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Web Connector for REST API and Streamlets support
/**
* 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 org.apache.activemq.web;
import org.apache.activemq.MessageAvailableConsumer;
import org.apache.activemq.MessageAvailableListener;
import org.eclipse.jetty.continuation.Continuation;
import org.eclipse.jetty.continuation.ContinuationSupport;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import javax.jms.*;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
/**
* A servlet for sending and receiving messages to/from JMS destinations using
* HTTP POST for sending and HTTP GET for receiving.
*
* You can specify the destination and whether it is a topic or queue via
* configuration details on the servlet or as request parameters.
*
* For reading messages you can specify a readTimeout parameter to determine how
* long the servlet should block for.
*
* One thing to keep in mind with this solution - due to the nature of REST,
* there will always be a chance of losing messages. Consider what happens when
* a message is retrieved from the broker but the web call is interrupted before
* the client receives the message in the response - the message is lost.
*/
public class MessageServlet extends MessageServletSupport {
// its a bit pita that this servlet got intermixed with jetty continuation/rest
// instead of creating a special for that. We should have kept a simple servlet
// for good old fashioned request/response blocked communication.
private static final long serialVersionUID = 8737914695188481219L;
private static final Logger LOG = LoggerFactory.getLogger(MessageServlet.class);
private final String readTimeoutParameter = "readTimeout";
private final String readTimeoutRequestAtt = "xamqReadDeadline";
private final String oneShotParameter = "oneShot";
private long defaultReadTimeout = -1;
private long maximumReadTimeout = 20000;
private long requestTimeout = 1000;
private String defaultContentType;
private final Map clients = new ConcurrentHashMap<>();
private final Set activeConsumers = ConcurrentHashMap.newKeySet();
@Override
public void init() throws ServletException {
ServletConfig servletConfig = getServletConfig();
String name = servletConfig.getInitParameter("defaultReadTimeout");
if (name != null) {
defaultReadTimeout = asLong(name);
}
name = servletConfig.getInitParameter("maximumReadTimeout");
if (name != null) {
maximumReadTimeout = asLong(name);
}
name = servletConfig.getInitParameter("replyTimeout");
if (name != null) {
requestTimeout = asLong(name);
}
name = servletConfig.getInitParameter("defaultContentType");
if (name != null) {
defaultContentType = name;
}
}
/**
* Sends a message to a destination
*
* @param request
* @param response
* @throws ServletException
* @throws IOException
*/
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// lets turn the HTTP post into a JMS Message
try {
String action = request.getParameter("action");
String clientId = request.getParameter("clientId");
if (clientId != null && "unsubscribe".equals(action)) {
LOG.info("Unsubscribing client " + clientId);
WebClient client = getWebClient(request);
client.close();
clients.remove(clientId);
return;
}
WebClient client = getWebClient(request);
String text = getPostedMessageBody(request);
// lets create the destination from the URI?
Destination destination = getDestination(client, request);
if (destination == null) {
throw new NoDestinationSuppliedException();
}
if (LOG.isDebugEnabled()) {
LOG.debug("Sending message to: " + destination + " with text: " + text);
}
boolean sync = isSync(request);
TextMessage message = client.getSession().createTextMessage(text);
appendParametersToMessage(request, message);
boolean persistent = isSendPersistent(request);
int priority = getSendPriority(request);
long timeToLive = getSendTimeToLive(request);
client.send(destination, message, persistent, priority, timeToLive);
// lets return a unique URI for reliable messaging
response.setHeader("messageID", message.getJMSMessageID());
response.setStatus(HttpServletResponse.SC_OK);
response.getWriter().write("Message sent");
} catch (JMSException e) {
throw new ServletException("Could not post JMS message: " + e, e);
}
}
/**
* Supports a HTTP DELETE to be equivalent of consuming a single message
* from a queue
*/
@Override
protected void doDelete(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doMessages(request, response);
}
/**
* Supports a HTTP DELETE to be equivalent of consuming a single message
* from a queue
*/
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doMessages(request, response);
}
/**
* Reads a message from a destination up to some specific timeout period
*
* @param request
* @param response
* @throws ServletException
* @throws IOException
*/
protected void doMessages(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
MessageAvailableConsumer consumer = null;
try {
WebClient client = getWebClient(request);
Destination destination = getDestination(client, request);
if (destination == null) {
throw new NoDestinationSuppliedException();
}
consumer = (MessageAvailableConsumer) client.getConsumer(destination, request.getHeader(WebClient.selectorName));
Continuation continuation = ContinuationSupport.getContinuation(request);
// Don't allow concurrent use of the consumer. Do make sure to allow
// subsequent calls on continuation to use the consumer.
