jdk/src/java.base/share/classes/java/lang/reflect/AccessibleObject.java

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package java.lang.reflect;

import java.security.AccessController;

import sun.reflect.CallerSensitive;
import sun.reflect.Reflection;
import sun.reflect.ReflectionFactory;
import java.lang.annotation.Annotation;

/**
 * The AccessibleObject class is the base class for Field, Method and
 * Constructor objects.  It provides the ability to flag a reflected
 * object as suppressing default Java language access control checks
 * when it is used. The access checks -- <em>module boundaries</em>,
 * public, default (package) access, protected, and private members --
 * are performed when Fields, Methods or Constructors are used to set
 * or get fields, to invoke methods or to create and initialize new
 * instances of classes, respectively. Unlike access control specified
 * in the <cite>The Java&trade; Language Specification</cite> and
 * <cite>The Java Virtual Machine Specification</cite>, access checks
 * with reflected objects assume {@link Module#canRead readability}.
 *
 * <p>Setting the {@code accessible} flag in a reflected object
 * permits sophisticated applications with sufficient privilege, such
 * as Java Object Serialization or other persistence mechanisms, to
 * manipulate objects in a manner that would normally be prohibited.
 *
 * <p>By default, a reflected object is <em>not</em> accessible.
 *
 * @see Field
 * @see Method
 * @see Constructor
 * @see ReflectPermission
 *
 * @since 1.2
 */
public class AccessibleObject implements AnnotatedElement {

    /**
     * The Permission object that is used to check whether a client
     * has sufficient privilege to defeat Java language access
     * control checks.
     */
    private static final java.security.Permission ACCESS_PERMISSION =
        new ReflectPermission("suppressAccessChecks");

    static void checkPermission() {
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
    }

    /**
     * Convenience method to set the {@code accessible} flag for an
     * array of objects with a single security check (for efficiency).
     *
     * <p>This method cannot be used to enable access to an object that is a
     * {@link Member member} of a class in a different module to the caller and
     * where the class is in a package that is not exported to the caller's
     * module. Additionally, this method cannot be used to enable access to
     * non-public members of {@code AccessibleObject} or {@link Module}.
     *
     * <p>If there is a security manager, its
     * {@code checkPermission} method is first called with a
     * {@code ReflectPermission("suppressAccessChecks")} permission.
     *
     * <p>A {@code SecurityException} is also thrown if any of the elements of
     * the input {@code array} is a {@link java.lang.reflect.Constructor}
     * object for the class {@code java.lang.Class} and {@code flag} is true.
     *
     * @param array the array of AccessibleObjects
     * @param flag  the new value for the {@code accessible} flag
     *              in each object
     * @throws InaccessibleObjectException if access cannot be enabled
     * @throws SecurityException if the request is denied.
     * @see SecurityManager#checkPermission
     * @see ReflectPermission
     */
    @CallerSensitive
    public static void setAccessible(AccessibleObject[] array, boolean flag) {
        checkPermission();
        if (flag) {
            Class<?> caller = Reflection.getCallerClass();
            array = array.clone();
            for (AccessibleObject ao : array) {
                ao.checkCanSetAccessible(caller);
            }
        }
        for (AccessibleObject ao : array) {
            ao.setAccessible0(flag);
        }
    }

    /**
     * Set the {@code accessible} flag for this object to
     * the indicated boolean value.  A value of {@code true} indicates that
     * the reflected object should suppress Java language access
     * checking when it is used.  A value of {@code false} indicates
     * that the reflected object should enforce Java language access checks
     * while assuming readability (as noted in the class description).
     *
     * <p>This method cannot be used to enable access to an object that is a
     * {@link Member member} of a class in a different module to the caller and
     * where the class is in a package that is not exported to the caller's
     * module. Additionally, this method cannot be used to enable access to
     * non-public members of {@code AccessibleObject} or {@link Module}.
     *
     * <p>If there is a security manager, its
     * {@code checkPermission} method is first called with a
     * {@code ReflectPermission("suppressAccessChecks")} permission.
     *
     * @param flag the new value for the {@code accessible} flag
     * @throws InaccessibleObjectException if access cannot be enabled
     * @throws SecurityException if the request is denied
     * @see SecurityManager#checkPermission
     * @see ReflectPermission
     */
    public void setAccessible(boolean flag) {
        AccessibleObject.checkPermission();
        setAccessible0(flag);
    }

    void setAccessible0(boolean flag) {
        this.override = flag;
    }

   /**
    * If the given AccessibleObject is a {@code Constructor}, {@code Method}
    * or {@code Field} then checks that its declaring class is in a package
    * that can be accessed by the given caller of setAccessible.
    */
    void checkCanSetAccessible(Class<?> caller) {
        // do nothing, needs to be overridden by Constructor, Method, Field
    }

    void checkCanSetAccessible(Class<?> caller, Class<?> declaringClass) {
        Module callerModule = caller.getModule();
        Module declaringModule = declaringClass.getModule();

        if (callerModule != declaringModule
                && callerModule != Object.class.getModule()) {

            // check exports to target module
            String pn = packageName(declaringClass);
            if (!declaringModule.isExported(pn, callerModule)) {
                String msg = "Unable to make member of "
                        + declaringClass + " accessible:  "
                        + declaringModule + " does not export "
                        + pn + " to " + callerModule;
                Reflection.throwInaccessibleObjectException(msg);
            }

        }

        if (declaringClass == Module.class
                || declaringClass == AccessibleObject.class) {
            int modifiers;
            if (this instanceof Executable) {
                modifiers = ((Executable) this).getModifiers();
            } else {
                modifiers = ((Field) this).getModifiers();
            }
            if (!Modifier.isPublic(modifiers)) {
                String msg = "Cannot make a non-public member of "
                        + declaringClass + " accessible";
                Reflection.throwInaccessibleObjectException(msg);
            }
        }
    }

