The bean implementation Contains the Java code that implements the methods defined in the home interface life cycle methods , remote interface business methods , and the required container methods container callback functions. The deployment descriptor Specifies attributes of the bean for deployment. These designate configuration specifics, such as environment, interface names, transactional support, type of EJB, and persistence information. The implementation contains logic for lifecycle methods defined in the home interface, business methods defined in the remote interface, and container callback functions defined in the SessionBean , EntityBean , or MessageDrivenBean interface.
A parameter that you pass to a bean method--or a return value from a bean method--can be any Java type that is serializable. Java primitive types, such as int , double , are serializable. Any non-remote object that implements the java. Serializable interface can be passed.
A non-remote object that is passed as a parameter to a bean or returned from a bean is passed by value, not by reference. So, for example, if you call a bean method as follows:. If the bean changes the value of theNumber object on the server, this change is not reflected back to the client, because of pass-by-value semantics.
If the non-remote object is complex--such as a class containing several fields--only the non-static and non-transient fields are copied. When passing a remote object as a parameter, the stub for the remote object is passed. A remote object passed as a parameter must extend remote interfaces. The next section demonstrates parameter passing to a bean, and remote objects as return values.
The EmployeeBean getEmployee method returns an EmpRecord object, so this object must be defined somewhere in the application. The class is declared as public and must implement the java. Serializable interface so that it can be passed back to the client by value, as a serialized remote object. The declaration is as follows:. Note: The java. Serializable interface specifies no methods; it just indicates that the class is serializable. Therefore, there is no need to implement extra methods in the EmpRecord class.
A session bean might contain methods that query and update data in a relational table. Session beans are often used to implement services. For example, an application developer might implement one or several session beans that retrieve and update inventory data in a database. Session beans are transient because they do not survive a server crash or a network failure.
If, after a crash, you instantiate a bean that had previously existed, the state of the previous instance is not restored. State can be restored only to entity beans. A session bean implements the javax.
SessionBean interface, which has the following definition:. At a minimum, an EJB must implement the following methods, as specified in the javax. SessionBean interface:. Stateless session beans must do nothing in this method.
Stateful session beans can initiate state in this method. This method performs any required clean-up--for example, closing external resources such as file handles. The container calls this method after the bean creation. The enterprise bean can store the reference to the context object in an instance variable, for use in transaction management. Beans that manage their own transactions can use the session context to get the transaction context.
Using setSessionContext You use this method to obtain a reference to the context of the bean. Session beans have session contexts that the container maintains and makes available to the beans. The bean may use the methods in the session context to make callback requests to the container. The container invokes setSessionContext method, after it first instantiates the bean, to enable the bean to retrieve the session context. The container will never call this method from within a transaction context.
If the bean does not save the session context at this point, the bean will never gain access to the session context. When the container calls this method, it passes the reference of the SessionContext object to the bean. The bean can then store the reference for later use. The following example shows the bean saving the session context in the sessctx variable.
A bean needs the session context when it wants to perform the operations listed in Table This is valid only for beans that have been designated transactional. There are two types of session beans:. Stateful Session Beans --Stateful session beans are useful for conversational sessions, in which it is necessary to maintain state, such as instance variable values or transactional state, between method invocations. These session beans are mapped to a single client for the life of that client.
Stateless Session Beans A stateless session bean does not maintain any state for the client. It is strictly a single invocation bean. It is employed for reusable business services that are not connected to any specific client, such as generic currency calculations, mortgage rate calculations, and so on. Stateless session beans may contain client-independent, read-only state across a call. Subsequent calls are handled by other stateless session beans in the pool. The information is used only for the single invocation.
The EJB container maintains a pool of these stateless beans to service multiple clients. An instance is taken out of the pool when a client sends a request. There is no need to initialize the bean with any information. In addition, there is no need for the intended use for these methods in a stateless session bean. Instead, these methods are used mostly for EJBs with state--for stateful session beans and entity beans. Thus, these methods should be empty or extremely simple. Implementation Methods Home Interface Extends javax.
EJBHome and requires a single create factory method, with no arguments, and a single remove method. Remote Interface Extends javax. EJBObject and defines the business logic methods, which are implemented in the bean implementation. Bean implementation Implements SessionBean.
This class must be declared as public, contain a public, empty, default constructor, no finalize method, and implements the methods defined in the remote interface. Must contain a single ejbCreate method, with no arguments, to match the create method in the home interface. Contains empty implementations for the container service methods, such as ejbRemove , and so on. Stateful Session Beans A stateful session bean maintains its state between method calls.
Thus, there is one instance of a stateful session bean created for each client. Each stateful session bean contains an identity and a one-to-one mapping with an individual client. The state of this type of bean is maintained across several calls through serialization of its state, called passivation. This is why the state that you passivate must be serializable. However, this information does not survive system crashes. To maintain state for several stateful beans in a pool, it serializes the conversational state of the least recently used stateful bean to a secondary storage.
When the bean instance is requested again by its client, the state is activated to a bean within the pool. Thus, all resources are used performantly, and the state is not lost.
The type of state that is saved does not include resources. The container invokes the ejbPassivate method within the bean to provide the bean with a chance to clean up its resources, such as sockets held, database connections, and hash tables with static information. Not using TJ? Create Account. Already a User? Old Fashioned? Sign Up Using Email. Display Name mandatory! Email Please enter a valid email id.
At least 6 characters required. Forgot Password. Type your email id here mandatory! Change Password Type your new password here mandatory! EJB is completely unrelated? This answer have useful information, but not complete. An EJB is a nonvisual, remote object. JavaBeans may have BeanInfo classes, property editors or customizers.
JavaBeans are not typed. EJBs are of two types - session beans and entity beans. No explicit support exists for transactions in JavaBeans. Johnny Baloney 3, 1 1 gold badge 28 28 silver badges 36 36 bronze badges. Charu Jain Charu Jain 71 1 1 silver badge 1 1 bronze badge. What do you mean session beans and entity beans? On the other hand, Java beans , is a simple plain Java class with getters and setters and that class is serialized, below is the example: public class MyBean implements java.
Vishrant Vishrant The Overflow Blog. Does ES6 make JavaScript frameworks obsolete? Podcast Do polyglots have an edge when it comes to mastering programming Featured on Meta. In this article, we have seen that EJB is a specification of J2EE, whereas Spring is a framework for easy implementation, even though there are some areas that do overlap. We have seen the differences in the architecture and discussed some of the EJB and spring offers to the developer. With the difference matrix, we can conclude this is if you want to use advanced features like AOP and want more control over the application, then go with the Spring framework.
This has been a guide to EJB vs Spring. Here we also discuss the key differences with infographics and comparison table.
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