if (continuation.isInitial() && !activeConsumers.add(consumer)) {
throw new ServletException("Concurrent access to consumer is not supported");
}
Message message = null;
long deadline = getReadDeadline(request);
long timeout = deadline - System.currentTimeMillis();
// Set the message available listener *before* calling receive to eliminate any
// chance of a missed notification between the time receive() completes without
// a message and the time the listener is set.
synchronized (consumer) {
Listener listener = (Listener) consumer.getAvailableListener();
if (listener == null) {
listener = new Listener(consumer);
consumer.setAvailableListener(listener);
}
}
if (LOG.isDebugEnabled()) {
LOG.debug("Receiving message(s) from: " + destination + " with timeout: " + timeout);
}
// Look for any available messages (need a little timeout). Always
// try at least one lookup; don't block past the deadline.
if (timeout <= 0) {
message = consumer.receiveNoWait();
} else if (timeout < 10) {
message = consumer.receive(timeout);
} else {
message = consumer.receive(10);
}
if (message == null) {
handleContinuation(request, response, client, destination, consumer, deadline);
} else {
writeResponse(request, response, message);
closeConsumerOnOneShot(request, client, destination);
activeConsumers.remove(consumer);
}
} catch (JMSException e) {
throw new ServletException("Could not post JMS message: " + e, e);
}
}
protected void handleContinuation(HttpServletRequest request, HttpServletResponse response, WebClient client, Destination destination,
MessageAvailableConsumer consumer, long deadline) {
// Get an existing Continuation or create a new one if there are no events.
Continuation continuation = ContinuationSupport.getContinuation(request);
long timeout = deadline - System.currentTimeMillis();
if ((continuation.isExpired()) || (timeout <= 0)) {
// Reset the continuation on the available listener for the consumer to prevent the
// next message receipt from being consumed without a valid, active continuation.
synchronized (consumer) {
Object obj = consumer.getAvailableListener();
if (obj instanceof Listener) {
((Listener) obj).setContinuation(null);
}
}
response.setStatus(HttpServletResponse.SC_NO_CONTENT);
closeConsumerOnOneShot(request, client, destination);
activeConsumers.remove(consumer);
return;
}
continuation.setTimeout(timeout);
continuation.suspend();
synchronized (consumer) {
Listener listener = (Listener) consumer.getAvailableListener();
// register this continuation with our listener.
listener.setContinuation(continuation);
}
}
protected void writeResponse(HttpServletRequest request, HttpServletResponse response, Message message) throws IOException, JMSException {
int messages = 0;
try {
response.setHeader("Cache-Control", "no-cache, no-store, must-revalidate"); // HTTP
// 1.1
response.setHeader("Pragma", "no-cache"); // HTTP 1.0
response.setDateHeader("Expires", 0);
// Set content type as in request. This should be done before calling getWriter by specification
String type = getContentType(request);
if (type != null) {
response.setContentType(type);
} else {
if (defaultContentType != null) {
response.setContentType(defaultContentType);
} else if (isXmlContent(message)) {
response.setContentType("application/xml");
} else {
response.setContentType("text/plain");
}
}
// write a responds
PrintWriter writer = response.getWriter();
// handle any message(s)
if (message == null) {
// No messages so OK response of for ajax else no content.
