If the above learning process is relatively smooth, the difficulty is difficult to improve. Because the above knowledge is only involved in one aspect, the J2EE specification such as EJB, JMS, JTA is often a crystallization of several Java technology, so it is relatively difficult to master.
First, you must learn JNDI, JNDI is an App Server Location Server Resource (EJB Components, Datasouce, JMS) Finding Method, if you are not familiar with JNDI, EJB, JMS these things are almost university can't go. JNDI is actually javax.naming. * This package is easy to use. The difficulty is the configuration of the server resource file. For the configuration of the server resource file, you need to take a look at the special document specification, such as the WEB.XML of WEB.XML, EJB-JAR.XML Writings, and so on. For each different app server, there is also your own service resource profile, it is also familiar.
You can then learn JTA, mainly to understand the method of JTA's control for transactions, and what is used in any occasion. Here you can make an example, we know that the general situation can be transactional for a database connection (Conn.commit (False), ...., as an atomic operation, but assumes me Business requirements are to make operations for two different databases as an atomic operation, can you do? At this time, I can only use JTA. Suppose the operation process is first inserting a record first to the A database, then deleting another record of the B database, our own writing code is not controlling the entire operation as an atomic operation. With JTA, the APP Server is used to complete the control.
Learn to serialize and RMI before learning EJB, RMI is the basis of EJB. Then learn JMS and EJB. For EJB, the most critical is to understand how EJB is called by RMI to the call to the remote object, and in what circumstances to use EJB.
After learning EJB, JMS these things, you may be aware of the knowledge of two fields, one is UML, and the other is Design Pattern. Java Enterprise Software Design is very valid to the framework design, and a good software framework is a necessary condition for software development. At this time, you should start the focus of learning in design patterns and frameworks, master EJB design patterns and J2EE's core mode through learning and practical programming experience.
Inside the J2EE specification, there are many business technologies in addition to EJB, JMS, JTA, Servlet / JSP, JDBC, which is not introduced here.
There is also a new field Web Services. Web Services also does not have any new things, it is like a binder, you can unify different services to provide a unified call interface. As a user, I just get the WSDL for the service provider (on service Description), it is enough, I don't know if the service provider is EJB component, or is it .NET component, or what CORBA component, or other implementation, I don't need to know. The greatest place in Web Services is to achieve sharing of Internet services through unified service providing methods and calls, is a very exciting technical field. Web Services seems to have no good books, but can learn by checking information on the network.
