"Content is not allowed in prolog" when parsing perfectly valid XML on GAE

Question

I've been beating my head against this absolutely infuriating bug for the last 48 hours, so I thought I'd finally throw in the towel and try asking here before I throw my laptop out the window.

I'm trying to parse the response XML from a call I made to AWS SimpleDB. The response is coming back on the wire just fine; for example, it may look like:

<?xml version="1.0" encoding="utf-8"?> 
<ListDomainsResponse xmlns="http://sdb.amazonaws.com/doc/2009-04-15/">
    <ListDomainsResult>
        <DomainName>Audio</DomainName>
        <DomainName>Course</DomainName>
        <DomainName>DocumentContents</DomainName>
        <DomainName>LectureSet</DomainName>
        <DomainName>MetaData</DomainName>
        <DomainName>Professors</DomainName>
        <DomainName>Tag</DomainName>
    </ListDomainsResult>
    <ResponseMetadata>
        <RequestId>42330b4a-e134-6aec-e62a-5869ac2b4575</RequestId>
        <BoxUsage>0.0000071759</BoxUsage>
    </ResponseMetadata>
</ListDomainsResponse>

I pass in this XML to a parser with

XMLEventReader eventReader = xmlInputFactory.createXMLEventReader(response.getContent());

and call eventReader.nextEvent(); a bunch of times to get the data I want.

Here's the bizarre part -- it works great inside the local server. The response comes in, I parse it, everyone's happy. The problem is that when I deploy the code to Google App Engine, the outgoing request still works, and the response XML seems 100% identical and correct to me, but the response fails to parse with the following exception:

com.amazonaws.http.HttpClient handleResponse: Unable to unmarshall response (ParseError at [row,col]:[1,1]
Message: Content is not allowed in prolog.): <?xml version="1.0" encoding="utf-8"?> 
<ListDomainsResponse xmlns="http://sdb.amazonaws.com/doc/2009-04-15/"><ListDomainsResult><DomainName>Audio</DomainName><DomainName>Course</DomainName><DomainName>DocumentContents</DomainName><DomainName>LectureSet</DomainName><DomainName>MetaData</DomainName><DomainName>Professors</DomainName><DomainName>Tag</DomainName></ListDomainsResult><ResponseMetadata><RequestId>42330b4a-e134-6aec-e62a-5869ac2b4575</RequestId><BoxUsage>0.0000071759</BoxUsage></ResponseMetadata></ListDomainsResponse>
javax.xml.stream.XMLStreamException: ParseError at [row,col]:[1,1]
Message: Content is not allowed in prolog.
    at com.sun.org.apache.xerces.internal.impl.XMLStreamReaderImpl.next(Unknown Source)
    at com.sun.xml.internal.stream.XMLEventReaderImpl.nextEvent(Unknown Source)
    at com.amazonaws.transform.StaxUnmarshallerContext.nextEvent(StaxUnmarshallerContext.java:153)
    ... (rest of lines omitted)

I have double, triple, quadruple checked this XML for 'invisible characters' or non-UTF8 encoded characters, etc. I looked at it byte-by-byte in an array for byte-order-marks or something of that nature. Nothing; it passes every validation test I could throw at it. Even stranger, it happens if I use a Saxon-based parser as well -- but ONLY on GAE, it always works fine in my local environment.

It makes it very hard to trace the code for problems when I can only run the debugger on an environment that works perfectly (I haven't found any good way to remotely debug on GAE). Nevertheless, using the primitive means I have, I've tried a million approaches including:

• XML with and without the prolog
• With and without newlines
• With and without the "encoding=" attribute in the prolog
• Both newline styles
• With and without the chunking information present in the HTTP stream

And I've tried most of these in multiple combinations where it made sense they would interact -- nothing! I'm at my wit's end. Has anyone seen an issue like this before that can hopefully shed some light on it?

Thanks!

Maladjusted

We are probably going to need to see some more code. Another possibility is that locally it is not getting chunked while on GAE it is. How are you handling the code before you pass it to the parser ? – Halimeda

I considered the chunking possibility too, but it doesn't seem to be the case since the error message that the parser is throwing contains the entire XML right there (it's pasted above). The entire modified SDK code can be found at github.com/AdrianP/aws-sdk-for-java (look at the most recent commits) but there's a LOT of code there. I will try to create a smaller reproducible sample soon, although even that will be hard. It's a big complicated piece of software... Thanks for your feedback though! :) – Maladjusted

possible duplicate of org.xml.sax.SAXParseException: Content is not allowed in prolog – Kentigera

@Raedwald, I don't think it is my question that is the duplicate, since my question was posted a year earlier than that one :) – Maladjusted

The other question is more useful as a canonical question, as it is more general. – Kentigera

@AdrianPetrescu see this MSE answer: meta.stackexchange.com/a/147651/170084 – Kentigera

This should be an example of how a question should be asked on SO, reading through it gave me various insights on how to debug as a developer (thanks OP) – Vargo

Answer 1

The encoding in your XML and XSD (or DTD) are different.
XML file header: <?xml version='1.0' encoding='utf-8'?>
XSD file header: <?xml version='1.0' encoding='utf-16'?>

Another possible scenario that causes this is when anything comes before the XML document type declaration. i.e you might have something like this in the buffer:

helloworld<?xml version="1.0" encoding="utf-8"?>  

or even a space or special character.

