with this URL. Unless a different path is set, all URLs
     from the same "directory" as the one which set the cookie, and in subdirectories, can all see the cookie.

public void  setSecure(boolean)
     Indicates to the user agent that the cookie should only be sent using a secure protocol (https). The server from where
     the cookie originate must use a secure protocol to be able to set the cookie's value.

public void  setValue(String)
     Sets the value of the cookie.

public void  setVersion(int)
     Sets the version of the cookie protocol used when this cookie saves itself.



HttpServlet: Abstract Class

The class extends GenericServlet and provides a base class for HTTP based servlets. The class is an abstract class and must be extended. Also the subclass must override at least one method. The following methods are generally overridden:

The service method is generally not overriden. As it is implemented, it calls the respective doXXX methods listed above for corresponding HTTP operations. service also supports TRACE and OPTIONS HTTP operations through doTrace and doOptions methods. This 2 methods are generally not overridden.

Methods:

protected void  doDelete(HttpServletRequest, HttpServletResponse) throws ServletException, IOException
     Performs the HTTP DELETE operation; the default implementation reports an HTTP BAD_REQUEST error.

protected void  doGet(HttpServletRequest, HttpServletResponse) throws ServletException, IOException
     Performs the HTTP GET operation; the default implementation reports an HTTP BAD_REQUEST error.
     In general, the servlet implementor must write the headers before the response data because the headers can be
     flushed at any time after the data starts to be written.

protected void  doOptions(HttpServletRequest, HttpServletResponse) throws ServletException, IOException
     Performs the HTTP OPTIONS operation; the default implementation of this method automatically determines
     what HTTP Options are supported.

protected void  doPost(HttpServletRequest, HttpServletResponse) throws ServletException, IOException
     Performs the HTTP POST operation; the default implementation reports an HTTP BAD_REQUEST error.

protected void  doPut(HttpServletRequest, HttpServletResponse) throws ServletException, IOException
     Performs the HTTP PUT operation; the default implementation reports an HTTP BAD_REQUEST error.

protected void  doTrace(HttpServletRequest, HttpServletResponse) throws ServletException, IOException
     Performs the HTTP TRACE operation; the default implementation of this method causes a response with a
     message containing all of the headers sent in the trace request.

protected long  getLastModified(HttpServletRequest)
     Gets the time the requested entity was last modified; the default implementation returns a negative number,
     indicating that the modification time is unknown and hence should not be used for conditional GET operations or
     for other cache control operations as this implementation will always return the contents.

     Implementations supporting the GET request should override this method to provide an accurate object
     modification time. This makes browser and proxy caches work more effectively, reducing the load on server and
     network resources.

protected void  service(HttpServletRequest, HttpServletResponse) throws ServletException, IOException
     This is an HTTP-specific version of the Servlet.service method, which accepts HTTP specific parameters.

protected void  service(HttpServletRequest, HttpServletResponse) throws ServletException, IOException
     Implements the high level Servlet.service method by delegating to the HTTP-specific service method.


HttpSessionBindingEvent: Class
This event is communicated to a HttpSessionBindingListener whenever the listener is bound to or unbound from a
HttpSession value.

The event's source is the HttpSession: binding occurs with a call to HttpSession.putValue; unbinding occurs with a call to
HttpSession.removeValue.

Constructor:
HttpSessionBindingEvent(HttpSession, String)
     Constructs a new HttpSessionBindingEvent

Methods:

public String  getName()
     Returns the name to which the object is being bound or the name from which the object is being unbound.

public HttpSession  getSession()
     Returns the session into which the listener is being bound or from which the listener is being unbound.


HttpUtils: Class
A collection of static utility methods useful for HTTP servlets.

Constructor:
HttpUtils()
Creates a HttpUtils object.

Methods:

public static StringBuffer  getRequestURL(HttpServletRequest)
     Reconstructs the URL used by the client used to make the request. This returns schme such as http, httpds etc but
     not the query string. As the result is a stringBuffer the URL can be modified efficiently.

public static Hashtable  parsePostData(int, ServletInputStream)
     Parses FORM data that is posted to the server using the HTTP POST method and the
     application/x-www-form-urlencoded mime type.

public static Hashtable  parseQueryString(String)
     Parses a query string and builds a hashtable of key-value pairs, where the values are arrays of strings.