Brian Moseley > libservlet-0.9.2 > Servlet::Http::HttpServlet

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NAME ^

Servlet::Http::HttpServlet - HTTP servlet base class

SYNOPSIS ^

  $servlet->doDelete($request, $response);

  $servlet->doGet($request, $response);

  $servlet->doHead($request, $response);

  $servlet->doOptions($request, $response);

  $servlet->doPost($request, $response);

  $servlet->doPut($request, $response);

  $servlet->doTrace($request, $response);

  my $time = $servlet->getLastModified($request);

  $servlet->service($request, $response);

DESCRIPTION ^

This class acts as a base class for HTTP servlets. Subclasses must override at least one method, usually one of these:

doGet()

if the servlet supports HTTP GET requests

doPost()

for HTTP POST requests

doPut()

for HTTP PUT requests

doDelete()

for HTTP DELETE requests

init() and destroy()

to manage resources that are held for the life of the servlet

getServletInfo()

which the servlet uses to provide information about itself

There's almost no reason to override the service() method, which handles standard HTTP requests by dispatching them to the handler methods for each HTTP request type (the doXXX() methods listed above).

Likewise, there's almost no reason to override the doOptions() and doTrace() methods.

Servlets typically run on multithreaded servers, so be aware that a servlet must handle concurrent requets and be careful to synchronize access to shared resources. Shared resources include in-memory data such as instance or class variables and external objects such as files, database connections, and network connections. See perlthrtut for more information on handling multiple threads in a Perl program.

CONSTRUCTOR ^

new()

Does nothing. All of the servlet initialization is done by the init() method.

METHODS ^

doDelete($request, $response)

Called by the server (via the service() method) to allow a servlet to handle a DELETE request. The DELETE operation allows a client to remove a document or Web page from the server.

This method does not need to be either safe or idempotent. Operations requested through DELETE can have side effects for which users can be held accountable. When using this method, it may be useful to save a copy of the affected resource in temporary storage.

If the request is incorrectly formatted, the method returns an HTTP "Bad Request" message.

Parameters:

$request

the Servlet::Http::HttpServletRequest object that contains the client request

$response

the Servlet::Http::HttpServletResponse object that contains the servlet response

Throws:

Servlet::ServletException

if the request cannot be handled

Servlet::Util::IOException

if an input or output error occurs

doGet($request, $response)

Called by the server (via the service() method) to allow a servlet to handle a GET request.

Overriding this method to support a GET request also automatically supports an HTTP HEAD request. A HEAD request is a GET request that returns no body in the response, only the response headers.

When overriding this method, read the request data, write the response headers, get the response's writer or output handle object, and finally, write the response data. It's best to include content type and encoding.

The servlet container must write the headers before committing the response, because in HTTP the headers must be sent before the response body.

Where possible, set the content length, to allow the servlet container to use a persistent connection to return its response to the client, improving performance. The content length is automatically set if the entire response fits inside the response buffer.

The GET method should be safe, that is, without any side effects for which users are held responsible. For example, most form queries have no side effects. If a client request is intended to change stored data, the request should use some other HTTP method.

The GET method should also be idempotent, meaning that it can be safely repeated. Sometimes making a method safe also makes it idempotent. For example, repeating queries is both safe and idempotent, but buying a product online or modifying data is neither safe nor idempotent.

If the request is incorrectly formatted, the method returns an HTTP "Bad Request" message.

Parameters:

$request

the Servlet::Http::HttpServletRequest object that contains the client request

$response

the Servlet::Http::HttpServletResponse object that contains the servlet response

Throws:

Servlet::ServletException

if the request cannot be handled

Servlet::Util::IOException

if an input or output error occurs

doHead($request, $response)

Called by the server (via the service() method) to allow a servlet to handle a HEAD request. The client sends a HEAD request when it wants to see only the headers. The HEAD method counts the output bytes in the response to set the content length accurately.

If you override this method, you can avoide computing the response body and just set the response ehaders directly to improve performance. Make sure the method you write is both safe and idempotent.

If the request is incorrectly formatted, the method returns an HTTP "Bad Request" message.

