# 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`.

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`.

## Deprecated Methods and Replacements

The following methods in this class for user-based authorization that are dependent on Security Manager APIs are deprecated for removal:

- `getSubject(AccessControlContext)`
- `doAs(Subject, PrivilegedAction)`
- `doAs(Subject, PrivilegedExceptionAction)`
- `doAsPrivileged(Subject, PrivilegedAction, AccessControlContext)`
- `doAsPrivileged(Subject, PrivilegedExceptionAction, AccessControlContext)`

Methods `current()` and `callAs(Subject, Callable)` are replacements for these methods, where `current` is equivalent to `getSubject(AccessController.getContext())` (as originally specified) and `callAs` is similar to `doAs` except that the input type and exceptions thrown are slightly different.

A `doAs` or `callAs` call binds a `Subject` object to the period of execution of an action, and the subject can be retrieved using the `current` method inside the action. This subject can be inherited by child threads if they are started and terminate within the execution of its parent thread using structured concurrency.

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`
  `callAs(Subject subject, Callable<T> action)`
  Executes a `Callable` with `subject` as the current subject.
  `static Subject`
  `current()`
  Returns the current subject.
  `static <T> T`
  `doAs(Subject subject, PrivilegedAction<T> action)`
  Deprecated, for removal: This API element is subject to removal in a future version.
  This method originally performed the specified `PrivilegedAction` with privileges enabled.
  `static <T> T`
  `doAs(Subject subject, PrivilegedExceptionAction<T> action)`
  Deprecated, for removal: This API element is subject to removal in a future version.
  This method originally performed the specified `PrivilegedExceptionAction` with privileges enabled.
  `static <T> T`
  `doAsPrivileged(Subject subject, PrivilegedAction<T> action, AccessControlContext acc)`
  Deprecated, for removal: This API element is subject to removal in a future version.
  This method originally performed the specified `PrivilegedAction` with privileges enabled and restricted by the specified `AccessControlContext`.
  `static <T> T`
  `doAsPrivileged(Subject subject, PrivilegedExceptionAction<T> action, AccessControlContext acc)`
  Deprecated, for removal: This API element is subject to removal in a future version.
  This method originally performed the specified `PrivilegedExceptionAction` with privileges enabled and restricted by the specified `AccessControlContext`.
  `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)`
  Deprecated, for removal: This API element is subject to removal in a future version.
  This method used to get the subject associated with the provided `AccessControlContext`, which was only useful in conjunction with the Security Manager, which is no longer supported.
  `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 Object

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

- ## Constructor Details

  - ### 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. These Sets also prohibit null elements, and attempts to add, query, or remove a null element will result in a `NullPointerException`.

  - ### 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. These Sets also prohibit null elements, and attempts to add, query, or remove a null element will result in a `NullPointerException`.

    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 Details

  - ### 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.

  - ### isReadOnly

    public boolean isReadOnly()
    Query whether this `Subject` is read-only.
    Returns:
      true if this `Subject` is read-only, false otherwise.

  - ### getSubject

    @Deprecated(since="17", forRemoval=true) public static Subject getSubject(AccessControlContext acc)
    Deprecated, for removal: This API element is subject to removal in a future version.
    This method used to get the subject associated with the provided `AccessControlContext`, which was only useful in conjunction with the Security Manager, which is no longer supported. This method has been changed to always throw `UnsupportedOperationException`. A replacement API named `current()` has been added which can be used to obtain the current subject. There is no replacement for the Security Manager.
    Throws `UnsupportedOperationException`. A replacement API named `current()` has been added which can be used to obtain the current subject.
    Parameters:
      `acc` - ignored
    Returns:
      n/a
    Throws:
      `UnsupportedOperationException` - always
    See Also:
      - `current()`

  - ### current

    public static Subject current()
    Returns the current subject.

    The current subject is installed by the `callAs(Subject, Callable)` method. When `callAs(subject, action)` is called, `action` is executed with `subject` as its current subject which can be retrieved by this method. After `action` is finished, the current subject is reset to its previous value. The current subject is `null` before the first call of `callAs()`.

    This method returns the `Subject` bound to the period of the execution of the current thread.

    Returns:
      the current subject, or `null` if a current subject is not installed or the current subject is set to `null`.
    Since:
      18
    See Also:
      - `callAs(Subject, Callable)`

  - ### callAs

    public static <T> T callAs(Subject subject, Callable<T> action) throws CompletionException
    Executes a `Callable` with `subject` as the current subject.

