Umarshalling JSON and XML

If you want to unmarshall json or xml inputstream to Java object, here are the functions :

public static <T> T unmarshalXML(InputStream is, Class<T> c)
   throws JAXBException {
  JAXBContext jc = JAXBContext.newInstance(c);
  Unmarshaller u = jc.createUnmarshaller();
  T response = (T) u.unmarshal(is);
  return response;
 }

 public static <T> T unmarshalJSON(InputStream is, Class<T> c)
   throws JAXBException, IOException, JSONException, XMLStreamException {
  JAXBContext jc = JAXBContext.newInstance(c);
  Unmarshaller u = jc.createUnmarshaller();
  String sJson = IOUtils.toString(is);
  JSONObject obj = new JSONObject(sJson);
  Configuration config = new Configuration();
  MappedNamespaceConvention con = new MappedNamespaceConvention(config);
  XMLStreamReader xmlStreamReader = new MappedXMLStreamReader(obj, con);
  T response = (T) u.unmarshal(xmlStreamReader);
  return response;
 }

Installing ReviewBoard plugin in Eclipse IDE

ReviewBoard (www.reviewboard.org/) is a nice code review web tool. ereviewboard (http://marketplace.eclipse.org/content/ereviewboard) is the corresponding plugin for Eclipse IDE. Below are the steps mentioned to integrate it with Eclipse IDE :

• Goto Help->Install New software
• Use URL http://rombert.github.com/ereviewboard/update/ and install "Mylyn Reviews Connector: ReviewBoard" and "Mylyn Reviews Connector: Review Board Subeclipse integration" (there are 3 connectors available, choose the appropriate one...here i am assuming subversion)
• If subeclipse is not installed, use url http://subclipse.tigris.org/update_1.6.x
• After installation, Open the task repositories view by navigating to Window -> Show View -> Other -> Mylyn -> Task Repositories
• Click the "Add Task Repository" button located in the view's toolbar.
• Select reviewboard and enter server as your reviewboard weburl (ex : http://192.168.x.x), username, password (Save password) and finish.
• Now, Right-click on a Project and select Team -> Create Review Request will post to reviewboard (if you dont see such a option trying restarting eclipse)

Some helpful links :
http://help.eclipse.org/galileo/index.jsp?topic=/org.eclipse.mylyn.help.ui/userguide/Task-Repositories.html
https://github.com/rombert/ereviewboard/wiki/Subclipse-integration

Remarks :
This tool can only post diff's of 1 project to reviewboard. Multiple project diff are not supported

Listing all entities in a JPA

Sometimes it may be a usecase scenario to find whether a particular class is an entity managed by persistence context. If you have entityManager or entityManagerFactory you can easily do that :

 Metamodel meta = entityManagerFactory.getMetamodel();
 // or
 Metamodel meta = entityManager.getEntityManagerFactory().getMetamodel();

 // to iterate over all classes
 for (EntityType<?> e : meta.getEntities()) {
  // get entity class
  Class c = e.getJavaType();
  // get entity name as string
  String entityName = e.getName(); //or c.getName()
 }

 // test a particular class is entity
 // will throw java.lang.IllegalArgumentException if not an entity
 meta.entity(inputClass);

Curious Case in MYSQL : Lock wait timeout exceeded on INSERT

Sounds strange, that how can a insert be locked or timed out . I had a innodb table with very frequent inserts, updated and deletes. After every few minutes, one of the inserts got timed out (50 sec is default value for innodb_lock_wait_timeout). My understanding was that timeouts happen when some other thread/transaction holds a exclusive record lock (select .. from update) for a long time. So how can a non-existent new row be already locked. I do not have a proper answer to this.

What solved my problem was dropping index and foreign key mapping, which were luckily irrelevant. Random guess is that innodb locks a range of index on insert. If you have an answer do let me know !