https://openjdk.java.net/ 
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package java.sql;


Interface for JDBC classes which provide the ability to retrieve the delegate instance when the instance
in question is in fact a proxy class.


The wrapper pattern is employed by many JDBC driver implementations to provide extensions beyond
the traditional JDBC API that are specific to a data source. Developers may wish to gain access to
these resources that are wrapped (the delegates) as  proxy class instances representing the
the actual resources. This interface describes a standard mechanism to access
these wrapped resources
represented by their proxy, to permit direct access to the resource delegates.

Since:1.6
/**
 * Interface for JDBC classes which provide the ability to retrieve the delegate instance when the instance
 * in question is in fact a proxy class.
 * <p>
 * The wrapper pattern is employed by many JDBC driver implementations to provide extensions beyond
 * the traditional JDBC API that are specific to a data source. Developers may wish to gain access to
 * these resources that are wrapped (the delegates) as  proxy class instances representing the
 * the actual resources. This interface describes a standard mechanism to access
 * these wrapped resources
 * represented by their proxy, to permit direct access to the resource delegates.
 *
 * @since 1.6
 */

public interface Wrapper {

    
Returns an object that implements the given interface to allow access to
non-standard methods, or standard methods not exposed by the proxy.
If the receiver implements the interface then the result is the receiver
or a proxy for the receiver. If the receiver is a wrapper
and the wrapped object implements the interface then the result is the
wrapped object or a proxy for the wrapped object. Otherwise return the
the result of calling unwrap recursively on the wrapped object
or a proxy for that result. If the receiver is not a
wrapper and does not implement the interface, then an SQLException is thrown.

Params:
  • iface – A Class defining an interface that the result must implement.
Type parameters:
  • <T> – the type of the class modeled by this Class object
Throws:
  • SQLException – If no object found that implements the interface
Returns:an object that implements the interface. May be a proxy for the actual implementing object.
Since:1.6
/**
     * Returns an object that implements the given interface to allow access to
     * non-standard methods, or standard methods not exposed by the proxy.
     *
     * If the receiver implements the interface then the result is the receiver
     * or a proxy for the receiver. If the receiver is a wrapper
     * and the wrapped object implements the interface then the result is the
     * wrapped object or a proxy for the wrapped object. Otherwise return the
     * the result of calling <code>unwrap</code> recursively on the wrapped object
     * or a proxy for that result. If the receiver is not a
     * wrapper and does not implement the interface, then an <code>SQLException</code> is thrown.
     *
     * @param <T> the type of the class modeled by this Class object
     * @param iface A Class defining an interface that the result must implement.
     * @return an object that implements the interface. May be a proxy for the actual implementing object.
     * @throws java.sql.SQLException If no object found that implements the interface
     * @since 1.6
     */
        <T> T unwrap(java.lang.Class<T> iface) throws java.sql.SQLException;

    
Returns true if this either implements the interface argument or is directly or indirectly a wrapper
for an object that does. Returns false otherwise. If this implements the interface then return true,
else if this is a wrapper then return the result of recursively calling isWrapperFor on the wrapped
object. If this does not implement the interface and is not a wrapper, return false.
This method should be implemented as a low-cost operation compared to unwrap so that
callers can use this method to avoid expensive unwrap calls that may fail. If this method
returns true then calling unwrap with the same argument should succeed.

Params:
  • iface – a Class defining an interface.
Throws:
  • SQLException –  if an error occurs while determining whether this is a wrapper
for an object with the given interface.
Returns:true if this implements the interface or directly or indirectly wraps an object that does.
Since:1.6
/**
     * Returns true if this either implements the interface argument or is directly or indirectly a wrapper
     * for an object that does. Returns false otherwise. If this implements the interface then return true,
     * else if this is a wrapper then return the result of recursively calling <code>isWrapperFor</code> on the wrapped
     * object. If this does not implement the interface and is not a wrapper, return false.
     * This method should be implemented as a low-cost operation compared to <code>unwrap</code> so that
     * callers can use this method to avoid expensive <code>unwrap</code> calls that may fail. If this method
     * returns true then calling <code>unwrap</code> with the same argument should succeed.
     *
     * @param iface a Class defining an interface.
     * @return true if this implements the interface or directly or indirectly wraps an object that does.
     * @throws java.sql.SQLException  if an error occurs while determining whether this is a wrapper
     * for an object with the given interface.
     * @since 1.6
     */
    boolean isWrapperFor(java.lang.Class<?> iface) throws java.sql.SQLException;

}