Welcome!

Java IoT Authors: Pat Romanski, Elizabeth White, Liz McMillan, Yeshim Deniz, Mehdi Daoudi

Related Topics: Java IoT

Java IoT: Article

Delivering JDBC-Based Applications

Delivering JDBC-Based Applications

Introduction
In this article, we take a look at using JDBC to build applications. Internet technology is changing so rapidly that some of the methods used today will become obsolete tomorrow. We are taking an approach that combines Java network programming and JDBC programming. Programming in JDBC is taking a step backward when you have mature 4GL tools like Sybase Powerbuilder. Programming in JDBC is similar to programming in any low level database library like ODBC or Sybase CT-LIB.

There is more than one way to deploy applications and applets using JDBC. The first approach is by using the JDBC-ODBC bridge that is part of JDK 1.1. You have to install ODBC Drivers and set the ODBC datasource in each client. If you are willing to do this existing client server tools will do a better job than Java. The second approach is to use a JDBC driver that is 100 Percent Java compliant. For writing Java applications, this method will work fine, but not for Java applets. Applets can not make arbitrary connection to other servers. You have to run your database server in the same machine where the Web server is running. This article will help you write Java applets or applications using JDBC without any of the above mentioned restrictions.

What are the Advantages?
This implementation follows a 3-tier client-server model. JDBC Client sends a request to JDBC server which processes the request, communicates to the database server and sends back the reply. Compatible with all Java enabled browsers. It's secure because the database server is not exposed. You can configure number of concurrent users allowed at any point of time. With little modification you can dynamically increase and decrease number of JDBC server listening for request or totally redirect the request to a different web server. You can also attach your own encryption and decryption routine before communicating with a remote client. JDBC server runs on the server side so you have total freedom to use any JDK, any ODBC driver and Java native methods. You can batch your request or can have real-time connection like any other client-server application.

There are some limitations in this implementation. If you want to have multiple connection you have to initialize multiple driver's in the client side. It will not handle blob or image data type even though it's very easy to implement one, by saving the image in the server and sending the filename back as URL. You can use the same method to transfer the whole ResultSet.

Architecture
There are three different functional pieces. Port allocator (PA) is a Java based server that listens on a predefined port. JDBC server listens for connection from client. JDBC client which makes the request. When client makes a request to Port Allocator it will send back a JDBC server port that is currently free. From that point onwards, JDBC client talks only to the JDBC server. Client sends a single byte command to server and waits for reply. The server sends back a status code and byte or string value. Commands can have arguments usually a byte or a string. While processing clients request, if server encounters an exception it converts the exception to a string and sends back an error code and the string to the client.

Let us look into the details. There are four client side classes RDriver, RConnection, Rstatement, RResultSet for connecting and fetching data. These are very similar to JDBC interfaces Driver, Connection, Statement, ResultSet. It does not implement these interfaces. JDBC client initializes the RDriver then creates a TCP socket to port allocator (PA) and gets a port to communicate to a JDBC server. It also sends command to initialize DriverManager in the server if everything is successful. This enables the client to connect directly to the JDBC server using RDriver.connect(username, password) and create a database connection. You only need username and password to create a database connection hiding all server details in the JDBC server code. You can call createStatement() method to create a RStatement() after successfully establishing a database connection. Send the SQL string to server using executeQuery function. It will create a ResultSet in the server and RResultSet in the client. Use executeUpdate() function for update and insert SQL statements. Access the ResultSet values using next() and getString() or getInt().

One of the advantages of this architecture is that all conversation between client and server happens as bytes and strings. If the client dies for some reason Driver.detach() will cleanup the connection, but if an exception occurs you have to take care of it. Rdriver has an overloaded finalize method which calls Driver.detach().

The example here shows how to connect to a Sybase SQL server using beta version of Jconnect. Before running the examples you may need to change hostname, port and any other parameters it may need in your environment.

Table 1 shows the commands, arguments and return code.

JDBC Protocol Implementation
JDBC Protocol is a layer above the Java socket layer. It hides the Java socket layer, but you have to still catch exceptions from this layer. Protocol structure follows the same structure as any other standard protocols (FTP, TELNET). JDBC protocol does session control by sending acknowledgment or negative acknowledgment after each request from client. Java takes care of presentation of data. This protocol fits in the top layers of OSI model. Like most other protocols this protocol has series of commands and expected return values. Most importantly these commands are not part of any standards. One other difference is it has only one path to the server, unlike FTP which uses a command port (21) and a data port (20).

