Arun Gupta, Miles to go ...

Metro and jMaki Q&A from a Preso

I presented on Metro and jMaki in a invitation-only gathering on Nov 15. The audience in both the sessions was pretty interactive. Even though the sessions were invitation-only, I'm posting some of the questions asked during the sessions along with their answers.

1. How to build support for jMaki in other languages such as Perl ?
   
   The best option is to check out jMaki workspace and look at Jmaki.php and XmlHttpProxy.php.
   
   The basics are relatively easy but not always obvious. There is no runtime spec so it's hard to get all the little details right: Theming, API keys, and the Proxy behavior are pretty specific. Please feel free to ask a question on jMaki Forums. It would be helpful if you can help us create such a document while adding support for Perl.
2. Is it possible to point a DataTable widget to a Database table, introspect the database table and auto-generate the rows/columns ?
   
   Java Persistence API (in Java) and ActiveRecord (in Rails) already serve this purpose. There are detailed instructions for jMaki/JPA and jMaki/ActiveRecord. At this time there are no plans to tie closely to the database. Please file an RFE if you like this feature.
3. Do we have any comparisons between jMaki and Open Laszlo ?
    
   We need to understand Open Laszlo better to prepare a comparison. At this time no comparison is available.
4. How are topics implemented ? What is the data structure that implements them ?
    
   The topic name is a String / Regular expression Object. The topic names can also include wildcards (start, include, end with a *). The payload must be an object (strings are objects). https://ajax.dev.java.net/publishsubscribe.html provides some more details.
5. Do we have any performance data on large data sets - e.g. 15,000 rows in a Data Table widget ?
   
   Carla has a good sample that explains how pagination can be achieved for large data sets. The real question is "how much can you realistically cache on the client?". There are lots of algorithms and that can be more application logic. If you are going to deal with sets like this then the Dojo Grid is supposed to be good as it handles client-side caching and paging. We'll be adding it as a widget for the dojo 1.0 push.
6. Are there any widgets that support streaming video ?
   
   Not yet but it would be very easy to wrap a widget like that. For example, please look at Sound extension that is available as wrapper over Flash.
7. How to prevent scripting attack on jMaki-wrapped widgets ?
   
   jMaki wrappers are very trivial. The data from an external domain is not processed in any manner and instead passed on to the underlying toolkits. We make sure the wrappers are well tested and rely on the underlying toolkits to test their widgets.

And now for the Metro session:

1. How more recent Metro jars be installed on GlassFish ?
   
   A stand-alone build of Metro can be downloaded from metro.dev.java.net. This build comes with wsit-on-glassfish.xml script and can be used to override the jars in an existing GlassFish v2 installation.
2. Why Reliable Messaging is required if TCP/IP already provides reliability ?
   
   TCP/IP provides reliability at the network level. The Reliable Messaging support in Metro implements a transport-independent messaging protocol (defined by the WS-Reliable Messaging spec) with a SOAP Binding. This allows the SOAP message to be used in alternate transports such as JMS or SMTP. It also enables Reliability between a Client and Endpoint with multiple intermediaries in-between which is not possible with TCP/IP.
3. Is the "Test Web service" feature available outside NetBeans ?
   
   The "Test Web service" feature in NetBeans makes use of Tester application in GlassFish. It is a web application that dynamically generates the JSP pages by introspecting the WSDL. Currently it only works only for methods that have primitive types in the signature.
4. What would it take to run Metro on Embedded Jetty ?
   
   Servlet-based endpoints can be easily deployed on Jetty as explained here. The different variants of Endpoint.publish() currently runs only on Light-weight HTTP server bundled along with Java SE 6. An RFE has already been filed for this functionality and it will be fixed in a future release of Metro.
5. Does Metro Security integrate with Active Directory ?
   
   Even though Metro Security cannot be directly integrated with ActiveDirectory, Authentication can be plugged through the integration of Metro with OpenSSO.
6. What specific performance improvements have we made in Metro ?
   
   Here are some of the key performance improvements:
   • Revisited some of the key abstractions. The physical data representation was hidden from the user and yet backed by different implementations such as InputStream, JAXB objects, DOM node, Source, etc.
   • Faster, type-safe read access to commonly used properties such as Target Endpoint Address and SOAPAction. Also lazy reading.
   • Headers are made randomly accessible.
   • Filtering of data was enabled by creating an additional wrapper instead and delaying the actual filtering
   • Mostly JAXB is used to write the JAX-WS payload. There were numerous improvements made in JAXB such as:
     • Collapsing the layers and write directly to OutputStream instead of using StAX.
     • Pre-encode tag names to UTF-8
     • Numbers are converted straight to byte stream
     • Namespace prefixes encoded just once and reused
     • Lazy reading and writing of attachments (for example image is encoded in to JPEG byte stream)

   Metro team also presented a BoF 2526 on these improvements at JavaOne 2006.

7. How much traffic is bloated because of enabling Reliability or Security ?
   
   There is a definite bloating of messages that happen when either Reliability or Security or Transactions are enabled. I'll provide the exact numbers in a later blog but all the messages are clearly defined by the existing specifications.

Feel free to ask any other questions in Metro Forum and jMaki Forum.

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Posted by Arun Gupta in webservices  |  Comments[1]