dekoh.portal.util
Class FileServer

java.lang.Object
  javax.servlet.GenericServlet
      javax.servlet.http.HttpServlet
          dekoh.portal.util.FileServer

All Implemented Interfaces:

Serializable, Servlet, ServletConfig

Direct Known Subclasses:

AbstractResizeImageServlet, AppIconServlet

public abstract class FileServer
extends HttpServlet

Provides an abstract class to be subclassed to create a HTTP servlet suitable for serving files which are not modified frequently.

A sub class of FileServer must implement method : FileServer.getRequestedFile(javax.servlet.http.HttpServletRequest).

The last modified time of the file returned by this method will be returned by getLastModified method. When this file is not modified since it was last served the web server will return a response with HTTP standard status code NOT_MODIFIED. Browser or a proxy cache upon noticing this status code in the response will not fetch actual bytes of the file being requested, and will serve the cached copy.

Hence subclassing this class makes browser and proxy caches work more effectively in serving this content, reducing the load on server and network resources.

Few examples in which extending FileServer makes sense:

• Serving a thumbnail image which will not change once created.
• Serving a RSS Feed (a XML file) which may be not be modified very frequently.

There's almost no reason to override the doGet, and doPost methods. doPost calls the doGet method which writes the bytes of the file returned by FileServer.getRequestedFile(javax.servlet.http.HttpServletRequest) method to the output stream of the HttpServletResponse.

In situations where lastModified time on the FileServer.getRequestedFile(javax.servlet.http.HttpServletRequest) does not represent availability of new information, sub classes can override the FileServer.getLastModified(javax.servlet.http.HttpServletRequest) method.

In situations where authorization should preceed file to be served sub classes can override FileServer.authorizedToAccessCachedCopy(javax.servlet.http.HttpServletRequest) method.

Thread Safety: This implementation is not thread safe. In particular no file lock is obtained while requested file is being served. Implementations have to make sure that when the method getRequestedFile is accessed concurrently, all the concurrent requests are served without errors.

Since:

Apr 30, 2007

See Also:

Serialized Form

Field Summary

static String	FILE_EXT_HEADER
protected static String	FILE_TO_SERVE Request attribute used with-in this servlet to store path to the file to be served.
protected static int	UNKNOWN

Constructor Summary

FileServer()

Method Summary

protected boolean	authorizedToAccessCachedCopy(HttpServletRequest request)
protected void	copyStream(InputStream in, OutputStream out)
protected void	doGet(HttpServletRequest request, HttpServletResponse response)
protected void	doPost(HttpServletRequest request, HttpServletResponse response)
protected long	getLastModified(HttpServletRequest request)
protected abstract File	getRequestedFile(HttpServletRequest request) Serves the resource requested in FileServer.doGet(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse) or FileServer.doPost(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse) method of this servlet.
protected long	handleExceptionInLastModified(Exception e)
protected void	serveRequestedFile(File file, HttpServletRequest request, HttpServletResponse response)

Methods inherited from class javax.servlet.http.HttpServlet

doDelete, doHead, doOptions, doPut, doTrace, service, service

Methods inherited from class javax.servlet.GenericServlet

destroy, getInitParameter, getInitParameterNames, getServletConfig, getServletContext, getServletInfo, getServletName, init, init, log, log

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

FILE_TO_SERVE

protected static final String FILE_TO_SERVE

Request attribute used with-in this servlet to store path to the file to be served.

See Also:

Constant Field Values

UNKNOWN

protected static final int UNKNOWN

See Also:

Constant Field Values

FILE_EXT_HEADER

public static final String FILE_EXT_HEADER

See Also:

Constant Field Values

Constructor Detail

FileServer

public FileServer()

Method Detail

getLastModified

protected long getLastModified(HttpServletRequest request)

Overrides:

getLastModified in class HttpServlet

authorizedToAccessCachedCopy

protected boolean authorizedToAccessCachedCopy(HttpServletRequest request)

Parameters:

request - HttpServletRequest

Returns:

true always

handleExceptionInLastModified

protected long handleExceptionInLastModified(Exception e)

doGet

protected void doGet(HttpServletRequest request,
                     HttpServletResponse response)
              throws ServletException,
                     IOException

Overrides:

doGet in class HttpServlet

Throws:

ServletException

IOException

doPost

protected void doPost(HttpServletRequest request,
                      HttpServletResponse response)
               throws ServletException,
                      IOException

Overrides:

doPost in class HttpServlet

Throws:

ServletException

IOException

getRequestedFile

protected abstract File getRequestedFile(HttpServletRequest request)
                                  throws ServletException,
                                         IOException

Serves the resource requested in FileServer.doGet(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse) or FileServer.doPost(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse) method of this servlet. Bytes of this file will be written to output stream of the HttpServletResponse.

Parameters:

request - - HttpServletRequest

Returns:

File if the return value is null or a File that does not exist on disc, a 404/Page not found response will be sent.

Throws:

ServletException - Servlet Exception

IOException - throws when could not create the requried file

serveRequestedFile

protected void serveRequestedFile(File file,
                                  HttpServletRequest request,
                                  HttpServletResponse response)
                           throws IOException

Throws:

IOException

copyStream

protected void copyStream(InputStream in,
                          OutputStream out)
                   throws IOException

Throws:

IOException