Module java.base
Package javax.security.auth

## Class Subject

- java.lang.Object
- - javax.security.auth.Subject

- All Implemented Interfaces:
    `Serializable`

      public final class Subject
      extends Object
      implements Serializable

  A `Subject` represents a grouping of related information for a single entity, such as a person. Such information includes the Subject's identities as well as its security-related attributes (passwords and cryptographic keys, for example).

  Subjects may potentially have multiple identities. Each identity is represented as a `Principal` within the `Subject`. Principals simply bind names to a `Subject`. For example, a `Subject` that happens to be a person, Alice, might have two Principals: one which binds "Alice Bar", the name on her driver license, to the `Subject`, and another which binds, "999-99-9999", the number on her student identification card, to the `Subject`. Both Principals refer to the same `Subject` even though each has a different name.

  A `Subject` may also own security-related attributes, which are referred to as credentials. Sensitive credentials that require special protection, such as private cryptographic keys, are stored within a private credential `Set`. Credentials intended to be shared, such as public key certificates or Kerberos server tickets are stored within a public credential `Set`. Different permissions are required to access and modify the different credential Sets.

  To retrieve all the Principals associated with a `Subject`, invoke the `getPrincipals` method. To retrieve all the public or private credentials belonging to a `Subject`, invoke the `getPublicCredentials` method or `getPrivateCredentials` method, respectively. To modify the returned `Set` of Principals and credentials, use the methods defined in the `Set` class. For example:

            Subject subject;
            Principal principal;
            Object credential;

            // add a Principal and credential to the Subject
            subject.getPrincipals().add(principal);
            subject.getPublicCredentials().add(credential);

  This `Subject` class implements `Serializable`. While the Principals associated with the `Subject` are serialized, the credentials associated with the `Subject` are not. Note that the `java.security.Principal` class does not implement `Serializable`. Therefore all concrete `Principal` implementations associated with Subjects must implement `Serializable`.

  Since:
    1.4
  See Also:
    `Principal`, `DomainCombiner`, Serialized Form

- - ### Constructor Summary

    Constructors
    Constructor | Description
    --- | ---
    `Subject()` | Create an instance of a `Subject` with an empty `Set` of Principals and empty Sets of public and private credentials.
    `Subject​(boolean readOnly, Set<? extends Principal> principals, Set<?> pubCredentials, Set<?> privCredentials)` | Create an instance of a `Subject` with Principals and credentials.

  - ### Method Summary

    Modifier and Type | Method | Description
    --- | --- | ---
    `static <T> T` | `doAs​(Subject subject, PrivilegedAction<T> action)` | Perform work as a particular `Subject`.
    `static <T> T` | `doAs​(Subject subject, PrivilegedExceptionAction<T> action)` | Perform work as a particular `Subject`.
    `static <T> T` | `doAsPrivileged​(Subject subject, PrivilegedAction<T> action, AccessControlContext acc)` | Perform privileged work as a particular `Subject`.
    `static <T> T` | `doAsPrivileged​(Subject subject, PrivilegedExceptionAction<T> action, AccessControlContext acc)` | Perform privileged work as a particular `Subject`.
    `boolean` | `equals​(Object o)` | Compares the specified Object with this `Subject` for equality.
    `Set<Principal>` | `getPrincipals()` | Return the `Set` of Principals associated with this `Subject`.
    `<T extends Principal> Set<T>` | `getPrincipals​(Class<T> c)` | Return a `Set` of Principals associated with this `Subject` that are instances or subclasses of the specified `Class`.
    `Set<Object>` | `getPrivateCredentials()` | Return the `Set` of private credentials held by this `Subject`.
    `<T> Set<T>` | `getPrivateCredentials​(Class<T> c)` | Return a `Set` of private credentials associated with this `Subject` that are instances or subclasses of the specified `Class`.
    `Set<Object>` | `getPublicCredentials()` | Return the `Set` of public credentials held by this `Subject`.
    `<T> Set<T>` | `getPublicCredentials​(Class<T> c)` | Return a `Set` of public credentials associated with this `Subject` that are instances or subclasses of the specified `Class`.
    `static Subject` | `getSubject​(AccessControlContext acc)` | Get the `Subject` associated with the provided `AccessControlContext`.
    `int` | `hashCode()` | Returns a hashcode for this `Subject`.
    `boolean` | `isReadOnly()` | Query whether this `Subject` is read-only.
    `void` | `setReadOnly()` | Set this `Subject` to be read-only.
    `String` | `toString()` | Return the String representation of this `Subject`.

