https://tomcat.apache.org/: jakarta.servlet package 
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package jakarta.servlet.http;

import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.text.MessageFormat;
import java.util.Enumeration;
import java.util.ResourceBundle;

import jakarta.servlet.DispatcherType;
import jakarta.servlet.GenericServlet;
import jakarta.servlet.ServletException;
import jakarta.servlet.ServletOutputStream;
import jakarta.servlet.ServletRequest;
import jakarta.servlet.ServletResponse;



Provides an abstract class to be subclassed to create
an HTTP servlet suitable for a Web site. A subclass of
HttpServlet 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. service handles standard HTTP
requests by dispatching them to the handler methods
for each HTTP request type (the doMethod
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
requests 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 the

Java Tutorial on Multithreaded Programming for more
information on handling multiple threads in a Java program.

/**
 * Provides an abstract class to be subclassed to create
 * an HTTP servlet suitable for a Web site. A subclass of
 * <code>HttpServlet</code> must override at least
 * one method, usually one of these:
 *
 * <ul>
 * <li> <code>doGet</code>, if the servlet supports HTTP GET requests
 * <li> <code>doPost</code>, for HTTP POST requests
 * <li> <code>doPut</code>, for HTTP PUT requests
 * <li> <code>doDelete</code>, for HTTP DELETE requests
 * <li> <code>init</code> and <code>destroy</code>,
 * to manage resources that are held for the life of the servlet
 * <li> <code>getServletInfo</code>, which the servlet uses to
 * provide information about itself
 * </ul>
 *
 * <p>There's almost no reason to override the <code>service</code>
 * method. <code>service</code> handles standard HTTP
 * requests by dispatching them to the handler methods
 * for each HTTP request type (the <code>do</code><i>Method</i>
 * methods listed above).
 *
 * <p>Likewise, there's almost no reason to override the
 * <code>doOptions</code> and <code>doTrace</code> methods.
 *
 * <p>Servlets typically run on multithreaded servers,
 * so be aware that a servlet must handle concurrent
 * requests 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 the
 * <a href="http://java.sun.com/Series/Tutorial/java/threads/multithreaded.html">
 * Java Tutorial on Multithreaded Programming</a> for more
 * information on handling multiple threads in a Java program.
 */
public abstract class HttpServlet extends GenericServlet {

    private static final long serialVersionUID = 1L;

    private static final String METHOD_DELETE = "DELETE";
    private static final String METHOD_HEAD = "HEAD";
    private static final String METHOD_GET = "GET";
    private static final String METHOD_OPTIONS = "OPTIONS";
    private static final String METHOD_POST = "POST";
    private static final String METHOD_PUT = "PUT";
    private static final String METHOD_TRACE = "TRACE";

    private static final String HEADER_IFMODSINCE = "If-Modified-Since";
    private static final String HEADER_LASTMOD = "Last-Modified";

    private static final String LSTRING_FILE =
        "jakarta.servlet.http.LocalStrings";
    private static final ResourceBundle lStrings =
        ResourceBundle.getBundle(LSTRING_FILE);

    private final Object cachedAllowHeaderValueLock = new Object();
    private volatile String cachedAllowHeaderValue = null;


    
Does nothing, because this is an abstract class.

/**
     * Does nothing, because this is an abstract class.
     */
    public HttpServlet() {
        // NOOP
    }


    
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 request header fields.

When overriding this method, read the request data,
write the response headers, get the response's writer or
output stream object, and finally, write the response data.
It's best to include content type and encoding. When using
a PrintWriter object to return the response,
set the content type before accessing the
PrintWriter object.

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 header (with the ServletResponse.setContentLength method), 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 header.

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, doGet
returns an HTTP "Bad Request" message.

