Application Server Architecture

This section describes Figure 1–1, which shows the high-level architecture of the Application Server.

Figure 1–1 Application Server Architecture

• Containers — A container is a runtime environment that provides services such as security and transaction management to Java EE components. Figure 1–1 shows the two types of Java EE containers: Web and EJB. Web components, such as JSP pages and servlets, run within the Web container. Enterprise beans, the components of EJB technology, run within the EJB container.

• Client Access — At runtime, browser clients access Web applications by communicating with the Web server via HTTP, the protocol used throughout the internet. The HTTPS protocol is for applications that require secure communication. Enterprise bean clients communicate with the Object Request Broker (ORB) through the IIOP or IIOP/SSL (secure) protocols. The Application Server has separate listeners for the HTTP, HTTPS, IIOP, and IIOP/SSL protocols. Each listener has exclusive use of a specific port number.

• Web Services — On the Java EE platform, it is possible to deploy a Web application that provides a Web service implemented by Java API for XML-Based RPC (JAX-RPC). A Java EE application or component can also be a client to other Web services. Applications access XML registries through the Java API for XML Registries (JAXR).

• Services for Applications — The Java EE platform was designed so that the containers provide services for applications. Figure 1–1 shows the following services:

  • Naming — A naming and directory service binds objects to names. A Java EE application locates an object by looking up its JNDI name. JNDI stands for the Java Naming and Directory Interface API.

  • Security — The Java Authorization Contract for Containers (JACC) is a set of security contracts defined for the Java EE containers. Based on the client’s identity, the containers restrict access to the container’s resources and services.

• Transaction management — A transaction is an indivisible unit of work. For example, transferring funds between bank accounts is a transaction. A transaction management service ensures that a transaction either completes fully or is rolled back.

Access to External Systems

The Java EE platform enables applications to access systems that are outside of the application server. Applications connect to these systems through objects called resources. One of the responsibilities of an administrator is resource configuration. The Java EE platform enables access to external systems through the following APIs and components:

• JDBC — A database management system (DBMS) provides facilities for storing, organizing, and retrieving data. Most business applications store data in relational databases, which applications access via the JDBC API. The information in databases is often described as persistent because it is saved on disk and exists after the application ends. The Application Server bundle includes the PointBase DBMS.

• Messaging — Messaging is a method of communication between software components or applications. A messaging client sends messages to, and receives messages from, any other client. Applications access the messaging provider through the Java Messaging Service (JMS) API. The Application Server includes a JMS provider.

• Connector — The Java EE Connector architecture enables integration between Java EE applications and existing Enterprise Information Systems (EIS). An application accesses an EIS through a portable Java EE component called a connector or resource adapter.

• JavaMail — Through the JavaMail API, applications connect to an SMTP server in order to send and receive email.

• Server Administration — The lower right-hand corner of Figure 1-1 shows some of the tasks performed by the administrator of the Application Server. For example, an administrator deploys (installs) applications and monitors the server’s performance. These tasks are performed with the administration tools provided by the Application Server.