AccessibleObject.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 *
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package java.lang.reflect;

import java.lang.annotation.Annotation;
import java.lang.invoke.MethodHandle;
import java.security.AccessController;
import jdk.internal.misc.VM;
import jdk.internal.module.IllegalAccessLogger;
import jdk.internal.reflect.CallerSensitive;
import jdk.internal.reflect.Reflection;
import jdk.internal.reflect.ReflectionFactory;
import sun.security.action.GetPropertyAction;
import sun.security.util.SecurityConstants;

/**
 * The {@code AccessibleObject} class is the base class for {@code Field},
 * {@code Method}, and {@code Constructor} objects (known as <em>reflected
 * objects</em>). It provides the ability to flag a reflected object as
 * suppressing checks for Java language access control when it is used. This
 * 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> Java language access control prevents use of private members outside
 * their top-level class; package access members outside their package; protected members
 * outside their package or subclasses; and public members outside their
 * module unless they are declared in an {@link Module#isExported(String, Module)
 * exported} package and the user {@link Module#canRead reads} their module. By
 * default, Java language access control is enforced (with one variation) when
 * {@code Field}s, {@code Method}s, or {@code Constructor}s are used to get or
 * set fields, to invoke methods, or to create and initialize new instances of
 * classes, respectively. Every reflected object checks that the code using it
 * is in an appropriate class, package, or module. </p>
 *
 * <p> The one variation from Java language access control is that the checks
 * by reflected objects assume readability. That is, the module containing
 * the use of a reflected object is assumed to read the module in which
 * the underlying field, method, or constructor is declared. </p>
 *
 * <p> Whether the checks for Java language access control can be suppressed
 * (and thus, whether access can be enabled) depends on whether the reflected
 * object corresponds to a member in an exported or open package
 * (see {@link #setAccessible(boolean)}). </p>
 *
 * @jls 6.6 Access Control
 * @revised 9
 * @spec JPMS
 * @since 1.2
 */
// 可访问的元素，例如：Constructor/Method/Field
public class AccessibleObject implements AnnotatedElement {
    
    /**
     * 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 ReflectionFactory.GetReflectionFactoryAction());
    
    /**
     * 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,targetClass},
     * or a caller (with targetClass implicitly equal to memberClass).
     * In the 2-array case, the targetClass is always different from the memberClass.
     */
    volatile Object securityCheckCache;
    
    /**
     * 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.
     */
    /*
     * 是否覆盖语言级别的访问安全检查，初始值为false。
     *
     * 如果覆盖了安全检查，那么反射访问畅行无阻；否则，反射访问元素时需要进行安全性检查。
     * 对于private元素，访问前需要手动开启访问权限，即将此值为设置为true。
     */ boolean override;
    
    /** true to print a stack trace when access fails */
    private static volatile boolean printStackWhenAccessFails;
    
    /** true if printStack* values are initialized */
    private static volatile boolean printStackPropertiesSet;
    
    
    
    /*▼ 构造器 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Constructor: only used by the Java Virtual Machine.
     */
    protected AccessibleObject() {
    }
    