response.setStatus(HttpServletResponse.SC_NO_CONTENT);
} else {
// We have at least one message so set up the response
messages = 1;
response.setStatus(HttpServletResponse.SC_OK);
setResponseHeaders(response, message);
writeMessageResponse(writer, message);
writer.flush();
}
} finally {
if (LOG.isDebugEnabled()) {
LOG.debug("Received " + messages + " message(s)");
}
}
}
protected void writeMessageResponse(PrintWriter writer, Message message) throws JMSException, IOException {
if (message instanceof TextMessage) {
TextMessage textMsg = (TextMessage) message;
String txt = textMsg.getText();
if (txt != null) {
if (txt.startsWith("") + 2);
}
writer.print(txt);
}
} else if (message instanceof ObjectMessage) {
ObjectMessage objectMsg = (ObjectMessage) message;
Object object = objectMsg.getObject();
if (object != null) {
writer.print(object.toString());
}
}
}
protected boolean isXmlContent(Message message) throws JMSException {
if (message instanceof TextMessage) {
TextMessage textMsg = (TextMessage) message;
String txt = textMsg.getText();
if (txt != null) {
// assume its xml when it starts with <
if (txt.startsWith("<")) {
return true;
}
}
}
// for any other kind of messages we dont assume xml
return false;
}
public WebClient getWebClient(HttpServletRequest request) {
String clientId = request.getParameter("clientId");
if (clientId != null) {
LOG.debug("Getting local client [" + clientId + "]");
return clients.computeIfAbsent(clientId, k -> new WebClient());
} else {
return WebClient.getWebClient(request);
}
}
protected String getContentType(HttpServletRequest request) {
String value = request.getParameter("xml");
if (value != null && "true".equalsIgnoreCase(value)) {
return "application/xml";
}
value = request.getParameter("json");
if (value != null && "true".equalsIgnoreCase(value)) {
return "application/json";
}
return null;
}
@SuppressWarnings("rawtypes")
protected void setResponseHeaders(HttpServletResponse response, Message message) throws JMSException {
response.setHeader("destination", message.getJMSDestination().toString());
response.setHeader("id", message.getJMSMessageID());
// Return JMS properties as header values.
for (Enumeration names = message.getPropertyNames(); names.hasMoreElements(); ) {
String name = (String) names.nextElement();
response.setHeader(name, message.getObjectProperty(name).toString());
}
}
/**
* @return the timeout value for read requests which is always >= 0 and <=
* maximumReadTimeout to avoid DoS attacks
*/
protected long getReadDeadline(HttpServletRequest request) {
Long answer;
answer = (Long) request.getAttribute(readTimeoutRequestAtt);
if (answer == null) {
long timeout = defaultReadTimeout;
String name = request.getParameter(readTimeoutParameter);
if (name != null) {
timeout = asLong(name);
}
if (timeout < 0 || timeout > maximumReadTimeout) {
timeout = maximumReadTimeout;
}
answer = Long.valueOf(System.currentTimeMillis() + timeout);
}
return answer.longValue();
}
/**
* Close the consumer if one-shot mode is used on the given request.
*/
protected void closeConsumerOnOneShot(HttpServletRequest request, WebClient client, Destination dest) {
if (asBoolean(request.getParameter(oneShotParameter), false)) {
try {
client.closeConsumer(dest);
} catch (JMSException jms_exc) {
LOG.warn("JMS exception on closing consumer after request with one-shot mode", jms_exc);
}
}
}
/*
* Listen for available messages and wakeup any continuations.
*/
private static class Listener implements MessageAvailableListener {
MessageConsumer consumer;
Continuation continuation;
Listener(MessageConsumer consumer) {
this.consumer = consumer;
}
public void setContinuation(Continuation continuation) {
synchronized (consumer) {
this.continuation = continuation;
}
}
@Override
public void onMessageAvailable(MessageConsumer consumer) {
assert this.consumer == consumer;
((MessageAvailableConsumer) consumer).setAvailableListener(null);
synchronized (this.consumer) {
if (continuation != null) {
continuation.resume();
}
}
}
}
}