0 Replies Latest reply on Nov 16, 2001 8:03 AM by Jochen Wiedmann

    EJB-based framework for XML

    Jochen Wiedmann Newbie


      Hi,

      we will possibly soon be realizing an EJB based
      framework for an XML application. As I am currently
      planning the details, it would be nice to have a
      discussion on that. That would help me a lot. Well, here's what I am currently considering.

      In particular I would like to know what people
      suggest on listXXX() methods returning a very
      large quantity of data. My question is: Who to
      read only partial results, for example the
      first 100 items, then the next 100, and so
      on, without performing the query again?


      Thanks,

      Jochen


      Conventions in addition to EJB standards

      All EntityBeans must have a method toXML().
      The method result is an XML document.
      Some sort Java-XML-binding is used, for
      performance reasons. In particular DOM
      and JDOM are forbidden.

      If the EntityBeans name is SomethingBean, then
      the XML document must have a document
      type of Something and the class of the corresponding should be ClsSomething.
      The Java package of SomethingBean and ClsSomething should the same.

      The Java class ClsSomething must
      have the following methods:


      void toSAX(org.xml.sax.ContentHandler ch)
      Marshal itself into a SAX content handler.


      void toWriter(java.io.Writer w)
      Marshal itself into a Writer.


      String toXML(java.io.Writer w)
      Marshal itself into a string.


      org.w3c.dom.Document toDOM()
      Marshal itself into a DOM document.


      static org.xml.sax.ContentHandler getSAXHandler()
      Returns a SAX handler for unmarshalling one
      or more documents of type Something.
      The SAX handler has a method

      Object getDocument()

      which may be called after endDocument(). It
      returns a successfully parsed instance of ClsSomething. The SAX handler must be able
      to be used multiple times. In other words,
      the method startDocument() must reset
      the SAX handlers state.


      static Object fromString(String s)
      A shortcut for the use of getSAXHandler(), that
      parses and returns a single instance of ClsSomething from the String s.


      static Object fromDOM(org.w3c.dom.Document d)
      static Object fromDOM(org.w3c.dom.Element e)
      static Object fromDOM(org.w3c.dom.ElementFragment ef)
      Shortcuts for the use of getSAXHandler(), that
      convert a DOM document into an instance of
      ClsSomething.


      All EntityBeans should have a method

      create(ClsSomething s).

      This constructor will
      typically read only those elements from the
      XML document, that aren't relevant of the work
      flow. The work flow elements will typically
      be initialized from defaults or with additional
      parameters. In other words: This method will
      leave the created entity in an initial state.


      All EntityBeans should have a method

      update(ClsSomething s)

      This method will update those parts of the XML
      document, that aren't relevant for the workflow. The update method
      will typically take the XML document, change
      the work flow elements to match the current
      state. In other words: This method won't change
      the entity beans current state.


      EntityBeans should not offer methods
      like getXXX() or setXXX(), with the exception
      of elements responsible for workflow or state.
      In particular EntityBeans should not use CMP
      (Container Managed Persistence).


      EntityBeans should have methods like

      Object listXXX(int format, ...)

      that return a Collection or List. If the format
      is FORMAT_PRIMKEY, then the collection items
      must be primary keys of the listed items
      and the caller needs to use findByPrimaryKey() to get
      access to details. If the format is FORMAT_XML,
      then the elements must be instances of ClsSomething. These elements may be incomplete,
      for performance reasons. For example, if the document is created as a result of a join, then
      the implementation might return the left part
      of the join only. The caller may again use
      findByPrimaryKey() to get access to details.
      If the format is FORMAT_XML_FULL, then the elements must be instances of ClsSomething. These instances must be complete, as returned by findByPrimaryKey().asXML().


      If the listXXX() methods return, then they
      must