Parameters:

$request

the Servlet::Http::HttpServletRequest object that contains the client request

$response

the Servlet::Http::HttpServletResponse object that contains the servlet response

Throws:

Servlet::ServletException

if the request cannot be handled

Servlet::Util::IOException

if an input or output error occurs

doOptions($request, $response)

Called by the server (via the service() method) to allow a servlet to handle a OPTIONS request. The OPTIONS request determines which HTTP methods the server supports and returns an appropriate header. For example, if a servlet overrides doGet(), this method returns the following header:

  Allow: GET, HEAD, TRACE, OPTIONS

There's no need to override this method unless the servlet implements new HTTP methods beyond those implemented by HTTP 1.1.

If the request is incorrectly formatted, the method returns an HTTP "Bad Request" message.

Parameters:

$request

the Servlet::Http::HttpServletRequest object that contains the client request

$response

the Servlet::Http::HttpServletResponse object that contains the servlet response

Throws:

Servlet::ServletException

if the request cannot be handled

Servlet::Util::IOException

if an input or output error occurs

doPost($request, $response)

Called by the server (via the service() method) to allow a servlet to handle a POST request. The POST method allows the client to send data of unlimited length to the Web server.

When overriding this method, read the request data, write the response headers, get the response's writer or output handle object, and finally, write the response data. It's best to include content type and encoding.

The servlet container must write the headers before committing the response, because in HTTP the headers must be sent before the response body.

Where possible, set the content length, to allow the servlet container to use a persistent connection to return its response to the client, improving performance. The content length is automatically set if the entire response fits inside the response buffer.

When using HTTP 1.1 chunked encoding (which means that the response has a Transfer-Encoding header), do not set the content length.

This method does not need to be either safe or idempotent. Operations requested through POST can have side effects for which the user can be held accountable, for example, updating stored data or buying items online.

If the request is incorrectly formatted, the method returns an HTTP "Bad Request" message.

Parameters:

$request

the Servlet::Http::HttpServletRequest object that contains the client request

$response

the Servlet::Http::HttpServletResponse object that contains the servlet response

Throws:

Servlet::ServletException

if the request cannot be handled

Servlet::Util::IOException

if an input or output error occurs

doPut($request, $response)

Called by the server (via the service() method) to allow a servlet to handle a Put request. The PUT operation allows a client to place a file on the server and is similar to sending a file by FTP.

When overriding this method, leave intact any content headers sent with the request (including Content-Length, Content-Type, Content-Transfer-Encoding, Content-Encoding, Content-Base, Content-Language, Content-Location, Content-MD5 and Content-Range). If your method cannot handle a content header, it must issue an error message (HTTP 501 - Not Implemented) and discard the request. For more information on HTTP 1.1, see RFC 2068.

This method does not need to be either safe or idempotent. Operations that it performs can have side effects for which the user can be held accountable. When using this method, it may be useful to save a copy of the affected URL in temporary storage.

If the request is incorrectly formatted, the method returns an HTTP "Bad Request" message.

Parameters:

$request

the Servlet::Http::HttpServletRequest object that contains the client request

$response

the Servlet::Http::HttpServletResponse object that contains the servlet response

Throws:

Servlet::ServletException

if the request cannot be handled

Servlet::Util::IOException

if an input or output error occurs

getLastModified($request)

Returns the time the requested resource was last modified, in milliseconds since midnight January 1, 1970 GMT. IF the time is unknown, this method returns a negative number (the default).

Servlets that support HTTP GET requests and can quickly determine their last modification time should override this method. This makes browser and proxy caches work more effectively, reducing the load on server and network resources.

Parameters:

$request

the Servlet::Http::HttpServletRequest object that contains the client request

service($request, $response)

Dispatches client requests to the doXXX methods defined in this class. There's no need to override this method.

Parameters:

$request

the Servlet::Http::HttpServletRequest object that contains the client request

$response

the Servlet::Http::HttpServletResponse object that contains the servlet response

Throws:

Servlet::ServletException

if the request cannot be handled

Servlet::Util::IOException

if an input or output error occurs

SEE ALSO ^

Servlet::GenericServlet, Servlet::Http::HttpServletRequest, Servlet::Http::HttpServletResponse

AUTHOR ^

Brian Moseley, bcm@maz.org

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