javax.servlet.http.HttpServlet Maven / Gradle / Ivy
/*
* Copyright (c) 1997-2018 Oracle and/or its affiliates and others.
* All rights reserved.
* Copyright 2004 The Apache Software Foundation
*
* Licensed 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 javax.servlet.http;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.OutputStreamWriter;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.Method;
import java.text.MessageFormat;
import java.util.Enumeration;
import java.util.ResourceBundle;
import javax.servlet.*;
/**
*
* 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 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 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.
*
* @author Various
*/
public abstract class HttpServlet extends GenericServlet {
private static final long serialVersionUID = 8466325577512134784L;
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 = "javax.servlet.http.LocalStrings";
private static ResourceBundle lStrings = ResourceBundle.getBundle(LSTRING_FILE);
/**
* Does nothing, because this is an abstract class.
*
*/
public HttpServlet() {
}
/**
*
* 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 {@link javax.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.
*
*
* 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.
*
* @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
*
* @throws IOException if an input or output error is detected when the servlet handles the GET request
*
* @throws ServletException if the request for the GET could not be handled
*
* @see javax.servlet.ServletResponse#setContentType
*/
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String protocol = req.getProtocol();
String msg = lStrings.getString("http.method_get_not_supported");
if (protocol.endsWith("1.1")) {
resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
} else {
resp.sendError(HttpServletResponse.SC_BAD_REQUEST, 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.
*
* @param req the HttpServletRequest object that is sent to the servlet
*
* @return 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
*/
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.
*
* @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 clien
*
* @throws IOException if an input or output error occurs
*
* @throws ServletException if the request for the HEAD could not be handled
*/
protected void doHead(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
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 {@link javax.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.
*
*
* 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.
*
*
* @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
*
* @throws IOException if an input or output error is detected when the servlet handles the request
*
* @throws ServletException if the request for the POST could not be handled
*
* @see javax.servlet.ServletOutputStream
* @see javax.servlet.ServletResponse#setContentType
*/
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String protocol = req.getProtocol();
String msg = lStrings.getString("http.method_post_not_supported");
if (protocol.endsWith("1.1")) {
resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
} else {
resp.sendError(HttpServletResponse.SC_BAD_REQUEST, 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.
*
* @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
*
* @throws IOException if an input or output error occurs while the servlet is handling the PUT request
*
* @throws ServletException if the request for the PUT cannot be handled
*/
protected void doPut(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String protocol = req.getProtocol();
String msg = lStrings.getString("http.method_put_not_supported");
if (protocol.endsWith("1.1")) {
resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
} else {
resp.sendError(HttpServletResponse.SC_BAD_REQUEST, 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.
*
* @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
*
* @throws IOException if an input or output error occurs while the servlet is handling the DELETE request
*
* @throws ServletException if the request for the DELETE cannot be handled
*/
protected void doDelete(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String protocol = req.getProtocol();
String msg = lStrings.getString("http.method_delete_not_supported");
if (protocol.endsWith("1.1")) {
resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
} else {
resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
}
}
private Method[] getAllDeclaredMethods(Class c) {
Class clazz = c;
Method[] allMethods = null;
while (!clazz.equals(HttpServlet.class)) {
Method[] thisMethods = clazz.getDeclaredMethods();
if (allMethods != null && allMethods.length > 0) {
Method[] subClassMethods = allMethods;
allMethods = new Method[thisMethods.length + subClassMethods.length];
System.arraycopy(thisMethods, 0, allMethods, 0, thisMethods.length);
System.arraycopy(subClassMethods, 0, allMethods, thisMethods.length, subClassMethods.length);
} else {
allMethods = thisMethods;
}
clazz = clazz.getSuperclass();
}
return ((allMethods != null) ? allMethods : new Method[0]);
}
/**
* 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.