    /**
     * Returns the package name of the given class.
     */
    private static String packageName(Class<?> c) {
        while (c.isArray()) {
            c = c.getComponentType();
        }
        String pn = c.getPackageName();
        return (pn != null) ? pn : "";
    }

    /**
     * Get the value of the {@code accessible} flag for this object.
     *
     * @return the value of the object's {@code accessible} flag
     */
    public boolean isAccessible() {
        return override;
    }

    /**
     * Constructor: only used by the Java Virtual Machine.
     */
    protected AccessibleObject() {}

    // Indicates whether language-level access checks are overridden
    // by this object. Initializes to "false". This field is used by
    // Field, Method, and Constructor.
    //
    // NOTE: for security purposes, this field must not be visible
    // outside this package.
    boolean override;

    // Reflection factory used by subclasses for creating field,
    // method, and constructor accessors. Note that this is called
    // very early in the bootstrapping process.
    static final ReflectionFactory reflectionFactory =
        AccessController.doPrivileged(
            new sun.reflect.ReflectionFactory.GetReflectionFactoryAction());

    /**
     * @throws NullPointerException {@inheritDoc}
     * @since 1.5
     */
    public <T extends Annotation> T getAnnotation(Class<T> annotationClass) {
        throw new AssertionError("All subclasses should override this method");
    }

    /**
     * {@inheritDoc}
     * @throws NullPointerException {@inheritDoc}
     * @since 1.5
     */
    @Override
    public boolean isAnnotationPresent(Class<? extends Annotation> annotationClass) {
        return AnnotatedElement.super.isAnnotationPresent(annotationClass);
    }

   /**
     * @throws NullPointerException {@inheritDoc}
     * @since 1.8
     */
    @Override
    public <T extends Annotation> T[] getAnnotationsByType(Class<T> annotationClass) {
        throw new AssertionError("All subclasses should override this method");
    }

    /**
     * @since 1.5
     */
    public Annotation[] getAnnotations() {
        return getDeclaredAnnotations();
    }

    /**
     * @throws NullPointerException {@inheritDoc}
     * @since 1.8
     */
    @Override
    public <T extends Annotation> T getDeclaredAnnotation(Class<T> annotationClass) {
        // Only annotations on classes are inherited, for all other
        // objects getDeclaredAnnotation is the same as
        // getAnnotation.
        return getAnnotation(annotationClass);
    }

    /**
     * @throws NullPointerException {@inheritDoc}
     * @since 1.8
     */
    @Override
    public <T extends Annotation> T[] getDeclaredAnnotationsByType(Class<T> annotationClass) {
        // Only annotations on classes are inherited, for all other
        // objects getDeclaredAnnotationsByType is the same as
        // getAnnotationsByType.
        return getAnnotationsByType(annotationClass);
    }

    /**
     * @since 1.5
     */
    public Annotation[] getDeclaredAnnotations()  {
        throw new AssertionError("All subclasses should override this method");
    }


    // Shared access checking logic.

    // For non-public members or members in package-private classes,
    // it is necessary to perform somewhat expensive security checks.
    // If the security check succeeds for a given class, it will
    // always succeed (it is not affected by the granting or revoking
    // of permissions); we speed up the check in the common case by
    // remembering the last Class for which the check succeeded.
    //
    // The simple security check for Constructor is to see if
    // the caller has already been seen, verified, and cached.
    // (See also Class.newInstance(), which uses a similar method.)
    //
    // A more complicated security check cache is needed for Method and Field
    // The cache can be either null (empty cache), a 2-array of {caller,target},
    // or a caller (with target implicitly equal to this.clazz).
    // In the 2-array case, the target is always different from the clazz.
    volatile Object securityCheckCache;

    void checkAccess(Class<?> caller, Class<?> clazz, Object obj, int modifiers)
        throws IllegalAccessException
    {
        if (caller == clazz) {  // quick check
            return;             // ACCESS IS OK
        }
        Object cache = securityCheckCache;  // read volatile
        Class<?> targetClass = clazz;
        if (obj != null
            && Modifier.isProtected(modifiers)
            && ((targetClass = obj.getClass()) != clazz)) {
            // Must match a 2-list of { caller, targetClass }.
            if (cache instanceof Class[]) {
                Class<?>[] cache2 = (Class<?>[]) cache;
                if (cache2[1] == targetClass &&
                    cache2[0] == caller) {
                    return;     // ACCESS IS OK
                }
                // (Test cache[1] first since range check for [1]
                // subsumes range check for [0].)
            }
        } else if (cache == caller) {
            // Non-protected case (or obj.class == this.clazz).
            return;             // ACCESS IS OK
        }

        // If no return, fall through to the slow path.
        slowCheckMemberAccess(caller, clazz, obj, modifiers, targetClass);
    }

    // Keep all this slow stuff out of line:
    void slowCheckMemberAccess(Class<?> caller, Class<?> clazz, Object obj, int modifiers,
                               Class<?> targetClass)
        throws IllegalAccessException
    {
        Reflection.ensureMemberAccess(caller, clazz, obj, modifiers);

        // Success: Update the cache.
        Object cache = ((targetClass == clazz)
                        ? caller
                        : new Class<?>[] { caller, targetClass });

        // Note:  The two cache elements are not volatile,
        // but they are effectively final.  The Java memory model
        // guarantees that the initializing stores for the cache
        // elements will occur before the volatile write.
        securityCheckCache = cache;         // write volatile
    }
}