Java and distributed object computing
Chaopeng Zhou,Pinglei Zhou, Junming wang
Overview
Since its inception in 1995, the Java language has generated intensive interest in the computer industry (Art Taylor 1997).
Distributed computing and Java go together naturally. As the first language designed from the bottom up with networking in mind, Java makes it very easy for computers to cooperate. Even the simplest applet running in a browser is a distributed application, if you think about it. The client running the browser downloads and executes code that is delivered by some other system.
When we think of distributed computing, we usually think of applications more complex than a client and server communicating with the same protocol. We usually think in terms of programs that make remote procedure calls, access remote databases, and collaborate with others to produce a single result. Java and Distributed Object Computing project will discuss how to design and write such applications. It pays special attention to distributed data systems, collaboration, and applications that have high bandwidth requirements.
We will mainly study Enterprise JavaBeans,Servelet, and JDBC.
Topics and Scopes
Enterprise JavaBean
The modern enterprise information system (EIS) requires the integration of numerous technologies such as distribution, transactions, data management, security, and naming. Off-the-shelf architectures such as Enterprise JavaBeansTM (EJB) provide a pre-integrated solution that supports the quick development and deployment of information systems.
The Enterprise JavaBeans is a server component model for Java and is a specification for creating server-side, scalable, transactional, multiuser, and secure enterprise-level applications. It provides a consistent component architecture framework for creating distributed n-tier middleware. Most important, EJBs can be deployed on top of existing transaction processing systems including traditional transaction processing monitors, Web servers, database servers, application servers, and so forth. The EJB programming model provides bean developers and EJB server vendors with a set of contracts that defines a common platform for development.
There are two kinds of Enterprise Javabean: entity EJBeans and session EJBeans. The entity beans are used to represent data in the database, while the session beans are used to manage the interactions of the entity and other session beans, access resources, and generally perform tasks on behalf of the client.
The primary advantages of going in for an EJB solution are: 1. EJB provides developers architectural independence. 2. WORA(Write Once, Run Anywhere) for server-side components. 3. EJB establishes roles for application development. 4. EJB takes care of transaction management. 5. EJB provides distributed transaction support. 6. EJB helps create portable and scalable solutions. 7. EJB seamlessly integrates with CORBA. 8. EJB provides for vendor specific enhancements.
The objective of this project is to discuss EJB(version 2.0) in detail and then try to build an application with EJB. We will show you how to build server side EJB components and applications step by step. This project will mainly focus on Entity EJBeans and Session EJBeans.
Servelet:
A few years ago, the hype surrounding applets put Java on the map as a programming language for the Web. Today, Java servlets stand poised to take Java to the next level as a Web development language. The main reason is that servlets offer a fast, powerful, portable replacement for CGI scripts.
The Java Servlet API, introduced as the first standard extension to Java, provides a generic mechanism to extend the functionality of any kind of server. Servlets are most commonly used, however, to extend Web servers, performing tasks traditionally handled by CGI programs. So far, many Web servers can support servlets, including Apache, Netscape's FastTrack and Enterprise Servers, Microsoft's IIS, O'Reilly's WebSite, and JavaSoft's Java Web Server.
The beauty of servlets is that they execute within the Web server's process space and they persist between invocations. This gives servlets tremendous performance benefits over CGI programs. Yet because they're written in Java, servlets are far less likely to crash a Web server than a C-based NSAPI or ISAPI extension. Servlets have full access to the various Java APIs and to third-party component classes, making them ideal for use in communicating with applets, databases, and RMI servers. Plus, servlets are portable between operating systems and between servers -- with servlets you can "write once, serve everywhere."
In this servelet project, I will show how to use servlets to serve dynamic Web content, including both HTML pages and multimedia data to interact with our bioinformactics database, also explores more topics like applet-servlet communication, inter-servlet communication, and internationalization.
JDBC
In a distributed object-oriented system, Java database support should be capable to integrate Java application with heterogeneous DBMS. We have a number of choices to program Java database that are JDBC, SQLJ, ODMG Java Binding.
We will mainly discuss the JDBC technology and do a real model of JDBC for Connecticut Climate Center.
Rather than simply being used to “bring life to Web pages”, Java with database now can fill the role of database –aware applications for a variety of needs. Where currently common gateway interface (CGI) applications are required to access databases from within Web browsers, Java applets with JDBC now have the potential to provide the functionality with more direct programming and the potential for improved performance.
Using this API , you can now use Java applications for standard database programming tasks such as reports or updates. With Java’s flexible network API, you can us Java/JDBC applications for filter programs, to read data from data stream, and to provide conversion facilities before updating database.
Java application written using JDBC are portable both for the hardware platform and the database. You can run a correctly written program on a variety platform against a variety of database without any code changes. JDBC is based on ODBC. ODBC is based on the X/Open CLI specification.The goals of X/Open groups have been met to the extent that database access standards have been accepted by the industry.Access to all major database is available through ODBC. JDBC-ODBC bridges are available to provide database access by mapping JDBC calls to their corresponding ODBC calls. So any database that can be accessed by ODBC driver can be accessed by Java/JDBC driver by using JDBC-ODBC bridges ( Art Taylor 1997).
The Java Database Connectivity (JDBC) standard was intended to allow Java developers to quickly start working with the pervasive relational database technology. It is also was designed to be a base upon which to build higher level interfaces and tools.
JDBC has two main components: Core API and Extension.
The new features supporting DOC included in the Core API are:
- SQL data type support
- Custom mapping of SQL3 user-defined types to Java classes.
The new features included in the Core API are:
- Rowset
- Establishing Database Connections Using DataSource Objects and the Java Naming and Directory Interface(JNDI).
- Connection Pooling.
- Distributed Transactions.
Plan
Servlet:
Present-Oct 30: work with Perl and other tool for CGI
Oct 1-Oct 24: Servlet and other package for network
Oct 25- Nov 25: build some program to demonstrate the Servlet, and CGI program,
apply this program to our bioinfomatics database, and show in our webpage.
Oct 26-Dec: prepare the final paper
Enterprise JavaBean
Now- Sep 30: Explore information of Enterprise Javabeans and Java.
Oct 1 – Oct 7: Build a general model of the component.
Oct 8 – Oct 31:Detailed design of the component and start coding.
Write mid-term paper meantime.
Nov 1 – Nov 30: Continue to build and implement the component.
Dec 1 – Dec 7: Write the final paper.
JDBC
Now-Sep 27: Study details of JDBC and Java.
Sep 28-Oct24: Basically build JDBC model of database for Connecticut Climate Center and write Mid-term report.
Oct 25 –Dec 7: Continue to build and complete the JDBC model. Write the final presentation.
References
Art Taylor 1997. JDBC Developer’s Resource. Prentice Hall PTR.XV
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