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package javax.naming.spi;

import java.util.Hashtable;

import javax.naming.*;

/**

  * This interface represents a factory for creating an object.

  *<p>

  * The JNDI framework allows for object implementations to

  * be loaded in dynamically via <em>object factories</em>.

  * 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.

  * <p>An <tt>ObjectFactory</tt> is responsible

  * for creating objects of a specific type.  In the above example,

  * you may have a PrinterObjectFactory for creating Printer objects.

  *<p>

  * An object factory must implement the <tt>ObjectFactory</tt> interface.

  * In addition, the factory class must be public and must have a

  * public constructor that accepts no parameters.

  *<p>

  * The <tt>getObjectInstance()</tt> method of an object factory may

  * be invoked multiple times, possibly using different parameters.

  * The implementation is thread-safe.

  *<p>

  * 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.

 * <p>

 * Special requirements of this object are supplied

 * using <code>environment</code>.

 * An example of such an environment property is user identity

 * information.

 *<p>

 * <tt>NamingManager.getObjectInstance()</tt>

 * 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 <tt>NamingManager.getObjectInstance()</tt>

 * (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.

 *<p>

 * A <em>URL context factory</em> is a special ObjectFactory that

 * creates contexts for resolving URLs or objects whose locations

 * are specified by URLs.  The <tt>getObjectInstance()</tt> method

 * of a URL context factory will obey the following rules.

 * <ol>

 * <li>If <code>obj</code> 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 <tt>getObjectInstance()</tt> with

 * <code>obj</code> 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".

 * <li>

 * If <code>obj</code> 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 <code>obj</code> 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.

 * <li>

 * If <code>obj</code> 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.

 * <li>

 * If <code>obj</code> is of any other type, the behavior of

 * <tt>getObjectInstance()</tt> is determined by the context factory

 * implementation.

 * </ol>

 *

 * <p>

 * The <tt>name</tt> and <tt>environment</tt> 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.

 *

 * <p>

 * <b>Name and Context Parameters.</b> &nbsp;&nbsp;&nbsp;

 * <a name=NAMECTX></a>

 *

 * The <code>name</code> and <code>nameCtx</code> parameters may

 * optionally be used to specify the name of the object being created.

 * <code>name</code> is the name of the object, relative to context

 * <code>nameCtx</code>.

 * 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 <code>nameCtx</code> is null, <code>name</code> is relative

 * to the default initial context.  If no name is being specified, the

 * <code>name</code> parameter should be null.

 * If a factory uses <code>nameCtx</code> it should synchronize its use

 * against concurrent access, since context implementations are not

 * guaranteed to be thread-safe.

 * <p>

 *

 * @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 <code>nameCtx</code>,

 *              or null if no name is specified.

 * @param nameCtx The context relative to which the <code>name</code>

 *              parameter is specified, or null if <code>name</code> 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;

}