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Java Database Connectivity

Encyclopedia : J : JA : JAV : Java Database Connectivity

JDBC is an API for the Java programming language that defines how a client may access a database. It provides methods for querying and updating data in a database. JDBC is oriented towards relational databases.

The Java Platform, Standard Edition includes the JDBC API together with an ODBC implementation of the API enabling connections to any relational database that supports ODBC. This driver is native code and not Java, and is closed source.[link]

Contents

Overview

JDBC has been part of the Java Standard Edition since the release of JDK 1.1. The JDBC classes are contained in the Java package . Starting with version 3.0, JDBC has been developed under the Java Community Process. JSR 54 specifies JDBC 3.0 (included in J2SE 1.3), JSR 114 specifies the JDBC Rowset additions, and JSR 221 is the specification of JDBC 4.0 (included in Java SE 6).

JDBC allows multiple implementations to exist and be used by the same application. The API provides a mechanism for dynamically loading the correct Java packages and registering them with the JDBC Driver Manager. The Driver Manager is used as a connection factory for creating JDBC connections.

JDBC connections support creating and executing statements. These statements may be update statements such as SQL INSERT, UPDATE and DELETE or they may be query statements using the SELECT statement. Additionally, stored procedures may be invoked through a statement. Statements are one of the following types:

Update statements such as INSERT, UPDATE and DELETE return an update count that indicates how many rows were affected in the database. These statements do not return any other information.

Query statements return a JDBC row result set. The row result set is used to walk over the result set. Individual columns in a row are retrieved either by name or by column number. There may be any number of rows in the result set. The row result set has metadata that describes the names of the columns and their types.

There is an extension to the basic JDBC API in the package that allows for scrollable result sets and cursor support among other things.

Example

The method is used to load the JDBC driver class. The line below causes the JDBC driver from some jdbc vendor to be loaded into the application.

Class.forName( "com.somejdbcvendor.TheirJdbcDriver" );
When a class is loaded, it creates an instance of itself and registers it with the . This can be done by including the needed code in the driver class's static block. e.g. DriverManager.registerDriver(Driver driver)

Now when a connection is needed, one of the DriverManager.getConnection() methods is used to create a JDBC connection.

Connection conn = DriverManager.getConnection(
"jdbc:somejdbcvendor:other data needed by some jdbc vendor",
"myLogin",
"myPassword" );
The URL used is dependent upon the particular JDBC driver. It will always begin with the "jdbc:" protocol, but the rest is upto the particular vendor. Once a connection is established, a statement must be created.

Statement stmt = conn.createStatement();
stmt.executeUpdate( "INSERT INTO MyTable( name ) VALUES ( 'my name' ) " );
Data is retrieved from the database using a database query mechanism. The example below shows creating a statement and executing a query.

Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery( "SELECT * FROM MyTable" );
while ( rs.next() ) 
}
rs.close();
stmt.close();
Typically, however, it would be rare for a seasoned Java programmer to code in such a fashion. The usual practice would be to abstract the database logic into an entirely different class and to pass preprocessed strings (perhaps derived themselves from a further abstracted class) containing SQL statements and the connection to the required methods. Abstracting the data model from the application code makes it more likely that changes to the application and data model can be made independently.

An example of a PreparedStatement query. Using conn and class from first example.

PreparedStatement ps = null;
ResultSet rs = null;
try 
}
}
catch (SQLException e) 
finally  catch( SQLException e)  // handle errors here or ignore them
}
Here are examples of host database types, Java can convert to with a function. 

setXXX() Methods

Oracle DatatypesetXXX()
CHAR 
setString()
VARCHAR2 
setString()
NUMBER 
setBigDecimal()
setBoolean() 
setByte() 
setShort() 
setInt() 
setLong() 
setFloat() 
setDouble()
INTEGERsetInt()
FLOATsetDouble() 
CLOB setClob() 
BLOB setBlob() 
RAW
setBytes()
LONGRAW 
setBytes() 
DATE 
setDate() 
setTime() 
setTimestamp() 

For an example of a CallableStatement (to call stored procedures in the database), see the [http://java.sun.com/j2se/1.5.0/docs/guide/jdbc/getstart/callablestatement.html JDBC API Guide].

Drivers

Types

There are commercial and free drivers available for most relational database servers. These drivers fall into one of the following types:

Sources

External links

 

From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.

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