org.mycore.backend.sql
Class MCRSQLConnection

java.lang.Object
  org.mycore.backend.sql.MCRSQLConnection

public class MCRSQLConnection
extends Object

Instances of this class represent a database connection to a relational database like DB2. MCRSQLConnection is a wrapper around java.sql.Connection and provides some convenience methods for easier SQL usage in MyCoRe. There are two types of methods in this class:

• Non-static methods that execute SQL statements on a certain instance of MCRSQLConnection. Use these if you want to execute multiple statements within a transaction
• Static methods that get a free MCRSQLConnection from the pool, execute the SQL statement and immediately return the connection back to the pool. Use these if you want to execute just single SQL statements without the need for transactions.

Author:

Frank Lützenkirchen, Johannes Buehler

See Also:

doQuery( String), Connection, MCRSQLConnectionPool

Field Summary

protected Connection	connection The wrapped JDBC connection
protected static Logger	LOGGER

Constructor Summary

MCRSQLConnection()
Creates a new connection.

Method Summary

(package private) void	close() Closes this connection to the underlying JDBC datastore.
(package private) void	closeJDBCConnection()
int	countRows(String condition) Executes an SQL "SELECT COUNT(*) FROM" statement on this connection, returning the number of rows that match the condition.
static boolean	doesTableExist(String tablename) Checks existence of table
MCRSQLRowReader	doQuery(String query) Executes an SQL select statement on this connection.
void	doUpdate(String statement) Executes an SQL update statement on this connection.
boolean	exists(String condition) Checks if there are any matching rows for a given SQL condition by executing an SQL select statement on this connection.
void	finalize()
Connection	getJDBCConnection() Returns the underlying JDBC java.sql.Connection object
String	getSingleValue(String query) Executes an SQL select statement on this connection, where the expected result is just a single value of a row.
static boolean	justCheckExists(String condition) Checks if there are any matching rows for a given SQL condition by executing an SQL select statement, using any currently free connection from the pool.
static int	justCountRows(String condition) Executes an SQL "SELECT COUNT(*) FROM" statement, returning the number of rows that match the condition, using any currently free connection from the pool.
static void	justDoUpdate(String statement) Executes an SQL update statement, using any currently free connection from the pool.
static String	justGetSingleValue(String query) Executes an SQL select statement where the expected result is just a single value of a row, using any currently free connection from the pool.
void	release() Releases this connection back to the connection pool, indicating that it is no longer needed by the current task.
(package private) void	use()

Methods inherited from class java.lang.Object

clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

connection

protected Connection connection

The wrapped JDBC connection

LOGGER

protected static Logger LOGGER

Constructor Detail

MCRSQLConnection

MCRSQLConnection()
           throws MCRPersistenceException

Creates a new connection. This constructor is used by the connection pool class.

Throws:

MCRPersistenceException

See Also:

MCRSQLConnectionPool.getConnection()

Method Detail

use

void use()

release

public void release()

Releases this connection back to the connection pool, indicating that it is no longer needed by the current task.

See Also:

MCRSQLConnectionPool.releaseConnection( MCRSQLConnection )

close

void close()
     throws MCRPersistenceException

Closes this connection to the underlying JDBC datastore. This is called when the connection pool is finalized.

Throws:

MCRPersistenceException

See Also:

MCRSQLConnectionPool.finalize()

closeJDBCConnection

void closeJDBCConnection()
                   throws MCRPersistenceException

Throws:

MCRPersistenceException

finalize

public void finalize()

Overrides:

finalize in class Object

getJDBCConnection

public Connection getJDBCConnection()

Returns the underlying JDBC java.sql.Connection object

Returns:

the underlying JDBC java.sql.Connection object

doQuery

public MCRSQLRowReader doQuery(String query)
                        throws MCRPersistenceException

Executes an SQL select statement on this connection. The results of the query are returned as MCRSQLRowReader instance.

Parameters:

query - the SQL select statement to be executed

Returns:

the MCRSQLRowReader that can be used for reading the result rows

Throws:

MCRPersistenceException

doUpdate

public void doUpdate(String statement)
              throws MCRPersistenceException

Executes an SQL update statement on this connection.

Parameters:

statement - the SQL create, insert or delete statement to be executed

Throws:

MCRPersistenceException

getSingleValue

public String getSingleValue(String query)
                      throws MCRPersistenceException

Executes an SQL select statement on this connection, where the expected result is just a single value of a row.

Parameters:

query - the SQL select statement to be executed

Returns:

the value of the first column of the first result row as a String

Throws:

MCRPersistenceException

countRows

public int countRows(String condition)
              throws MCRPersistenceException

Executes an SQL "SELECT COUNT(*) FROM" statement on this connection, returning the number of rows that match the condition.

Parameters:

condition - the SQL select statement to be executed, beginning at the SQL "FROM" keyword

Returns:

the number of matching rows, or 0 if no rows match

Throws:

MCRPersistenceException

exists

public boolean exists(String condition)
               throws MCRPersistenceException

Checks if there are any matching rows for a given SQL condition by executing an SQL select statement on this connection.

Parameters:

condition - the condition of an SQL select statement to be executed, beginning at the SQL "FROM" keyword

Returns:

true, if there are any rows matching this condition

Throws:

MCRPersistenceException

justDoUpdate

public static void justDoUpdate(String statement)
                         throws MCRPersistenceException

Executes an SQL update statement, using any currently free connection from the pool.

Parameters:

statement - the SQL create, insert or delete statement to be executed

Throws:

MCRPersistenceException

justGetSingleValue

public static String justGetSingleValue(String query)
                                 throws MCRPersistenceException

Executes an SQL select statement where the expected result is just a single value of a row, using any currently free connection from the pool.

Parameters:

query - the SQL select statement to be executed

Returns:

the value of the first column of the first result row as a String

Throws:

MCRPersistenceException

justCountRows

public static int justCountRows(String condition)
                         throws MCRPersistenceException

Executes an SQL "SELECT COUNT(*) FROM" statement, returning the number of rows that match the condition, using any currently free connection from the pool.

Parameters:

condition - the SQL select statement to be executed, beginning at the SQL "FROM" keyword

Returns:

the number of matching rows, or 0 if no rows match

Throws:

MCRPersistenceException

justCheckExists

public static boolean justCheckExists(String condition)
                               throws MCRPersistenceException

Checks if there are any matching rows for a given SQL condition by executing an SQL select statement, using any currently free connection from the pool.

Parameters:

condition - the condition of an SQL select statement to be executed, beginning at the SQL "FROM" keyword

Returns:

true, if there are any rows matching this condition

Throws:

MCRPersistenceException

doesTableExist

public static boolean doesTableExist(String tablename)
                              throws MCRPersistenceException

Checks existence of table

Parameters:

tablename -

Returns:

true or false

Throws:

MCRPersistenceException - if the JDBC driver could not be loaded or initial connections could not be created or can not get a connection