"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!

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]+)<","<");

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)

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/

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

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

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.

Answer 7

Removing the xml declaration solved it

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

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.

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));

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.

Answer 11

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.

Answer 12

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

Answer 13

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'?>

Answer 14

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.

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);

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.