Solved

sending xml message in a java udp packet

Posted on 2008-06-12
11
1,569 Views
Last Modified: 2013-11-23
I'm trying to send an xml message to a Java SAX parser listening on a UDP port.
When I send a message the parser it gives the error message

 [Fatal Error] :1:1 Content is not allowed in prolog.

I've reduced my UDP packet to just the prolog and I still get the error

Here is what I'm sending

String xmlMsg = new String("<?xml version=\"1.0\" encoding=\"UTF-8\"?>");

byte buffer[] = xmlMsg.getBytes();
DatagramSocket sndSocket = new DatagramSocket();
sndSocket.send(new DatagramPacket(buffer,buffer.length,InetAddress.getByName("127.0.0.1"),Integer.parseInt("3031")));

I want to find out what I'm doing wrong and how do I send an XML message in a UDP packet that the SAX parser will accept?
0
Comment
Question by:mitchguy
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 6
  • 5
11 Comments
 
LVL 86

Expert Comment

by:CEHJ
ID: 21772083
>> [Fatal Error] :1:1 Content is not allowed in prolog.

That sounds more like an error with reading xml, not writing it. At what point are you getting that message
0
 

Author Comment

by:mitchguy
ID: 21772265
The reader is doing this

DatagramPacket incomingPacket = new DatagramPacket(buffer,buffer.length);
listenSocket.receive(incomingPacket);
byte data[] = incomingPacket.getData();
InputSource source = new InputSource(new StringReader(data.toString()));
fromXML(source);

private synchronized fromXML(InputSource in) throws Exception
{
  XMLReader xr;
  xr.setContentHandler(this);
  xr.parse(in);
}
0
 
LVL 86

Expert Comment

by:CEHJ
ID: 21772450
>>InputSource source = new InputSource(new StringReader(data.toString()));

should be as below
InputSource source = new InputSource(new StringReader(new String(data)));

Open in new window

0
Cloud Training Guides

FREE GUIDES: In-depth and hand-crafted Linux, AWS, OpenStack, DevOps, Azure, and Cloud training guides created by Linux Academy instructors and the community.

 

Author Comment

by:mitchguy
ID: 21772538
I'm not sure I understand the difference between data.toString() and new String(data) ?

I made the change and ran it again I get this error listed below still



[Fatal Error] :1:39: Content is not allowed in prolog.
org.xml.sax.SAXParseException: Content is not allowed in prolog

Which is actually a little different than before, the difference being
before the numbers after [Fatal Error] were 1:1 and now it is 1:39
The size of the message is 38 maybe I have some sort of missing character
that is supposed to be at the end of the data for the parser?
0
 
LVL 86

Expert Comment

by:CEHJ
ID: 21772641
Well  byte[] doesn't have a toString method that will be of any use to you. Can you instead do this and tell us what gets printed?
String s = new String(data);
System.out.println(data);
InputSource source = new InputSource(new StringReader(s));

Open in new window

0
 

Author Comment

by:mitchguy
ID: 21772798
The output is certainly not what I expected

[B@1113708

Since I'm sending and receiving on the same machine it shouldn't be a byte swap problem right?
0
 
LVL 86

Accepted Solution

by:
CEHJ earned 125 total points
ID: 21772904
>>[B@1113708

That looks suspiciously like the output of data.toString, which i've already said not to use ..;-)
0
 

Author Comment

by:mitchguy
ID: 21773164
If I do this
String myString = new String(incomingPacket.getData());
The output is
<?xml version="1.0" encoding="UTF-8"?>

However after that I did
InputSource source = new InputSource(new StringReader(myString));

and unfortunately still got the error
[Fatal Error] :1:39: Content is not allowed in prolog.
org.xml.sax.SAXParseException: Content is not allowed in prolog
0
 
LVL 86

Expert Comment

by:CEHJ
ID: 21773306
Well of course your software is expecting to parse a document. 'myString' is just a header. You need the rest of the doc in there too
0
 

Author Comment

by:mitchguy
ID: 21773433
That did the Trick:)
Thanks!
0
 
LVL 86

Expert Comment

by:CEHJ
ID: 21773461
:-)
0

Featured Post

Creating Instructional Tutorials  

For Any Use & On Any Platform

Contextual Guidance at the moment of need helps your employees/users adopt software o& achieve even the most complex tasks instantly. Boost knowledge retention, software adoption & employee engagement with easy solution.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

For beginner Java programmers or at least those new to the Eclipse IDE, the following tutorial will show some (four) ways in which you can import your Java projects to your Eclipse workbench. Introduction While learning Java can be done with…
Introduction This article is the first of three articles that explain why and how the Experts Exchange QA Team does test automation for our web site. This article explains our test automation goals. Then rationale is given for the tools we use to a…
Viewers will learn about arithmetic and Boolean expressions in Java and the logical operators used to create Boolean expressions. We will cover the symbols used for arithmetic expressions and define each logical operator and how to use them in Boole…
This theoretical tutorial explains exceptions, reasons for exceptions, different categories of exception and exception hierarchy.
Suggested Courses

628 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question