Information AboutJdbc |
| CATEGORIES ABOUT JAVA DATABASE CONNECTIVITY | |
| java platform | |
| java specification requests | |
| application programming interfaces | |
| sql data access | |
| databases | |
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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 without Title} . 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, JSR 114 specifies the JDBC Rowset additions, and JSR 221 is the specification of JDBC 4.0. 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();
while ( rs.next() ) { int numColumns = rs.getMetaData().getColumnCount(); for ( int i = 1 ; i <= numColumns ; i++ ) { //Column numbers start at 1. //Also there are many methods on the result set to return // the column as a particular type. Refer to the Sun documentation // for the list of valid conversions. System.out.println( "COLUMN " + i + " = " + rs.getObject(i) ); } } 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 {
+ "WHERE i = ? AND j = ?" ); // In the prepared statement ps, the question mark denotes variable input, // which can be passed through a parameter list, for example. // The following replaces the question marks, // with the string or int, before sending it to SQL. // The first parameter corresponds to the nth occurrence of the ?, // the second parameter tells Java to replace it with // the second item. ps.setString(1, "Poor Yorick"); ps.setInt(2, 8008); // The ResultSet rs, receives the SQL Query response. rs = ps.executeQuery(); while ( rs.next() ) { int numColumns = rs.getMetaData().getColumnCount(); for ( int i = 1 ; i <= numColumns ; i++ ) { //Column numbers start at 1. //Also there are many methods on the result set to return // the column as a particular type. Refer to the Sun documentation // for the list of valid conversions. System.out.println( "COLUMN " + i + " = " + rs.getObject(i) ); } } } catch (SQLException e) { // typical exception handling here } finally { // note that these resources need to be closed in the finally clause to avoid try { // a resource leak since it should always be called rs.close(); ps.close(); } catch( SQLException e){} // handle errors here or ignore them } Here are examples of host database types, Java can convert to with a function.
For an example of a CallableStatement (to call stored procedures in the database), see the .DRIVERS Types There are commercial and free drivers available for most relational database servers. These drivers fall into one of the following types:
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