Obviously, even casual inspection of this reasoning shows the flaws. I also take issue that the complexity is somehow the fault of EJBs. Certainly, they could be simplified and EJB 3. Delivering components that have transactional support, security, location transparency, discovery, scalability and concurrency is not easy. However, I will admit that using EJB 2.
|Published (Last):||1 December 2016|
|PDF File Size:||17.15 Mb|
|ePub File Size:||6.17 Mb|
|Price:||Free* [*Free Regsitration Required]|
Table summarizes the important parts of an EJB 2. The following procedure describes how to implement these parts. For a typical implementation, see "Using Java". For more information, see "What is an EJB 2. Extends javax.
EJBHome for the remote home interface, javax. EJBLocalHome for the local home interface, and requires a single create factory method, with no arguments, and a single remove method. EJBObject for the remote interface and javax. EJBLocalObject for the local interface. It defines the business logic methods, which are implemented in the bean implementation.
Implements EntityBean. This class must be declared as public, contain a public, empty, default constructor, no finalize method, and implements the methods defined in the component interface.
Must contain one or more ejbCreate methods to match the create methods in the home interface. Contains complete implementations for the container service methods, such as ejbStore , ejbLoad , ejbRemove , and so on. Create the home interfaces for the bean see "Implementing the EJB 2. The remote home interface defines the create method that a client can invoke remotely to instantiate your bean.
The local home interface defines the create method that a collocated bean can invoke locally to instantiate your bean. To create the remote home interface, extend javax. To create the local home interface, extend javax. Create the component interfaces for the bean see "Implementing the EJB 2. The remote component interface declares the business methods that a client can invoke remotely. The local interface declares the business methods that a collocated bean can invoke locally.
To create the remote component interface, extend javax. To create the local component interface, extend javax. The primary key identifies each entity bean instance and is a serializable class. You can use a simple data type class, such as java. String , or define a complex class, such as one with two or more objects as components of the primary key.
Implement the entity bean with bean-managed persistence:. Provide a complete implementation of the get and set methods that correspond to the get and set method s declared in the home interfaces. For an entity bean with bean-managed persistence, the getter and setter methods are public, because you are responsible for their implementation.
Implement the business methods that you declared in the home and component interfaces if any. The signature for each of these methods must match the signature in the remote or local interface, except that the bean does not throw the RemoteException. Since both the local and the remote interfaces use the bean implementation, the bean implementation cannot throw the RemoteException.
For an entity bean, these methods are often delegated to a session bean see "What is a Session Bean? Implement any methods that are private to the bean or package used for facilitating the business logic. This includes private methods that your public methods use for completing the tasks requested of them. Implement the ejbCreate methods that correspond to the create method s declared in the home interfaces. The container invokes the appropriate ejbCreate method when the client invokes the corresponding create method.
For an entity bean with bean-managed persistence, provide create methods that allow the client to pass in values that the container will persist to your database.
You are responsible for providing an implementation that interacts with your database usually through straight JDBC calls to create an instance in the database. Provide a complete implementation for each of the javax. For an entity bean with bean-managed persistence, you are responsible for providing an implementation for each these methods that interacts with your database usually through straight JDBC calls to manage persistence in the database. Create the appropriate database schema tables and columns for the entity bean.
For an entity bean with bean-managed persistence, you are responsible for creating this schema in the database defined in the data-sources. Configure your ejb-jar. Complete the configuration of your entity bean see "Using an EJB 2. Example shows a typical implementation of an EJB 2. Example shows the corresponding home interface and Example shows the corresponding remote interface. Example Implementation of an EJB 2. Example shows the ejb-jar. Example ejb-jar. Example shows the data-sources.
Example data-sources. The ejbCreate method is responsible primarily for the creation of the primary key. This includes the following:. The following example shows the ejbCreate method for the employee example, which initializes the primary key, empNo. It should automatically generate a primary key that is the next available number in the employee number sequence.
However, for this example to be simple, the ejbCreate method requires that the user provide the unique employee number. In addition, because the full data for the employee is provided within this method, the data is saved within the context variables of this instance. After initialization, it returns this key to the container. Because the bean is saving the data, there is no definition of persistence data in the deployment descriptor.
Alternatively, you can create a complex primary key based on several data types. You define a complex primary key within its own class as follows:. The employee example requires that the employee number is given to the bean by the user. Another method would generate the employee number by computing the next available employee number, and use this in combination with the employee's name and office location.
After defining the complex primary key class, you would create your primary key within the ejbCreate method as follows:. The other task that the ejbCreate or ejbPostCreate should handle is allocating any resources necessary for the life of the bean.
For this example, because there is already the information for the employee, the ejbCreate performs the following:. Retrieves a connection to the database. This connection remains open for the life of the bean. It is used to update employee information within the database. It should be released in ejbPassivate and ejbRemove , and reallocated in ejbActivate. Skip Headers. Implementing an EJB 2. Table Parts of an EJB 2. Component Interface remote or local Extends javax.
Bean implementation Implements EntityBean. Example EJB 2. This includes the following: Creating the primary key. Creating the persistent data representation for the key. Initializing the key to a unique value and ensuring no duplication.
Returning this key to the container. The container maps the key to the entity bean reference. Note : For simplicity, the try blocks within the samples have been removed in this example. Book List. Contact Us. Legal Notices.
Who Says EJB 2.1 is Too Hard?
EJB 3. Take a look at org. Note that the class is annotated with RemoteHome and the ejbCreate method is annotated with Init. The former annotation indicates that the bean provides a EJB 2. The latter annotation indicates that when the create method is invoked from the home interface, the bean is initialized via the ejbCreate method. The initialization method annotated with Init name is not restricted to be ejbCreate.
Implementing an EJB 2.1 Stateless Session Bean
In EJB 3. In EJB 2. Namely, you had to have a "home" interface that extended javax. EJBHome or javax. This interface served as a sort of factory to create your bean's interface which itself had to extend either javax. EJBObject or javax.