add showcase for async plugin

apps/showcase/pom.xml

@@ -89,6 +89,11 @@
             <artifactId>struts2-bean-validation-plugin</artifactId>
         </dependency>
 
+        <dependency>
+            <groupId>org.apache.struts</groupId>
+            <artifactId>struts2-async-plugin</artifactId>
+        </dependency>
+
         <dependency>
             <groupId>javax.servlet</groupId>
             <artifactId>servlet-api</artifactId>

apps/showcase/src/main/java/org/apache/struts2/showcase/async/AsyncFilter.java

@@ -0,0 +1,53 @@
+/*
+ * 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.struts2.showcase.async;
+
+import javax.servlet.Filter;
+import javax.servlet.FilterChain;
+import javax.servlet.FilterConfig;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+import javax.servlet.http.HttpServletRequest;
+import java.io.IOException;
+
+/**
+ * Filters async actions directly to Struts servlet
+ */
+public class AsyncFilter implements Filter {
+    @Override
+    public void init(FilterConfig filterConfig) throws ServletException {
+
+    }
+
+    @Override
+    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
+        String requestURI = ((HttpServletRequest) servletRequest).getRequestURI();
+        if (!requestURI.contains("/async/receiveNewMessages")) {
+            filterChain.doFilter(servletRequest, servletResponse); // Just continue chain.
+        } else {
+            servletRequest.getRequestDispatcher("/async/receiveNewMessages").forward(servletRequest, servletResponse);
+        }
+    }
+
+    @Override
+    public void destroy() {
+
+    }
+}

apps/showcase/src/main/java/org/apache/struts2/showcase/async/ChatRoomAction.java

@@ -0,0 +1,68 @@
+/*
+ * 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.struts2.showcase.async;
+
+import com.opensymphony.xwork2.ActionSupport;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.Callable;
+
+/**
+ * Example to illustrate the <code>async</code> plugin.
+ */
+public class ChatRoomAction extends ActionSupport {
+    private String message;
+    private Integer lastIndex;
+    private List<String> newMessages;
+
+    private static final List<String> messages = new ArrayList<>();
+
+    public void setMessage(String message) {
+        this.message = message;
+    }
+
+    public void setLastIndex(Integer lastIndex) {
+        this.lastIndex = lastIndex;
+    }
+
+    public List<String> getNewMessages() {
+        return newMessages;
+    }
+
+    public Callable<String> receiveNewMessages() throws Exception {
+        return new Callable<String>() {
+            @Override
+            public String call() throws Exception {
+                while (lastIndex >= messages.size()) {
+                    Thread.sleep(3000);
+                }
+                newMessages = messages.subList(lastIndex, messages.size());
+                return SUCCESS;
+            }
+        };
+    }
+
+    public String sendMessage() {
+        synchronized (messages) {
+            messages.add(message);
+        }
+        return SUCCESS;
+    }
+}

apps/showcase/src/main/resources/struts-async.xml

@@ -0,0 +1,49 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<!--
+/*
+ * 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.
+ */
+-->
+<!DOCTYPE struts PUBLIC
+	"-//Apache Software Foundation//DTD Struts Configuration 2.5//EN"
+	"http://struts.apache.org/dtds/struts-2.5.dtd">
+
+<struts>
+    <package name="async" extends="json-default" namespace="/async">
+
+        <action name="receiveNewMessages" class="org.apache.struts2.showcase.async.ChatRoomAction" method="receiveNewMessages">
+            <result name="success" type="json">
+                <param name="root">newMessages</param>
+            </result>
+            <result name="timeout" type="json">
+                <param name="root">newMessages</param>
+            </result>
+        </action>
+
+        <action name="sendMessage" class="org.apache.struts2.showcase.async.ChatRoomAction" method="sendMessage">
+            <result name="success" type="json">
+                <param name="root">newMessages</param>
+            </result>
+            <result name="timeout" type="json">
+                <param name="root">newMessages</param>
+            </result>
+        </action>
+
+    </package>
+
+</struts>

apps/showcase/src/main/resources/struts.xml

@@ -74,6 +74,8 @@
 
     <include file="struts-xslt.xml" />
 
+    <include file="struts-async.xml" />
+
     <package name="default" extends="struts-default">
         <interceptors>
             <interceptor-stack name="crudStack">

apps/showcase/src/main/webapp/WEB-INF/decorators/main.jsp

@@ -235,6 +235,7 @@
                             <li><s:a value="/token/index.html">Token</s:a></li>
                             <li><s:url var="url" namespace="/modelDriven" action="modelDriven"/><s:a
                                     href="%{url}">Model Driven</s:a></li>
+                            <li><s:a value="/async/index.html">Async</s:a></li>
                         </ul>
                     </li>
                     <li class="dropdown">

apps/showcase/src/main/webapp/WEB-INF/web.xml

@@ -23,7 +23,13 @@
 	xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
 
     <display-name>Struts Showcase Application</display-name>
-	
+
+    <filter>
+        <filter-name>async</filter-name>
+        <filter-class>org.apache.struts2.showcase.async.AsyncFilter</filter-class>
+        <async-supported>true</async-supported>
+    </filter>
+
     <filter>
         <filter-name>struts-prepare</filter-name>
         <filter-class>org.apache.struts2.dispatcher.filter.StrutsPrepareFilter</filter-class>
@@ -40,6 +46,11 @@
        <filter-class>com.opensymphony.sitemesh.webapp.SiteMeshFilter</filter-class>
    </filter>
 
