Wrapper


1   /*
2    * @(#)Wrapper.java 1.6 06/05/28
3    *
4    * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   
8   package java.sql;
9    
10  /**
11   * Interface for JDBC classes which provide the ability to retrieve the delegate instance when the instance
12   * in question is in fact a proxy class.
13   * <p>
14   * The wrapper pattern is employed by many JDBC driver implementations to provide extensions beyond
15   * the traditional JDBC API that are specific to a data source. Developers may wish to gain access to
16   * these resources that are wrapped (the delegates) as  proxy class instances representing the
17   * the actual resources. This interface describes a standard mechanism to access 
18   * these wrapped resources
19   * represented by their proxy, to permit direct access to the resource delegates.
20   * 
21   * @since 1.6 
22   */
23  
24  public interface Wrapper {
25  
26      /**
27       * Returns an object that implements the given interface to allow access to
28       * non-standard methods, or standard methods not exposed by the proxy.
29       * 
30       * If the receiver implements the interface then the result is the receiver 
31       * or a proxy for the receiver. If the receiver is a wrapper
32       * and the wrapped object implements the interface then the result is the
33       * wrapped object or a proxy for the wrapped object. Otherwise return the
34       * the result of calling <code>unwrap</code> recursively on the wrapped object 
35       * or a proxy for that result. If the receiver is not a
36       * wrapper and does not implement the interface, then an <code>SQLException</code> is thrown.
37       *
38       * @param iface A Class defining an interface that the result must implement.
39       * @return an object that implements the interface. May be a proxy for the actual implementing object.
40       * @throws java.sql.SQLException If no object found that implements the interface 
41       * @since 1.6
42       */
43      <T> T unwrap(java.lang.Class  <T> iface) throws java.sql.SQLException  ;
44  
45      /**
46       * Returns true if this either implements the interface argument or is directly or indirectly a wrapper
47       * for an object that does. Returns false otherwise. If this implements the interface then return true,
48       * else if this is a wrapper then return the result of recursively calling <code>isWrapperFor</code> on the wrapped
49       * object. If this does not implement the interface and is not a wrapper, return false.
50       * This method should be implemented as a low-cost operation compared to <code>unwrap</code> so that
51       * callers can use this method to avoid expensive <code>unwrap</code> calls that may fail. If this method
52       * returns true then calling <code>unwrap</code> with the same argument should succeed.
53       *
54       * @param iface a Class defining an interface.
55       * @return true if this implements the interface or directly or indirectly wraps an object that does.
56       * @throws java.sql.SQLException  if an error occurs while determining whether this is a wrapper
57       * for an object with the given interface.
58       * @since 1.6
59       */
60      boolean isWrapperFor(java.lang.Class  <?> iface) throws java.sql.SQLException  ;
61  
62  }
63  
64  
65
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