Jakarta Enterprise Beans facts for kids

Jakarta Enterprise Beans (EJB) are like special building blocks for creating big computer programs, especially those used by businesses. Think of them as smart helpers that handle important jobs in the background, like keeping your information safe, making sure online purchases go through correctly, and managing how different parts of a program talk to each other.

EJBs are part of a larger set of tools called Jakarta EE. They help programmers build the "brain" of an application, which is where all the main actions and rules happen. This means programmers can focus on what the program needs to do, instead of worrying about tricky technical details like security or saving data.

What EJBs Do

The EJB system helps computer programs with many important tasks. It's like having a helpful assistant for your code. Here are some of the things EJBs can do:

• Handling Transactions: This means making sure a series of steps in a program either all happen successfully or none of them do. For example, when you transfer money online, the EJB makes sure the money leaves one account and arrives in another, or it cancels the whole process if something goes wrong.
• Saving Data: EJBs work with other tools to help programs save and retrieve information from databases.
• Controlling Access: They manage who can use certain parts of the program at the same time, so things don't get mixed up.
• Sending Messages: EJBs can send and receive messages between different parts of a program or even other programs. This is useful for tasks that don't need an immediate answer.
• Scheduling Tasks: They can set up tasks to run automatically at specific times, like sending out daily reports.
• Security: EJBs help make sure only authorized users can access sensitive information or perform certain actions.

How EJBs Have Evolved

The idea for EJBs started in 1997. Over the years, they have changed a lot to become easier and more powerful for programmers to use.

• Early Days (EJB 1.0 and 1.1): In the beginning, EJBs were quite complex to set up. Programmers had to write many extra files to tell the system how their EJB should work.
• Making Things Simpler (EJB 3.0): A big change happened around 2006. This version made it much easier to write EJBs. Programmers could use special "annotations" (like small notes in the code) instead of complicated separate files. This made EJBs much more popular because they were less work to use.
• Adding New Features (EJB 3.1 and 3.2): Later versions, like EJB 3.1 (released in 2009) and EJB 3.2 (released in 2013), added even more helpful features. These included new types of EJBs and ways to make them run faster or handle tasks in the background.
• Renaming and Updates (EJB 3.2.6 and 4.0): By 2019, the name officially changed to "Jakarta Enterprise Beans." The latest version, EJB 4.0 (released in 2020), mainly updated the internal names of the tools to fit with the new "Jakarta EE" family. It also removed some older, less used parts of the system.

Types of Enterprise Beans

There are two main kinds of Enterprise Beans that help programs in different ways:

• Session Beans: These are like temporary helpers that do specific jobs for a user.
• Message Driven Beans: These beans are triggered by messages and are great for tasks that don't need an immediate response.

Session Beans

Session Beans are used for handling business tasks. They can be one of three types:

Stateful Session Beans

These beans remember what's happening during a conversation with a user. Imagine you're filling out an online order form. A Stateful Session Bean would keep track of the items in your cart as you add them. It's like a personal assistant who remembers your specific requests throughout your shopping session.

Stateless Session Beans

These beans don't remember anything about past interactions. They are like a helpful robot that performs a single task and then forgets everything. If you ask it to do something again, it treats it as a brand new request. This makes them very efficient for quick, one-time jobs, like sending an email confirmation after a purchase. Many users can use the same Stateless Session Bean because it doesn't hold onto any specific user's information.

Singleton Session Beans

A Singleton Session Bean is a special kind of bean where only one copy of it exists in the entire program. It's like a central information desk that everyone shares. This is useful for things that need to be the same for all users, like a daily price list or a list of common settings.

Message Driven Beans

Message Driven Beans (MDBs) are different because they don't wait for a direct request. Instead, they listen for messages. When a message arrives, the MDB automatically starts working on it.

Think of it like a post office. You send a letter (a message), and the MDB (the postal worker) picks it up and processes it when it's ready. This is great for tasks that can happen in the background, like updating a database or sending notifications, without slowing down the main program.

How EJBs Run

EJBs run inside a special environment called an "EJB container," which is usually part of a larger "application server." When a program needs an EJB, it doesn't create it directly. Instead, it asks the EJB container for one. The container then provides a special "proxy" (a stand-in) that acts like the EJB.

This proxy is very clever! It allows the EJB container to add extra services automatically, like:

• Transactions: Making sure all steps of a task are completed or none are.
• Security: Checking if the user has permission to do something.
• Interceptions: Doing something before or after a main task, like logging information.

So, when you ask the proxy to do something, it first lets the container handle any extra services (like starting a transaction), then it tells the actual EJB to do the work, and finally, the container finishes up (like saving the transaction). This makes programming much simpler because the programmer doesn't have to write all these extra service steps themselves.

Handling Transactions

EJBs are very good at managing transactions. A transaction is a group of operations that must all succeed or all fail together. For example, if you're moving money from your savings to your checking account, both the deduction from savings and the addition to checking must happen. If one fails, the whole transaction should be canceled.

EJBs can handle transactions in two main ways:

• Container-Managed Transactions (CMT): This is the most common way. The EJB container automatically manages the transactions for you. You can simply tell the container what you want it to do (e.g., "start a new transaction for this method," or "join an existing transaction"). This is done using simple annotations in your code.
• Bean-Managed Transactions (BMT): In this case, the programmer writes the code to manage the transactions themselves. This gives more control but is also more complex.

Sending and Receiving Messages

EJBs use a system called Java Message Service (JMS) to send and receive messages. This is how Message Driven Beans work. They can listen to specific "queues" (like a line of messages) or "topics" (where messages are broadcast to many listeners) and process messages as they arrive. This is very useful for tasks that can happen in the background without needing an immediate reply.

Connecting to EJBs

Programs can connect to EJBs in a few ways:

• Injection: This is the easiest way. You simply tell the system that your program needs an EJB, and the system automatically provides it.
• Looking Up: Sometimes, programs need to find an EJB by its name. This is done using a "naming and directory service" called Java Naming and Directory Interface (JNDI). It's like looking up a phone number in a directory.

Remote Access

Sometimes, a program running on one computer needs to use an EJB running on a different computer. EJBs can be set up to allow this "remote access." This is useful for very large systems where different parts of the program are spread across many servers. EJBs can also be set up as "web services," which allows programs written in different computer languages to communicate with them.

See also

In Spanish: Enterprise JavaBeans para niños