Input (fullInput
)
Imagine I have the following as an InputStream
(or as a String
in memory read from that stream):
<?xml version="1.0" ?>
<root>
<element attr="val1"><x /><y /></element>
<element attr="val2"><y /></element>
<element attr="val3"><x /><x /></element>
<element attr="val4"><z /><y /></element>
</root>
How I want to use the solution (bridgeXml
)
IProprietaryUnmarshaller UNMARSHALLER = ...;
List<Element> parseFullXml(String fullInput) throws UnmarshallException {
List<String> inputs = bridgeXml(fullInput);
List<Element> outputs = new ArrayList();
for(String input : inputs) {
Element e = UNMARSHALLER.unmarshall(input);
outputs.add(e);
}
return outputs;
}
What I'm looking for
I'm looking for an implementation of/idea for bridgeXml
where the input String
/*Stream
is split up into smaller chucks of Strings which are well-formed XML documents (without XML declaration) by themselves.
The trivial implementation I want to avoid
The below implementation is error prone, inflexible and should not be used, I'm looking for a proper one using some kind of a library or XML parser!
List<String> bridgeXml(String input) {
// strip anything up to the opening root element, and LTrim the remainder
input = input.replaceAll("(?s)^.*<root.*?>\\s*", "");
// strip anything after the closing root element, and RTrim the remainder
input = input.replaceAll("(?s)\\s*</root.*$", "");
// split at </element> closing tags, not removing them (?<= does the magic)
return Arrays.asList(input.split("(?<=</element>)"));
}
Restrictions
- The XML input can't be changed and is a fully valid XML.
- The proprietary unmarshaller must be used and cannot be modified.
- I'm looking for a solution where the file is not XML unmarshalled, XML marshalled, proprietary unmarshalled.
- (Don't pick at XML/Java code style, formatting, visibility modifiers, etc.!
These are simplified codes for easier communication.)
Solution (edit)
I ended up writing this piece... I ended up double-parsing the XML (see getOuterXml
), because it was premature to assume that it's slow. I have a huge DB query following this which is way slower.
protected <T> List<T> read(InputStream inputStream, String tagName) throws XMLStreamException,
TransformerException, DecodingException
{
List<T> result = new ArrayList<T>();
XMLInputFactory xmlFactory = XMLInputFactory.newInstance();
XMLStreamReader xmlReader = xmlFactory.createXMLStreamReader(inputStream, "ISO-8859-1");
while (xmlReader.hasNext()) {
xmlReader.next();
if (xmlReader.isStartElement() && tagName.equals(xmlReader.getLocalName())) {
String output = getOuterXml(xmlReader);
@SuppressWarnings("unchecked")
T object = (T) UNMARSHALLER.unmarshall(output);
result.add(object);
}
}
return result;
}
protected String getOuterXml(XMLStreamReader xmlr) throws TransformerException
{
Transformer transformer = TransformerFactory.newInstance().newTransformer();
StringWriter stringWriter = new StringWriter();
transformer.transform(new StAXSource(xmlr), new StreamResult(stringWriter));
return stringWriter.toString();
}
protected <T> List<T> getObjects(String urlString, String tagName)
{
LOG.info("Downloading [{}] updates from [{}].", tagName, urlString);
HttpURLConnection conn = null;
InputStream inputStream = null;
try {
URL url = new URL(urlString);
conn = (HttpURLConnection) url.openConnection();
conn.connect();
inputStream = conn.getInputStream();
return read(inputStream, tagName);
} catch (Exception ex) {
String exceptionMessage = "Updating [" + tagName + "] from [" + urlString + "] failed.";
LOG.error(exceptionMessage, ex);
throw new MyFancyWrapperException(exceptionMessage, ex);
} finally {
if (inputStream != null) {
try {
inputStream.close();
} catch (IOException ex) {
LOG.warn("Cannot close HTTP's input stream", ex);
}
}
if (conn != null) {
conn.disconnect();
}
}
}