+    <filter-mapping>
+        <filter-name>async</filter-name>
+        <url-pattern>/async/*</url-pattern>
+    </filter-mapping>
+
     <filter-mapping>
         <filter-name>struts-prepare</filter-name>
         <url-pattern>/*</url-pattern>
@@ -113,6 +124,13 @@
         <load-on-startup>1</load-on-startup>
     </servlet>
 
+    <servlet>
+        <servlet-name>strutsServlet</servlet-name>
+        <servlet-class>org.apache.struts2.dispatcher.servlet.StrutsServlet</servlet-class>
+        <load-on-startup>1</load-on-startup>
+        <async-supported>true</async-supported>
+    </servlet>
+
     <servlet-mapping>
         <servlet-name>dwr</servlet-name>
         <url-pattern>/dwr/*</url-pattern>
@@ -128,6 +146,11 @@
         <url-pattern>*.vm</url-pattern>
     </servlet-mapping>
 
+    <servlet-mapping>
+        <servlet-name>strutsServlet</servlet-name>
+        <url-pattern>/async/receiveNewMessages</url-pattern>
+    </servlet-mapping>
+
     <!-- END SNIPPET: dwr -->
 
     <!-- SNIPPET START: example.velocity.filter.chain

apps/showcase/src/main/webapp/async/index.html

@@ -0,0 +1,119 @@
+<!--
+/*
+ * 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.
+ */
+-->
+<html>
+<head>
+	<title>Struts2 Showcase - Async Example</title>
+	<script>
+        function User () {
+            this.lastIndex = 0;
+            this.sendMessage = function(message) {
+                $.ajax({
+                    url: "sendMessage",
+                    data: {
+                        message: message
+                    }
+                });
+            };
+            this.receiveNewMessages = function() {
+                $.ajax({
+                    url: "receiveNewMessages",
+                    context: this,
+                    data: {
+                        lastIndex: this.lastIndex
+                    },
+                    success: function (result) {
+                        if (result != null) {//result is null on timeout
+                            var msgs = $('#msgs');
+                            var messages = msgs.val();
+                            msgs.val(messages + result + '\n');
+                            this.lastIndex += result.length;
+                        }
+                        this.receiveNewMessages();
+                    }
+                });
+            };
+            this.receiveNewMessages();
+        }
+
+        var user;
+        
+        function sendMessage() {
+            var msg = $('#msg');
+            var message = msg.val();
+            if (message.length > 0) {
+                user.sendMessage(message);
+                msg.val('');
+            }
+            return false;
+        }
+
+        $(function() {
+            user = new User();
+        });
+
+	</script>
+</head>
+
+<body>
+<div class="page-header">
+	<h1>Async Example</h1>
+</div>
+
+
+
+<div class="container-fluid">
+	<div class="row">
+		<div class="col-md-12" style="text-align: center;">
+
+			<p>
+				These examples illustrate Struts build in support for async request processing.
+			</p>
+			<p>
+				When you have a process that takes a long time, it can make your app not scalable under heavy load conditions.
+				Scalability limitations include running out of memory or exhausting the pool of container threads.
+				To create scalable web applications, you must ensure that no threads associated with a request
+				are sitting idle, so the container can use them to process new requests.
+				Asynchronous processing refers to assigning these blocking operations to a new thread and returning
+				the thread associated with the request immediately to the container.
+                <br/> Reference: <a href="https://docs.oracle.com/javaee/7/tutorial/servlets012.htm">Asynchronous Processing</a>
+				<br/> An interesting and vital use case for the async request processing is server push.
+				A good solution is to use the Servlet 3.0+ asynchronous feature.
+			</p>
+
+			<br/>
+            <h2>Example: A minimal chat room using server push</h2>
+            <h3>Open current page in different tabs, browsers and computers then send messages.</h3>
+            <h4>This is a minimal chat room which uses server push to retrieve new messages.
+            It doesn't poll the server frequently to check if a new message is available to display.
+            Instead it waits for the server to push back new messages. This approach has two obvious advantages:
+            low-lag communication without requests being sent, and no waste of server resources and network bandwidth.</h4>
+            <h5>Reference: <a href="https://www.javaworld.com/article/2077995/java-concurrency/java-concurrency-asynchronous-processing-support-in-servlet-3-0.html">
+                Asynchronous processing support in Servlet 3.0</a></h5>
+            <textarea id="msgs" cols="40" rows="5" title="messages" readonly></textarea><br/>
+			<form>
+				<input name="msg" id="msg" type="text" title="message" required />
+				<input type="submit" value="Send" onclick="return sendMessage();" />
+			</form>
+		</div>
+	</div>
+</div>
+</body>
+</html>

apps/showcase/src/test/java/it/org/apache/struts2/showcase/AsyncTest.java

@@ -0,0 +1,30 @@
+/*
+ * 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 it.org.apache.struts2.showcase;
+
+public class AsyncTest extends ITBaseTest {
+    public void testChatRoom() throws InterruptedException {
+        beginAt("/async/index.html");
+
+        setTextField("msg", "hello");
+        submit();
+        Thread.sleep(4000);
+        assertTextInElement("msgs", "hello");
+    }
+}