KeyTab (Java Platform SE 8 )
Keywords: javax.security.auth.kerberos.KeyTab class
Date: 2016-12-09

compact3
javax.security.auth.kerberos

## Class KeyTab

- java.lang.Object
- - javax.security.auth.kerberos.KeyTab

-     public final class KeyTab
      extends Object

  This class encapsulates a keytab file.

  A Kerberos JAAS login module that obtains long term secret keys from a keytab file should use this class. The login module will store an instance of this class in the private credential set of a `Subject` during the commit phase of the authentication process.

  If a `KeyTab` object is obtained from `getUnboundInstance()` or `getUnboundInstance(java.io.File)`, it is unbound and thus can be used by any service principal. Otherwise, if it's obtained from `getInstance(KerberosPrincipal)` or `getInstance(KerberosPrincipal, java.io.File)`, it is bound to the specific service principal and can only be used by it.

  Please note the constructors `getInstance()` and `getInstance(java.io.File)` were created when there was no support for unbound keytabs. These methods should not be used anymore. An object created with either of these methods are considered to be bound to an unknown principal, which means, its `isBound()` returns true and `getPrincipal()` returns null.

  It might be necessary for the application to be granted a `PrivateCredentialPermission` if it needs to access the KeyTab instance from a Subject. This permission is not needed when the application depends on the default JGSS Kerberos mechanism to access the KeyTab. In that case, however, the application will need an appropriate `ServicePermission`.

  The keytab file format is described at http://www.ioplex.com/utilities/keytab.txt.

  Since:
    1.7

- - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `boolean` | `equals(Object other)` Compares the specified Object with this KeyTab for equality.
    `boolean` | `exists()` Checks if the keytab file exists.
    `static KeyTab` | `getInstance()` Returns the default `KeyTab` instance that is bound to an unknown service principal.
    `static KeyTab` | `getInstance(File file)` Returns a `KeyTab` instance from a `File` object that is bound to an unknown service principal.
    `static KeyTab` | `getInstance(KerberosPrincipal princ)` Returns the default `KeyTab` instance that is bound to the specified service principal.
    `static KeyTab` | `getInstance(KerberosPrincipal princ, File file)` Returns a `KeyTab` instance from a `File` object that is bound to the specified service principal.
    `KerberosKey[]` | `getKeys(KerberosPrincipal principal)` Returns fresh keys for the given Kerberos principal.
    `KerberosPrincipal` | `getPrincipal()` Returns the service principal this `KeyTab` object is bound to.
    `static KeyTab` | `getUnboundInstance()` Returns the default unbound `KeyTab` instance.
    `static KeyTab` | `getUnboundInstance(File file)` Returns an unbound `KeyTab` instance from a `File` object.
    `int` | `hashCode()` Returns a hashcode for this KeyTab.
    `boolean` | `isBound()` Returns if the keytab is bound to a principal
    `String` | `toString()` Returns a string representation of the object.

    - ### Methods inherited from class java.lang.Object

      `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

- - ### Method Detail

    - #### getInstance

          public static KeyTab getInstance(File file)

      Returns a `KeyTab` instance from a `File` object that is bound to an unknown service principal.

      The result of this method is never null. This method only associates the returned `KeyTab` object with the file and does not read it.

      Developers should call `getInstance(KerberosPrincipal,File)` when the bound service principal is known.

      Parameters:
        `file` - the keytab `File` object, must not be null
      Returns:
        the keytab instance
      Throws:
        `NullPointerException` - if the `file` argument is null

    - #### getUnboundInstance

          public static KeyTab getUnboundInstance(File file)

      Returns an unbound `KeyTab` instance from a `File` object.

      The result of this method is never null. This method only associates the returned `KeyTab` object with the file and does not read it.

      Parameters:
        `file` - the keytab `File` object, must not be null
      Returns:
        the keytab instance
      Throws:
        `NullPointerException` - if the file argument is null
      Since:
        1.8

    - #### getInstance

          public static KeyTab getInstance(KerberosPrincipal princ,
                                           File file)

      Returns a `KeyTab` instance from a `File` object that is bound to the specified service principal.

      The result of this method is never null. This method only associates the returned `KeyTab` object with the file and does not read it.

      Parameters:
        `princ` - the bound service principal, must not be null
        `file` - the keytab `File` object, must not be null
      Returns:
        the keytab instance
      Throws:
        `NullPointerException` - if either of the arguments is null
      Since:
        1.8

    - #### getInstance

          public static KeyTab getInstance()

      Returns the default `KeyTab` instance that is bound to an unknown service principal.