    This method launches `action` and binds `subject` to the period of its execution.

    Type Parameters:
      `T` - the type of value returned by the `call` method of `action`
    Parameters:
      `subject` - the `Subject` that the specified `action` will run as. This parameter may be `null`.
      `action` - the code to be run with `subject` as its current subject. Must not be `null`.
    Returns:
      the value returned by the `call` method of `action`
    Throws:
      `NullPointerException` - if `action` is `null`
      `CompletionException` - if `action.call()` throws an exception. The cause of the `CompletionException` is set to the exception thrown by `action.call()`.
    Since:
      18
    See Also:
      - `current()`

  - ### doAs

    @Deprecated(since="18", forRemoval=true) public static <T> T doAs(Subject subject, PrivilegedAction<T> action)
    Deprecated, for removal: This API element is subject to removal in a future version.
    This method originally performed the specified `PrivilegedAction` with privileges enabled. Running the action with privileges enabled was only useful in conjunction with the Security Manager, which is no longer supported. This method has been changed to launch the action as is and bind the subject to the period of its execution. A replacement API named `callAs(Subject, Callable)` has been added which can be used to perform the same work. There is no replacement for the Security Manager.
    Perform work as a particular `Subject`.

    This method launches `action` and binds `subject` to the period of its execution.

    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`.
    See Also:
      - `callAs(Subject, Callable)`

  - ### doAs

    @Deprecated(since="18", forRemoval=true) public static <T> T doAs(Subject subject, PrivilegedExceptionAction<T> action) throws PrivilegedActionException
    Deprecated, for removal: This API element is subject to removal in a future version.
    This method originally performed the specified `PrivilegedExceptionAction` with privileges enabled. Running the action with privileges enabled was only useful in conjunction with the Security Manager, which is no longer supported. This method has been changed to launch the action as is and bind the subject to the period of its execution. A replacement API named `callAs(Subject, Callable)` has been added which can be used to perform the same work. There is no replacement for the Security Manager.
    Perform work as a particular `Subject`.

    This method launches `action` and binds `subject` to the period of its execution.

    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`.
    See Also:
      - `callAs(Subject, Callable)`

  - ### doAsPrivileged

    @Deprecated(since="17", forRemoval=true) public static <T> T doAsPrivileged(Subject subject, PrivilegedAction<T> action, AccessControlContext acc)
    Deprecated, for removal: This API element is subject to removal in a future version.
    This method originally performed the specified `PrivilegedAction` with privileges enabled and restricted by the specified `AccessControlContext`. Running the action with privileges enabled was only useful in conjunction with the Security Manager, which is no longer supported. This method has been changed to ignore the `AccessControlContext` and launch the action as is and bind the subject to the period of its execution. A replacement API named `callAs(Subject, Callable)` has been added which can be used to perform the same work. There is no replacement for the Security Manager.
    Perform work as a particular `Subject`.

    This method launches `action` and binds `subject` to the period of its execution.

    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` - ignored
    Returns:
      the value returned by the PrivilegedAction's `run` method.
    Throws:
      `NullPointerException` - if the `PrivilegedAction` is `null`.
    See Also:
      - `callAs(Subject, Callable)`

  - ### doAsPrivileged

    @Deprecated(since="17", forRemoval=true) public static <T> T doAsPrivileged(Subject subject, PrivilegedExceptionAction<T> action, AccessControlContext acc) throws PrivilegedActionException
    Deprecated, for removal: This API element is subject to removal in a future version.
    This method originally performed the specified `PrivilegedExceptionAction` with privileges enabled and restricted by the specified `AccessControlContext`. Running the action with privileges enabled was only useful in conjunction with the Security Manager, which is no longer supported. This method has been changed to ignore the `AccessControlContext` and launch the action as is and bind the subject to the period of its execution. A replacement API named `callAs(Subject, Callable)` has been added which can be used to perform the same work. There is no replacement for the Security Manager.
    Perform work as a particular `Subject`.

    This method launches `action` and binds `subject` to the period of its execution.

    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` - ignored
    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`.
    See Also:
      - `callAs(Subject, Callable)`

  - ### 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.

    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.

    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.

    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`.

    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`.
    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`
    See Also:
      - `Object.equals(java.lang.Object)`
      - `System.identityHashCode(Object)`