There are some special characters called byte order markers that could be in the buffer. Before passing the buffer to the Parser do this...

String xml = "<?xml ...";
xml = xml.trim().replaceFirst("^([\\W]+)<","<");

Halimeda

Hi Romain, thanks for the response! I've double and triple checked many times for anything in the buffer prior to the prolog (including hidden characters) but there simply isn't anything else there. I'll give switching to utf-16 encoding a try, however -- out of curiousity, where did you get the information that the XSD uses UTF-16? – Maladjusted

@Adrian Petrescu Sorry, these are just examples If you are using DTDs or XSDs make sure they match with your XML. Before you parse the XML capture it in a String and surround it with '|' and print it to the console. This will tell you if you are passing in some extra characters. – Halimeda

Ah, I see :) Unfortunately I tried it and it doesn't appear to be the case in this situation. Thanks anyway! – Maladjusted

@Adrian Petrescu I updated my post for you to try something else. Change your XMLEventReader eventReader = xmlInputFactory.createXMLEventReader(response.getContent()); to ... String xml = response.getContent(); xml = xml.trim().replaceFirst("^([\\W]+)<","<"); XMLEventReader eventReader = xmlInputFactory.createXMLEventReader(xml); – Halimeda

Thanks, I'll give this a try soon, even though I previously already checked for byte-order marks; maybe they're being introduced somewhere between the input stream and the XMLReader. – Maladjusted

helloworld<?xml version="1.0" encoding="utf-8"?> [something before <?xml .. ] worked for me – Rollins

Thanks! This saved me as well. xml.trim().replaceFirst("^([\\W]+)<","<"); – Merri

Someone please make this the accepted answer. Solved my problem straight away. I was parsing a Message that started with "Message: <?xml version...." The problem was the text before the xml bit. Thanks :) – Ashelyashen

This solves my problem that am facing with a feed xml from one site. But it breaks for other URL where the parser did not have any problem earlier. I am not quite able to figure out exactly what the regex: "^([\\W]+)<" does. I am getting the XML from an input stream. Please explain how this regex works exactly. – Giuliana

@Giuliana the regex replaces all starting whitespaces and starting < with < – Halimeda

@Kentigera compare the dates. This was answered 3 years earlier. – Halimeda

@RomainHippeau see this MSE answer: meta.stackexchange.com/a/147651/170084 – Kentigera

I also had a case where a character at the end of the prolog was causing the problem. I was getting XML messages where they were putting period after every >, like so ">." This results in a first line that looks like this: "<?xml version="1.0" encoding="UTF-8" standalone="yes"?>." – Sunfast

@ Romain We can change the encoding using Notepad++. Will it work then? – Cale

@peter maybe but I describe two possible issues in my answer. – Halimeda

In my case there was a hidden character in the before <?xml what was not shown from editor what caused the issue. – Elephantine

The IDE consoles also hide these special BOM characters, they appear only when the String is pasted inside the IDE editor. – Quantify

Answer 2

I had issue while inspecting the xml file in notepad++ and saving the file, though I had the top utf-8 xml tag as <?xml version="1.0" encoding="utf-8"?>

Got fixed by saving the file in notpad++ with Encoding(Tab) > Encode in UTF-8:selected (was Encode in UTF-8-BOM)

Ulloa

I had a similar issue. In my case the XML header did not have an encoding attribute. Notepad++ defaulted to UTF-8 encoding. Once I switched Notepad++ encoding to ANSI, the issue stopped. – Steeplebush

Removing BOMs from all XML files in working directory by Vim: vim -c ":bufdo set nobomb|update" -c "q" *.xml . – Equally

Answer 3

This error message is always caused by the invalid XML content in the beginning element. For example, extra small dot “.” in the beginning of XML element.

Any characters before the “<?xml….” will cause above “org.xml.sax.SAXParseException: Content is not allowed in prolog” error message.

A small dot “.” before the “<?xml….

To fix it, just delete all those weird characters before the “<?xml“.