Params:
  • req –  an HttpServletRequest object that contains the request the client has made of the servlet
  • resp –  an HttpServletResponse object that contains the response the servlet sends to the client
Throws:
  • IOException –   if an input or output error is
                             detected when the servlet handles
                             the GET request
  • ServletException –  if the request for the GET
                                 could not be handled
See Also:
/**
     * Called by the server (via the <code>service</code> method) to
     * allow a servlet to handle a GET request.
     *
     * <p>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 request header fields.
     *
     * <p>When overriding this method, read the request data,
     * write the response headers, get the response's writer or
     * output stream object, and finally, write the response data.
     * It's best to include content type and encoding. When using
     * a <code>PrintWriter</code> object to return the response,
     * set the content type before accessing the
     * <code>PrintWriter</code> object.
     *
     * <p>The servlet container must write the headers before
     * committing the response, because in HTTP the headers must be sent
     * before the response body.
     *
     * <p>Where possible, set the Content-Length header (with the
     * {@link jakarta.servlet.ServletResponse#setContentLength} method),
     * 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.
     *
     * <p>When using HTTP 1.1 chunked encoding (which means that the response
     * has a Transfer-Encoding header), do not set the Content-Length header.
     *
     * <p>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.
     *
     * <p>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.
     *
     * <p>If the request is incorrectly formatted, <code>doGet</code>
     * returns an HTTP "Bad Request" message.
     *
     * @param req   an {@link HttpServletRequest} object that
     *                  contains the request the client has made
     *                  of the servlet
     *
     * @param resp  an {@link HttpServletResponse} object that
     *                  contains the response the servlet sends
     *                  to the client
     *
     * @exception IOException   if an input or output error is
     *                              detected when the servlet handles
     *                              the GET request
     *
     * @exception ServletException  if the request for the GET
     *                                  could not be handled
     *
     * @see jakarta.servlet.ServletResponse#setContentType
     */
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {
        String msg = lStrings.getString("http.method_get_not_supported");
        sendMethodNotAllowed(req, resp, msg);
    }


    
Returns the time the HttpServletRequest
object 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.

Params:
  • req –   the HttpServletRequest
                 object that is sent to the servlet
Returns: a long integer specifying
             the time the HttpServletRequest
             object was last modified, in milliseconds
             since midnight, January 1, 1970 GMT, or
             -1 if the time is not known
/**
     * Returns the time the <code>HttpServletRequest</code>
     * object was last modified,
     * in milliseconds since midnight January 1, 1970 GMT.
     * If the time is unknown, this method returns a negative
     * number (the default).
     *
     * <p>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.
     *
     * @param req   the <code>HttpServletRequest</code>
     *                  object that is sent to the servlet
     *
     * @return  a <code>long</code> integer specifying
     *              the time the <code>HttpServletRequest</code>
     *              object was last modified, in milliseconds
     *              since midnight, January 1, 1970 GMT, or
     *              -1 if the time is not known
     */
    protected long getLastModified(HttpServletRequest req) {
        return -1;
    }


    
Receives an HTTP HEAD request from the protected
service method and handles the
request.
The client sends a HEAD request when it wants
to see only the headers of a response, such as
Content-Type or Content-Length. The HTTP HEAD
method counts the output bytes in the response
to set the Content-Length header accurately.

If you override this method, you can avoid computing
the response body and just set the response headers
directly to improve performance. Make sure that the
doHead method you write is both safe
and idempotent (that is, protects itself from being
called multiple times for one HTTP HEAD request).

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

Params:
  • req –   the request object that is passed to the servlet
  • resp –  the response object that the servlet
                 uses to return the headers to the client
Throws:
/**
     * <p>Receives an HTTP HEAD request from the protected
     * <code>service</code> method and handles the
     * request.
     * The client sends a HEAD request when it wants
     * to see only the headers of a response, such as
     * Content-Type or Content-Length. The HTTP HEAD
     * method counts the output bytes in the response
     * to set the Content-Length header accurately.
     *
     * <p>If you override this method, you can avoid computing
     * the response body and just set the response headers
     * directly to improve performance. Make sure that the
     * <code>doHead</code> method you write is both safe
     * and idempotent (that is, protects itself from being
     * called multiple times for one HTTP HEAD request).
     *
     * <p>If the HTTP HEAD request is incorrectly formatted,
     * <code>doHead</code> returns an HTTP "Bad Request"
     * message.
     *
     * @param req   the request object that is passed to the servlet
     *
     * @param resp  the response object that the servlet
     *                  uses to return the headers to the client
     *
     * @exception IOException   if an input or output error occurs
     *
     * @exception ServletException  if the request for the HEAD
     *                                  could not be handled
     */
    protected void doHead(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {

