* The JNDI framework allows for object implementations to * be loaded in dynamically via object factories. * For example, when looking up a printer bound in the name space, * if the print service binds printer names to References, the printer * Reference could be used to create a printer object, so that * the caller of lookup can directly operate on the printer object * after the lookup. *
An ObjectFactory is responsible * for creating objects of a specific type. In the above example, * you may have a PrinterObjectFactory for creating Printer objects. *
* An object factory must implement the ObjectFactory interface. * In addition, the factory class must be public and must have a * public constructor that accepts no parameters. *
* The getObjectInstance() method of an object factory may * be invoked multiple times, possibly using different parameters. * The implementation is thread-safe. *
* The mention of URL in the documentation for this class refers to * a URL string as defined by RFC 1738 and its related RFCs. It is * any string that conforms to the syntax described therein, and * may not always have corresponding support in the java.net.URL * class or Web browsers. * * @author Rosanna Lee * @author Scott Seligman * * @see NamingManager#getObjectInstance * @see NamingManager#getURLContext * @see ObjectFactoryBuilder * @see StateFactory * @since 1.3 */ public interface ObjectFactory { /** * Creates an object using the location or reference information * specified. *
* Special requirements of this object are supplied
* using environment.
* An example of such an environment property is user identity
* information.
*
* NamingManager.getObjectInstance() * successively loads in object factories and invokes this method * on them until one produces a non-null answer. When an exception * is thrown by an object factory, the exception is passed on to the caller * of NamingManager.getObjectInstance() * (and no search is made for other factories * that may produce a non-null answer). * An object factory should only throw an exception if it is sure that * it is the only intended factory and that no other object factories * should be tried. * If this factory cannot create an object using the arguments supplied, * it should return null. *
* A URL context factory is a special ObjectFactory that * creates contexts for resolving URLs or objects whose locations * are specified by URLs. The getObjectInstance() method * of a URL context factory will obey the following rules. *
obj is null, create a context for resolving URLs of the
* scheme associated with this factory. The resulting context is not tied
* to a specific URL: it is able to handle arbitrary URLs with this factory's
* scheme id. For example, invoking getObjectInstance() with
* obj set to null on an LDAP URL context factory would return a
* context that can resolve LDAP URLs
* such as "ldap://ldap.wiz.com/o=wiz,c=us" and
* "ldap://ldap.umich.edu/o=umich,c=us".
* obj is a URL string, create an object (typically a context)
* identified by the URL. For example, suppose this is an LDAP URL context
* factory. If obj is "ldap://ldap.wiz.com/o=wiz,c=us",
* getObjectInstance() would return the context named by the distinguished
* name "o=wiz, c=us" at the LDAP server ldap.wiz.com. This context can
* then be used to resolve LDAP names (such as "cn=George")
* relative to that context.
* obj is an array of URL strings, the assumption is that the
* URLs are equivalent in terms of the context to which they refer.
* Verification of whether the URLs are, or need to be, equivalent is up
* to the context factory. The order of the URLs in the array is
* not significant.
* The object returned by getObjectInstance() is like that of the single
* URL case. It is the object named by the URLs.
* obj is of any other type, the behavior of
* getObjectInstance() is determined by the context factory
* implementation.
* * The name and environment parameters * are owned by the caller. * The implementation will not modify these objects or keep references * to them, although it may keep references to clones or copies. * *
* Name and Context Parameters.
*
*
* The name and nameCtx parameters may
* optionally be used to specify the name of the object being created.
* name is the name of the object, relative to context
* nameCtx.
* If there are several possible contexts from which the object
* could be named -- as will often be the case -- it is up to
* the caller to select one. A good rule of thumb is to select the
* "deepest" context available.
* If nameCtx is null, name is relative
* to the default initial context. If no name is being specified, the
* name parameter should be null.
* If a factory uses nameCtx it should synchronize its use
* against concurrent access, since context implementations are not
* guaranteed to be thread-safe.
*
*
* @param obj The possibly null object containing location or reference
* information that can be used in creating an object.
* @param name The name of this object relative to nameCtx,
* or null if no name is specified.
* @param nameCtx The context relative to which the name
* parameter is specified, or null if name is
* relative to the default initial context.
* @param environment The possibly null environment that is used in
* creating the object.
* @return The object created; null if an object cannot be created.
* @exception Exception if this object factory encountered an exception
* while attempting to create an object, and no other object factories are
* to be tried.
*
* @see NamingManager#getObjectInstance
* @see NamingManager#getURLContext
*/
public Object getObjectInstance(Object obj, Name name, Context nameCtx,
Hashtable environment)
throws Exception;
}