An abstract class that performs one or more checks on an {@code X509Certificate}.
A concrete implementation of the {@code PKIXCertPathChecker} classcan be created to extend the PKIX certification path validation algorithm. For example, an implementation may check for and process a critical private extension of each certificate in a certification path.
Instances of {@code PKIXCertPathChecker} are passed as parametersusing the {@link PKIXParameters#setCertPathCheckers setCertPathCheckers}or {@link PKIXParameters#addCertPathChecker addCertPathChecker} methodsof the {@code PKIXParameters} and {@code PKIXBuilderParameters}class. Each of the {@code PKIXCertPathChecker}s {@link #check check}methods will be called, in turn, for each certificate processed by a PKIX {@code CertPathValidator} or {@code CertPathBuilder}implementation.
A {@code PKIXCertPathChecker} may be called multiple times onsuccessive certificates in a certification path. Concrete subclasses are expected to maintain any internal state that may be necessary to check successive certificates. The {@link #init init} method is usedto initialize the internal state of the checker so that the certificates of a new certification path may be checked. A stateful implementation must override the {@link #clone clone} method if necessary inorder to allow a PKIX {@code CertPathBuilder} to efficientlybacktrack and try other paths. In these situations, the {@code CertPathBuilder} is able to restore prior path validationstates by restoring the cloned {@code PKIXCertPathChecker}s.
The order in which the certificates are presented to the {@code PKIXCertPathChecker} may be either in the forward direction(from target to most-trusted CA) or in the reverse direction (from most-trusted CA to target). A {@code PKIXCertPathChecker} implementationmust support reverse checking (the ability to perform its checks when it is presented with certificates in the reverse direction) and may support forward checking (the ability to perform its checks when it is presented with certificates in the forward direction). The {@link #isForwardCheckingSupported isForwardCheckingSupported} methodindicates whether forward checking is supported.
Additional input parameters required for executing the check may be specified through constructors of concrete implementations of this class.
Concurrent Access
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 PKIXParameters
@see PKIXBuilderParameters
@since 1.4
@author Yassir Elley
@author Sean Mullan