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 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.lang.reflect;

import java.security.AccessController;
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--for 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.
 *
 * <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
 */
@SuppressWarnings("ALL")
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.
 */
 static final private java.security.Permission ACCESS_PERMISSION =
 new ReflectPermission("suppressAccessChecks");

 /**
 * Convenience method to set the {@code accessible} flag for an
 * array of objects with a single security check (for efficiency).
 *
 * <p>First, if there is a security manager, its
 * {@code checkPermission} method is called with a
 * {@code ReflectPermission("suppressAccessChecks")} permission.
 *
 * <p>A {@code SecurityException} is raised if {@code flag} is
 * {@code true} but accessibility of any of the elements of the input
 * {@code array} may not be changed (for example, if the element
 * object is a {@link Constructor} object for the class {@link
 * java.lang.Class}). In the event of such a SecurityException, the
 * accessibility of objects is set to {@code flag} for array elements
 * upto (and excluding) the element for which the exception occurred; the
 * accessibility of elements beyond (and including) the element for which
 * the exception occurred is unchanged.
 *
 * @param array the array of AccessibleObjects
 * @param flag the new value for the {@code accessible} flag
 * in each object
 * @throws SecurityException if the request is denied.
 * @see SecurityManager#checkPermission
 * @see java.lang.RuntimePermission
 */
 // setAccessible(boolean flag)的批量操作方法
 public static void setAccessible(AccessibleObject[] array, boolean flag)
 throws SecurityException {
 SecurityManager sm = System.getSecurityManager();
 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
 for (int i = 0; i < array.length; i++) {
 setAccessible0(array[i], 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.
 *
 * <p>First, if there is a security manager, its
 * {@code checkPermission} method is called with a
 * {@code ReflectPermission("suppressAccessChecks")} permission.
 *
 * <p>A {@code SecurityException} is raised if {@code flag} is
 * {@code true} but accessibility of this object may not be changed
 * (for example, if this element object is a {@link Constructor} object for
 * the class {@link java.lang.Class}).
 *
 * <p>A {@code SecurityException} is raised if this object is a {@link
 * java.lang.reflect.Constructor} object for the class
 * {@code java.lang.Class}, and {@code flag} is true.
 *
 * @param flag the new value for the {@code accessible} flag
 * @throws SecurityException if the request is denied.
 * @see SecurityManager#checkPermission
 * @see java.lang.RuntimePermission
 */
 // 设置实例是否可以访问,如果设置为true,可以抑制修饰符,直接进行访问
 public void setAccessible(boolean flag) throws SecurityException {
 SecurityManager sm = System.getSecurityManager();
 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
 setAccessible0(this, flag);
 }

 /* Check that you aren't exposing java.lang.Class.<init> or sensitive
 fields in java.lang.Class. */
 private static void setAccessible0(AccessibleObject obj, boolean flag)
 throws SecurityException
 {
 if (obj instanceof Constructor && flag == true) {
 Constructor<?> c = (Constructor<?>)obj;
 if (c.getDeclaringClass() == Class.class) {
 throw new SecurityException("Cannot make a java.lang.Class" +
 " constructor accessible");
 }
 }
 obj.override = flag;
 }

 /**
 * Get the value of the {@code accessible} flag for this object.
 *
 * @return the value of the object's {@code accessible} flag
 */
 // 返回实例是否可以访问,实际上这个值并不准确,它只有在setAccessible被调用的时候才会更新
 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
 }
}