1   /*
    2    * Copyright (c) 2005, 2006, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   
   26   package java.sql;
   27   
   28   /**
   29    * Interface for JDBC classes which provide the ability to retrieve the delegate instance when the instance
   30    * in question is in fact a proxy class.
   31    * <p>
   32    * The wrapper pattern is employed by many JDBC driver implementations to provide extensions beyond
   33    * the traditional JDBC API that are specific to a data source. Developers may wish to gain access to
   34    * these resources that are wrapped (the delegates) as  proxy class instances representing the
   35    * the actual resources. This interface describes a standard mechanism to access
   36    * these wrapped resources
   37    * represented by their proxy, to permit direct access to the resource delegates.
   38    *
   39    * @since 1.6
   40    */
   41   
   42   public interface Wrapper {
   43   
   44       /**
   45        * Returns an object that implements the given interface to allow access to
   46        * non-standard methods, or standard methods not exposed by the proxy.
   47        *
   48        * If the receiver implements the interface then the result is the receiver
   49        * or a proxy for the receiver. If the receiver is a wrapper
   50        * and the wrapped object implements the interface then the result is the
   51        * wrapped object or a proxy for the wrapped object. Otherwise return the
   52        * the result of calling <code>unwrap</code> recursively on the wrapped object
   53        * or a proxy for that result. If the receiver is not a
   54        * wrapper and does not implement the interface, then an <code>SQLException</code> is thrown.
   55        *
   56        * @param iface A Class defining an interface that the result must implement.
   57        * @return an object that implements the interface. May be a proxy for the actual implementing object.
   58        * @throws java.sql.SQLException If no object found that implements the interface
   59        * @since 1.6
   60        */
   61           <T> T unwrap(java.lang.Class<T> iface) throws java.sql.SQLException;
   62   
   63       /**
   64        * Returns true if this either implements the interface argument or is directly or indirectly a wrapper
   65        * for an object that does. Returns false otherwise. If this implements the interface then return true,
   66        * else if this is a wrapper then return the result of recursively calling <code>isWrapperFor</code> on the wrapped
   67        * object. If this does not implement the interface and is not a wrapper, return false.
   68        * This method should be implemented as a low-cost operation compared to <code>unwrap</code> so that
   69        * callers can use this method to avoid expensive <code>unwrap</code> calls that may fail. If this method
   70        * returns true then calling <code>unwrap</code> with the same argument should succeed.
   71        *
   72        * @param iface a Class defining an interface.
   73        * @return true if this implements the interface or directly or indirectly wraps an object that does.
   74        * @throws java.sql.SQLException  if an error occurs while determining whether this is a wrapper
   75        * for an object with the given interface.
   76        * @since 1.6
   77        */
   78       boolean isWrapperFor(java.lang.Class<?> iface) throws java.sql.SQLException;
   79   
   80   }