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httpServlet源码:

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/*
* 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 javax.servlet.http;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.Method;
import java.text.MessageFormat;
import java.util.Enumeration;
import java.util.ResourceBundle;
import javax.servlet.DispatcherType;
import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
/**
* 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>
*
* 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>Method
* methods listed above).
*
* Likewise, there's almost no reason to override the
* <code>doOptions</code> and <code>doTrace</code> 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
* <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 =
"javax.servlet.http.LocalStrings";
private static final ResourceBundle lStrings =
ResourceBundle.getBundle(LSTRING_FILE);
/**
* Does nothing, because this is an abstract class.
*/
public HttpServlet() {
// NOOP
}
/**
* Called by the server (via the <code>service</code> 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 <code>PrintWriter</code> object to return the response,
* set the content type before accessing the
* <code>PrintWriter</code> 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, <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 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 <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).
*
* 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
* <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.
*
* 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).
*
* 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 <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.
*
* 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.
*
* 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,
* <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 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 <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.
*
* 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>.
*
* 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.
*
* 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 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 <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.
*
* 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,
* <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 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 static Method[] getAllDeclaredMethods(Class<?> c) {
if (c.equals(javax.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 <code>service</code> 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 <code>doGet</code>, this method returns the
* following header:
*
* <code>Allow: GET, HEAD, TRACE, OPTIONS</code>
*
* 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 {
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++) {
Method m = methods[i];
if (m.getName().equals("doGet")) {
ALLOW_GET = true;
ALLOW_HEAD = true;
}
if (m.getName().equals("doPost"))
ALLOW_POST = true;
if (m.getName().equals("doPut"))
ALLOW_PUT = true;
if (m.getName().equals("doDelete"))
ALLOW_DELETE = true;
}
String allow = null;
if (ALLOW_GET)
allow=METHOD_GET;
if (ALLOW_HEAD)
if (allow==null) allow=METHOD_HEAD;
else allow += ", " + METHOD_HEAD;
if (ALLOW_POST)
if (allow==null) allow=METHOD_POST;
else allow += ", " + METHOD_POST;
if (ALLOW_PUT)
if (allow==null) allow=METHOD_PUT;
else allow += ", " + METHOD_PUT;
if (ALLOW_DELETE)
if (allow==null) allow=METHOD_DELETE;
else allow += ", " + METHOD_DELETE;
if (ALLOW_TRACE)
if (allow==null) allow=METHOD_TRACE;
else allow += ", " + METHOD_TRACE;
if (ALLOW_OPTIONS)
if (allow==null) allow=METHOD_OPTIONS;
else allow += ", " + METHOD_OPTIONS;
resp.setHeader("Allow", allow);
}
/**
* 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();
return;
}
/**
* Receives standard HTTP requests from the public
* <code>service</code> method and dispatches
* them to the <code>do</code>Method 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
*
* @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 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;
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
* <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 javax.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("non-HTTP request or response");
}
service(request, response);
}
}
/*
* 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();
}
// 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 =
"javax.servlet.http.LocalStrings";
private static final ResourceBundle lStrings =
ResourceBundle.getBundle(LSTRING_FILE);
private int contentLength = 0;
// file private
NoBodyOutputStream() {
// NOOP
}
// 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() {
// TODO SERVLET 3.1
return false;
}
@Override
public void setWriteListener(javax.servlet.WriteListener listener) {
// TODO SERVLET 3.1
}
}

GenericServlet源码:

[java] view plain copy

/*
* 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 javax.servlet;
import java.io.IOException;
import java.util.Enumeration;
/**
* Defines a generic, protocol-independent servlet. To write an HTTP servlet for
* use on the Web, extend {@link javax.servlet.http.HttpServlet} instead.
*
* <code>GenericServlet</code> implements the <code>Servlet</code> and
* <code>ServletConfig</code> interfaces. <code>GenericServlet</code> may be
* directly extended by a servlet, although it's more common to extend a
* protocol-specific subclass such as <code>HttpServlet</code>.
*
* <code>GenericServlet</code> makes writing servlets easier. It provides simple
* versions of the lifecycle methods <code>init</code> and <code>destroy</code>
* and of the methods in the <code>ServletConfig</code> interface.
* <code>GenericServlet</code> also implements the <code>log</code> method,
* declared in the <code>ServletContext</code> interface.
*
* To write a generic servlet, you need only override the abstract
* <code>service</code> method.
*/
public abstract class GenericServlet implements Servlet, ServletConfig,
java.io.Serializable {
private static final long serialVersionUID = 1L;
private transient ServletConfig config;
/**
* Does nothing. All of the servlet initialization is done by one of the
* <code>init</code> methods.
*/
public GenericServlet() {
// NOOP
}
/**
* Called by the servlet container to indicate to a servlet that the servlet
* is being taken out of service. See {@link Servlet#destroy}.
*/
@Override
public void destroy() {
// NOOP by default
}
/**
* Returns a <code>String</code> containing the value of the named
* initialization parameter, or <code>null</code> if the parameter does not
* exist. See {@link ServletConfig#getInitParameter}.
*
* This method is supplied for convenience. It gets the value of the named
* parameter from the servlet's <code>ServletConfig</code> object.
*
* @param name
* a <code>String</code> specifying the name of the
* initialization parameter
* @return String a <code>String</code> containing the value of the
* initialization parameter
*/
@Override
public String getInitParameter(String name) {
return getServletConfig().getInitParameter(name);
}
/**
* Returns the names of the servlet's initialization parameters as an
* <code>Enumeration</code> of <code>String</code> objects, or an empty
* <code>Enumeration</code> if the servlet has no initialization parameters.
* See {@link ServletConfig#getInitParameterNames}.
*
* This method is supplied for convenience. It gets the parameter names from
* the servlet's <code>ServletConfig</code> object.
*
* @return Enumeration an enumeration of <code>String</code> objects
* containing the names of the servlet's initialization parameters
*/
@Override
public Enumeration<String> getInitParameterNames() {
return getServletConfig().getInitParameterNames();
}
/**
* Returns this servlet's {@link ServletConfig} object.
*
* @return ServletConfig the <code>ServletConfig</code> object that
* initialized this servlet
*/
@Override
public ServletConfig getServletConfig() {
return config;
}
/**
* Returns a reference to the {@link ServletContext} in which this servlet
* is running. See {@link ServletConfig#getServletContext}.
*
* This method is supplied for convenience. It gets the context from the
* servlet's <code>ServletConfig</code> object.
*
* @return ServletContext the <code>ServletContext</code> object passed to
* this servlet by the <code>init</code> method
*/
@Override
public ServletContext getServletContext() {
return getServletConfig().getServletContext();
}
/**
* Returns information about the servlet, such as author, version, and
* copyright. By default, this method returns an empty string. Override this
* method to have it return a meaningful value. See
* {@link Servlet#getServletInfo}.
*
* @return String information about this servlet, by default an empty string
*/
@Override
public String getServletInfo() {
return "";
}
/**
* Called by the servlet container to indicate to a servlet that the servlet
* is being placed into service. See {@link Servlet#init}.
*
* This implementation stores the {@link ServletConfig} object it receives
* from the servlet container for later use. When overriding this form of
* the method, call <code>super.init(config)</code>.
*
* @param config
* the <code>ServletConfig</code> object that contains
* configuration information for this servlet
* @exception ServletException
* if an exception occurs that interrupts the servlet's
* normal operation
* @see UnavailableException
*/
@Override
public void init(ServletConfig config) throws ServletException {
this.config = config;
this.init();
}
/**
* A convenience method which can be overridden so that there's no need to
* call <code>super.init(config)</code>.
*
* Instead of overriding {@link #init(ServletConfig)}, simply override this
* method and it will be called by
* <code>GenericServlet.init(ServletConfig config)</code>. The
* <code>ServletConfig</code> object can still be retrieved via
* {@link #getServletConfig}.
*
* @exception ServletException
* if an exception occurs that interrupts the servlet's
* normal operation
*/
public void init() throws ServletException {
// NOOP by default
}
/**
* Writes the specified message to a servlet log file, prepended by the
* servlet's name. See {@link ServletContext#log(String)}.
*
* @param msg
* a <code>String</code> specifying the message to be written to
* the log file
*/
public void log(String msg) {
getServletContext().log(getServletName() + ": " + msg);
}
/**
* Writes an explanatory message and a stack trace for a given
* <code>Throwable</code> exception to the servlet log file, prepended by
* the servlet's name. See {@link ServletContext#log(String, Throwable)}.
*
* @param message
* a <code>String</code> that describes the error or exception
* @param t
* the <code>java.lang.Throwable</code> error or exception
*/
public void log(String message, Throwable t) {
getServletContext().log(getServletName() + ": " + message, t);
}
/**
* Called by the servlet container to allow the servlet to respond to a
* request. See {@link Servlet#service}.
*
* This method is declared abstract so subclasses, such as
* <code>HttpServlet</code>, must override it.
*
* @param req
* the <code>ServletRequest</code> object that contains the
* client's request
* @param res
* the <code>ServletResponse</code> object that will contain the
* servlet's response
* @exception ServletException
* if an exception occurs that interferes with the servlet's
* normal operation occurred
* @exception IOException
* if an input or output exception occurs
*/
@Override
public abstract void service(ServletRequest req, ServletResponse res)
throws ServletException, IOException;
/**
* Returns the name of this servlet instance. See
* {@link ServletConfig#getServletName}.
*
* @return the name of this servlet instance
*/
@Override
public String getServletName() {
return config.getServletName();
}
}