        if (DispatcherType.INCLUDE.equals(req.getDispatcherType())) {
            doGet(req, resp);
        } else {
            NoBodyResponse response = new NoBodyResponse(resp);
            doGet(req, response);
            response.setContentLength();
        }
    }


    
Called by the server (via the service method)
to allow a servlet to handle a POST request.
The HTTP POST method allows the client to send
data of unlimited length to the Web server a single time
and is useful when posting information such as
credit card numbers.

When overriding this method, read the request data,
write the response headers, get the response's writer or output
stream object, and finally, write the response data. It's best
to include content type and encoding. When using a
PrintWriter object to return the response, set the
content type before accessing the PrintWriter object.

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 header (with the ServletResponse.setContentLength method), 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 header.

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 HTTP POST request is incorrectly formatted,
doPost returns an HTTP "Bad Request" message.

Params:
  • req –  an HttpServletRequest object that contains the request the client has made of the servlet
  • resp –  an HttpServletResponse object that contains the response the servlet sends to the client
Throws:
  • IOException –   if an input or output error is
                             detected when the servlet handles
                             the request
  • ServletException –  if the request for the POST
                                 could not be handled
See Also:
/**
     * Called by the server (via the <code>service</code> method)
     * to allow a servlet to handle a POST request.
     *
     * The HTTP POST method allows the client to send
     * data of unlimited length to the Web server a single time
     * and is useful when posting information such as
     * credit card numbers.
     *
     * <p>When overriding this method, read the request data,
     * write the response headers, get the response's writer or output
     * stream object, and finally, write the response data. It's best
     * to include content type and encoding. When using a
     * <code>PrintWriter</code> object to return the response, set the
     * content type before accessing the <code>PrintWriter</code> object.
     *
     * <p>The servlet container must write the headers before committing the
     * response, because in HTTP the headers must be sent before the
     * response body.
     *
     * <p>Where possible, set the Content-Length header (with the
     * {@link jakarta.servlet.ServletResponse#setContentLength} method),
     * 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.
     *
     * <p>When using HTTP 1.1 chunked encoding (which means that the response
     * has a Transfer-Encoding header), do not set the Content-Length header.
     *
     * <p>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.
     *
     * <p>If the HTTP POST request is incorrectly formatted,
     * <code>doPost</code> returns an HTTP "Bad Request" message.
     *
     *
     * @param req   an {@link HttpServletRequest} object that
     *                  contains the request the client has made
     *                  of the servlet
     *
     * @param resp  an {@link HttpServletResponse} object that
     *                  contains the response the servlet sends
     *                  to the client
     *
     * @exception IOException   if an input or output error is
     *                              detected when the servlet handles
     *                              the request
     *
     * @exception ServletException  if the request for the POST
     *                                  could not be handled
     *
     * @see jakarta.servlet.ServletOutputStream
     * @see jakarta.servlet.ServletResponse#setContentType
     */
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {

        String msg = lStrings.getString("http.method_post_not_supported");
        sendMethodNotAllowed(req, resp, msg);
    }


    
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 2616
.

This method does not need to be either safe or idempotent.
Operations that doPut 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 HTTP PUT request is incorrectly formatted,
doPut returns an HTTP "Bad Request" message.

