Ejb architecture pdf

This remote interface implementation illustrates the minimum methods required for an EJB implementation. At a minimum, an EJB must implement the following methods, as specified in the javax. SessionBean interface:. 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. 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. The Deployment Descriptor The most convenient way to implement the deployment descriptor for a bean is to write a descriptor file in text form.

The EJB deployment tool can read the text form descriptor, parse it, signal parse errors, and then verify that the descriptor itself, and the interface and bean implementation declarations meet the standard.

For example, bean implementations and interface specifications must be declared as throwing certain specified exceptions. If they do not, the deployment tool see "deployejb" lists the errors and exits. The text form deployment descriptor is usually stored in a file with a. In the EJB examples that are shipped with this product, the deployment descriptors are in the base directory of the example, along with the client application implementations and the Makefile and Windows NT batch files.

Here is the deployment descriptor for this example. For a complete description of the deployment descriptor attributes, see "Deploying an EJB".

This section shows the client code that you can use to send messages to the example bean described above, and get and print results from it. This client code demonstrates how a client:. To get a remote object reference you must know:.

JNDI is an interface to a naming and directory service. For example, JNDI can serve as an interface to a file system that you can use to look up directories and the files they contain. This section briefly describes JNDI. To start, all you must know is how to use the JNDI methods used to access permanently-stored home interface objects and how to set up the environment for the JNDI Context object. The remainder of this JNDI section describes the data structures and methods of the javax.

The first Context object that you receive is bound to the root naming context of the Oracle8i publishing context. EJB home interfaces are published in the database, and are arranged in a manner similar to a file system hierarchy. See "publish" for more details about publishing EJB home interfaces and about the Oracle8i published object directory structure. The environment parameter is a Java hashtable.

Table contains the six properties that you can set in the hashtable that are passed to the javax. Property Purpose javax. You must use the value "oracle. The three possible values are: oracle. Once you have the "initial references" context, you can invoke its methods to get a reference to an EJB home interface. To do this, you must know the published full pathname of the object, the host system where the object is located, the IIOP port for the listener on that system, and the database system identifier SID.

The listener port for IIOP requests is configured in the listener. The default for Oracle8i is You get the home interface using the lookup method on the initial context, passing the URL as the parameter. Once you have the home interface for the bean, you can invoke one of the bean's create methods to instantiate a bean. For example:.

Develop a deployment descriptor for each bean. Run the deployejb tool, which: reads the deployment descriptor and the bean JAR file loads the bean classes into the Oracle8i database publishes the bean home interface Make sure that the application developer has the information necessary about the bean remote interface and the name of the published beans. Write the Deployment Descriptor The enterprise bean deployer supplies a deployment descriptor for each EJB in the application. There is a text form of the descriptor, which is described in this section.

You can also use the Oracle8i JServer ejbdescriptor command-line tool to convert a text form of the deployment descriptor to the serialized class, or to convert back from the serialized object to a text file. The ejbdescriptor is documented in "ejbdescriptor". Text Format The text form of the session bean descriptor follows the conventions of Java code-- the descriptor has the syntax of a Java class.

The text format always begins with a SessionBean keyword, which is followed by the fully-qualified class name of the bean. The body of the declaration contains a list of descriptor attributes and their values. In this example, ejb. Note: Bean deployment will change significantly for the next release of the EJB specification. The preliminary version of that specification calls for the bean deployment information to be specified using XML.

There are three different types of bean attributes:. For example, you can specify that a method of a bean runs with a different identity user or schema name from other methods in the same bean. Or, you can set transaction properties on a method so that it runs with different transaction properties from the rest of the bean.

The transaction and security properties can apply to the bean as a whole or be specified on a method-by-method basis. The attributes of a session bean descriptor correspond to the attributes of the class javax.

SessionDescriptor and its super class javax. Table lists the attributes that you can use in the deployment descriptor. Attribute Name Values Required?

Yes Reentrant The literal "true" or "false". For entity beans. No SessionTimeout In seconds from the time that the last bean client disconnects. The default value is 0, which means that the session terminates when the last connection has terminated. Not relevant for the Oracle8i implementation. Cannot be a role. Yes, if RunAsMode is used. AllowedIdentities A list of usernames or roles in the database, enclosed in braces. No The example below demonstrates a deployment descriptor:.

The deployejb command-line tool creates a JAR file to use on the client side to access the bean. A bean provider must make the bean's home interface available for JNDI lookup so that clients can find and activate the bean. In JServer, you publish the bean home interface in an Oracle8i database with the deployejb command-line tool.

It publishes the bean in the instance CosNaming namespace under the name that you specify in the BeanHomeName attribute of the deployment descriptor. Use the session shell tool to remove the bean home interface name from the published object name space. See Chapter 6, "Tools" , for documentation of the dropjava and session shell tools.

Enterprise JavaBeans are inherently transactional. Transaction support is supplied for the bean by the EJB container. Sagar Gheewala. Abhijit Patwari. Vickram Jain. Shyamali Mishra.

Ariel Cupertino. Aaron Jude Pael. Irfan Muddassir. Nidhun M. Hemant Tulsani. Popular in Computing Platforms. John Smith. Ionut Ionut. Yoga Setiawan. P Venu Gopala Rao. Anonymous 8u1eidt. Song Soo Jae. Patricia Zick Ferreira. Ritu Raj.

Andi Septian Nasruloh. Juan Carlos Ruiz. Renzo Paolo Quintanilla. Dingtang Tikhak. Mahmood Uddin Ahmed. Evaldo Wolkers. Robbin Pinto. Tory Pradana. The name parameter for the EJB specifies the name with which the 2. The mapped-name parameter specifies the global JNDI binding of the 2. Also note that since the bean being looked up is a EJB2.

To build and run the example, make sure you have installed JBoss 5. This will create the EAR in the target folder of the tutorial. Then follow the steps mentioned above, to access the servlet from the web browser. Stateless3Bean also exposes a business-remote interface, so that the org.

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