XOM API for Processing XML with Java

[Wolfgang Hoschek <wolfgang.hoschek AT mac.com>]

How do this compare to this streaming XOM serializer: http:// 
dsd.lbl.gov/nux/api/nux/xom/io/StreamingSerializer.html
Wolfgang.

On Oct 22, 2007, at 1:16 AM, Asgeir Frimannsson wrote:

> Hi all,
>
> I wrote a streaming serializer for XOM this weekend, and thought  
> perhaps it
> might be useful to someone else, so I'll throw it on the list.
>
> StreamingSerializer is based on the existing Serializer, however,  
> it is not
> a subclass of Serializer. It allows for creating very large  
> documents and
> writing them to an outputstream. The serializer removes any nodes  
> in the
> Document that is out-of-context (already serialized), and thereby  
> frees up
> memory.
>
> Central to this serializer is the concept of a 'context node', which
> determines the parent of newly inserted nodes. When inserting  
> Elements, the
> new context node is always set to the last descendant Element of  
> the element
> being inserted. Rather than inserting children on Elements (using e.g.
> appendChild) and creating a large in-memory model, use the  
> writeNextChild()
> methods of the serializer. Alternatively, create small in-memory  
> Element
> trees and use the writeNextChild() method on the Element. Start the
> serialization by calling the write(Document) method. The new  
> context is then
> set to the last descendant Element of the root element. After that,  
> use the
> public methods of the StreamingSerializer to build your document.
>
> // main api
> class StreamingSerializer{
>
>   // sets the new context to the parent context
>   ParentNode popContext()
>
>   // retrieves the current context node
>   ParentNode getContext()
>
>   // sets the new context node
>   // must be a parent of the current context node
>   void setContext(ParentNode node)
>
>   // Serializes a document.
>   // The context node is set to the last
>   // Element descendant of the root element
>   void write(Document)
>
>   // Serializes an element
>   // The context node is set to the last
>   // Element descendant of the element
>   void writeNextChild(Element)
>
>   // serializes nodes as children of
>   // the current context node.
>   void writeNextChild(Text)
>   void writeNextChild(Comment)
>   void writeNextChild(ProcessingInstruction)
>
>   // completes the serialization of the document
>   void finishDocument();
>
> }
>
> An example application:
>
> public static void main(String[] args) throws IOException{
>
>     StreamingSerializer serializer = new StreamingSerializer 
> (System.out);
>     serializer.setIndent(2);
>     Element root = new Element("root-element");
>     Document doc = new Document(root);
>
>     serializer.write(doc);
>
>     Element child = new Element("child");
>
>     for(int i=0;i<100;i++){ // create a small sub-tree and  
> serialize it
>         serializer.setContext(root);
>
>         Element childX = new Element(child);
>         childX.addAttribute(new Attribute("id",String.valueOf(i)));
>
>         if(i%7 == 0){
>             childX.appendChild("I'm one out of 7!");
>         }
>         if(i%9 == 0){
>             childX.appendChild(new ProcessingInstruction("php","echo 
> ('I'm
> one out of 9..');"));
>         }
>
>         serializer.setContext(root);
>         serializer.writeNextChild(childX);
>     }
>
>     serializer.finishDocument();
> }
>
> StreamingSerializerTest passes most tests from the existing  
> SerializerTest,
> except those where   subclassing is used in a Serializer-specific  
> way (most
> of these are not relevant for StreamingSerializer).
>
> I have written two sample applications:
>  - ExampleStreamingWriter - creates an XML document using the  
> streaming
> serializer (similar to example).
>  - ExampleStreamingIndenter - Streams an XML document through a  
> NodeFactory
> and writes it out with the streaming serializer indented...
>
> Some unresolved issues:
> - The Serializer calls removeChildren() on Elements. Element  
> subclasses
> might not allow removal of certain nodes, causing this to break..
> - Haven't put much thought into use-cases for Subclassing
> StreamingSerializer, some methods should be declared final for now...
> - Unit tests doesn't cover the new methods
>
> Hope this is useful to someone, and that something similar makes it  
> into the
> main XOM library some day. There's definitely a need for a streaming
> serializer in XOM...
>
> I've put the code up here:
> http://camouflage.googlecode.com/files/StreamingSerializer.zip
> Copy the files to the nu.xom source tree, and it should work.
>
> cheers,
> asgeir
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