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Input/output (I/O) I/O ports are a section of memory that a hardware device uses to commuport nicate with the operating system. When a microprocessor receives an IRQ, the operating system checks the I/O port address to retrieve additional information about what the hardware device wants it to do. An I/O port is represented as a hexadecimal number. Direct memory access (DMA) DMAs are channels that allow a hardware device, such as a floppy disk drive, to access memory directly, without interrupting the microprocessor. DMA channels speed up access to memory. Windows XP Professional assigns eight DMA channels, numbered 0 through 7. Many hardware devices, such as a network interface card (NIC), use onboard memory or reserve system memory. This reserved memory is unavailable for use by other devices or Windows XP Professional.

A MessageHandler can save and show messages; it s straightforward. The actual EJB implements this business interface, which is by default considered a local interface (that is, remote EJB clients cannot call it); see listing 2.15.

After you determine which resources a hardware device requires, you can look for an available resource. Device Manager provides a list of all hardware resources and their availability, as shown in Figure 6-4.

Figure 6-4

1. 2. 3.

package hello; import javax.ejb.Stateless; import javax.persistence.*; import java.util.List; @Stateless public class MessageHandlerBean implements MessageHandler { @PersistenceContext EntityManager em; public void saveMessages() { Message message = new Message("Hello World"); em.persist(message); } public void showMessages() { List messages = em.createQuery("select m from Message m order by m.text asc") .getResultList(); System.out.println(messages.size() + " message(s) found:"); for (Object m : messages) { Message loadedMsg = (Message) m; System.out.println(loadedMsg.getText()); } } }

To view the hardware resource lists in Device Manager, follow these steps: 1. In Device Manager, click the View menu, and then click Resources By Connection. 2. The Device Manager displays the resources that are currently in use (for example, IRQs). To view a list of resources for another type of hardware resource, on the View menu, click the type of hardware resource you want to see. After you know which hardware resources are available, you can configure the device to use those resources and then install the hardware manually with the Add Hardware Wizard.

Note If you select a hardware resource during manual installation, you might need to configure the hardware device so that it can use the resource. For example, for a network adapter to use IRQ 5, you might have to set a jumper on the adapter and configure Windows XP Professional so that it recognizes that the adapter now uses IRQ 5.

There are several interesting things to observe in this implementation. First, it s a plain Java class with no hard dependencies on any other package. It becomes an EJB only with a single metadata annotation, @Stateless. EJBs support containermanaged services, so you can apply the @PersistenceContext annotation, and the server injects a fresh EntityManager instance whenever a method on this stateless bean is called. Each method is also assigned a transaction automatically by the container. The transaction starts when the method is called, and commits when the method returns. (It would be rolled back when an exception is thrown inside the method.) You can now modify the HelloWorld main class and delegate all the work of storing and showing messages to the MessageHandler. Running the application The main class of the Hello World application calls the MessageHandler stateless session bean after looking it up in the JNDI registry. Obviously, the managed environment and the whole application server, including the JNDI registry, must be booted first. You do all of this in the main() method of HelloWorld.java (see listing 2.16).

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In this practice, you use System Monitor to monitor system resources. You add objects and counters to control what is being monitored, and you then view the three views graph, histogram, and report for output. 1. Click Start, click Control Panel, and then click Performance And Maintenance. 2. Click Administrative Tools, and then double-click the Performance shortcut. Windows XP Professional starts the Performance console with the System Monitor selected. 3. What objects and counters are monitored by default