Params:
  • req –  the HttpServletRequest object that contains the request the client made of the servlet
  • resp –  the HttpServletResponse object that contains the response the servlet returns to the client
Throws:
  • IOException –   if an input or output error occurs
                             while the servlet is handling the
                             PUT request
  • ServletException –  if the request for the PUT
                                 cannot be handled
/**
     * Called by the server (via the <code>service</code> 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.
     *
     * <p>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 2616
     * <a href="http://www.ietf.org/rfc/rfc2616.txt"></a>.
     *
     * <p>This method does not need to be either safe or idempotent.
     * Operations that <code>doPut</code> 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.
     *
     * <p>If the HTTP PUT request is incorrectly formatted,
     * <code>doPut</code> returns an HTTP "Bad Request" message.
     *
     * @param req   the {@link HttpServletRequest} object that
     *                  contains the request the client made of
     *                  the servlet
     *
     * @param resp  the {@link HttpServletResponse} object that
     *                  contains the response the servlet returns
     *                  to the client
     *
     * @exception IOException   if an input or output error occurs
     *                              while the servlet is handling the
     *                              PUT request
     *
     * @exception ServletException  if the request for the PUT
     *                                  cannot be handled
     */
    protected void doPut(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {

        String msg = lStrings.getString("http.method_put_not_supported");
        sendMethodNotAllowed(req, resp, msg);
    }


    
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 URL in temporary storage.

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

Params:
  • req –  the HttpServletRequest object that contains the request the client made of the servlet
  • resp –  the HttpServletResponse object that contains the response the servlet returns to the client
Throws:
  • IOException –   if an input or output error occurs
                             while the servlet is handling the
                             DELETE request
  • ServletException –  if the request for the
                                 DELETE cannot be handled
/**
     * Called by the server (via the <code>service</code> 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.
     *
     * <p>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 URL in temporary storage.
     *
     * <p>If the HTTP DELETE request is incorrectly formatted,
     * <code>doDelete</code> returns an HTTP "Bad Request"
     * message.
     *
     * @param req   the {@link HttpServletRequest} object that
     *                  contains the request the client made of
     *                  the servlet
     *
     *
     * @param resp  the {@link HttpServletResponse} object that
     *                  contains the response the servlet returns
     *                  to the client
     *
     * @exception IOException   if an input or output error occurs
     *                              while the servlet is handling the
     *                              DELETE request
     *
     * @exception ServletException  if the request for the
     *                                  DELETE cannot be handled
     */
    protected void doDelete(HttpServletRequest req,
                            HttpServletResponse resp)
        throws ServletException, IOException {

        String msg = lStrings.getString("http.method_delete_not_supported");
        sendMethodNotAllowed(req, resp, msg);
    }


    private void sendMethodNotAllowed(HttpServletRequest req, HttpServletResponse resp, String msg) throws IOException {
        String protocol = req.getProtocol();
        // Note: Tomcat reports "" for HTTP/0.9 although some implementations
        //       may report HTTP/0.9
        if (protocol.length() == 0 || protocol.endsWith("0.9") || protocol.endsWith("1.0")) {
            resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
        } else {
            resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
        }
    }


    private String getCachedAllowHeaderValue() {
        if (cachedAllowHeaderValue == null) {
            synchronized (cachedAllowHeaderValueLock) {
                if (cachedAllowHeaderValue == null) {

                    Method[] methods = getAllDeclaredMethods(this.getClass());

                    // RFC 7230 does not define an order for this header
                    // This code aims to retain, broadly, the order of method
                    // tokens returned in earlier versions of this code. If that
                    // constraint is dropped then the code can be simplified
                    // further.

                    boolean allowGet = false;
                    boolean allowHead = false;
                    boolean allowPost = false;
                    boolean allowPut = false;
                    boolean allowDelete = false;

                    for (Method method : methods) {
                        switch (method.getName()) {
                            case "doGet": {
                                allowGet = true;
                                allowHead = true;
                                break;
                            }
                            case "doPost": {
                                allowPost = true;
                                break;
                            }
                            case "doPut": {
                                allowPut = true;
                                break;
                            }
                            case "doDelete": {
                                allowDelete = true;
                                break;
                            }
                            default:
                                // NO-OP
                        }

