314 lines
22 KiB
HTML
314 lines
22 KiB
HTML
<html><head><META http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><title>Apache Tomcat 6.0 - Advanced IO and Tomcat</title><meta name="author" value="Remy Maucherat"><meta name="email" value=""></head><body bgcolor="#ffffff" text="#000000" link="#525D76" alink="#525D76" vlink="#525D76"><table border="0" width="100%" cellspacing="0"><!--PAGE HEADER--><tr><td><!--PROJECT LOGO--><a href="http://tomcat.apache.org/"><img src="./images/tomcat.gif" align="right" alt="
|
|
The Apache Tomcat Servlet/JSP Container
|
|
" border="0"></a></td><td><font face="arial,helvetica,sanserif"><h1>Apache Tomcat 6.0</h1></font></td><td><!--APACHE LOGO--><a href="http://www.apache.org/"><img src="./images/asf-logo.gif" align="right" alt="Apache Logo" border="0"></a></td></tr></table><table border="0" width="100%" cellspacing="4"><!--HEADER SEPARATOR--><tr><td colspan="2"><hr noshade="noshade" size="1"></td></tr><tr><!--LEFT SIDE NAVIGATION--><td width="20%" valign="top" nowrap="true"><p><strong>Links</strong></p><ul><li><a href="index.html">Docs Home</a></li><li><a href="http://tomcat.apache.org/faq">FAQ</a></li></ul><p><strong>User Guide</strong></p><ul><li><a href="introduction.html">1) Introduction</a></li><li><a href="setup.html">2) Setup</a></li><li><a href="appdev/index.html">3) First webapp</a></li><li><a href="deployer-howto.html">4) Deployer</a></li><li><a href="manager-howto.html">5) Manager</a></li><li><a href="realm-howto.html">6) Realms and AAA</a></li><li><a href="security-manager-howto.html">7) Security Manager</a></li><li><a href="jndi-resources-howto.html">8) JNDI Resources</a></li><li><a href="jndi-datasource-examples-howto.html">9) JDBC DataSources</a></li><li><a href="class-loader-howto.html">10) Classloading</a></li><li><a href="jasper-howto.html">11) JSPs</a></li><li><a href="ssl-howto.html">12) SSL</a></li><li><a href="ssi-howto.html">13) SSI</a></li><li><a href="cgi-howto.html">14) CGI</a></li><li><a href="proxy-howto.html">15) Proxy Support</a></li><li><a href="mbeans-descriptor-howto.html">16) MBean Descriptor</a></li><li><a href="default-servlet.html">17) Default Servlet</a></li><li><a href="cluster-howto.html">18) Clustering</a></li><li><a href="balancer-howto.html">19) Load Balancer</a></li><li><a href="connectors.html">20) Connectors</a></li><li><a href="monitoring.html">21) Monitoring and Management</a></li><li><a href="logging.html">22) Logging</a></li><li><a href="apr.html">23) APR</a></li><li><a href="virtual-hosting-howto.html">24) Virtual Hosting</a></li><li><a href="aio.html">25) Advanced IO</a></li><li><a href="extras.html">26) Additional Components</a></li><li><a href="maven-jars.html">27) Mavenized</a></li></ul><p><strong>Reference</strong></p><ul><li><a href="RELEASE-NOTES.txt">Release Notes</a></li><li><a href="config/index.html">Configuration</a></li><li><a href="api/index.html">Javadocs</a></li><li><a href="http://tomcat.apache.org/connectors-doc/">JK 1.2 Documentation</a></li></ul><p><strong>Apache Tomcat Development</strong></p><ul><li><a href="building.html">Building</a></li><li><a href="changelog.html">Changelog</a></li><li><a href="status.html">Status</a></li><li><a href="developers.html">Developers</a></li><li><a href="architecture/index.html">Architecture</a></li><li><a href="funcspecs/index.html">Functional Specs.</a></li></ul></td><!--RIGHT SIDE MAIN BODY--><td width="80%" valign="top" align="left"><table border="0" width="100%" cellspacing="4"><tr><td align="left" valign="top"><h1>Apache Tomcat 6.0</h1><h2>Advanced IO and Tomcat</h2></td><td align="right" valign="top" nowrap="true"><small><a href="printer/aio.html"><img src="./images/printer.gif" border="0" alt="Printer Friendly Version"><br>print-friendly<br>version
|
|
</a></small></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Introduction"><strong>Introduction</strong></a></font></td></tr><tr><td><blockquote>
|
|
|
|
<p>
|
|
With usage of APR or NIO APIs as the basis of its connectors, Tomcat is
|
|
able to provide a number of extensions over the regular blocking IO
|
|
as provided with support for the Servlet API.