Servlet源码:

[java] view plain copy

/*
* 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 javax.servlet;
import java.io.IOException;
/**
* Defines methods that all servlets must implement.
*
*
* A servlet is a small Java program that runs within a Web server. Servlets
* receive and respond to requests from Web clients, usually across HTTP, the
* HyperText Transfer Protocol.
*
*
* To implement this interface, you can write a generic servlet that extends
* <code>javax.servlet.GenericServlet</code> or an HTTP servlet that extends
* <code>javax.servlet.http.HttpServlet</code>.
*
*
* This interface defines methods to initialize a servlet, to service requests,
* and to remove a servlet from the server. These are known as life-cycle
* methods and are called in the following sequence:
* <ol>
* <li>The servlet is constructed, then initialized with the <code>init</code>
* method.
* <li>Any calls from clients to the <code>service</code> method are handled.
* <li>The servlet is taken out of service, then destroyed with the
* <code>destroy</code> method, then garbage collected and finalized.
* </ol>
*
*
* In addition to the life-cycle methods, this interface provides the
* <code>getServletConfig</code> method, which the servlet can use to get any
* startup information, and the <code>getServletInfo</code> method, which allows
* the servlet to return basic information about itself, such as author,
* version, and copyright.
*
* @see GenericServlet
* @see javax.servlet.http.HttpServlet
*/
public interface Servlet {
/**
* Called by the servlet container to indicate to a servlet that the servlet
* is being placed into service.
*
*
* The servlet container calls the <code>init</code> method exactly once
* after instantiating the servlet. The <code>init</code> method must
* complete successfully before the servlet can receive any requests.
*
*
* The servlet container cannot place the servlet into service if the
* <code>init</code> method
* <ol>
* <li>Throws a <code>ServletException</code>
* <li>Does not return within a time period defined by the Web server
* </ol>
*
*
* @param config
* a <code>ServletConfig</code> object containing the servlet's
* configuration and initialization parameters
*
* @exception ServletException
* if an exception has occurred that interferes with the
* servlet's normal operation
*
* @see UnavailableException
* @see #getServletConfig
*/
public void init(ServletConfig config) throws ServletException;
/**
*
* Returns a {@link ServletConfig} object, which contains initialization and
* startup parameters for this servlet. The <code>ServletConfig</code>
* object returned is the one passed to the <code>init</code> method.
*
*
* Implementations of this interface are responsible for storing the
* <code>ServletConfig</code> object so that this method can return it. The
* {@link GenericServlet} class, which implements this interface, already
* does this.
*
* @return the <code>ServletConfig</code> object that initializes this
* servlet
*
* @see #init
*/
public ServletConfig getServletConfig();
/**
* Called by the servlet container to allow the servlet to respond to a
* request.
*
*
* This method is only called after the servlet's <code>init()</code> method
* has completed successfully.
*
*
* The status code of the response always should be set for a servlet that
* throws or sends an error.
*
*
*
* Servlets typically run inside multithreaded servlet containers that can
* handle multiple requests concurrently. Developers must be aware to
* synchronize access to any shared resources such as files, network
* connections, and as well as the servlet's class and instance variables.
* More information on multithreaded programming in Java is available in <a
* href
* ="http://java.sun.com/Series/Tutorial/java/threads/multithreaded.html">
* the Java tutorial on multi-threaded programming</a>.
*
*
* @param req
* the <code>ServletRequest</code> object that contains the
* client's request
*
* @param res
* the <code>ServletResponse</code> object that contains the
* servlet's response
*
* @exception ServletException
* if an exception occurs that interferes with the servlet's
* normal operation
*
* @exception IOException
* if an input or output exception occurs
*/
public void service(ServletRequest req, ServletResponse res)
throws ServletException, IOException;
/**
* Returns information about the servlet, such as author, version, and
* copyright.
*
*
* The string that this method returns should be plain text and not markup
* of any kind (such as HTML, XML, etc.).
*
* @return a <code>String</code> containing servlet information
*/
public String getServletInfo();
/**
* Called by the servlet container to indicate to a servlet that the servlet
* is being taken out of service. This method is only called once all
* threads within the servlet's <code>service</code> method have exited or
* after a timeout period has passed. After the servlet container calls this
* method, it will not call the <code>service</code> method again on this
* servlet.
*
*
* This method gives the servlet an opportunity to clean up any resources
* that are being held (for example, memory, file handles, threads) and make
* sure that any persistent state is synchronized with the servlet's current
* state in memory.
*/
public void destroy();
}

httpServlet，GenericServlet，Servlet源码分析

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