                    }

                    StringBuilder allow = new StringBuilder();

                    if (allowGet) {
                        allow.append(METHOD_GET);
                        allow.append(", ");
                    }

                    if (allowHead) {
                        allow.append(METHOD_HEAD);
                        allow.append(", ");
                    }

                    if (allowPost) {
                        allow.append(METHOD_POST);
                        allow.append(", ");
                    }

                    if (allowPut) {
                        allow.append(METHOD_PUT);
                        allow.append(", ");
                    }

                    if (allowDelete) {
                        allow.append(METHOD_DELETE);
                        allow.append(", ");
                    }

                    // Options is always allowed
                    allow.append(METHOD_OPTIONS);

                    cachedAllowHeaderValue = allow.toString();
                }
            }
        }

        return cachedAllowHeaderValue;
    }


    private static Method[] getAllDeclaredMethods(Class<?> c) {

        if (c.equals(jakarta.servlet.http.HttpServlet.class)) {
            return null;
        }

        Method[] parentMethods = getAllDeclaredMethods(c.getSuperclass());
        Method[] thisMethods = c.getDeclaredMethods();

        if ((parentMethods != null) && (parentMethods.length > 0)) {
            Method[] allMethods =
                new Method[parentMethods.length + thisMethods.length];
            System.arraycopy(parentMethods, 0, allMethods, 0,
                             parentMethods.length);
            System.arraycopy(thisMethods, 0, allMethods, parentMethods.length,
                             thisMethods.length);

            thisMethods = allMethods;
        }

        return thisMethods;
    }


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

Params:
  • req –  the HttpServletRequest object that contains the request the client made of the servlet
  • resp –  the HttpServletResponse object that contains the response the servlet returns to the client
Throws:
  • IOException –   if an input or output error occurs
                             while the servlet is handling the
                             OPTIONS request
  • ServletException –  if the request for the
                                 OPTIONS cannot be handled
/**
     * Called by the server (via the <code>service</code> method)
     * to allow a servlet to handle an OPTIONS request.
     *
     * The OPTIONS request determines which HTTP methods
     * the server supports and
     * returns an appropriate header. For example, if a servlet
     * overrides <code>doGet</code>, this method returns the
     * following header:
     *
     * <p><code>Allow: GET, HEAD, TRACE, OPTIONS</code>
     *
     * <p>There's no need to override this method unless the
     * servlet implements new HTTP methods, beyond those
     * implemented by HTTP 1.1.
     *
     * @param req   the {@link HttpServletRequest} object that
     *                  contains the request the client made of
     *                  the servlet
     *
     * @param resp  the {@link HttpServletResponse} object that
     *                  contains the response the servlet returns
     *                  to the client
     *
     * @exception IOException   if an input or output error occurs
     *                              while the servlet is handling the
     *                              OPTIONS request
     *
     * @exception ServletException  if the request for the
     *                                  OPTIONS cannot be handled
     */
    protected void doOptions(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {

        String allow = getCachedAllowHeaderValue();

        // Tomcat specific hack to see if TRACE is allowed
        if (TomcatHack.getAllowTrace(req)) {
            if (allow.length() == 0) {
                allow = METHOD_TRACE;
            } else {
                allow = allow + ", " + METHOD_TRACE;
            }
        }

        resp.setHeader("Allow", allow);
    }


    
Called by the server (via the service method)
to allow a servlet to handle a TRACE request.
A TRACE returns the headers sent with the TRACE
request to the client, so that they can be used in
debugging. There's no need to override this method.