    /*▲ 构造器 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 安全检查 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Set the {@code accessible} flag for this reflected object to
     * the indicated boolean value.  A value of {@code true} indicates that
     * the reflected object should suppress checks for Java language access
     * control when it is used. A value of {@code false} indicates that
     * the reflected object should enforce checks for Java language access
     * control when it is used, with the variation noted in the class description.
     *
     * <p> This method may be used by a caller in class {@code C} to enable
     * access to a {@link Member member} of {@link Member#getDeclaringClass()
     * declaring class} {@code D} if any of the following hold: </p>
     *
     * <ul>
     * <li> {@code C} and {@code D} are in the same module. </li>
     *
     * <li> The member is {@code public} and {@code D} is {@code public} in
     * a package that the module containing {@code D} {@link
     * Module#isExported(String, Module) exports} to at least the module
     * containing {@code C}. </li>
     *
     * <li> The member is {@code protected} {@code static}, {@code D} is
     * {@code public} in a package that the module containing {@code D}
     * exports to at least the module containing {@code C}, and {@code C}
     * is a subclass of {@code D}. </li>
     *
     * <li> {@code D} is in a package that the module containing {@code D}
     * {@link Module#isOpen(String, Module) opens} to at least the module
     * containing {@code C}.
     * All packages in unnamed and open modules are open to all modules and
     * so this method always succeeds when {@code D} is in an unnamed or
     * open module. </li>
     * </ul>
     *
     * <p> This method cannot be used to enable access to private members,
     * members with default (package) access, protected instance members, or
     * protected constructors when the declaring class is in a different module
     * to the caller and the package containing the declaring class is not open
     * to the caller's module. </p>
     *
     * <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 by the security manager
     * @revised 9
     * @spec JPMS
     * @see #trySetAccessible
     * @see java.lang.invoke.MethodHandles#privateLookupIn
     */
    // 开启/关闭对当前成员的反射访问权限。访问private的Method/Field/Constructor时必须禁用安全检查，以开启访问权限，即setAccessible(true)
    @CallerSensitive
    public void setAccessible(boolean flag) {
        AccessibleObject.checkPermission();
        setAccessible0(flag);
    }
    
    /**
     * Convenience method to set the {@code accessible} flag for an
     * array of reflected objects with a single security check (for efficiency).
     *
     * <p> This method may be used to enable access to all reflected objects in
     * the array when access to each reflected object can be enabled as
     * specified by {@link #setAccessible(boolean) setAccessible(boolean)}. </p>
     *
     * <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 for all
     *                                     objects in the array
     * @throws SecurityException           if the request is denied by the security manager
     *                                     or an element in the array is a constructor for {@code
     *                                     java.lang.Class}
     * @revised 9
     * @spec JPMS
     * @see SecurityManager#checkPermission
     * @see ReflectPermission
     */
    // 批量开启/关闭对指定成员的反射访问权限
    @CallerSensitive
    public static void setAccessible(AccessibleObject[] array, boolean flag) {
        checkPermission();
    
        // 如果需要开启访问权限
        if(flag) {
            // 获取setAccessible()的调用者所处的类
            Class<?> caller = Reflection.getCallerClass();
        
            array = array.clone();
        
            // 遍历所有待访问元素
            for(AccessibleObject accessibleObject : array) {
                // 判断caller是否可以访问accessibleObject元素(由子类实现其逻辑)
                accessibleObject.checkCanSetAccessible(caller);
            }
        }
    
        for(AccessibleObject accessibleObject : array) {
            accessibleObject.setAccessible0(flag);
        }
    }
    
    /**
     * Set the {@code accessible} flag for this reflected object to {@code true}
     * if possible. This method sets the {@code accessible} flag, as if by
     * invoking {@link #setAccessible(boolean) setAccessible(true)}, and returns
     * the possibly-updated value for the {@code accessible} flag. If access
     * cannot be enabled, i.e. the checks or Java language access control cannot
     * be suppressed, this method returns {@code false} (as opposed to {@code
     * setAccessible(true)} throwing {@code InaccessibleObjectException} when
     * it fails).
     *
     * <p> This method is a no-op if the {@code accessible} flag for
     * this reflected object is {@code true}.
     *
     * <p> For example, a caller can invoke {@code trySetAccessible}
     * on a {@code Method} object for a private instance method
     * {@code p.T::privateMethod} to suppress the checks for Java language access
     * control when the {@code Method} is invoked.
     * If {@code p.T} class is in a different module to the caller and
     * package {@code p} is open to at least the caller's module,
     * the code below successfully sets the {@code accessible} flag
     * to {@code true}.
     *
     * <pre>
     * {@code
     *     p.T obj = ....;  // instance of p.T
     *     :
     *     Method m = p.T.class.getDeclaredMethod("privateMethod");
     *     if (m.trySetAccessible()) {
     *         m.invoke(obj);
     *     } else {
     *         // package p is not opened to the caller to access private member of T
     *         ...
     *     }
     * }</pre>
     *
     * <p> If there is a security manager, its {@code checkPermission} method
     * is first called with a {@code ReflectPermission("suppressAccessChecks")}
     * permission. </p>
     *
     * @return {@code true} if the {@code accessible} flag is set to {@code true};
     * {@code false} if access cannot be enabled.
     *
     * @throws SecurityException if the request is denied by the security manager
     * @spec JPMS
     * @see java.lang.invoke.MethodHandles#privateLookupIn
     * @since 9
     */
    // 尝试开启对指定成员的反射访问权限(禁用安全检查)
    @CallerSensitive
    public final boolean trySetAccessible() {
        AccessibleObject.checkPermission();
    
