Policy (Java Platform SE 8 )
Keywords: java.security.Policy class
Date: 2020-03-26

compact1, compact2, compact3
java.security

## Class Policy

- java.lang.Object
- - java.security.Policy

-     public abstract class Policy
      extends Object

  A Policy object is responsible for determining whether code executing in the Java runtime environment has permission to perform a security-sensitive operation.

  There is only one Policy object installed in the runtime at any given time. A Policy object can be installed by calling the `setPolicy` method. The installed Policy object can be obtained by calling the `getPolicy` method.

  If no Policy object has been installed in the runtime, a call to `getPolicy` installs an instance of the default Policy implementation (a default subclass implementation of this abstract class). The default Policy implementation can be changed by setting the value of the `policy.provider` security property to the fully qualified name of the desired Policy subclass implementation.

  Application code can directly subclass Policy to provide a custom implementation. In addition, an instance of a Policy object can be constructed by invoking one of the `getInstance` factory methods with a standard type. The default policy type is "JavaPolicy".

  Once a Policy instance has been installed (either by default, or by calling `setPolicy`), the Java runtime invokes its `implies` method when it needs to determine whether executing code (encapsulated in a ProtectionDomain) can perform SecurityManager-protected operations. How a Policy object retrieves its policy data is up to the Policy implementation itself. The policy data may be stored, for example, in a flat ASCII file, in a serialized binary file of the Policy class, or in a database.

  The `refresh` method causes the policy object to refresh/reload its data. This operation is implementation-dependent. For example, if the policy object stores its data in configuration files, calling `refresh` will cause it to re-read the configuration policy files. If a refresh operation is not supported, this method does nothing. Note that refreshed policy may not have an effect on classes in a particular ProtectionDomain. This is dependent on the Policy provider's implementation of the `implies` method and its PermissionCollection caching strategy.

  See Also:
    `Provider`, `ProtectionDomain`, `Permission`, `security properties`

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `static interface` | `Policy.Parameters` This represents a marker interface for Policy parameters.

  - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static PermissionCollection` | `UNSUPPORTED_EMPTY_COLLECTION` A read-only empty PermissionCollection instance.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `Policy()`

  - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `static Policy` | `getInstance(String type, Policy.Parameters params)` Returns a Policy object of the specified type.
    `static Policy` | `getInstance(String type, Policy.Parameters params, Provider provider)` Returns a Policy object of the specified type.
    `static Policy` | `getInstance(String type, Policy.Parameters params, String provider)` Returns a Policy object of the specified type.
    `Policy.Parameters` | `getParameters()` Return Policy parameters.
    `PermissionCollection` | `getPermissions(CodeSource codesource)` Return a PermissionCollection object containing the set of permissions granted to the specified CodeSource.
    `PermissionCollection` | `getPermissions(ProtectionDomain domain)` Return a PermissionCollection object containing the set of permissions granted to the specified ProtectionDomain.
    `static Policy` | `getPolicy()` Returns the installed Policy object.
    `Provider` | `getProvider()` Return the Provider of this Policy.
    `String` | `getType()` Return the type of this Policy.
    `boolean` | `implies(ProtectionDomain domain, Permission permission)` Evaluates the global policy for the permissions granted to the ProtectionDomain and tests whether the permission is granted.
    `void` | `refresh()` Refreshes/reloads the policy configuration.
    `static void` | `setPolicy(Policy p)` Sets the system-wide Policy object.

