hirondelle.web4j.database
Interface ConnectionSource

public interface ConnectionSource

Return a Connection to a database, using a policy defined by the application.

See BuildImpl for important information on how this item is configured. BuildImpl.forConnectionSource() returns the configured implementation of this interface.

Here is an example implementation, taken from the WEB4J example application.

There are many alternatives for creating or accessing database connections. The application programmer can use any technique whatsoever to implement this interface. For example, an implementation may :

• use a connection pool configured in the server environment (the style used in the example application)
• create a Connection directly, using the database driver. (Some modern drivers have connection pooling built directly into the driver.)
• use some other means

The design of this interface is slightly skewed towards applications that use more than one database. If only one database is used in an application, then this interface is simply implemented 'as if' there were more than one. In practice, this should be only a minor nuisance. In addition, if a single-database application is extended to use more than one database, the changes will be absorbed naturally by the existing implementation.

If no database is used at all, then getDatabaseNames() returns an emtpy Set.

See SqlId for related information.

Method Summary

Connection	getConnection() Return a Connection to the default database.
Connection	getConnection(String aDatabaseName) Return a Connection for a specified database (default or non-default).
Set<String>	getDatabaseNames() Return the database names accepted by getConnection(String).
void	init(Map<String,String> aConfig) Read in any necessary configuration parameters.

Method Detail

init

void init(Map<String,String> aConfig)

Read in any necessary configuration parameters.

This method is called by the framework early during startup processing. If your implementation of this interface does not use any sort of config information, then it can simply ignore the given Map parameter.

In the context of a web application, the given Map is populated with the servlet's init-param settings in web.xml.

getDatabaseNames

Set<String> getDatabaseNames()

Return the database names accepted by getConnection(String).

Return a Set with one or more entries. Each entry must have content. If your application does not use a database at all, then you must return an empty Set.

getConnection

Connection getConnection()
                         throws DAOException

Return a Connection to the default database.

The default database is selected by the application programmer as representing the principal or main database in the application, against which the majority of SQL statements are executed. (For most applications, this choice will be obvious.) In .sql files, SQL statements against the default database do not need an extra qualifier in their identifiers, while those against a non-default database do need an extra qualifier.

Implementations must translate any exceptions into a DAOException. Examples of exceptions that may need translation are SQLException and javax.naming.NamingException.

Throws:

DAOException

getConnection

Connection getConnection(String aDatabaseName)
                         throws DAOException

Return a Connection for a specified database (default or non-default).

The getConnection() method is intended for the "default" or principal database used in the application, while this method is intended for all other databases (but may be used for the default as well).

See SqlId for related information. Here, aDatabaseName is a prefix used in .sql files as a qualifer to a SQL statement identifier. For example, in an .sql file, the SQL statement identifier:

• LIST_MEMBERS refers to the default database (no qualifier)
• TRANSLATION.LOCALE_LIST refers to the 'TRANSLATION' database. It is this string - 'TRANSLATION' - which is passed to this method.

The values taken by aDatabaseName are those returned by getDatabaseNames(). They may be chosen by the application programmer in any desired way, to clarify the SQL statement identifiers appearing in the .sql file(s). Typically, an implementation of this interface will internally map these database identifiers into specific connection strings, such as 'java:comp/env/jdbc/blah' (or whatever is required).

Implementations must translate any exceptions into a DAOException. Examples of exceptions that may need translation are SQLException and javax.naming.NamingException.

Throws:

DAOException