The following sections describe problems that have been resolved by Service Packs for WebLogic Server 6. WebLogic Server 6. The following sections describe problems that have been resolved for the release of WebLogic Server 6. This caused the deployer tool to incorrectly create an additional deployment repository for this application when it was updated. Navigation through the directories did not go through action servlet, so encoding was not set properly.
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In this tutorial, we learn how to use Enterprise JavaBeans. Enterprise JavaBean EJB is a server-side component that encapsulates the business logic of an application. EJBs are run in an EJB container, which is responsible for various system-level services, including transaction management, security, and concurrency control.
We will run our examples in GlassFish. Apache Derby is an open source relational database implemented entirely in Java. Oracle distributes the same binaries under the name Java DB. We create a new web application in NetBeans. From the Server and Settings page, we select GlassFish server and change the context to myfirstejb. This is our index. It will be returned if we access the root page of the application. We call the bean MyFirstBean , type in com.
Stateless session bean does not maintain a conversational state with the client. When a client invokes the methods of a stateless bean, the bean's instance variables may contain a state specific to that client but only for the duration of the invocation. When the method is finished, the client-specific state is lost. MyFirstBean is a stateless session bean. A stateless session bean is created with the Stateless decoration.
It has a no-interface view , where local business interfaces are not used and all public methods of the bean class are automatically exposed to the caller. Next, we create a new servlet by right-clicking on the project icon and selecting a Servlet file type from the Web category. We call the servlet Greet and type in the com. The Greet servlet reads a name parameter from the URL sent by the client, calls EJB's createMessage business method and returns a response in plain text.
We build the application and deploy it to the GlassFish server. To build the application, right-click on the project icon and select Build; to deploy the application, right-click on the project icon and select Deploy. With the curl tool, we connect to the Greet servlet of the myfirstejb web application and pass it a parameter. The web application responds with a greeting. In the second example, we create a web application that will read and save cars.
The car objects will be saved in the Derby database. We create a new Java web application with a car-app name. Then we create a new Car entity. Entity class file type is located in the persistence category. The package will be com.
The primary key type is Long and the create persistence unit option is checked. In the next page, we change the persistence unit name to carpu , and select the default EclipseLink persistence provider.
In this view we provide the persistence unit name, persistence provider, data source, and table generation strategy. Entity Bean is a type of Enterprise JavaBean that represents a business entity object existing in a persistent storage. An entity bean is identified by a primary key.
Unlike session beans, which live during the lifetime of a client session, entity beans survive even EJB container crashes. Car is an EJB entity bean. It is a business object to be stored in the Derby database.
Entity beans are decorated with the Entity annotation. The entity maps to the Cars table. Each entity has a unique object identifier. This unique identifier, or primary key, enables clients to locate a particular entity instance.
The Id declares the identifier property of this entity bean, the GeneratedValue annotation is used to specify how the primary key is generated, and the Column maps the identifier to the Id column of the database table. We create a local, stateless ManageCarBean enterprise bean.
This time the EJB is having a local interface view. The interface defines the methods to be used by the clients of the EJB. A client can access a session bean only through the methods defined in the bean's business interface.
The Local decoration designates that the interface is a local business interface. The EntityManager is created by the container using the information in the persistence. The PersistenceContext annotation injects the entity manager into the bean.
The manager is mapped to the carpu persistence unit. Entity manager is used to interact with the data via the persistence context. The saveCar method saves a car object into the database; in our case it is Derby.
The persistence. In our application, we save our data in the Derby's pre-created sample database. The eclipselink. We can use NetBeans Derby tool to connect and manage our data in the database. The tool is located in the Services window. We create two servlets: SaveCar and ReadCar. We place them into the com. Servlets are created from the NetBeans Web category. Both servlets respond in plain text.
The library can be downloaded from the project website. A ValidateParameter class is used to validate the request parameters. Parameters may not be null or empty, and ID and price values must be numbers.
In addition, the price must be within a reasonable range. The data for the car object are read from the URL sent by the client. A new car object is created and saved to the database.
To save the car object, we utilize the ManageCarBean's saveCar method. The ReadCar servlet calls the ManageCarBean enterprise bean to read data from the database; it selects a car object based on the provided ID. The ManageCarBean's readCar method is used to retrieve the car object. In the web. The error. Note that error We place the two text files inside web pages.
It's time to deploy the application. The application is deployed by right-clicking on the web project and selecting the Deploy command. Note that when we clean the project, the application is undeployed. The deploy command also starts the selected application server if it is not already running. The GlassFish's asadmin tool can be used to determine the currently deployed applications. NetBeans automatically starts the Derby server when GlassFish starts.
This can be turned off in the GlassFish server settings. There we can see the Start Registered Derby Server option.
NetBeans saves us a lot of tedious work during development. But it is beneficial to build the project manually with Maven. Don't forget to copy the web. The pom. We instruct Maven to use Java 8. The final build file is called car-app. The Derby server is started. NetBeans creates the Derby system home in the. There we can find the sample database that we have worked with earlier. We deploy the application. This is the consequence of the eclipselink. We can ignore the warning.
In this tutorial, we have created Enterprise JavaBeans for some simple business logic. We have used NetBeans, Derby, and Maven for our examples.
Introduction to EJBs
In this tutorial, we learn how to use Enterprise JavaBeans. Enterprise JavaBean EJB is a server-side component that encapsulates the business logic of an application. EJBs are run in an EJB container, which is responsible for various system-level services, including transaction management, security, and concurrency control. We will run our examples in GlassFish. Apache Derby is an open source relational database implemented entirely in Java. Oracle distributes the same binaries under the name Java DB. We create a new web application in NetBeans.
Java Server-Side Programming
As the industry standard for platform-independent reusable business components, EJB has just become Sun Microsystem's latest developer certification. Whether you want to be certifiable or just want to learn the technology inside and out, Head First EJB will get you there in the least painful way. And with the greatest understanding. You'll learn not just what the technology is , but more importantly, why it is, and what it is and isn't good for.