src/javax/persistence/spi/ClassTransformer.java

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package javax.persistence.spi;

import java.security.ProtectionDomain;
import java.lang.instrument.IllegalClassFormatException;
/**
 * A persistence provider supplies an instance of this
 * interface to the {@link PersistenceUnitInfo#addTransformer 
 * PersistenceUnitInfo.addTransformer}
 * method. The supplied transformer instance will get
 * called to transform entity class files when they are
 * loaded or redefined. The transformation occurs before
 * the class is defined by the JVM.
 *
 * @since Java Persistence 1.0
 */
public interface ClassTransformer {
	/**
	* Invoked when a class is being loaded or redefined.
	* The implementation of this method may transform the
	* supplied class file and return a new replacement class
	* file.
	*
	* @param loader The defining loader of the class to be
	* transformed, may be null if the bootstrap loader
	* @param className The name of the class in the internal form
	* of fully qualified class and interface names
	* @param classBeingRedefined If this is a redefine, the
	* class being redefined, otherwise null
	* @param protectionDomain The protection domain of the
	* class being defined or redefined
	* @param classfileBuffer The input byte buffer in class
	* file format - must not be modified
	* @return A well-formed class file buffer (the result of
	* the transform), or null if no transform is performed
	* @throws IllegalClassFormatException If the input does
	* not represent a well-formed class file
	*/
	byte[] transform(ClassLoader loader, String className, 
		Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) 
        throws IllegalClassFormatException;
}