*
* @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
*
* @throws IOException if an input or output error occurs while the servlet is handling the OPTIONS request
*
* @throws ServletException if the request for the OPTIONS cannot be handled
*/
protected void doOptions(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
Method[] methods = getAllDeclaredMethods(this.getClass());
boolean ALLOW_GET = false;
boolean ALLOW_HEAD = false;
boolean ALLOW_POST = false;
boolean ALLOW_PUT = false;
boolean ALLOW_DELETE = false;
boolean ALLOW_TRACE = true;
boolean ALLOW_OPTIONS = true;
for (int i = 0; i < methods.length; i++) {
String methodName = methods[i].getName();
if (methodName.equals("doGet")) {
ALLOW_GET = true;
ALLOW_HEAD = true;
} else if (methodName.equals("doPost")) {
ALLOW_POST = true;
} else if (methodName.equals("doPut")) {
ALLOW_PUT = true;
} else if (methodName.equals("doDelete")) {
ALLOW_DELETE = true;
}
}
// we know "allow" is not null as ALLOW_OPTIONS = true
// when this method is invoked
StringBuilder allow = new StringBuilder();
if (ALLOW_GET) {
allow.append(METHOD_GET);
}
if (ALLOW_HEAD) {
if (allow.length() > 0) {
allow.append(", ");
}
allow.append(METHOD_HEAD);
}
if (ALLOW_POST) {
if (allow.length() > 0) {
allow.append(", ");
}
allow.append(METHOD_POST);
}
if (ALLOW_PUT) {
if (allow.length() > 0) {
allow.append(", ");
}
allow.append(METHOD_PUT);
}
if (ALLOW_DELETE) {
if (allow.length() > 0) {
allow.append(", ");
}
allow.append(METHOD_DELETE);
}
if (ALLOW_TRACE) {
if (allow.length() > 0) {
allow.append(", ");
}
allow.append(METHOD_TRACE);
}
if (ALLOW_OPTIONS) {
if (allow.length() > 0) {
allow.append(", ");
}
allow.append(METHOD_OPTIONS);
}
resp.setHeader("Allow", allow.toString());
}
/**
* 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.
*
* @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
*
* @throws IOException if an input or output error occurs while the servlet is handling the TRACE request
*
* @throws 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 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());
}
/**
* Receives standard HTTP requests from the public service method and dispatches them to the
* doXXX methods defined in this class. This method is an HTTP-specific version of the
* {@link javax.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
*
* @throws IOException if an input or output error occurs while the servlet is handling the HTTP request
*
* @throws ServletException if the HTTP request cannot be handled
*
* @see javax.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 = req.getDateHeader(HEADER_IFMODSINCE);
if (ifModifiedSince < lastModified) {
// 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.
*
* @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
*
* @throws IOException if an input or output error occurs while the servlet is handling the HTTP request
*
* @throws ServletException if the HTTP request cannot be handled or if either parameter is not an instance of its
* respective {@link HttpServletRequest} or {@link HttpServletResponse} counterparts.
*
* @see javax.servlet.Servlet#service
*/
@Override
public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
HttpServletRequest request;
HttpServletResponse response;
if (!(req instanceof HttpServletRequest && res instanceof HttpServletResponse)) {
throw new ServletException("non-HTTP request or response");
}
request = (HttpServletRequest) req;
response = (HttpServletResponse) res;
service(request, response);
}
}
/*
* A response that includes no body, 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 directly to the wrapped HTTP Servlet
* Response object.
*/
// file private
class NoBodyResponse extends HttpServletResponseWrapper {
private static final ResourceBundle lStrings = ResourceBundle.getBundle("javax.servlet.http.LocalStrings");
private NoBodyOutputStream noBody;
private PrintWriter writer;
private boolean didSetContentLength;
private boolean usingOutputStream;
// file private
NoBodyResponse(HttpServletResponse r) {
super(r);
noBody = new NoBodyOutputStream();
}
// file private
void setContentLength() {
if (!didSetContentLength) {
if (writer != null) {
writer.flush();
}
setContentLength(noBody.getContentLength());
}
}
@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 {
if (writer != null) {
throw new IllegalStateException(lStrings.getString("err.ise.getOutputStream"));
}
usingOutputStream = true;
return noBody;
}
@Override
public PrintWriter getWriter() throws UnsupportedEncodingException {
if (usingOutputStream) {
throw new IllegalStateException(lStrings.getString("err.ise.getWriter"));
}
if (writer == null) {
OutputStreamWriter 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 = "javax.servlet.http.LocalStrings";
private static ResourceBundle lStrings = ResourceBundle.getBundle(LSTRING_FILE);
private int contentLength = 0;
// file private
NoBodyOutputStream() {
}
// file private
int getContentLength() {
return contentLength;
}
@Override
public void write(int b) {
contentLength++;
}
@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;
}
@Override
public boolean isReady() {
return false;
}
@Override
public void setWriteListener(WriteListener writeListener) {
}
}