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

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### UNSUPPORTED_EMPTY_COLLECTION

          public static final PermissionCollection UNSUPPORTED_EMPTY_COLLECTION

      A read-only empty PermissionCollection instance.
      Since:
        1.6

  - ### Constructor Detail

    - #### Policy

          public Policy()

  - ### Method Detail

    - #### getPolicy

          public static Policy getPolicy()

      Returns the installed Policy object. This value should not be cached, as it may be changed by a call to `setPolicy`. This method first calls `SecurityManager.checkPermission` with a `SecurityPermission("getPolicy")` permission to ensure it's ok to get the Policy object.
      Returns:
        the installed Policy.
      Throws:
        `SecurityException` - if a security manager exists and its `checkPermission` method doesn't allow getting the Policy object.
      See Also:
        `SecurityManager.checkPermission(Permission)`, `setPolicy(java.security.Policy)`

    - #### setPolicy

          public static void setPolicy(Policy p)

      Sets the system-wide Policy object. This method first calls `SecurityManager.checkPermission` with a `SecurityPermission("setPolicy")` permission to ensure it's ok to set the Policy.
      Parameters:
        `p` - the new system Policy object.
      Throws:
        `SecurityException` - if a security manager exists and its `checkPermission` method doesn't allow setting the Policy.
      See Also:
        `SecurityManager.checkPermission(Permission)`, `getPolicy()`

    - #### getInstance

          public static Policy getInstance(String type,
                                           Policy.Parameters params)
                                    throws NoSuchAlgorithmException

      Returns a Policy object of the specified type.

      This method traverses the list of registered security providers, starting with the most preferred Provider. A new Policy object encapsulating the PolicySpi implementation from the first Provider that supports the specified type is returned.

      Note that the list of registered providers may be retrieved via the `Security.getProviders()` method.

      Parameters:
        `type` - the specified Policy type. See the Policy section in the Java Cryptography Architecture Standard Algorithm Name Documentation for a list of standard Policy types.
        `params` - parameters for the Policy, which may be null.
      Returns:
        the new Policy object.
      Throws:
        `SecurityException` - if the caller does not have permission to get a Policy instance for the specified type.
        `NullPointerException` - if the specified type is null.
        `IllegalArgumentException` - if the specified parameters are not understood by the PolicySpi implementation from the selected Provider.
        `NoSuchAlgorithmException` - if no Provider supports a PolicySpi implementation for the specified type.
      Since:
        1.6
      See Also:
        `Provider`

    - #### getInstance

          public static Policy getInstance(String type,
                                           Policy.Parameters params,
                                           String provider)
                                    throws NoSuchProviderException,
                                           NoSuchAlgorithmException

      Returns a Policy object of the specified type.

      A new Policy object encapsulating the PolicySpi implementation from the specified provider is returned. The specified provider must be registered in the provider list.

      Note that the list of registered providers may be retrieved via the `Security.getProviders()` method.

      Parameters:
        `type` - the specified Policy type. See the Policy section in the Java Cryptography Architecture Standard Algorithm Name Documentation for a list of standard Policy types.
        `params` - parameters for the Policy, which may be null.
        `provider` - the provider.
      Returns:
        the new Policy object.
      Throws:
        `SecurityException` - if the caller does not have permission to get a Policy instance for the specified type.
        `NullPointerException` - if the specified type is null.
        `IllegalArgumentException` - if the specified provider is null or empty, or if the specified parameters are not understood by the PolicySpi implementation from the specified provider.
        `NoSuchProviderException` - if the specified provider is not registered in the security provider list.
        `NoSuchAlgorithmException` - if the specified provider does not support a PolicySpi implementation for the specified type.
      Since:
        1.6
      See Also:
        `Provider`

    - #### getInstance

          public static Policy getInstance(String type,
                                           Policy.Parameters params,
                                           Provider provider)
                                    throws NoSuchAlgorithmException

      Returns a Policy object of the specified type.

      A new Policy object encapsulating the PolicySpi implementation from the specified Provider object is returned. Note that the specified Provider object does not have to be registered in the provider list.

      Parameters:
        `type` - the specified Policy type. See the Policy section in the Java Cryptography Architecture Standard Algorithm Name Documentation for a list of standard Policy types.
        `params` - parameters for the Policy, which may be null.
        `provider` - the Provider.
      Returns:
        the new Policy object.
      Throws:
        `SecurityException` - if the caller does not have permission to get a Policy instance for the specified type.
        `NullPointerException` - if the specified type is null.
        `IllegalArgumentException` - if the specified Provider is null, or if the specified parameters are not understood by the PolicySpi implementation from the specified Provider.
        `NoSuchAlgorithmException` - if the specified Provider does not support a PolicySpi implementation for the specified type.
      Since:
        1.6
      See Also:
        `Provider`

    - #### getProvider

          public Provider getProvider()

      Return the Provider of this Policy.

