Java for freshers

get() vs load() Hibernate session comes with different methods to load data from database. get and load are most used methods, at first look they seems similar but there are some differences between them. when we use get() to retrieve data that doesn’t exists, it returns null. It fires database query and throws org.hibernate.ObjectNotFoundException if there is no record found with the given identifier. It’s hibernate specific Runtime Exception, so we don’t need to catch it explicitly./li> Hibernate first level cache Hibernate first level cache is associated with the Session object. Hibernate first level cache is enabled by default and there is no way to disable it. However hibernate provides methods through which we can delete selected objects from the cache or clear the cache completely. Any object cached in a session will not be visible to other sessions and when the session is closed, all the cached objects will also be lost.

Inversion of Control As the name implies Inversion of control means now we have inverted the control of creating the object from our own using new operator to container or framework. Now it’s the responsibility of container to create an object as required. Dependency Injection The technology that Spring is most identified with is the Dependency Injection (DI) flavor of Inversion of Control. The Inversion of Control (IoC) is a general concept, and it can be expressed in many ways. Dependency Injection is merely one concrete example of Inversion of Control. When writing a complex Java application, application classes should be as independent as possible of other Java classes to increase the possibility to reuse these classes and to test them independently of other classes while unit testing. Dependency Injection helps in gluing these classes together and at the same time keeping them independent. What is dependency injection exactly? Let's look at these two words separately. ...

Matcher vs Pattern Pattern : A compiled representation of a regular expression. Matcher : An engine that performs match operations on a character sequence by interpreting a Pattern. A regular expression, specified as a string, must first be compiled into an instance of this class. The resulting pattern can then be used to create a Matcher object that can match arbitrary character sequences against the regular expression. All of the state involved in performing a match resides in the matcher, so many matchers can share the same pattern. A typical invocation sequence is thus Pattern p = Pattern.compile("a*b"); Matcher m = p.matcher("aaaaab"); boolean b = m.matches(); A matches method is defined by this class as a convenience for when a regular expression is used just once. This method compiles an expression and matches an input sequence against it in a single invocation. The statement boolean b = Pattern.matches("a*b", "aaaaab"); is e...

Step 1: First request will be received by DispatcherServlet. Step 2: DispatcherServlet will take the help of HandlerMapping and get to know the Controller class name associated with the given request. Step 3: So request transfer to the Controller, and then controller will process the request by executing appropriate methods and returns ModeAndView object (contains Model data and View name) back to the DispatcherServlet. Step 4: Now DispatcherServlet send the model object to the ViewResolver to get the actual view page. Step 5: Finally DispatcherServlet will pass the Model object to the View page to display the result.