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From "Derek Foster (JIRA)" <j...@apache.org>
Subject [jira] Commented: (AXIS2-919) Unable to print out entire SOAP message: bug in OMElement.serialize()
Date Wed, 06 Sep 2006 19:28:24 GMT
    [ http://issues.apache.org/jira/browse/AXIS2-919?page=comments#action_12432945 ] 
            
Derek Foster commented on AXIS2-919:
------------------------------------

For closing this bug (and getting Axis 1.1 out the door), I don't care if Iterator-related
interface changes are made. I think that' s a longer term problem, and I don't think it has
to be fixed in this release. 

I do care, however, that the following code:

final StringWriter writer = new StringWriter();
messageContext.getEnvelope().serialize(writer);
System.out.println(writer.toString());

should not throw any exceptions when run, and should produce the correct results (namely,
the XML representing the message envelope). That is what this specific bug report is about,
and that is what caused me to list it as a blocker for Axis 1.1. This bug is preventing me
from being able to list the contents of a SOAP message I have received so that I can diagnose
another problem, and is also preventing me from being able to implement part of my webservice
that worked fine in Axis 1.4 (namely, the part where incoming SOAP messages are logged to
a file so that our Operations staff can later analyze and diagnose any problems that occur).

Whether or not this bugfix is accomplished by changing the interfaces as per the above discussions,
I don't care for the moment. But I do want the getEnvelope().serialize(Writer) call to work,
and to not break as it does now. It seems to me that the shortest route to a fix would be
to make whatever changes are necessary to the XMLBeans binding code so that the above code
works and does not hit the end-of-file condition that it is apparently hitting now (and which
is being reported incorrectly due to the iterator issues). Maybe this is just a question of
calling setParent(null) at the appropriate point in the code, or making sure that Axiom can
handle an end-of-file condition correctly without always assuming there is a 'next' element.
Regardless, I need a reliable way to be able to get the compete XML for a SOAP envelope, which
I cannot currently do due to the presence of this bug. I have so far not found a workaround
for this.

I think that this specific bug report (that getEnvelope().serialize() does not work) should
be a blocker for Axis2 release. I don't think it needs to be a blocker for Axiom, unless the
core problem really is in Axiom and not in the XMLBeans binding code, as our prior discussion
suggests. When I get a chance, I will file a new bug report with a lower priority for the
Axiom interface issues.

Derek


> Unable to print out entire SOAP message: bug in OMElement.serialize()
> ---------------------------------------------------------------------
>
>                 Key: AXIS2-919
>                 URL: http://issues.apache.org/jira/browse/AXIS2-919
>             Project: Apache Axis 2.0 (Axis2)
>          Issue Type: Bug
>          Components: core, om
>    Affects Versions: 1.0
>            Reporter: Derek Foster
>         Assigned To: Eran Chinthaka
>            Priority: Blocker
>
> I was attempting, inside an XMLBeans-generated service method, to print out the entire
SOAP message to a log file. Towards that end, I tried to execute the following code:
> final StringWriter writer = new StringWriter();
> messageContext.getEnvelope().serialize(writer);
> System.out.println(writer.toString());
> However, I was surprised to get the following exception resulting from this:
> org.apache.axiom.om.OMException
> 	at org.apache.axiom.om.impl.llom.OMElementImpl.getNextOMSibling(OMElementImpl.java:266)
> 	at org.apache.axiom.om.impl.traverse.OMChildrenIterator.next(OMChildrenIterator.java:111)
> 	at org.apache.axiom.om.impl.llom.OMElementImpl.internalSerialize(OMElementImpl.java:771)
> 	at org.apache.axiom.soap.impl.llom.SOAPEnvelopeImpl.internalSerialize(SOAPEnvelopeImpl.java:177)
> 	at org.apache.axiom.om.impl.llom.OMElementImpl.internalSerialize(OMElementImpl.java:756)
> 	at org.apache.axiom.om.impl.llom.OMNodeImpl.serialize(OMNodeImpl.java:310)
> 	at org.apache.axiom.om.impl.llom.OMNodeImpl.serialize(OMNodeImpl.java:352)
>        ...
> The cause of the problem appears to be the fact that the SOAP envelope is a top-level
XML object. Thus, the item immediately following it is a DOCUMENT_END. The OMElementImpl.internalSerialize(XMLStreamWriter,
boolean cache) method contains the following code:
>             Iterator children = this.getChildren();
>             while (children.hasNext()) {
>                 ((OMNodeEx) children.next()).internalSerialize(writer);
> which seems plausible. However, the iterator that is returned is of type OMChildrenIterator.
Its hasNext method looks like this:
>     /**
>      * Returns <tt>true</tt> if the iteration has more elements. (In other
>      * words, returns <tt>true</tt> if <tt>next</tt> would return
an element
>      * rather than throwing an exception.)
>      *
>      * @return Returns <tt>true</tt> if the iterator has more elements.
>      */
>     public boolean hasNext() {
>         return (currentChild != null);
>     }
> but its next() method looks like this:
>     /**
>      * Returns the next element in the iteration.
>      *
>      * @return Returns the next element in the iteration.
>      * @throws java.util.NoSuchElementException
>      *          iteration has no more elements.
>      */
>     public Object next() {
>         nextCalled = true;
>         removeCalled = false;
>         if (hasNext()) {
>             lastChild = currentChild;
>             currentChild = currentChild.getNextOMSibling();
>             return lastChild;
>         }
>         return null;
>     }
> which is a problem, because currentChild.getNextOMSibling() looks like this:
>     /**
>      * Gets the next sibling. This can be an OMAttribute or OMText or
>      * OMELement for others.
>      *
>      * @throws OMException
>      */
>     public OMNode getNextOMSibling() throws OMException {
>         while (!done) {
>             int token = builder.next();
>             if (token == XMLStreamConstants.END_DOCUMENT) {
>                 throw new OMException();
>             }
>         }
>         return super.getNextOMSibling();
>     }
> which will under some circumstances throw an OMException, which is not in the contract
of the iterator's next() method to throw.
> Thus, iterator.hasNext() is returning true, implying that there is a next element, but
when next() is actually called, the iterator discovers that it has reached the end of the
document, and that therefore there really is no next element. It therefore throws an OMException.
> Firstly, if the next() method is going to be implemented this way, then hasNext() should
perform enough lookahead on the document to detect that the next item in the input stream
is indeed a END_DOCUMENT, and should therefore return false, since under these circumstances
there truly isn't a next element (and calling next() would therefore always throw an OMException).
That way, when the end of the document is hit, the serialize method will simply stop and return
its results rather than trying to advance past the end of the document as it does now.
> Secondly, this OMException really should have some meaningful error text in it, such
as "Can't call 'next()' on an iterator which is positioned at element 'foo' which is the last
element in the document" or even better, "Can't call next() when hasNext() returns false"
(see below). I can't think of any cases in typical library code where it is desirable to throw
exceptions that don't have any message text. This is really unpleasant for anybody that is
trying to debug a problem. I would encourage someone to do a search through the source code
for "throw new OMException()" and add an explanatory error message wherever one is found.

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