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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
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   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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   */
  
  package java.security.cert;
  
  import java.security.KeyStore;
  import java.security.KeyStoreException;
  import java.security.InvalidAlgorithmParameterException;
  import java.security.InvalidParameterException;
  import java.util.Set;
  
  /**
   * Parameters used as input for the PKIX {@code CertPathBuilder}
   * algorithm.
   * <p>
   * A PKIX {@code CertPathBuilder} uses these parameters to {@link
   * CertPathBuilder#build build} a {@code CertPath} which has been
   * validated according to the PKIX certification path validation algorithm.
   *
   * <p>To instantiate a {@code PKIXBuilderParameters} object, an
   * application must specify one or more <i>most-trusted CAs</i> as defined by
   * the PKIX certification path validation algorithm. The most-trusted CA
   * can be specified using one of two constructors. An application
   * can call {@link #PKIXBuilderParameters(Set, CertSelector)
   * PKIXBuilderParameters(Set, CertSelector)}, specifying a
   * {@code Set} of {@code TrustAnchor} objects, each of which
   * identifies a most-trusted CA. Alternatively, an application can call
   * {@link #PKIXBuilderParameters(KeyStore, CertSelector)
   * PKIXBuilderParameters(KeyStore, CertSelector)}, specifying a
   * {@code KeyStore} instance containing trusted certificate entries, each
   * of which will be considered as a most-trusted CA.
   *
   * <p>In addition, an application must specify constraints on the target
   * certificate that the {@code CertPathBuilder} will attempt
   * to build a path to. The constraints are specified as a
   * {@code CertSelector} object. These constraints should provide the
   * {@code CertPathBuilder} with enough search criteria to find the target
   * certificate. Minimal criteria for an {@code X509Certificate} usually
   * include the subject name and/or one or more subject alternative names.
   * If enough criteria is not specified, the {@code CertPathBuilder}
   * may throw a {@code CertPathBuilderException}.
   * <p>
   * <b>Concurrent Access</b>
   * <p>
   * Unless otherwise specified, the methods defined in this class are not
   * thread-safe. Multiple threads that need to access a single
   * object concurrently should synchronize amongst themselves and
   * provide the necessary locking. Multiple threads each manipulating
   * separate objects need not synchronize.
   *
   * @see CertPathBuilder
   *
   * @since       1.4
   * @author      Sean Mullan
   */
  public class PKIXBuilderParameters extends PKIXParameters {
  
      private int maxPathLength = 5;
  
      /**
       * Creates an instance of {@code PKIXBuilderParameters} with
       * the specified {@code Set} of most-trusted CAs.
       * Each element of the set is a {@link TrustAnchor TrustAnchor}.
       *
       * <p>Note that the {@code Set} is copied to protect against
       * subsequent modifications.
       *
       * @param trustAnchors a {@code Set} of {@code TrustAnchor}s
       * @param targetConstraints a {@code CertSelector} specifying the
       * constraints on the target certificate
       * @throws InvalidAlgorithmParameterException if {@code trustAnchors}
       * is empty {@code (trustAnchors.isEmpty() == true)}
       * @throws NullPointerException if {@code trustAnchors} is
       * {@code null}
       * @throws ClassCastException if any of the elements of
       * {@code trustAnchors} are not of type
       * {@code java.security.cert.TrustAnchor}
       */
      public PKIXBuilderParameters(Set<TrustAnchor> trustAnchors, CertSelector
          targetConstraints) throws InvalidAlgorithmParameterException
      {
          super(trustAnchors);
          setTargetCertConstraints(targetConstraints);
      }
  
      /**
       * Creates an instance of {@code PKIXBuilderParameters} that
       * populates the set of most-trusted CAs from the trusted
       * certificate entries contained in the specified {@code KeyStore}.
       * Only keystore entries that contain trusted {@code X509Certificate}s
       * are considered; all other certificate types are ignored.
       *
       * @param keystore a {@code KeyStore} from which the set of
       * most-trusted CAs will be populated
       * @param targetConstraints a {@code CertSelector} specifying the
       * constraints on the target certificate
       * @throws KeyStoreException if {@code keystore} has not been
       * initialized
       * @throws InvalidAlgorithmParameterException if {@code keystore} does
       * not contain at least one trusted certificate entry
       * @throws NullPointerException if {@code keystore} is
       * {@code null}
       */
      public PKIXBuilderParameters(KeyStore keystore,
          CertSelector targetConstraints)
          throws KeyStoreException, InvalidAlgorithmParameterException
      {
          super(keystore);
          setTargetCertConstraints(targetConstraints);
      }
  
      /**
       * Sets the value of the maximum number of non-self-issued intermediate
       * certificates that may exist in a certification path. A certificate
       * is self-issued if the DNs that appear in the subject and issuer
       * fields are identical and are not empty. Note that the last certificate
       * in a certification path is not an intermediate certificate, and is not
       * included in this limit. Usually the last certificate is an end entity
       * certificate, but it can be a CA certificate. A PKIX
       * {@code CertPathBuilder} instance must not build
       * paths longer than the length specified.
       *
       * <p> A value of 0 implies that the path can only contain
       * a single certificate. A value of -1 implies that the
       * path length is unconstrained (i.e. there is no maximum).
       * The default maximum path length, if not specified, is 5.
       * Setting a value less than -1 will cause an exception to be thrown.
       *
       * <p> If any of the CA certificates contain the
       * {@code BasicConstraintsExtension}, the value of the
       * {@code pathLenConstraint} field of the extension overrides
       * the maximum path length parameter whenever the result is a
       * certification path of smaller length.
       *
       * @param maxPathLength the maximum number of non-self-issued intermediate
       *  certificates that may exist in a certification path
       * @throws InvalidParameterException if {@code maxPathLength} is set
       *  to a value less than -1
       *
       * @see #getMaxPathLength
       */
      public void setMaxPathLength(int maxPathLength) {
          if (maxPathLength < -1) {
              throw new InvalidParameterException("the maximum path "
                  + "length parameter can not be less than -1");
          }
          this.maxPathLength = maxPathLength;
      }
  
      /**
       * Returns the value of the maximum number of intermediate non-self-issued
       * certificates that may exist in a certification path. See
       * the {@link #setMaxPathLength} method for more details.
       *
       * @return the maximum number of non-self-issued intermediate certificates
       *  that may exist in a certification path, or -1 if there is no limit
       *
       * @see #setMaxPathLength
       */
      public int getMaxPathLength() {
          return maxPathLength;
      }
  
      /**
       * Returns a formatted string describing the parameters.
       *
       * @return a formatted string describing the parameters
       */
      public String toString() {
          StringBuffer sb = new StringBuffer();
          sb.append("[\n");
          sb.append(super.toString());
          sb.append("  Maximum Path Length: " + maxPathLength + "\n");
          sb.append("]\n");
          return sb.toString();
      }
  }
  