過去 48 時間、この非常に腹立たしいバグに頭を悩ませてきましたが、ついに諦めて、ノートパソコンを窓から投げ出す前にここで質問してみようと思いました。
AWS SimpleDB への呼び出しからの応答 XML を解析しようとしています。応答は問題なくネットワーク経由で返されます。たとえば、次のようになります。
<?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>
このXMLをパーサーに渡すと、
XMLEventReader eventReader = xmlInputFactory.createXMLEventReader(response.getContent());
eventReader.nextEvent();必要なデータを取得するために何度も呼び出します。
奇妙なのは、ローカル サーバー内では問題なく動作するということです。応答が届き、解析すれば、誰もが満足します。問題は、コードを Google App Engine にデプロイすると、送信リクエストは引き続き動作し、応答 XML は 100% 同一で正しいように見えますが、応答が次の例外で解析に失敗することです。
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!
ベストアンサー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]+)<","<");