    - ### Methods declared in class java.lang.Object

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

- - ### Constructor Detail

    - #### Subject

          public Subject()

      Create an instance of a `Subject` with an empty `Set` of Principals and empty Sets of public and private credentials.

      The newly constructed Sets check whether this `Subject` has been set read-only before permitting subsequent modifications. The newly created Sets also prevent illegal modifications by ensuring that callers have sufficient permissions. These Sets also prohibit null elements, and attempts to add or query a null element will result in a `NullPointerException`.

      To modify the Principals Set, the caller must have `AuthPermission("modifyPrincipals")`. To modify the public credential Set, the caller must have `AuthPermission("modifyPublicCredentials")`. To modify the private credential Set, the caller must have `AuthPermission("modifyPrivateCredentials")`.

    - #### Subject

          public Subject​(boolean readOnly,
                         Set<? extends Principal> principals,
                         Set<?> pubCredentials,
                         Set<?> privCredentials)

      Create an instance of a `Subject` with Principals and credentials.

      The Principals and credentials from the specified Sets are copied into newly constructed Sets. These newly created Sets check whether this `Subject` has been set read-only before permitting subsequent modifications. The newly created Sets also prevent illegal modifications by ensuring that callers have sufficient permissions. These Sets also prohibit null elements, and attempts to add or query a null element will result in a `NullPointerException`.

      To modify the Principals Set, the caller must have `AuthPermission("modifyPrincipals")`. To modify the public credential Set, the caller must have `AuthPermission("modifyPublicCredentials")`. To modify the private credential Set, the caller must have `AuthPermission("modifyPrivateCredentials")`.

      Parameters:
        `readOnly` - true if the `Subject` is to be read-only, and false otherwise.
        `principals` - the `Set` of Principals to be associated with this `Subject`.
        `pubCredentials` - the `Set` of public credentials to be associated with this `Subject`.
        `privCredentials` - the `Set` of private credentials to be associated with this `Subject`.
      Throws:
        `NullPointerException` - if the specified `principals`, `pubCredentials`, or `privCredentials` are `null`, or a null value exists within any of these three Sets.

  - ### Method Detail

    - #### setReadOnly

          public void setReadOnly()

      Set this `Subject` to be read-only.

      Modifications (additions and removals) to this Subject's `Principal` `Set` and credential Sets will be disallowed. The `destroy` operation on this Subject's credentials will still be permitted.

      Subsequent attempts to modify the Subject's `Principal` and credential Sets will result in an `IllegalStateException` being thrown. Also, once a `Subject` is read-only, it can not be reset to being writable again.

      Throws:
        `SecurityException` - if a security manager is installed and the caller does not have an `AuthPermission("setReadOnly")` permission to set this `Subject` to be read-only.

    - #### isReadOnly

          public boolean isReadOnly()

      Query whether this `Subject` is read-only.
      Returns:
        true if this `Subject` is read-only, false otherwise.

    - #### getSubject

          public static Subject getSubject​(AccessControlContext acc)

      Get the `Subject` associated with the provided `AccessControlContext`.

      The `AccessControlContext` may contain many Subjects (from nested `doAs` calls). In this situation, the most recent `Subject` associated with the `AccessControlContext` is returned.

      Parameters:
        `acc` - the `AccessControlContext` from which to retrieve the `Subject`.
      Returns:
        the `Subject` associated with the provided `AccessControlContext`, or `null` if no `Subject` is associated with the provided `AccessControlContext`.
      Throws:
        `SecurityException` - if a security manager is installed and the caller does not have an `AuthPermission("getSubject")` permission to get the `Subject`.
        `NullPointerException` - if the provided `AccessControlContext` is `null`.

    - #### doAs

          public static <T> T doAs​(Subject subject,
                                   PrivilegedAction<T> action)

      Perform work as a particular `Subject`.

      This method first retrieves the current Thread's `AccessControlContext` via `AccessController.getContext`, and then instantiates a new `AccessControlContext` using the retrieved context along with a new `SubjectDomainCombiner` (constructed using the provided `Subject`). Finally, this method invokes `AccessController.doPrivileged`, passing it the provided `PrivilegedAction`, as well as the newly constructed `AccessControlContext`.

      Type Parameters:
        `T` - the type of the value returned by the PrivilegedAction's `run` method.
      Parameters:
        `subject` - the `Subject` that the specified `action` will run as. This parameter may be `null`.
        `action` - the code to be run as the specified `Subject`.
      Returns:
        the value returned by the PrivilegedAction's `run` method.
      Throws:
        `NullPointerException` - if the `PrivilegedAction` is `null`.
        `SecurityException` - if a security manager is installed and the caller does not have an `AuthPermission("doAs")` permission to invoke this method.

