Containers are a central theme in the Java EE architecture. Earlier in this chapter, we talked about application infrastructure in terms of the plumbing and electricity that a house provides for its inhabitants. Containers are like the rooms in the house. People and things exist in the rooms, and interface with the infrastructure through well-defined interfaces. In an application server, web and business components exist inside containers and interface with the Java EE infrastructure through well-defined interfaces.
In the same way that application developers can partition application logic into tiers of specific functionality, the designers of Java EE have partitioned the infrastructure logic into logical tiers. They have done the work of writing the application support infrastructure—things that you would otherwise need to build yourself. These include security, data access, transaction handling, naming, resource location, and the guts of network communications that connect the client to the server. Java EE provides a set of interfaces that allow you to plug your application logic into that infrastructure and access those services.
Think of containers as playing a role much like a video gaming console into which you plug game cartridges. As shown in next Figure, the gaming console provides a point of interface for the game—a suite of services that lets the game be accessed by the user and allows the game to interact with the user. The game cartridge needs to be concerned only with itself; it doesn’t need to concern itself with how the game is displayed to the user, what sort of controller is being used, or even if the household electricity is 120VAC or 220VAC. The console provides a container that abstracts all of that stuff out for the game, allowing the game programmer to focus solely on the game and not worry about the infrastructure.
If you’ve ever created an applet, you’re already familiar with the concept of containers. Most web browsers provide a container for applet components, as illustrated in next Figure. The browser’s container for applets provides an environment for the applet. The browser and the container know how to interact with any applet because all applets implement the java.applet.Applet class interface. When you develop applets, you are relieved of the burden of interfacing with a web browser, and are free to spend your time and effort on the applet logic. You do not need to be concerned with the issues associated with making your application appear to be an integral part of the web browsers.
Java EE provides server-side containers for the same reason: To provide a well-defined interface, along with a host of services that allow application developers to focus on the business problems they’re trying to solve, without worrying about the plumbing and electricity. Containers handle all of the mundane details involved with starting up services on the server side, activating the application logic, and cleaning up the component.
Java EE and the Java platform provide containers for web components and business components. These containers—like the gaming console analogy presented earlier in the chapter—provide an environment and interface for components that conform to the container’s established interfaces. The containers defined in Java EE include a container for Servlets, JSPs, and EJBs.
In the same way that application developers can partition application logic into tiers of specific functionality, the designers of Java EE have partitioned the infrastructure logic into logical tiers. They have done the work of writing the application support infrastructure—things that you would otherwise need to build yourself. These include security, data access, transaction handling, naming, resource location, and the guts of network communications that connect the client to the server. Java EE provides a set of interfaces that allow you to plug your application logic into that infrastructure and access those services.
Think of containers as playing a role much like a video gaming console into which you plug game cartridges. As shown in next Figure, the gaming console provides a point of interface for the game—a suite of services that lets the game be accessed by the user and allows the game to interact with the user. The game cartridge needs to be concerned only with itself; it doesn’t need to concern itself with how the game is displayed to the user, what sort of controller is being used, or even if the household electricity is 120VAC or 220VAC. The console provides a container that abstracts all of that stuff out for the game, allowing the game programmer to focus solely on the game and not worry about the infrastructure.
If you’ve ever created an applet, you’re already familiar with the concept of containers. Most web browsers provide a container for applet components, as illustrated in next Figure. The browser’s container for applets provides an environment for the applet. The browser and the container know how to interact with any applet because all applets implement the java.applet.Applet class interface. When you develop applets, you are relieved of the burden of interfacing with a web browser, and are free to spend your time and effort on the applet logic. You do not need to be concerned with the issues associated with making your application appear to be an integral part of the web browsers.
Java EE provides server-side containers for the same reason: To provide a well-defined interface, along with a host of services that allow application developers to focus on the business problems they’re trying to solve, without worrying about the plumbing and electricity. Containers handle all of the mundane details involved with starting up services on the server side, activating the application logic, and cleaning up the component.
Java EE and the Java platform provide containers for web components and business components. These containers—like the gaming console analogy presented earlier in the chapter—provide an environment and interface for components that conform to the container’s established interfaces. The containers defined in Java EE include a container for Servlets, JSPs, and EJBs.
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