Wednesday, 5 November 2014

Java Database Connectivity (JDBC) basics

Simple JDBC program demonstrating java connectivity with database.

Drivers:
The DriverManager will try to load as many drivers as it can find and then for any given connection request, it will ask each driver in turn to try to connect to the target URL.

When a Driver class is loaded, it should create an instance of itself and register it with the DriverManager. This means that a user can load and register a driver by calling

Class.forName("foo.bah.Driver")

Connection:
A Connection is like a session with database. Applications should not invoke SQL commands directly to change the connection's configuration when there is a JDBC method available. By default a Connection object is in auto-commit mode, which means that it automatically commits changes after executing each statement. If auto-commit mode has been disabled, the method commit must be called explicitly in order to commit changes; otherwise, database changes will not be saved. Following code is used for getting connection.
DriverManager.getConnection(java.lang.String, java.util.Properties)

Note:In JDBC 4.0, we no longer need to explicitly load JDBC drivers using Class.forName().

Statement:
Statements are  used for executing a static SQL statement and returning the results it produces.

By default, only one ResultSet object per Statement object can be open at the same time. Therefore, if the reading of one ResultSet object is interleaved with the reading of another, each must have been generated by different Statement objects. All execution methods in the Statement interface implicitly close a statment's current ResultSet object if an open one exists.
Connection.createStatement(),

ResultSet:
ResultSet is a table of data representing a database result set.
A ResultSet object maintains a cursor pointing to its current row of data. Initially the cursor is positioned before the first row. The next method moves the cursor to the next row, and because it returns false when there are no more rows in the ResultSet object, it can be used in a while loop to iterate through the result set.
A default ResultSet object is not updatable and has a cursor that moves forward only. Thus, you can iterate through it only once and only from the first row to the last row. It is possible to produce ResultSet objects that are scrollable and/or updatable.
Statement stmt = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
ResultSet rs = stmt.executeQuery("SELECT id, name FROM employees");

 

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