Params:
  • req –  the HttpServletRequest object that contains the request the client made of the servlet
  • resp –  the HttpServletResponse object that contains the response the servlet returns to the client
Throws:
  • IOException –   if an input or output error occurs
                             while the servlet is handling the
                             TRACE request
  • ServletException –  if the request for the
                                 TRACE cannot be handled
/**
     * Called by the server (via the <code>service</code> method)
     * to allow a servlet to handle a TRACE request.
     *
     * A TRACE returns the headers sent with the TRACE
     * request to the client, so that they can be used in
     * debugging. There's no need to override this method.
     *
     * @param req   the {@link HttpServletRequest} object that
     *                  contains the request the client made of
     *                  the servlet
     *
     * @param resp  the {@link HttpServletResponse} object that
     *                  contains the response the servlet returns
     *                  to the client
     *
     * @exception IOException   if an input or output error occurs
     *                              while the servlet is handling the
     *                              TRACE request
     *
     * @exception ServletException  if the request for the
     *                                  TRACE cannot be handled
     */
    protected void doTrace(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {

        int responseLength;

        String CRLF = "\r\n";
        StringBuilder buffer = new StringBuilder("TRACE ").append(req.getRequestURI())
            .append(" ").append(req.getProtocol());

        Enumeration<String> reqHeaderEnum = req.getHeaderNames();

        while( reqHeaderEnum.hasMoreElements() ) {
            String headerName = reqHeaderEnum.nextElement();
            buffer.append(CRLF).append(headerName).append(": ")
                .append(req.getHeader(headerName));
        }

        buffer.append(CRLF);

        responseLength = buffer.length();

        resp.setContentType("message/http");
        resp.setContentLength(responseLength);
        ServletOutputStream out = resp.getOutputStream();
        out.print(buffer.toString());
        out.close();
    }


    
Receives standard HTTP requests from the public
service method and dispatches
them to the doMethod methods defined in this class. This method is an HTTP-specific version of the Servlet.service method. There's no need to override this method. 
Params:
  • req –  the HttpServletRequest object that contains the request the client made of the servlet
  • resp –  the HttpServletResponse object that contains the response the servlet returns to the client
Throws:
  • IOException –   if an input or output error occurs
                             while the servlet is handling the
                             HTTP request
  • ServletException –  if the HTTP request
                                 cannot be handled
See Also:
/**
     * Receives standard HTTP requests from the public
     * <code>service</code> method and dispatches
     * them to the <code>do</code><i>Method</i> methods defined in
     * this class. This method is an HTTP-specific version of the
     * {@link jakarta.servlet.Servlet#service} method. There's no
     * need to override this method.
     *
     * @param req   the {@link HttpServletRequest} object that
     *                  contains the request the client made of
     *                  the servlet
     *
     * @param resp  the {@link HttpServletResponse} object that
     *                  contains the response the servlet returns
     *                  to the client
     *
     * @exception IOException   if an input or output error occurs
     *                              while the servlet is handling the
     *                              HTTP request
     *
     * @exception ServletException  if the HTTP request
     *                                  cannot be handled
     *
     * @see jakarta.servlet.Servlet#service
     */
    protected void service(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {

        String method = req.getMethod();

        if (method.equals(METHOD_GET)) {
            long lastModified = getLastModified(req);
            if (lastModified == -1) {
                // servlet doesn't support if-modified-since, no reason
                // to go through further expensive logic
                doGet(req, resp);
            } else {
                long ifModifiedSince;
                try {
                    ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
                } catch (IllegalArgumentException iae) {
                    // Invalid date header - proceed as if none was set
                    ifModifiedSince = -1;
                }
                if (ifModifiedSince < (lastModified / 1000 * 1000)) {
                    // If the servlet mod time is later, call doGet()
                    // Round down to the nearest second for a proper compare
                    // A ifModifiedSince of -1 will always be less
                    maybeSetLastModified(resp, lastModified);
                    doGet(req, resp);
                } else {
                    resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
                }
            }

        } else if (method.equals(METHOD_HEAD)) {
            long lastModified = getLastModified(req);
            maybeSetLastModified(resp, lastModified);
            doHead(req, resp);