    - #### doAs

          public static <T> T doAs​(Subject subject,
                                   PrivilegedExceptionAction<T> action)
                            throws PrivilegedActionException

      Perform work as a particular `Subject`.

      This method first retrieves the current Thread's `AccessControlContext` via `AccessController.getContext`, and then instantiates a new `AccessControlContext` using the retrieved context along with a new `SubjectDomainCombiner` (constructed using the provided `Subject`). Finally, this method invokes `AccessController.doPrivileged`, passing it the provided `PrivilegedExceptionAction`, as well as the newly constructed `AccessControlContext`.

      Type Parameters:
        `T` - the type of the value returned by the PrivilegedExceptionAction's `run` method.
      Parameters:
        `subject` - the `Subject` that the specified `action` will run as. This parameter may be `null`.
        `action` - the code to be run as the specified `Subject`.
      Returns:
        the value returned by the PrivilegedExceptionAction's `run` method.
      Throws:
        `PrivilegedActionException` - if the `PrivilegedExceptionAction.run` method throws a checked exception.
        `NullPointerException` - if the specified `PrivilegedExceptionAction` is `null`.
        `SecurityException` - if a security manager is installed and the caller does not have an `AuthPermission("doAs")` permission to invoke this method.

    - #### doAsPrivileged

          public static <T> T doAsPrivileged​(Subject subject,
                                             PrivilegedAction<T> action,
                                             AccessControlContext acc)

      Perform privileged work as a particular `Subject`.

      This method behaves exactly as `Subject.doAs`, except that instead of retrieving the current Thread's `AccessControlContext`, it uses the provided `AccessControlContext`. If the provided `AccessControlContext` is `null`, this method instantiates a new `AccessControlContext` with an empty collection of ProtectionDomains.

      Type Parameters:
        `T` - the type of the value returned by the PrivilegedAction's `run` method.
      Parameters:
        `subject` - the `Subject` that the specified `action` will run as. This parameter may be `null`.
        `action` - the code to be run as the specified `Subject`.
        `acc` - the `AccessControlContext` to be tied to the specified subject and action.
      Returns:
        the value returned by the PrivilegedAction's `run` method.
      Throws:
        `NullPointerException` - if the `PrivilegedAction` is `null`.
        `SecurityException` - if a security manager is installed and the caller does not have a `AuthPermission("doAsPrivileged")` permission to invoke this method.

    - #### doAsPrivileged

          public static <T> T doAsPrivileged​(Subject subject,
                                             PrivilegedExceptionAction<T> action,
                                             AccessControlContext acc)
                                      throws PrivilegedActionException

      Perform privileged work as a particular `Subject`.

      This method behaves exactly as `Subject.doAs`, except that instead of retrieving the current Thread's `AccessControlContext`, it uses the provided `AccessControlContext`. If the provided `AccessControlContext` is `null`, this method instantiates a new `AccessControlContext` with an empty collection of ProtectionDomains.

      Type Parameters:
        `T` - the type of the value returned by the PrivilegedExceptionAction's `run` method.
      Parameters:
        `subject` - the `Subject` that the specified `action` will run as. This parameter may be `null`.
        `action` - the code to be run as the specified `Subject`.
        `acc` - the `AccessControlContext` to be tied to the specified subject and action.
      Returns:
        the value returned by the PrivilegedExceptionAction's `run` method.
      Throws:
        `PrivilegedActionException` - if the `PrivilegedExceptionAction.run` method throws a checked exception.
        `NullPointerException` - if the specified `PrivilegedExceptionAction` is `null`.
        `SecurityException` - if a security manager is installed and the caller does not have a `AuthPermission("doAsPrivileged")` permission to invoke this method.

    - #### getPrincipals

          public Set<Principal> getPrincipals()

      Return the `Set` of Principals associated with this `Subject`. Each `Principal` represents an identity for this `Subject`.

      The returned `Set` is backed by this Subject's internal `Principal` `Set`. Any modification to the returned `Set` affects the internal `Principal` `Set` as well.

      If a security manager is installed, the caller must have a `AuthPermission("modifyPrincipals")` permission to modify the returned set, or a `SecurityException` will be thrown.

      Returns:
        the `Set` of Principals associated with this `Subject`.

    - #### getPrincipals

          public <T extends Principal> Set<T> getPrincipals​(Class<T> c)

      Return a `Set` of Principals associated with this `Subject` that are instances or subclasses of the specified `Class`.

