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package javax.xml.transform;

/**
 * <p>To provide customized error handling, implement this interface and
 * use the <code>setErrorListener</code> method to register an instance of the
 * implmentation with the {@link javax.xml.transform.Transformer}.  The
 * <code>Transformer</code> then reports all errors and warnings through this
 * interface.</p>
 *
 * <p>If an application does <em>not</em> register its own custom
 * <code>ErrorListener</code>, the default <code>ErrorListener</code>
 * is used which reports all warnings and errors to <code>System.err</code>
 * and does not throw any <code>Exception</code>s.
 * Applications are <em>strongly</em> encouraged to register and use
 * <code>ErrorListener</code>s that insure proper behavior for warnings and
 * errors.</p>
 *
 * <p>For transformation errors, a <code>Transformer</code> must use this
 * interface instead of throwing an <code>Exception</code>: it is up to the
 * application to decide whether to throw an <code>Exception</code> for
 * different types of errors and warnings.  Note however that the
 * <code>Transformer</code> is not required to continue with the transformation
 * after a call to {@link #fatalError(TransformerException exception)}.</p>
 *
 * <p><code>Transformer</code>s may use this mechanism to report XML parsing
 * errors as well as transformation errors.</p>
 */
public interface ErrorListener {

    /**
     * Receive notification of a warning.
     *
     * <p>{@link javax.xml.transform.Transformer} can use this method to report
     * conditions that are not errors or fatal errors.  The default behaviour
     * is to take no action.</p>
     *
     * <p>After invoking this method, the Transformer must continue with
     * the transformation. It should still be possible for the
     * application to process the document through to the end.</p>
     *
     * @param exception The warning information encapsulated in a
     *                  transformer exception.
     *
     * @throws javax.xml.transform.TransformerException if the application
     * chooses to discontinue the transformation.
     *
     * @see javax.xml.transform.TransformerException
     */
    public abstract void warning(TransformerException exception)
        throws TransformerException;

    /**
     * Receive notification of a recoverable error.
     *
     * <p>The transformer must continue to try and provide normal transformation
     * after invoking this method.  It should still be possible for the
     * application to process the document through to the end if no other errors
     * are encountered.</p>
     *
     * @param exception The error information encapsulated in a
     *                  transformer exception.
     *
     * @throws javax.xml.transform.TransformerException if the application
     * chooses to discontinue the transformation.
     *
     * @see javax.xml.transform.TransformerException
     */
    public abstract void error(TransformerException exception)
        throws TransformerException;

    /**
     * <p>Receive notification of a non-recoverable error.</p>
     *
     * <p>The processor may choose to continue, but will not normally
     * proceed to a successful completion.</p>
     *
     * <p>The method should throw an exception if it is unable to
     * process the error, or if it wishes execution to terminate
     * immediately. The processor will not necessarily honor this
     * request.</p>
     *
     * @param exception The error information encapsulated in a
     *    <code>TransformerException</code>.
     *
     * @throws javax.xml.transform.TransformerException if the application
     * chooses to discontinue the transformation.
     *
     * @see javax.xml.transform.TransformerException
     */
    public abstract void fatalError(TransformerException exception)
        throws TransformerException;
}