        } else if (method.equals(METHOD_POST)) {
            doPost(req, resp);

        } else if (method.equals(METHOD_PUT)) {
            doPut(req, resp);

        } else if (method.equals(METHOD_DELETE)) {
            doDelete(req, resp);

        } else if (method.equals(METHOD_OPTIONS)) {
            doOptions(req,resp);

        } else if (method.equals(METHOD_TRACE)) {
            doTrace(req,resp);

        } else {
            //
            // Note that this means NO servlet supports whatever
            // method was requested, anywhere on this server.
            //

            String errMsg = lStrings.getString("http.method_not_implemented");
            Object[] errArgs = new Object[1];
            errArgs[0] = method;
            errMsg = MessageFormat.format(errMsg, errArgs);

            resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
        }
    }


    /*
     * Sets the Last-Modified entity header field, if it has not
     * already been set and if the value is meaningful.  Called before
     * doGet, to ensure that headers are set before response data is
     * written.  A subclass might have set this header already, so we
     * check.
     */
    private void maybeSetLastModified(HttpServletResponse resp,
                                      long lastModified) {
        if (resp.containsHeader(HEADER_LASTMOD))
            return;
        if (lastModified >= 0)
            resp.setDateHeader(HEADER_LASTMOD, lastModified);
    }


    
Dispatches client requests to the protected
service method. There's no need to
override this method.

Params:
  • req –  the HttpServletRequest object that contains the request the client made of the servlet
  • res –  the HttpServletResponse object that contains the response the servlet returns to the client
Throws:
  • IOException –   if an input or output error occurs
                             while the servlet is handling the
                             HTTP request
  • ServletException –  if the HTTP request cannot
                                 be handled
See Also:
/**
     * Dispatches client requests to the protected
     * <code>service</code> method. There's no need to
     * override this method.
     *
     * @param req   the {@link HttpServletRequest} object that
     *                  contains the request the client made of
     *                  the servlet
     *
     * @param res   the {@link HttpServletResponse} object that
     *                  contains the response the servlet returns
     *                  to the client
     *
     * @exception IOException   if an input or output error occurs
     *                              while the servlet is handling the
     *                              HTTP request
     *
     * @exception ServletException  if the HTTP request cannot
     *                                  be handled
     *
     * @see jakarta.servlet.Servlet#service
     */
    @Override
    public void service(ServletRequest req, ServletResponse res)
        throws ServletException, IOException {

        HttpServletRequest  request;
        HttpServletResponse response;

        try {
            request = (HttpServletRequest) req;
            response = (HttpServletResponse) res;
        } catch (ClassCastException e) {
            throw new ServletException(lStrings.getString("http.non_http"));
        }
        service(request, response);
    }


    private static class TomcatHack {

        private static final Class<?> REQUEST_FACADE_CLAZZ;
        private static final Method GET_ALLOW_TRACE;


        static {
            Method m1 = null;
            Class<?> c1 = null;
            try {
                c1 = Class.forName("org.apache.catalina.connector.RequestFacade");
                m1 = c1.getMethod("getAllowTrace", (Class<?>[]) null);
            } catch (ReflectiveOperationException | SecurityException | IllegalArgumentException e) {
                // Ignore. Not running on Tomcat. TRACE is always allowed.
            }
            REQUEST_FACADE_CLAZZ = c1;
            GET_ALLOW_TRACE = m1;
        }

        public static boolean getAllowTrace(HttpServletRequest req) {
            if (REQUEST_FACADE_CLAZZ != null && GET_ALLOW_TRACE != null) {
                if (REQUEST_FACADE_CLAZZ.isAssignableFrom(req.getClass())) {
                    try {
                        return ((Boolean) GET_ALLOW_TRACE.invoke(req, (Object[]) null)).booleanValue();
                    } catch (IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {
                        // Should never happen given the checks in place.
                        // Ignore
                    }
                }
            }
            return true;
        }
    }
}