|
|
</p>
|
|
|
|
<p>
|
|
<b>IMPORTANT NOTE: Usage of these features requires using the APR or NIO
|
|
HTTP connectors. The classic java.io HTTP connector and the AJP connectors
|
|
do not support them.</b>
|
|
</p>
|
|
|
|
</blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Comet support"><strong>Comet support</strong></a></font></td></tr><tr><td><blockquote>
|
|
|
|
<p>
|
|
Comet support allows a servlet to process IO aynchronously, recieving
|
|
events when data is available for reading on the connection (rather than
|
|
always using a blocking read), and writing data back on connections
|
|
asychnonously (most likely responding to some event raised from some
|
|
other source).
|
|
</p>
|
|
|
|
<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="CometEvent"><strong>CometEvent</strong></a></font></td></tr><tr><td><blockquote>
|
|
|
|
<p>
|
|
Servlets which implement the <code>org.apache.catalina.CometProcessor</code>
|
|
interface will have their event method invoked rather than the usual service
|
|
method, according to the event which occurred. The event object gives
|
|
access to the usual request and response objects, which may be used in the
|
|
usual way. The main difference is that those objects remain valid and fully
|
|
functional at any time between processing of the BEGIN event until processing
|
|
an END or ERROR event.
|
|
The following event types exist:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>EventType.BEGIN: will be called at the beginning
|
|
of the processing of the connection. It can be used to initialize any relevant
|
|
fields using the request and response objects. Between the end of the processing
|
|
of this event, and the beginning of the processing of the end or error events,
|
|
it is possible to use the response object to write data on the open connection.
|
|
Note that the response object and depedent OutputStream and Writer are still
|
|
not synchronized, so when they are accessed by multiple threads,
|
|
synchronization is mandatory. After processing the initial event, the request
|
|
is considered to be committed.</li>
|
|
<li>EventType.READ: This indicates that input data is available, and that one read can be made
|
|
without blocking. The available and ready methods of the InputStream or
|
|
Reader may be used to determine if there is a risk of blocking: the servlet
|
|
should read while data is reported available, and can make one additional read
|
|
should read while data is reported available. When encountering a read error,
|
|
the servlet should report it by propagating the exception properly. Throwing
|
|
an exception will cause the error event to be invoked, and the connection
|
|
will be closed.
|
|
Alternately, it is also possible to catch any exception, perform clean up
|
|
on any data structure the servlet may be using, and using the close method
|
|
of the event. It is not allowed to attempt reading data from the request
|
|
object outside of the execution of this method.<br>
|
|
On some platforms, like Windows, a client disconnect is indicated by a READ event.
|
|
Reading from the stream may result in -1, an IOException or an EOFException.
|
|
Make sure you properly handle all these three cases.
|
|
If you don't catch the IOException, Tomcat will instantly invoke your event chain with an ERROR as
|
|
it catches the error for you, and you will be notified of the error at that time.
|
|
</li>
|
|
<li>EventType.END: End may be called to end the processing of the request. Fields that have
|
|
been initialized in the begin method should be reset. After this event has
|
|
been processed, the request and response objects, as well as all their dependent
|
|
objects will be recycled and used to process other requests. End will also be
|
|
called when data is available and the end of file is reached on the request input
|
|
(this usually indicates the client has pipelined a request).</li>
|
|
<li>EventType.ERROR: Error will be called by the container in the case where an IO exception
|
|
or a similar unrecoverable error occurs on the connection. Fields that have
|
|
been initialized in the begin method should be reset. After this event has
|
|
been processed, the request and response objects, as well as all their dependent
|
|
objects will be recycled and used to process other requests.</li>
|
|
</ul>
|
|
|
|
<p>
|
|
There are some event subtypes which allow finer processing of events (note: some of these
|
|
events require usage of the org.apache.catalina.valves.CometConnectionManagerValve valve):
|
|
</p>
|
|
|
|
<ul>
|
|
<li>EventSubType.TIMEOUT: The connection timed out (sub type of ERROR); note that this ERROR
|
|
type is not fatal, and the connection will not be closed unless the servlet uses the close
|
|
method of the event.
|
|
</li>
|
|
<li>EventSubType.CLIENT_DISCONNECT: The client connection was closed (sub type of ERROR).
|
|
method of the event.
|
|
</li>
|
|
<li>EventSubType.IOEXCEPTION: An IO exception occurred, such as invalid content, for example,
|
|
an invalid chunk block (sub type of ERROR).
|
|
</li>
|
|
<li>EventSubType.WEBAPP_RELOAD: The web application is being reloaded (sub type of END).
|
|
</li>
|
|
<li>EventSubType.SESSION_END: The servlet ended the session (sub type of END).
