ContentsPresentation


1   /**
2    *  Andy John
3    *  2/99
4    *  chat room
5    *  andy@enhydra.org
6    *  www.enhydra.org
7    *
8    *   This is a "by hand" presentation object (Enhydra Jolt was not used).
9    *  This is because there is so much java code and so little static HTML that
10   *  it is easier to write it by hand.
11   *    This page and the Discussion business object are the core of the
12   *  "on hold push" algorithm (see the Discussion object). The browser has
13   *  asked for a snapshot. They may have sent in a state id. If so, then they
14   *  already have something on their screen, and they are really asking for
15   *  something new. This state id (or 0 if none was sent), is passed on to
16   *  the Discussion object when we ask for a snapshot. It uses it to (maybe)
17   *  block (not return) until there is some new state (a message has been
18   *  added or deleted from the list).
19   *  The browser also probably specified a time limit it is willing to wait.
20   *  The browser will time out before TCP/IP will, so we use a one minute
21   *  timeout. If the browser times out, it breaks the reload cycle, and the
22   *  user stops seeing messages.
23   *    Becuase the call to the Discussion object might block for up to a
24   *  minute, there may be several threads waiting around in this object.
25   */
26  
27  package chat.presentation;
28  
29  import java.util.Vector  ;
30  import com.lutris.appserver.server.httpPresentation.*;
31  import chat.ChatApplication;
32  import chat.spec.*;
33  
34  /**
35   *  Because this page has alot more code than html content, and because
36   *  so much of the page is generated in Java anyway, I chose to write this
37   *  presentation object by hand, ranther than using Jolt.
38   */
39  public class ContentsPresentation implements HttpPresentation {
40  
41      /*
42       *  How long can we make the browsers wait till they time out.
43       *  This is a conservative guess (one minute).
44       */
45      private static final int refreshWait = 60;
46  
47      /*
48       *  This is used with the "unique" query string parameter. It is a
49       *  psued-hack to make every page look unique. Otherwise sometimes the
50       *  browser will think that a request looks like an old one and try
51       *  to slip you results from the cache. By using the counter, each
52       *  request is guarenteed to look unique. The actual value is not
53       *  used by the program.
54       */
55      private static long counter = 0;
56  
57  
58      /**
59       *  The main body of a presentation object. See the class comments above.
60       */
61      public void run(HttpPresentationComms comms) throws Exception   {
62          // Try to get the current state, default to zero.
63          long state = 0;
64          try {
65              String   stateStr = comms.request.getParameter("state");
66              if (stateStr != null)
67                  state = Long.parseLong(stateStr);
68          } catch (Exception   e) {
69          }
70          // Try to get the wait timeout. Default to zero.
71          long wait = 0;
72          try {
73              String   waitStr = comms.request.getParameter("wait");
74              if (waitStr != null)
75                  wait = Long.parseLong(waitStr);
76          } catch (Exception   e) {
77          }
78          /*
79           *  Get a snapshot! This may take up to wait seconds.
80           */
81       
82             DiscussionManager discussionManager = DiscussionManagerFactory.getDiscussionManager("chat.business.DiscussionManagerImpl");
83     
84     
85     
86  
87    
88        
89        
90          /*
91           *  Start writing out the page.
92           */
93          ChatApplication myApp = (ChatApplication) comms.application;
94  
95          comms.response.setContentType("text/html");
96          comms.response.setHeader("Expires", "Tue, 01 Jan 1980 1:00:00 GMT");
97          comms.response.setHeader("Pragma", "no-cache");
98          HttpPresentationOutputStream out = comms.response.getOutputStream();
99  
100         out.println("<HTML>");
101         out.println("<HEAD></HEAD>");
102         out.println("<BODY onload=\"loadOn();\" BGCOLOR=" + myApp.getBgColor() +">");
103         out.println("<h3><center><font color=purple>" +
104                     myApp.getRoomName() +
105                     "</font></center></h3>");
106 
107 /*
108  * Catch Null pointer exception ( we canot make a instances of classes from business layer when we run chat_pres )
109  * We need  to allow chat_pres to be functional , so if the requested url is /chat_pres/..... the response
110  * will be default HTML page
111  */ 
112    
113  try{  
114         Snapshot snap = discussionManager.getContents(state, wait);
115       
116         if ((snap.getContents() == null) || (snap.getContents().size() == 0)) {
117             out.println("<center><i><br><br><br><font color=purple><b>" +
118                         "There are currently no messages." +
119                         "</b></font></i></center>\n");
120         } else {
121             for (int i=snap.getContents().size()-1; i>=0; i--) {
122                 /*
123                  *  I used to display the messages in the "normal" order,
124                  *  but ran into browser incompatabilites with scrolling,
125                  *  named anchors, meta refresh tags etc...
126                  *  This way it works on all browsers (which is a good
127                  *  thing for a demo).
128                  */
129                 
130             Message msg = (Message) snap.getContents().elementAt(i);
131                                  
132                 if (msg == null)
133                     continue;
134                 out.print("<b>");
135                 if ((msg.getHtmlName() == null) || (msg.getHtmlName().length() == 0))
136                      out.print("<i>Anonymous</i>");
137                 else
138                      out.print(msg.getHtmlName());
139                 out.print(":</b> ");
140                 if (msg.getHtmlChunks().size() > 1)
141                     out.print("<br>\n&nbsp;&nbsp;&nbsp;&nbsp;");
142                 for (int j=0; j<((Vector  )msg.getHtmlChunks()).size(); j++) {
143                     if (j != 0)
144                         out.print("&nbsp;&nbsp;&nbsp;&nbsp;");
145                     out.print((String  ) ((Vector  )msg.getHtmlChunks()).elementAt(j));
146                     out.println("<br>");
147                 }
148             }
149         }
150   
151         
152         /*
153          *  A key part of the "on hold push" algorithm is that the client
154          *  asks for a new snapshot as soon as it is done processing the
155          *  current snapshot. This synamic Javascript triggers the browser to
156          *  reload, passing on the current state id.
157          *  I used to use a refresh HTTP header, but IE has problems with
158          *  that when you add a query string.
159          */
160         
161         out.println("<SCRIPT TYPE=\"text/javascript\" LANGUAGE=\"JavaScript\" id=\"RealScript\">\n"
162                 + "<!--\n"
163                 + "  function loadOn() {\n"
164                 + "    window.location.href = \"ContentsPresentation.po?state=" + snap.getState() + "&wait=" + refreshWait + "&uniqe=" + counter +"\"\n"
165                 + "  }\n"
166                 + "//-->\n"
167                 + "</SCRIPT>");
168    
169   }catch(NullPointerException   e){}
170         /*
171          *  Close out the page.
172          */
173         out.println("</BODY>");
174         out.println("</HTML>");
175     }
176 
177 }
178 
179
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