# Interface Wrapper

All Known Subinterfaces:
  `CachedRowSet, CallableStatement, Connection, DatabaseMetaData, DataSource, FilteredRowSet, JdbcRowSet, JoinRowSet, ParameterMetaData, PreparedStatement, ResultSet, ResultSetMetaData, RowSet, RowSetMetaData, Statement, SyncResolver, WebRowSet`

All Known Implementing Classes:
  `RowSetMetaDataImpl`

public interface Wrapper
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

- ## Method Summary

  Modifier and Type
  Method
  Description
  `boolean`
  `isWrapperFor(Class<?> iface)`
  Returns true if this either implements the interface argument or is directly or indirectly a wrapper for an object that does.
  `<T> T`
  `unwrap(Class<T> iface)`
  Returns an object that implements the given interface to allow access to non-standard methods, or standard methods not exposed by the proxy.

- ## Method Details

  - ### unwrap

    <T> T unwrap(Class<T> iface) throws SQLException
    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.
    Type Parameters:
      `T` - the type of the class modeled by this Class object
    Parameters:
      `iface` - A Class defining an interface that the result must implement.
    Returns:
      an object that implements the interface. May be a proxy for the actual implementing object.
    Throws:
      `SQLException` - If no object found that implements the interface
    Since:
      1.6

  - ### isWrapperFor

    boolean isWrapperFor(Class<?> iface) throws 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.
    Parameters:
      `iface` - a Class defining an interface.
    Returns:
      true if this implements the interface or directly or indirectly wraps an object that does.
    Throws:
      `SQLException` - if an error occurs while determining whether this is a wrapper for an object with the given interface.
    Since:
      1.6