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
As described above, the typical lifecycle of a Comet request will consist in a series of
|
|
events such as: BEGIN -> READ -> READ -> READ -> ERROR/TIMEOUT. At any time, the servlet
|
|
may end processing of the request by using the close method of the event object.
|
|
</p>
|
|
|
|
</blockquote></td></tr></table>
|
|
|
|
<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="CometFilter"><strong>CometFilter</strong></a></font></td></tr><tr><td><blockquote>
|
|
|
|
<p>
|
|
Similar to regular filters, a filter chain is invoked when comet events are processed.
|
|
These filters should implement the CometFilter interface (which works in the same way as
|
|
the regular Filter interface), and should be declared and mapped in the deployment
|
|
descriptor in the same way as a regular filter. The filter chain when processing an event
|
|
will only include filters which match all the usual mapping rules, and also implement
|
|
the CometFiler interface.
|
|
</p>
|
|
|
|
</blockquote></td></tr></table>
|
|
|
|
<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Example code"><strong>Example code</strong></a></font></td></tr><tr><td><blockquote>
|
|
|
|
<p>
|
|
The following pseudo code servlet implments asynchronous chat functionality using the API
|
|
described above:
|
|
</p>
|
|
|
|
<div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
|
|
public class ChatServlet
|
|
extends HttpServlet implements CometProcessor {
|
|
|
|
protected ArrayList<HttpServletResponse> connections =
|
|
new ArrayList<HttpServletResponse>();
|
|
protected MessageSender messageSender = null;
|
|
|
|
public void init() throws ServletException {
|
|
messageSender = new MessageSender();
|
|
Thread messageSenderThread =
|
|
new Thread(messageSender, "MessageSender[" + getServletContext().getContextPath() + "]");
|
|
messageSenderThread.setDaemon(true);
|
|
messageSenderThread.start();
|
|
}
|
|
|
|
public void destroy() {
|
|
connections.clear();
|
|
messageSender.stop();
|
|
messageSender = null;
|
|
}
|
|
|
|
/**
|
|
* Process the given Comet event.
|
|
*
|
|
* @param event The Comet event that will be processed
|
|
* @throws IOException
|
|
* @throws ServletException
|
|
*/
|
|
public void event(CometEvent event)
|
|
throws IOException, ServletException {
|
|
HttpServletRequest request = event.getHttpServletRequest();
|
|
HttpServletResponse response = event.getHttpServletResponse();
|
|
if (event.getEventType() == CometEvent.EventType.BEGIN) {
|
|
log("Begin for session: " + request.getSession(true).getId());
|
|
PrintWriter writer = response.getWriter();
|
|
writer.println("<!doctype html public \"-//w3c//dtd html 4.0 transitional//en\">");
|
|
writer.println("<head><title>JSP Chat</title></head><body bgcolor=\"#FFFFFF\">");
|
|
writer.flush();
|
|
synchronized(connections) {
|
|
connections.add(response);
|
|
}
|
|
} else if (event.getEventType() == CometEvent.EventType.ERROR) {
|
|
log("Error for session: " + request.getSession(true).getId());
|
|
synchronized(connections) {
|
|
connections.remove(response);
|
|
}
|
|
event.close();
|
|
} else if (event.getEventType() == CometEvent.EventType.END) {
|
|
log("End for session: " + request.getSession(true).getId());
|
|
synchronized(connections) {
|
|
connections.remove(response);
|
|
}
|
|
PrintWriter writer = response.getWriter();
|
|
writer.println("</body></html>");
|
|
event.close();
|
|
} else if (event.getEventType() == CometEvent.EventType.READ) {
|
|
InputStream is = request.getInputStream();
|
|
byte[] buf = new byte[512];
|
|
do {
|
|
int n = is.read(buf); //can throw an IOException
|
|
if (n > 0) {
|
|
log("Read " + n + " bytes: " + new String(buf, 0, n)
|
|
+ " for session: " + request.getSession(true).getId());
|
|
} else if (n < 0) {
|
|
error(event, request, response);
|
|
return;
|
|
}
|
|
} while (is.available() > 0);
|
|
}
|
|
}
|
|
|
|
public class MessageSender implements Runnable {
|
|
|
|
protected boolean running = true;
|
|
protected ArrayList<String> messages = new ArrayList<String>();
|
|
|
|
public MessageSender() {
|
|
}
|
|
|
|
public void stop() {
|
|
running = false;
|
|
}
|
|
|
|
/**
|
|
* Add message for sending.