        // 如果已经覆盖(禁用)了安全检查，直接返回true
        if(override) {
            return true;
        }
    
        // if it's not a Constructor, Method, Field then no access check
        if(!Member.class.isInstance(this)) {
            return setAccessible0(true);
        }
    
        // does not allow to suppress access check for Class's constructor
        Class<?> declaringClass = ((Member) this).getDeclaringClass();
        if(declaringClass == Class.class && this instanceof Constructor) {
            return false;
        }
        
        if(checkCanSetAccessible(Reflection.getCallerClass(), declaringClass, false)) {
            return setAccessible0(true);
        } else {
            return false;
        }
    }
    
    /**
     * Test if the caller can access this reflected object. If this reflected
     * object corresponds to an instance method or field then this method tests
     * if the caller can access the given {@code obj} with the reflected object.
     * For instance methods or fields then the {@code obj} argument must be an
     * instance of the {@link Member#getDeclaringClass() declaring class}. For
     * static members and constructors then {@code obj} must be {@code null}.
     *
     * <p> This method returns {@code true} if the {@code accessible} flag
     * is set to {@code true}, i.e. the checks for Java language access control
     * are suppressed, or if the caller can access the member as
     * specified in <cite>The Java&trade; Language Specification</cite>,
     * with the variation noted in the class description. </p>
     *
     * @param obj an instance object of the declaring class of this reflected
     *            object if it is an instance method or field
     *
     * @return {@code true} if the caller can access this reflected object.
     *
     * @throws IllegalArgumentException <ul>
     *                                  <li> if this reflected object is a static member or constructor and
     *                                  the given {@code obj} is non-{@code null}, or </li>
     *                                  <li> if this reflected object is an instance method or field
     *                                  and the given {@code obj} is {@code null} or of type
     *                                  that is not a subclass of the {@link Member#getDeclaringClass()
     *                                  declaring class} of the member.</li>
     *                                  </ul>
     * @spec JPMS
     * @jls 6.6 Access Control
     * @see #trySetAccessible
     * @see #setAccessible(boolean)
     * @since 9
     */
    /*
     * 判断obj是否可以显式访问当前元素；
     * 如果当前元素是静态方法或静态字段，或为构造器，则要求obj为null
     * （private元素不能直接访问）
     */
    @CallerSensitive
    public final boolean canAccess(Object obj) {
        if(!(this instanceof Member)) {
            return override;
        }
    
        // 获取当前元素所在的类
        Class<?> declaringClass = ((Member) this).getDeclaringClass();
    
        // 获取当前元素上的修饰符
        int modifiers = ((Member) this).getModifiers();
    
        // 如果当前元素是非静态方法或非静态字段，需要确保obj为null
        if(!Modifier.isStatic(modifiers) && (this instanceof Method || this instanceof Field)) {
            if(obj == null) {
                throw new IllegalArgumentException("null object for " + this);
            }
        
            /*
             * if this object is an instance member, the given object must be a subclass of the declaring class of this reflected object
             */
            // 如果obj不是当前元素所在类的实例，抛异常
            if(!declaringClass.isAssignableFrom(obj.getClass())) {
                throw new IllegalArgumentException("object is not an instance of " + declaringClass.getName());
            }
        } else if(obj != null) {
            throw new IllegalArgumentException("non-null object for " + this);
        }
    
        // 如果已经覆盖(禁用)了安全检查，直接返回true
        if(override) {
            return true;
        }
    
