Java’s transient keyword is used to denote that a field is not to be serialized, whereas JPA’s @Transient annotation is used to indicate that a field is not to be persisted in the database, i.e. their semantics are different.
A servlet is simply a class which responds to a particular type of network request – most commonly an HTTP request. Basically servlets are usually used to implement web applications – but there are also various frameworks which operate on top of servlets (e.g. Struts) to give a higher-level abstraction than the “here’s an HTTP … Read more
because when the constructor is called, the bean is not yet initialized – i.e. no dependencies are injected. In the @PostConstruct method the bean is fully initialized and you can use the dependencies. because this is the contract that guarantees that this method will be invoked only once in the bean lifecycle. It may happen … Read more
A WAR (Web Archive) is a module that gets loaded into a Web container of a Java Application Server. A Java Application Server has two containers (runtime environments) – one is a Web container and the other is a EJB container. The Web container hosts Web applications based on JSP or the Servlets API – … Read more
As you state JPA is just a specification, meaning there is no implementation. You can annotate your classes as much as you would like with JPA annotations, however without an implementation nothing will happen. Think of JPA as the guidelines that must be followed or an interface, while Hibernate’s JPA implementation is code that meets … Read more
Introduction To browse and select a file for upload you need a HTML <input type=”file”> field in the form. As stated in the HTML specification you have to use the POST method and the enctype attribute of the form has to be set to “multipart/form-data”. <form action=”upload” method=”post” enctype=”multipart/form-data”> <input type=”text” name=”description” /> <input type=”file” … Read more
JSP (JavaServer Pages) JSP is a Java view technology running on the server machine which allows you to write template text in client side languages (like HTML, CSS, JavaScript, ect.). JSP supports taglibs, which are backed by pieces of Java code that let you control the page flow or output dynamically. A well-known taglib is … Read more