/**
* 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.
AccessibleObject类是Field,Method和Constructor对象的父类，它提供了将反射对象标记
为在使用它时抑制默认java语言访问控制检查的功能。当使用Fields，Methods或Constructor来
设置或获取字段，调用方法，或创建和初始化新的类实例时，执行访问检查（对于public,默认（包）访问
，受保护和私有成员）
*
* <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.
在反射对象中设置accessible标志允许具有足够权限的复杂应用程序（如java对象序列化
或其他持久性机制）以通常被禁止的方式操纵对象
* <p>By default, a reflected object is <em>not</em> accessible.
默认情况下，反射对象不可访问
*/
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.
Permission对象，用于检查客户端是否具有足够的权限来阻止java语言访问控制检查
*/
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).
使用单一安全检查来设置对象数组的可访问标志的一个方便的方法（为了效率）*/
public static void setAccessible(AccessibleObject[] array, boolean flag)
throws SecurityException {
SecurityManager sm = System.getSecurityManager();//获取系统安全的接口
if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
for (int i = 0; i < array.length; i++) {
setAccessible0(array[i], flag);
}
}
/**
将对象的可访问标志设置为指示的布尔值*/
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;
}
/**
获取此对象的accessible标志的值（布尔类型）*/
public boolean isAccessible() {
return override;
}
/**
* Constructor: only used by the Java Virtual Machine.
构造函数，仅有java虚拟机使用
*/
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.
通过这个对象，指示是否覆盖语言级别访问检查权限，初始化为false,该字段用于Field,
Method和Constructor
// NOTE: for security purposes, this field must not be visible
// outside this package.
出于安全考虑，此字段不得显示出包外
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.
子类用于创建字段，方法和构造函数的反射工厂
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
}
}