|
|
*/
|
|
public void send(String user, String message) {
|
|
synchronized (messages) {
|
|
messages.add("[" + user + "]: " + message);
|
|
messages.notify();
|
|
}
|
|
}
|
|
|
|
public void run() {
|
|
|
|
while (running) {
|
|
|
|
if (messages.size() == 0) {
|
|
try {
|
|
synchronized (messages) {
|
|
messages.wait();
|
|
}
|
|
} catch (InterruptedException e) {
|
|
// Ignore
|
|
}
|
|
}
|
|
|
|
synchronized (connections) {
|
|
String[] pendingMessages = null;
|
|
synchronized (messages) {
|
|
pendingMessages = messages.toArray(new String[0]);
|
|
messages.clear();
|
|
}
|
|
// Send any pending message on all the open connections
|
|
for (int i = 0; i < connections.size(); i++) {
|
|
try {
|
|
PrintWriter writer = connections.get(i).getWriter();
|
|
for (int j = 0; j < pendingMessages.length; j++) {
|
|
writer.println(pendingMessages[j] + "<br>");
|
|
}
|
|
writer.flush();
|
|
} catch (IOException e) {
|
|
log("IOExeption sending message", e);
|
|
}
|
|
}
|
|
}
|
|
|
|
}
|
|
|
|
}
|
|
|
|
}
|
|
|
|
}
|
|
</pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>
|
|
|
|
</blockquote></td></tr></table>
|
|
<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Comet timeouts"><strong>Comet timeouts</strong></a></font></td></tr><tr><td><blockquote>
|
|
<p>If you are using the NIO connector, you can set individual timeouts for your different comet connections.
|
|
To set a timeout, simple set a request attribute like the following code shows:
|
|
<div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>CometEvent event.... event.setTimeout(30*1000);</pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div> or
|
|
<div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>event.getHttpServletRequest().setAttribute("org.apache.tomcat.comet.timeout", new Integer(30 * 1000));</pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>
|
|
This sets the timeout to 30 seconds.
|
|
Important note, in order to set this timeout, it has to be done on the <code>BEGIN</code> event.
|
|
The default value is <code>soTimeout</code>
|
|
</p>
|
|
<p>If you are using the APR connector, all Comet connections will have the same timeout value. It is <code>soTimeout*50</code>
|
|
</p>
|
|
</blockquote></td></tr></table>
|
|
|
|
</blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Asynchronous writes"><strong>Asynchronous writes</strong></a></font></td></tr><tr><td><blockquote>
|
|
|
|
<p>
|
|
When APR or NIO is enabled, Tomcat supports using sendfile to send large static files.
|
|
These writes, as soon as the system load increases, will be performed
|
|
asynchronously in the most efficient way. Instead of sending a large response using
|
|
blocking writes, it is possible to write content to a static file, and write it
|
|
using a sendfile code. A caching valve could take advantage of this to cache the
|
|
response data in a file rather than store it in memory. Sendfile support is
|
|
available if the request attribute <code>org.apache.tomcat.sendfile.support</code>
|
|
is set to <code>Boolean.TRUE</code>.
|
|
</p>
|
|
|
|
<p>
|
|
Any servlet can instruct Tomcat to perform a sendfile call by setting the appropriate
|
|
response attributes. When using sendfile, it is best to ensure that neither the
|
|
request or response have been wrapped, since as the response body will be sent later
|
|
by the connector itself, it cannot be filtered. Other than setting the 3 needed
|
|
response attributes, the servlet should not send any response data, but it may use
|
|
any method which will result in modifying the response header (like setting cookies).
|
|
</p>
|
|
|
|
<ul>
|
|
<li>org.apache.tomcat.sendfile.filename: Canonical filename of the file which will be sent as
|
|
a String</li>
|
|
<li>org.apache.tomcat.sendfile.start: Start offset as a Long</li>
|
|
<li>org.apache.tomcat.sendfile.start: End offset as a Long</li>
|
|
</ul>
|
|
|
|
</blockquote></td></tr></table></td></tr><!--FOOTER SEPARATOR--><tr><td colspan="2"><hr noshade="noshade" size="1"></td></tr><!--PAGE FOOTER--><tr><td colspan="2"><div align="center"><font color="#525D76" size="-1"><em>
|
|
Copyright © 1999-2006, Apache Software Foundation
|
|
</em></font></div></td></tr></table></body></html> |