/*
 * A response wrapper for use in (dumb) "HEAD" support.
 * This just swallows that body, counting the bytes in order to set
 * the content length appropriately.  All other methods delegate to the
 * wrapped HTTP Servlet Response object.
 */
// file private
class NoBodyResponse extends HttpServletResponseWrapper {
    private final NoBodyOutputStream noBody;
    private PrintWriter writer;
    private boolean didSetContentLength;

    // file private
    NoBodyResponse(HttpServletResponse r) {
        super(r);
        noBody = new NoBodyOutputStream(this);
    }

    // file private
    void setContentLength() {
        if (!didSetContentLength) {
            if (writer != null) {
                writer.flush();
            }
            super.setContentLength(noBody.getContentLength());
        }
    }


    // SERVLET RESPONSE interface methods

    @Override
    public void setContentLength(int len) {
        super.setContentLength(len);
        didSetContentLength = true;
    }

    @Override
    public void setContentLengthLong(long len) {
        super.setContentLengthLong(len);
        didSetContentLength = true;
    }

    @Override
    public void setHeader(String name, String value) {
        super.setHeader(name, value);
        checkHeader(name);
    }

    @Override
    public void addHeader(String name, String value) {
        super.addHeader(name, value);
        checkHeader(name);
    }

    @Override
    public void setIntHeader(String name, int value) {
        super.setIntHeader(name, value);
        checkHeader(name);
    }

    @Override
    public void addIntHeader(String name, int value) {
        super.addIntHeader(name, value);
        checkHeader(name);
    }

    private void checkHeader(String name) {
        if ("content-length".equalsIgnoreCase(name)) {
            didSetContentLength = true;
        }
    }

    @Override
    public ServletOutputStream getOutputStream() throws IOException {
        return noBody;
    }

    @Override
    public PrintWriter getWriter() throws UnsupportedEncodingException {

        if (writer == null) {
            OutputStreamWriter w;

            w = new OutputStreamWriter(noBody, getCharacterEncoding());
            writer = new PrintWriter(w);
        }
        return writer;
    }
}


/*
 * Servlet output stream that gobbles up all its data.
 */

// file private
class NoBodyOutputStream extends ServletOutputStream {

    private static final String LSTRING_FILE =
        "jakarta.servlet.http.LocalStrings";
    private static final ResourceBundle lStrings =
        ResourceBundle.getBundle(LSTRING_FILE);

    private final HttpServletResponse response;
    private boolean flushed = false;
    private int contentLength = 0;

    // file private
    NoBodyOutputStream(HttpServletResponse response) {
        this.response = response;
    }

    // file private
    int getContentLength() {
        return contentLength;
    }

    @Override
    public void write(int b) throws IOException {
        contentLength++;
        checkCommit();
    }

    @Override
    public void write(byte buf[], int offset, int len) throws IOException {
        if (buf == null) {
            throw new NullPointerException(
                    lStrings.getString("err.io.nullArray"));
        }

        if (offset < 0 || len < 0 || offset+len > buf.length) {
            String msg = lStrings.getString("err.io.indexOutOfBounds");
            Object[] msgArgs = new Object[3];
            msgArgs[0] = Integer.valueOf(offset);
            msgArgs[1] = Integer.valueOf(len);
            msgArgs[2] = Integer.valueOf(buf.length);
            msg = MessageFormat.format(msg, msgArgs);
            throw new IndexOutOfBoundsException(msg);
        }

        contentLength += len;
        checkCommit();
    }

    @Override
    public boolean isReady() {
        // TODO SERVLET 3.1
        return false;
    }

    @Override
    public void setWriteListener(jakarta.servlet.WriteListener listener) {
        // TODO SERVLET 3.1
    }

    private void checkCommit() throws IOException {
        if (!flushed && contentLength > response.getBufferSize()) {
            response.flushBuffer();
            flushed = true;
        }
    }
}