        // 获取canAccess()方法调用者所处的类
        Class<?> caller = Reflection.getCallerClass();
        Class<?> targetClass;
    
        if(this instanceof Constructor) {
            targetClass = declaringClass;
        } else {
            targetClass = Modifier.isStatic(modifiers) ? null : obj.getClass();
        }
    
        // 判断是否可以在caller中通过targetClass类型的对象来显式访问memberClass中具有modifiers修饰符的成员(如果访问的是静态成员，则targetClass为null)
        return verifyAccess(caller, declaringClass, targetClass, modifiers);
    }
    
    /**
     * Get the value of the {@code accessible} flag for this reflected object.
     *
     * @return the value of the object's {@code accessible} flag
     *
     * @revised 9
     * @spec JPMS
     *
     * @deprecated This method is deprecated because its name hints that it checks
     * if the reflected object is accessible when it actually indicates
     * if the checks for Java language access control are suppressed.
     * This method may return {@code false} on a reflected object that is
     * accessible to the caller. To test if this reflected object is accessible,
     * it should use {@link #canAccess(Object)}.
     */
    // 判断当前元素是否允许被反问；该方法已过时，应当用canAccess(Object)替代
    @Deprecated(since = "9")
    public boolean isAccessible() {
        return override;
    }
    
    /*▲ 安全检查 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 注解 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * {@inheritDoc}
     *
     * @throws NullPointerException {@inheritDoc}
     * @since 1.5
     */
    // 判断当前元素上是否存在注解
    @Override
    public boolean isAnnotationPresent(Class<? extends Annotation> annotationClass) {
        return AnnotatedElement.super.isAnnotationPresent(annotationClass);
    }
    
    /**
     * @since 1.5
     */
    // 1-1 返回该元素上所有类型的注解
    public Annotation[] getAnnotations() {
        return getDeclaredAnnotations();
    }
    
    /**
     * @throws NullPointerException {@inheritDoc}
     * @since 1.5
     */
    // 1-2 返回该元素上指定类型的注解
    public <T extends Annotation> T getAnnotation(Class<T> annotationClass) {
        throw new AssertionError("All subclasses should override this method");
    }
    
    /**
     * @throws NullPointerException {@inheritDoc}
     * @since 1.8
     */
    // 1-3 返回该元素上指定类型的注解[支持获取@Repeatable类型的注解]
    @Override
    public <T extends Annotation> T[] getAnnotationsByType(Class<T> annotationClass) {
        throw new AssertionError("All subclasses should override this method");
    }
    
    /**
     * @since 1.5
     */
    // 2-1 返回该元素上所有类型的注解
    public Annotation[] getDeclaredAnnotations() {
        throw new AssertionError("All subclasses should override this method");
    }
    
    /**
     * @throws NullPointerException {@inheritDoc}
     * @since 1.8
     */
    // 2-2 返回该元素上指定类型的注解
    @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
     */
    // 2-3 返回该元素上指定类型的注解[支持获取@Repeatable类型的注解]
    @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);
    }
    
    /*▲ 注解 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    // 判断是否可以在caller中通过targetClass类型的对象来显式访问memberClass中具有modifiers修饰符的成员(如果访问的是静态成员，则targetClass为null)
    final void checkAccess(Class<?> caller, Class<?> memberClass, Class<?> targetClass, int modifiers) throws IllegalAccessException {
        // 判断是否可以在caller中通过targetClass类型的对象来显式访问memberClass中具有modifiers修饰符的成员(如果访问的是静态成员，则targetClass为null)
        if(verifyAccess(caller, memberClass, targetClass, modifiers)) {
            return;
        }
    
        // 构造一个非法访问异常
        IllegalAccessException exception = Reflection.newIllegalAccessException(caller, memberClass, targetClass, modifiers);
        if(printStackTraceWhenAccessFails()) {
            exception.printStackTrace(System.err);
        }
    
        throw exception;
    }
    
    // 判断是否可以在caller中通过targetClass类型的对象来显式访问memberClass中具有modifiers修饰符的成员(如果访问的是静态成员，则targetClass为null)
    final boolean verifyAccess(Class<?> caller, Class<?> memberClass, Class<?> targetClass, int modifiers) {
        if(caller == memberClass) {  // quick check
            return true;             // ACCESS IS OK
        }
        
