Parsing a stream of continous XML documents

Question

I have a socket connection for an external system which accept commands and sends results in XML. Every command and result is a standalone XML document.

Which Java parser (/combination) should i use to:

• parse the stream continuously without closing the connection (i know it's stupid, but i tried DOMParser in the past and it throws an exception when an another document root encountered on the stream which is perfectly understandable). I need something like: continously read the stream and when a document is fully received, do it's processing. I don't know how big the document is, so i need to leave to the parser to figure out the end of the document.
• deserialize every incoming document into bean instances (similary like XStream does)
• serialize command object to the output stream from annotated class instances (similarly like XStream does). I don't want to use two separate libraries for sending and receiving.

Answer 1

Well... XStream.createObjectInputStream seems to be what you need. I'm not sure if the stream provided must enclose all objects into a root node, but anyway you could arrange an inputstreams that add some virtual content to accomodate to XStream needs. I'll expand this answer later...

http://x-stream.github.io/objectstream.html has some samples...

Root node

Indeed the reader needs a root node. So you need an inputstream that reads <object-stream> plus the real byte content, plus a </object-stream> at the end (if you mind about that end). Depending on what you need (inputstream, readers) the implementation can be slighly different but it can be done.

Sample

You can use SequenceInputStream to concatenate virtual content to the original inputstream:

InputStream realOne = ..
// beware of the encoding!
InputStream root = new ByteArrayInputStream("<object-stream>".toBytes("UTF-8")); 
InputStream all = new SequenceInputStream(root, realOne);

xstream.createObjectInputStream(withRoot); // voi lá

If you use readers... well. There must be something equivalent :)

Answer 2

I'd say you read one full complete response, then parse it. Then read the other. I see no need to continuously read responses.

Answer 3

Your best bet is probably SAX parser. With it, you can implement ContentHandler document and in there, in endDocument method, do the processing and prepare for the next document. Have a look at this page: http://docs.oracle.com/javase/tutorial/jaxp/sax/parsing.html - for explanation and examples.