Class CGIServlet

  extended byjavax.servlet.GenericServlet
      extended byjavax.servlet.http.HttpServlet
          extended byorg.apache.catalina.servlets.CGIServlet
All Implemented Interfaces:, javax.servlet.Servlet, javax.servlet.ServletConfig

public class CGIServlet
extends javax.servlet.http.HttpServlet

CGI-invoking servlet for web applications, used to execute scripts which comply to the Common Gateway Interface (CGI) specification and are named in the path-info used to invoke this servlet.

Note: This code compiles and even works for simple CGI cases. Exhaustive testing has not been done. Please consider it beta quality. Feedback is appreciated to the author (see below).

If an instance of this servlet was mapped (using <web-app>/WEB-INF/web.xml) to:


then the following request:


would result in the execution of the script


with the script's PATH_INFO set to /pathinfo1.

Recommendation: House all your CGI scripts under <webapp>/WEB-INF/cgi. This will ensure that you do not accidentally expose your cgi scripts' code to the outside world and that your cgis will be cleanly ensconced underneath the WEB-INF (i.e., non-content) area.

The default CGI location is mentioned above. You have the flexibility to put CGIs wherever you want, however:

The CGI search path will start at webAppRootDir + File.separator + cgiPathPrefix (or webAppRootDir alone if cgiPathPrefix is null).

cgiPathPrefix is defined by setting this servlet's cgiPathPrefix init parameter

CGI Specification:
derived from A work-in-progress & expired Internet Draft. Note no actual RFC describing the CGI specification exists. Where the behavior of this servlet differs from the specification cited above, it is either documented here, a bug, or an instance where the specification cited differs from Best Community Practice (BCP). Such instances should be well-documented here. Please email the Jakarta Tomcat group [] with amendments.

Canonical metavariables:
The CGI specification defines the following canonical metavariables:
[excerpt from CGI specification]


Metavariables with names beginning with the protocol name (e.g., "HTTP_ACCEPT") are also canonical in their description of request header fields. The number and meaning of these fields may change independently of this specification. (See also section 6.1.5 [of the CGI specification].)

[end excerpt]

Implementation notes

standard input handling: If your script accepts standard input, then the client must start sending input within a certain timeout period, otherwise the servlet will assume no input is coming and carry on running the script. The script's the standard input will be closed and handling of any further input from the client is undefined. Most likely it will be ignored. If this behavior becomes undesirable, then this servlet needs to be enhanced to handle threading of the spawned process' stdin, stdout, and stderr (which should not be too hard).
If you find your cgi scripts are timing out receiving input, you can set the init parameter of your webapps' cgi-handling servlet to be

Metavariable Values: According to the CGI specificion, implementations may choose to represent both null or missing values in an implementation-specific manner, but must define that manner. This implementation chooses to always define all required metavariables, but set the value to "" for all metavariables whose value is either null or undefined. PATH_TRANSLATED is the sole exception to this rule, as per the CGI Specification.

NPH -- Non-parsed-header implementation: This implementation does not support the CGI NPH concept, whereby server ensures that the data supplied to the script are preceisely as supplied by the client and unaltered by the server.

The function of a servlet container (including Tomcat) is specifically designed to parse and possible alter CGI-specific variables, and as such makes NPH functionality difficult to support.

The CGI specification states that compliant servers MAY support NPH output. It does not state servers MUST support NPH output to be unconditionally compliant. Thus, this implementation maintains unconditional compliance with the specification though NPH support is not present.

The CGI specification is located at


Tomcat 4.0
$Revision: 466595 $, $Date: 2006-10-21 23:24:41 +0100 (Sat, 21 Oct 2006) $
Martin T Dengler [], Amy Roh
See Also:
Serialized Form

Nested Class Summary
protected  class CGIServlet.CGIEnvironment
          Encapsulates the CGI environment and rules to derive that environment from the servlet container and request information.
protected  class CGIServlet.CGIRunner
          Encapsulates the knowledge of how to run a CGI script, given the script's desired environment and (optionally) input/output streams
protected  class CGIServlet.HTTPHeaderInputStream
          This is an input stream specifically for reading HTTP headers.
protected  class CGIServlet.NameValuePair
          This is a simple class for storing name-value pairs.
Constructor Summary
Method Summary
protected  void doGet(javax.servlet.http.HttpServletRequest req, javax.servlet.http.HttpServletResponse res)
          Provides CGI Gateway service
protected  void doPost(javax.servlet.http.HttpServletRequest req, javax.servlet.http.HttpServletResponse res)
          Provides CGI Gateway service -- delegates to doGet
 void init(javax.servlet.ServletConfig config)
          Sets instance variables.
static void main(java.lang.String[] args)
          For future testing use only; does nothing right now
protected  void printServletEnvironment(javax.servlet.ServletOutputStream out, javax.servlet.http.HttpServletRequest req, javax.servlet.http.HttpServletResponse res)
          Prints out important Servlet API and container information
Methods inherited from class javax.servlet.http.HttpServlet
doDelete, doHead, doOptions, doPut, doTrace, getLastModified, service, service
Methods inherited from class javax.servlet.GenericServlet
destroy, getInitParameter, getInitParameterNames, getServletConfig, getServletContext, getServletInfo, getServletName, init, log, log
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail


public CGIServlet()
Method Detail


public void init(javax.servlet.ServletConfig config)
          throws javax.servlet.ServletException
Sets instance variables.

Modified from Craig R. McClanahan's InvokerServlet

config - a ServletConfig object containing the servlet's configuration and initialization parameters
javax.servlet.ServletException - if an exception has occurred that interferes with the servlet's normal operation


protected void printServletEnvironment(javax.servlet.ServletOutputStream out,
                                       javax.servlet.http.HttpServletRequest req,
                                       javax.servlet.http.HttpServletResponse res)
Prints out important Servlet API and container information

Copied from SnoopAllServlet by Craig R. McClanahan

out - ServletOutputStream as target of the information
req - HttpServletRequest object used as source of information
res - HttpServletResponse object currently not used but could provide future information
Throws: - if a write operation exception occurs


protected void doPost(javax.servlet.http.HttpServletRequest req,
                      javax.servlet.http.HttpServletResponse res)
Provides CGI Gateway service -- delegates to doGet

req - HttpServletRequest passed in by servlet container
res - HttpServletResponse passed in by servlet container
javax.servlet.ServletException - if a servlet-specific exception occurs - if a read/write exception occurs
See Also:


protected void doGet(javax.servlet.http.HttpServletRequest req,
                     javax.servlet.http.HttpServletResponse res)
              throws javax.servlet.ServletException,
Provides CGI Gateway service

req - HttpServletRequest passed in by servlet container
res - HttpServletResponse passed in by servlet container
javax.servlet.ServletException - if a servlet-specific exception occurs - if a read/write exception occurs
See Also:


public static void main(java.lang.String[] args)
For future testing use only; does nothing right now

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