All commands are single byte followed by a byte or string. In special cases it is more than one string. For each command sent from client JDBC server replies with a return status of SUCCESS or FAIL. If the return status from the server is SUCCESS it returns either string, byte or no value depending on type of command. If an error occurs in the server the return status is FAIL server then sends a SQLExeption string to the client.

Table 2 explains the protocol implementation.

More Stories By Paul Ananth

Paul Ananth works with Barclays Global Investors, San Francisco, as a software engineer. He is a senior member in the client/server development team, specializing in building object-oriented software using C++, Java, PowerBuilder 5.0 and PFC.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


IoT & Smart Cities Stories
The platform combines the strengths of Singtel's extensive, intelligent network capabilities with Microsoft's cloud expertise to create a unique solution that sets new standards for IoT applications," said Mr Diomedes Kastanis, Head of IoT at Singtel. "Our solution provides speed, transparency and flexibility, paving the way for a more pervasive use of IoT to accelerate enterprises' digitalisation efforts. AI-powered intelligent connectivity over Microsoft Azure will be the fastest connected pat...
There are many examples of disruption in consumer space – Uber disrupting the cab industry, Airbnb disrupting the hospitality industry and so on; but have you wondered who is disrupting support and operations? AISERA helps make businesses and customers successful by offering consumer-like user experience for support and operations. We have built the world’s first AI-driven IT / HR / Cloud / Customer Support and Operations solution.
Codete accelerates their clients growth through technological expertise and experience. Codite team works with organizations to meet the challenges that digitalization presents. Their clients include digital start-ups as well as established enterprises in the IT industry. To stay competitive in a highly innovative IT industry, strong R&D departments and bold spin-off initiatives is a must. Codete Data Science and Software Architects teams help corporate clients to stay up to date with the mod...
At CloudEXPO Silicon Valley, June 24-26, 2019, Digital Transformation (DX) is a major focus with expanded DevOpsSUMMIT and FinTechEXPO programs within the DXWorldEXPO agenda. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive over the long term. A total of 88% of Fortune 500 companies from a generation ago are now out of business. Only 12% still survive. Similar percentages are found throug...
Druva is the global leader in Cloud Data Protection and Management, delivering the industry's first data management-as-a-service solution that aggregates data from endpoints, servers and cloud applications and leverages the public cloud to offer a single pane of glass to enable data protection, governance and intelligence-dramatically increasing the availability and visibility of business critical information, while reducing the risk, cost and complexity of managing and protecting it. Druva's...
BMC has unmatched experience in IT management, supporting 92 of the Forbes Global 100, and earning recognition as an ITSM Gartner Magic Quadrant Leader for five years running. Our solutions offer speed, agility, and efficiency to tackle business challenges in the areas of service management, automation, operations, and the mainframe.
The Jevons Paradox suggests that when technological advances increase efficiency of a resource, it results in an overall increase in consumption. Writing on the increased use of coal as a result of technological improvements, 19th-century economist William Stanley Jevons found that these improvements led to the development of new ways to utilize coal. In his session at 19th Cloud Expo, Mark Thiele, Chief Strategy Officer for Apcera, compared the Jevons Paradox to modern-day enterprise IT, examin...
With 10 simultaneous tracks, keynotes, general sessions and targeted breakout classes, @CloudEXPO and DXWorldEXPO are two of the most important technology events of the year. Since its launch over eight years ago, @CloudEXPO and DXWorldEXPO have presented a rock star faculty as well as showcased hundreds of sponsors and exhibitors! In this blog post, we provide 7 tips on how, as part of our world-class faculty, you can deliver one of the most popular sessions at our events. But before reading...
DSR is a supplier of project management, consultancy services and IT solutions that increase effectiveness of a company's operations in the production sector. The company combines in-depth knowledge of international companies with expert knowledge utilising IT tools that support manufacturing and distribution processes. DSR ensures optimization and integration of internal processes which is necessary for companies to grow rapidly. The rapid growth is possible thanks, to specialized services an...
At CloudEXPO Silicon Valley, June 24-26, 2019, Digital Transformation (DX) is a major focus with expanded DevOpsSUMMIT and FinTechEXPO programs within the DXWorldEXPO agenda. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive over the long term. A total of 88% of Fortune 500 companies from a generation ago are now out of business. Only 12% still survive. Similar percentages are found throug...