      The result of this method is never null. This method only associates the returned `KeyTab` object with the default keytab file and does not read it.

      Developers should call `getInstance(KerberosPrincipal)` when the bound service principal is known.

      Returns:
        the default keytab instance.

    - #### getUnboundInstance

          public static KeyTab getUnboundInstance()

      Returns the default unbound `KeyTab` instance.

      The result of this method is never null. This method only associates the returned `KeyTab` object with the default keytab file and does not read it.

      Returns:
        the default keytab instance
      Since:
        1.8

    - #### getInstance

          public static KeyTab getInstance(KerberosPrincipal princ)

      Returns the default `KeyTab` instance that is bound to the specified service principal.

      The result of this method is never null. This method only associates the returned `KeyTab` object with the default keytab file and does not read it.

      Parameters:
        `princ` - the bound service principal, must not be null
      Returns:
        the default keytab instance
      Throws:
        `NullPointerException` - if `princ` is null
      Since:
        1.8

    - #### getKeys

          public KerberosKey[] getKeys(KerberosPrincipal principal)

      Returns fresh keys for the given Kerberos principal.

      Implementation of this method should make sure the returned keys match the latest content of the keytab file. The result is a newly created copy that can be modified by the caller without modifying the keytab object. The caller should `destroy` the result keys after they are used.

      Please note that the keytab file can be created after the `KeyTab` object is instantiated and its content may change over time. Therefore, an application should call this method only when it needs to use the keys. Any previous result from an earlier invocation could potentially be expired.

      If there is any error (say, I/O error or format error) during the reading process of the KeyTab file, a saved result should be returned. If there is no saved result (say, this is the first time this method is called, or, all previous read attempts failed), an empty array should be returned. This can make sure the result is not drastically changed during the (probably slow) update of the keytab file.

      Each time this method is called and the reading of the file succeeds with no exception (say, I/O error or file format error), the result should be saved for `principal`. The implementation can also save keys for other principals having keys in the same keytab object if convenient.

      Any unsupported key read from the keytab is ignored and not included in the result.

      If this keytab is bound to a specific principal, calling this method on another principal will return an empty array.

      Parameters:
        `principal` - the Kerberos principal, must not be null.
      Returns:
        the keys (never null, may be empty)
      Throws:
        `NullPointerException` - if the `principal` argument is null
        `SecurityException` - if a security manager exists and the read access to the keytab file is not permitted

    - #### exists

          public boolean exists()

      Checks if the keytab file exists. Implementation of this method should make sure that the result matches the latest status of the keytab file.

      The caller can use the result to determine if it should fallback to another mechanism to read the keys.

      Returns:
        true if the keytab file exists; false otherwise.
      Throws:
        `SecurityException` - if a security manager exists and the read access to the keytab file is not permitted

    - #### toString

          public String toString()

      Description copied from class: `Object`
      Returns a string representation of the object. In general, the `toString` method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

      The `toString` method for class `Object` returns a string consisting of the name of the class of which the object is an instance, the at-sign character ``@`', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

      >      getClass().getName() + '@' + Integer.toHexString(hashCode())

      Overrides:
        `toString` in class `Object`
      Returns:
        a string representation of the object.

    - #### hashCode

          public int hashCode()

      Returns a hashcode for this KeyTab.
      Overrides:
        `hashCode` in class `Object`
      Returns:
        a hashCode() for the `KeyTab`
      See Also:
        `Object.equals(java.lang.Object)`, `System.identityHashCode(java.lang.Object)`

    - #### equals

          public boolean equals(Object other)

      Compares the specified Object with this KeyTab for equality. Returns true if the given object is also a `KeyTab` and the two `KeyTab` instances are equivalent.
      Overrides:
        `equals` in class `Object`
      Parameters:
        `other` - the Object to compare to
      Returns:
        true if the specified object is equal to this KeyTab
      See Also:
        `Object.hashCode()`, `HashMap`

    - #### getPrincipal

          public KerberosPrincipal getPrincipal()

      Returns the service principal this `KeyTab` object is bound to. Returns `null` if it's not bound.

      Please note the deprecated constructors create a KeyTab object bound for some unknown principal. In this case, this method also returns null. User can call `isBound()` to verify this case.

      Returns:
        the service principal
      Since:
        1.8

    - #### isBound

          public boolean isBound()

      Returns if the keytab is bound to a principal
      Returns:
        if the keytab is bound to a principal
      Since:
        1.8

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