      The returned `Set` is not backed by this Subject's internal `Principal` `Set`. A new `Set` is created and returned for each method invocation. Modifications to the returned `Set` will not affect the internal `Principal` `Set`.

      Type Parameters:
        `T` - the type of the class modeled by `c`
      Parameters:
        `c` - the returned `Set` of Principals will all be instances of this class.
      Returns:
        a `Set` of Principals that are instances of the specified `Class`.
      Throws:
        `NullPointerException` - if the specified `Class` is `null`.

    - #### getPublicCredentials

          public Set<Object> getPublicCredentials()

      Return the `Set` of public credentials held by this `Subject`.

      The returned `Set` is backed by this Subject's internal public Credential `Set`. Any modification to the returned `Set` affects the internal public Credential `Set` as well.

      If a security manager is installed, the caller must have a `AuthPermission("modifyPublicCredentials")` permission to modify the returned set, or a `SecurityException` will be thrown.

      Returns:
        a `Set` of public credentials held by this `Subject`.

    - #### getPrivateCredentials

          public Set<Object> getPrivateCredentials()

      Return the `Set` of private credentials held by this `Subject`.

      The returned `Set` is backed by this Subject's internal private Credential `Set`. Any modification to the returned `Set` affects the internal private Credential `Set` as well.

      If a security manager is installed, the caller must have a `AuthPermission("modifyPrivateCredentials")` permission to modify the returned set, or a `SecurityException` will be thrown.

      While iterating through the `Set`, a `SecurityException` is thrown if a security manager is installed and the caller does not have a `PrivateCredentialPermission` to access a particular Credential. The `Iterator` is nevertheless advanced to the next element in the `Set`.

      Returns:
        a `Set` of private credentials held by this `Subject`.

    - #### getPublicCredentials

          public <T> Set<T> getPublicCredentials​(Class<T> c)

      Return a `Set` of public credentials associated with this `Subject` that are instances or subclasses of the specified `Class`.

      The returned `Set` is not backed by this Subject's internal public Credential `Set`. A new `Set` is created and returned for each method invocation. Modifications to the returned `Set` will not affect the internal public Credential `Set`.

      Type Parameters:
        `T` - the type of the class modeled by `c`
      Parameters:
        `c` - the returned `Set` of public credentials will all be instances of this class.
      Returns:
        a `Set` of public credentials that are instances of the specified `Class`.
      Throws:
        `NullPointerException` - if the specified `Class` is `null`.

    - #### getPrivateCredentials

          public <T> Set<T> getPrivateCredentials​(Class<T> c)

      Return a `Set` of private credentials associated with this `Subject` that are instances or subclasses of the specified `Class`.

      If a security manager is installed, the caller must have a `PrivateCredentialPermission` to access all of the requested Credentials, or a `SecurityException` will be thrown.

      The returned `Set` is not backed by this Subject's internal private Credential `Set`. A new `Set` is created and returned for each method invocation. Modifications to the returned `Set` will not affect the internal private Credential `Set`.

      Type Parameters:
        `T` - the type of the class modeled by `c`
      Parameters:
        `c` - the returned `Set` of private credentials will all be instances of this class.
      Returns:
        a `Set` of private credentials that are instances of the specified `Class`.
      Throws:
        `NullPointerException` - if the specified `Class` is `null`.

    - #### equals

          public boolean equals​(Object o)

      Compares the specified Object with this `Subject` for equality. Returns true if the given object is also a Subject and the two `Subject` instances are equivalent. More formally, two `Subject` instances are equal if their `Principal` and `Credential` Sets are equal.
      Overrides:
        `equals` in class `Object`
      Parameters:
        `o` - Object to be compared for equality with this `Subject`.
      Returns:
        true if the specified Object is equal to this `Subject`.
      Throws:
        `SecurityException` - if a security manager is installed and the caller does not have a `PrivateCredentialPermission` permission to access the private credentials for this `Subject` or the provided `Subject`.
      See Also:
        `Object.hashCode()`, `HashMap`

    - #### toString

          public String toString()

      Return the String representation of this `Subject`.
      Overrides:
        `toString` in class `Object`
      Returns:
        the String representation of this `Subject`.

    - #### hashCode

          public int hashCode()

      Returns a hashcode for this `Subject`.
      Overrides:
        `hashCode` in class `Object`
      Returns:
        a hashcode for this `Subject`.
      Throws:
        `SecurityException` - if a security manager is installed and the caller does not have a `PrivateCredentialPermission` permission to access this Subject's private credentials.
      See Also:
        `Object.equals(java.lang.Object)`, `System.identityHashCode(java.lang.Object)`