Monday, March 30, 2009

what is JDBC.

JDBC : ( Connecting Java and Databases )
Java Database Connectivity is a standard SQL database access interface, providing uniform access to a wide range of relational databases. It also provides a common base on which higher-level tools and interfaces can be built. This comes with an "ODBC Bridge". The Bridge is a library which implements JDBC in terms of the ODBC standard C API.
What Is JDBC ?
JDBC is a Java API for executing SQL statements. As a point of interest, JDBC is a trademarked name and is not an acronym; nevertheless, JDBC is often thought of as standing for "Java Database Connectivity". It consists of a set of classes and interfaces written in the Java programming language. JDBC provides a standard API for tool/database developers and makes it possible to write database applications using a pure Java API.

Using JDBC, it is easy to send SQL statements to virtually any relational database. In other words, with the JDBC API, it isn't necessary to write one program to access a Sybase database, another program to access an Oracle database, another program to access an Informix database, and so on. One can write a single program using the JDBC API, and the program will be able to send SQL statements to the appropriate database. And, with an application written in the Java programming language, one also doesn't have to worry about writing different applications to run on different platforms. The combination of Java and JDBC lets a programmer write it once and run it anywhere.

Java, being robust, secure, easy to use, easy to understand, and automatically downloadable
on a network, is an excellent language basis for database applications. What is needed is a way for Java applications to talk to a variety of different databases. JDBC is the mechanism for doing this.

JDBC extends what can be done in Java. For example, with Java and the JDBC API, it is possible to publish a web page containing an applet that uses information obtained from a remote database. Or an enterprise can use JDBC to connect all its employees (even if they are using a conglomeration of Windows, Macintosh, and UNIX machines) to one or more internal databases via an intranet. With more and more programmers using the Java programming language, the need for easy database access from Java is continuing to grow.

What Does JDBC Do?
Simply put, JDBC makes it possible to do three things:

  • establish a connection with a database
  • send SQL statements
  • process the results.

The following code fragment gives a basic example of these three steps:
Connection con = DriverManager.getConnection(
"jdbc:odbc:wombat", "login", "password");
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM Table1");
while ( {
int x = getInt("a");
String s = getString("b");
float f = getFloat("c");
JDBC Is a Low-level API and a Base for Higher-level APIs :
JDBC is a "low-level" interface, which means that it is used to invoke (or "call") SQL commands directly. It works very well in this capacity and is easier to use than other database connectivity APIs, but it was designed also to be a base upon which to build higher-level interfaces and tools. A higher-level interface is "user-friendly," using a more understandable or more convenient API that is translated behind the scenes into a low-level interface such as JDBC. At the time of this writing, two kinds of higher-level APIs are under development on top of JDBC:

An embedded SQL for Java. At least one vendor plans to build this. DBMSs implement SQL, a language designed specifically for use with databases. JDBC requires that the SQL statements be passed as Strings to Java methods. An embedded SQL preprocessor allows a programmer to instead mix SQL statements directly with Java: for example, a Java variable can be used in a SQL statement to receive or provide SQL values. The embedded SQL preprocessor then translates this Java/SQL mix into Java with JDBC calls.

A direct mapping of relational database tables to Java classes. JavaSoft and others have announced plans to implement this. In this "object/relational" mapping, each row of the table becomes an instance of that class, and each column value corresponds to an attribute of that instance. Programmers can then operate directly on Java objects; the required SQL calls to fetch and store data are automatically generated "beneath the covers." More sophisticated mappings are also provided, for example, where rows of multiple tables are combined in a Java class.

As interest in JDBC has grown, more developers have been working on JDBC-based tools to make building programs easier, as well. Programmers have also been writing applications that make accessing a database easier for the end user. For example, an application might present a menu of database tasks from which to choose. After a task is selected, the application presents prompts and blanks for filling in information needed to carry out the selected task. With the requested input typed in, the application then automatically invokes the necessary SQL commands. With the help of such an application, users can perform database tasks even when they have little or no knowledge of SQL syntax.


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