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Java > Open Source Codes > com > oreilly > servlet > MultipartResponse


1 // Copyright (C) 1998-2001 by Jason Hunter <jhunter_AT_acm_DOT_org>.
2 // All rights reserved. Use of this class is limited.
3 // Please see the LICENSE for more information.
4
5 package com.oreilly.servlet;
6
7 import java.io.*;
8 import javax.servlet.*;
9 import javax.servlet.http.*;
10
11 /**
12  * A utility class to generate <tt>multipart/x-mixed-replace</tt> responses,
13  * the kind of responses that implement server push. Note that Microsoft
14  * Internet Explorer does not understand this sort of response.
15  * <p>
16  * To use this class, first construct a new MultipartResponse
17  * passing to its constructor the servlet's response parameter.
18  * MultipartResponse uses the response object to fetch the
19  * servlet's output stream and to set the response's content type.
20  * <p>
21  * Then, for each page of content, begin by calling <tt>startResponse()</tt>
22  * passing in the content type for that page. Send the content for the
23  * page by writing to the output stream as usual. A call to
24  * <tt>endResponse()</tt> ends the page and flushes the content so the
25  * client can see it. At this point a <tt>sleep()</tt> or other delay
26  * can be added until the next page is ready for sending.
27  * <p>
28  * The call to <tt>endResponse()</tt> is optional. The
29  * <tt>startResponse()</tt> method knows whether the last response has
30  * been ended, and ends it itself if necessary. However, it's wise to
31  * call <tt>endResponse()</tt> if there's to be a delay between the
32  * time one response ends and the next begins. It lets the client display
33  * the latest response during the time it waits for the next one.
34  * <p>
35  * Finally, after each response page has been sent, a call to the
36  * <tt>finish()</tt> method finishes the multipart response and sends a
37  * code telling the client there will be no more responses.
38  * <p>
39  * For example:
40  * <blockquote><pre>
41  * MultipartResponse multi = new MultipartResponse(res);
42  * &nbsp;
43  * multi.startResponse("text/plain");
44  * out.println("On your mark");
45  * multi.endResponse();
46  * &nbsp;
47  * try { Thread.sleep(1000); } catch (InterruptedException e) { }
48  * &nbsp;
49  * multi.startResponse("text/plain");
50  * out.println("Get set");
51  * multi.endResponse();
52  * &nbsp;
53  * try { Thread.sleep(1000); } catch (InterruptedException e) { }
54  * &nbsp;
55  * multi.startResponse("image/gif");
56  * ServletUtils.returnFile(req.getRealPath("/images/go.gif"), out);
57  * &nbsp;
58  * multi.finish();
59  * </pre></blockquote>
60  *
61  * @see ServletUtils
62  *
63  * @author <b>Jason Hunter</b>, Copyright &#169; 1998
64  * @version 1.0, 98/09/18
65  */
66 public class MultipartResponse {
67
68   HttpServletResponse res;
69   ServletOutputStream out;
70   boolean endedLastResponse = true;
71
72   /**
73    * Constructs a new MultipartResponse to send content to the given
74    * servlet response.
75    *
76    * @param response the servlet response
77    * @exception IOException if an I/O error occurs
78    */
79   public MultipartResponse(HttpServletResponse response) throws IOException {
80     // Save the response object and output stream
81 res = response;
82     out = res.getOutputStream();
83
84     // Set things up
85 res.setContentType("multipart/x-mixed-replace;boundary=End");
86     out.println();
87     out.println("--End");
88   }
89
90   /**
91    * Begins a single response with the specified content type.
92    * This method knows whether the last response has been ended, and
93    * ends it itself if necessary.
94    *
95    * @param contentType the content type of this response part
96    * @exception IOException if an I/O error occurs
97    */
98   public void startResponse(String JavaDoc contentType) throws IOException {
99     // End the last response if necessary
100 if (!endedLastResponse) {
101       endResponse();
102     }
103     // Start the next one
104 out.println("Content-type: " + contentType);
105     out.println();
106     endedLastResponse = false;
107   }
108
109   /**
110    * Ends a single response. Flushes the output.
111    *
112    * @exception IOException if an I/O error occurs
113    */
114   public void endResponse() throws IOException {
115     // End the last response, and flush so the client sees the content
116 out.println();
117     out.println("--End");
118     out.flush();
119     endedLastResponse = true;
120   }
121
122   /**
123    * Finishes the multipart response. Sends a code telling the client
124    * there will be no more responses and flushes the output.
125    *
126    * @exception IOException if an I/O error occurs
127    */
128   public void finish() throws IOException {
129     out.println("--End--");
130     out.flush();
131   }
132 }
133
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