https://openjdk.java.net/ 
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package javax.activation;

import java.io.IOException;


JavaBeans components that are Activation Framework aware implement
this interface to find out which command verb they're being asked
to perform, and to obtain the DataHandler representing the
data they should operate on.  JavaBeans that don't implement
this interface may be used as well.  Such commands may obtain
the data using the Externalizable interface, or using an
application-specific method.

Since:1.6
/**
 * JavaBeans components that are Activation Framework aware implement
 * this interface to find out which command verb they're being asked
 * to perform, and to obtain the DataHandler representing the
 * data they should operate on.  JavaBeans that don't implement
 * this interface may be used as well.  Such commands may obtain
 * the data using the Externalizable interface, or using an
 * application-specific method.
 *
 * @since 1.6
 */
public interface CommandObject {

    
Initialize the Command with the verb it is requested to handle
and the DataHandler that describes the data it will
operate on. NOTE: it is acceptable for the caller
to pass null as the value for DataHandler. 
Params:
  • verb – The Command Verb this object refers to.
  • dh – The DataHandler.
Throws:
/**
     * Initialize the Command with the verb it is requested to handle
     * and the DataHandler that describes the data it will
     * operate on. <b>NOTE:</b> it is acceptable for the caller
     * to pass <i>null</i> as the value for {@code DataHandler}.
     *
     * @param verb The Command Verb this object refers to.
     * @param dh The DataHandler.
     * @exception       IOException     for failures accessing data
     */
    public void setCommandContext(String verb, DataHandler dh)
                                                throws IOException;
}