Ref: http://www.mkyong.com/java/sax-error-content-is-not-allowed-in-prolog/

Ironclad

You should mention where you referred that mkyong.com/java/sax-error-content-is-not-allowed-in-prolog – Deandreadeane

Answer 4

I catched the same error message today. The solution was to change the document from UTF-8 with BOM to UTF-8 without BOM

Skees

I had the same issue. Changing file format resolved the issue. Thanks! – Dunois

Damn, you are a champ! Would have never guessed this! – Darlenedarline

Answer 5

I was facing the same issue. In my case XML files were generated from c# program and feeded into AS400 for further processing. After some analysis identified that I was using UTF8 encoding while generating XML files whereas javac(in AS400) uses "UTF8 without BOM". So, had to write extra code similar to mentioned below:

//create encoding with no BOM
Encoding outputEnc = new UTF8Encoding(false); 
//open file with encoding
TextWriter file = new StreamWriter(filePath, false, outputEnc);           

file.Write(doc.InnerXml);
file.Flush();
file.Close(); // save and close it

Tolman

Answer 6

In my xml file, the header looked like this:

<?xml version="1.0" encoding="utf-16"? />

In a test file, I was reading the file bytes and decoding the data as UTF-8 (not realizing the header in this file was utf-16) to create a string.

byte[] data = Files.readAllBytes(Paths.get(path));
String dataString = new String(data, "UTF-8");

When I tried to deserialize this string into an object, I was seeing the same error:

javax.xml.stream.XMLStreamException: ParseError at [row,col]:[1,1]
Message: Content is not allowed in prolog.

When I updated the second line to

String dataString = new String(data, "UTF-16");

I was able to deserialize the object just fine. So as Romain had noted above, the encodings need to match.

Fiddle

Answer 7

Removing the xml declaration solved it

<?xml version='1.0' encoding='utf-8'?>

Christensen

Answer 8

Unexpected reason: # character in file path

Due to some internal bug, the error Content is not allowed in prolog also appears if the file content itself is 100% correct but you are supplying the file name like C:\Data\#22\file.xml.

This may possibly apply to other special characters, too.

How to check: If you move your file into a path without special characters and the error disappears, then it was this issue.

Richards

Took me two days to realize that this was the issue. Problem was caused by the Windows-User-Name under which the Tomcat-Service is running. The user name contains a # character, so the User-Profiles path also contains this character.... – Rasberry

Answer 9

I was facing the same problem called "Content is not allowed in prolog" in my xml file.

Solution

Initially my root folder was '#Filename'.

When i removed the first character '#' ,the error got resolved.

No need of removing the #filename... Try in this way..

Instead of passing a File or URL object to the unmarshaller method, use a FileInputStream.

File myFile = new File("........");
Object obj = unmarshaller.unmarshal(new FileInputStream(myFile));

Madgemadhouse

Answer 10

In the spirit of "just delete all those weird characters before the <?xml", here's my Java code, which works well with input via a BufferedReader:

    BufferedReader test = new BufferedReader(new InputStreamReader(fisTest));
    test.mark(4);
    while (true) {
        int earlyChar = test.read();
        System.out.println(earlyChar);
        if (earlyChar == 60) {
            test.reset();
            break;
        } else {
            test.mark(4);
        }
    }

FWIW, the bytes I was seeing are (in decimal): 239, 187, 191.

Nucleonics

Answer 11

I zipped the xml in a Mac OS and sent it to a Windows machine, the default compression changes these files so the encoding sent this message.

Amateurish

Answer 12

I had a tab character instead of spaces. Replacing the tab '\t' fixed the problem.

Cut and paste the whole doc into an editor like Notepad++ and display all characters.

Sequestrate

Answer 13

In my instance of the problem, the solution was to replace german umlauts (äöü) with their HTML-equivalents...

Outsert

Answer 14

bellow are cause above “org.xml.sax.SAXParseException: Content is not allowed in prolog” exception.

1. First check the file path of schema.xsd and file.xml.
2. The encoding in your XML and XSD (or DTD) should be same.
   XML file header: <?xml version='1.0' encoding='utf-8'?>
   XSD file header: <?xml version='1.0' encoding='utf-8'?>
3. if anything comes before the XML document type declaration.i.e: hello<?xml version='1.0' encoding='utf-16'?>

Isoleucine

Answer 15

Happened to me with @JsmListener with Spring Boot when listening to IBM MQ. My method received String parameter and got this exception when I tried to deserialize it using JAXB.

It seemed that that the string I got was a result of byte[].toString(). It was a list of comma separated numbers.

I solved it by changing the parameter type to byte[] and then created a String from it:

@JmsListener(destination = "Q1")
public void receiveQ1Message(byte[] msgBytes) {
    var msg = new String(msgBytes);

Pralltriller

Answer 16

I had encountered this message when running a test case in SoapUI:

org.xml.sax.SAXParseException; systemId: file://; lineNumber: 1; columnNumber: 1; Content is not allowed in prolog.

After quite some time I figured out the reason being the following line:

def holder = groovyUtils.getXmlHolder("SoapCall#Request") // Get Request body

And the reason was that the test step was actually named "SOAPCall" and not "SoapCall". I suppose the returned string was empty, which caused the "prolog" error.

Isomer