      This Policy instance will only have a Provider if it was obtained via a call to `Policy.getInstance`. Otherwise this method returns null.

      Returns:
        the Provider of this Policy, or null.
      Since:
        1.6

    - #### getType

          public String getType()

      Return the type of this Policy.

      This Policy instance will only have a type if it was obtained via a call to `Policy.getInstance`. Otherwise this method returns null.

      Returns:
        the type of this Policy, or null.
      Since:
        1.6

    - #### getParameters

          public Policy.Parameters getParameters()

      Return Policy parameters.

      This Policy instance will only have parameters if it was obtained via a call to `Policy.getInstance`. Otherwise this method returns null.

      Returns:
        Policy parameters, or null.
      Since:
        1.6

    - #### getPermissions

          public PermissionCollection getPermissions(CodeSource codesource)

      Return a PermissionCollection object containing the set of permissions granted to the specified CodeSource.

      Applications are discouraged from calling this method since this operation may not be supported by all policy implementations. Applications should solely rely on the `implies` method to perform policy checks. If an application absolutely must call a getPermissions method, it should call `getPermissions(ProtectionDomain)`.

      The default implementation of this method returns Policy.UNSUPPORTED_EMPTY_COLLECTION. This method can be overridden if the policy implementation can return a set of permissions granted to a CodeSource.

      Parameters:
        `codesource` - the CodeSource to which the returned PermissionCollection has been granted.
      Returns:
        a set of permissions granted to the specified CodeSource. If this operation is supported, the returned set of permissions must be a new mutable instance and it must support heterogeneous Permission types. If this operation is not supported, Policy.UNSUPPORTED_EMPTY_COLLECTION is returned.

    - #### getPermissions

          public PermissionCollection getPermissions(ProtectionDomain domain)

      Return a PermissionCollection object containing the set of permissions granted to the specified ProtectionDomain.

      Applications are discouraged from calling this method since this operation may not be supported by all policy implementations. Applications should rely on the `implies` method to perform policy checks.

      The default implementation of this method first retrieves the permissions returned via `getPermissions(CodeSource)` (the CodeSource is taken from the specified ProtectionDomain), as well as the permissions located inside the specified ProtectionDomain. All of these permissions are then combined and returned in a new PermissionCollection object. If `getPermissions(CodeSource)` returns Policy.UNSUPPORTED_EMPTY_COLLECTION, then this method returns the permissions contained inside the specified ProtectionDomain in a new PermissionCollection object.

      This method can be overridden if the policy implementation supports returning a set of permissions granted to a ProtectionDomain.

      Parameters:
        `domain` - the ProtectionDomain to which the returned PermissionCollection has been granted.
      Returns:
        a set of permissions granted to the specified ProtectionDomain. If this operation is supported, the returned set of permissions must be a new mutable instance and it must support heterogeneous Permission types. If this operation is not supported, Policy.UNSUPPORTED_EMPTY_COLLECTION is returned.
      Since:
        1.4

    - #### implies

          public boolean implies(ProtectionDomain domain,
                                 Permission permission)

      Evaluates the global policy for the permissions granted to the ProtectionDomain and tests whether the permission is granted.
      Parameters:
        `domain` - the ProtectionDomain to test
        `permission` - the Permission object to be tested for implication.
      Returns:
        true if "permission" is a proper subset of a permission granted to this ProtectionDomain.
      Since:
        1.4
      See Also:
        `ProtectionDomain`

    - #### refresh

          public void refresh()

      Refreshes/reloads the policy configuration. The behavior of this method depends on the implementation. For example, calling `refresh` on a file-based policy will cause the file to be re-read.

      The default implementation of this method does nothing. This method should be overridden if a refresh operation is supported by the policy implementation.

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