        Object cache = securityCheckCache;  // read volatile
        
        if(targetClass != null                  // instance member or constructor
            && Modifier.isProtected(modifiers) && targetClass != memberClass) {
            // Must match a 2-list of { caller, targetClass }.
            if(cache instanceof Class[]) {
                Class<?>[] cache2 = (Class<?>[]) cache;
                if(cache2[1] == targetClass && cache2[0] == caller) {
                    return true;     // 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 targetClass == memberClass or static member).
            return true;             // ACCESS IS OK
        }
        
        /* If no return, fall through to the slow path */
        // 判断是否可以在caller中通过targetClass类型的对象来显式访问memberClass中具有modifiers修饰符的成员(如果访问的是静态成员，则targetClass为null)
        return slowVerifyAccess(caller, memberClass, targetClass, modifiers);
    }
    
    // 判断是否可以在caller中通过targetClass类型的对象来显式访问memberClass中具有modifiers修饰符的成员(如果访问的是静态成员，则targetClass为null)。
    private boolean slowVerifyAccess(Class<?> caller, Class<?> memberClass, Class<?> targetClass, int modifiers) {
        // 判断是否可以在caller中通过targetClass类型的对象来显式访问memberClass中具有modifiers修饰符的成员(如果访问的是静态成员，则targetClass为null)。
        if(!Reflection.verifyMemberAccess(caller, memberClass, targetClass, modifiers)) {
            // access denied
            return false;
        }
        
        // access okay
        logIfExportedForIllegalAccess(caller, memberClass);
        
        // Success: Update the cache.
        Object cache = (targetClass != null && Modifier.isProtected(modifiers) && targetClass != memberClass) ? new Class<?>[]{caller, targetClass} : caller;
        
        /*
         * 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
        
        return true;
    }
    
    
    static void checkPermission() {
        SecurityManager sm = System.getSecurityManager();
        if(sm != null) {
            // SecurityConstants.ACCESS_PERMISSION is used to check whether a client has sufficient privilege to defeat Java language access control checks.
            sm.checkPermission(SecurityConstants.ACCESS_PERMISSION);
        }
    }
    
    /**
     * 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.
     */
    // 判断caller是否可以访问当前元素(由子类实现其逻辑)
    void checkCanSetAccessible(Class<?> caller) {
        // do nothing, needs to be overridden by Constructor, Method, Field
    }
    
    /**
     * Sets the accessible flag and returns the new value
     */
    // 开启/关闭对当前成员的反射访问权限
    boolean setAccessible0(boolean flag) {
        this.override = flag;
        return flag;
    }
    
    // 判断caller是否可以访问位于declaringClass类中的当前元素(涉及到exports和opens的判断)
    final void checkCanSetAccessible(Class<?> caller, Class<?> declaringClass) {
        checkCanSetAccessible(caller, declaringClass, true);
    }
    
    // 判断caller是否可以访问位于declaringClass类中的当前元素(涉及到exports和opens的判断)
    private boolean checkCanSetAccessible(Class<?> caller, Class<?> declaringClass, boolean throwExceptionIfDenied) {
        if(caller == MethodHandle.class) {
            throw new IllegalCallerException();   // should not happen
        }
        
        Module callerModule = caller.getModule();
        Module declaringModule = declaringClass.getModule();
        
        // caller与declaringClass位于相同模块
        if(callerModule == declaringModule) {
            return true;
        }
        
        // caller位于"java.base"模块
        if(callerModule == Object.class.getModule()) {
            return true;
        }
        
        // declaringClass是未命名模块
        if(!declaringModule.isNamed()) {
            return true;
        }
        
        // declaringClass所在的包
        String pn = declaringClass.getPackageName();
        
        // declaringClass的修饰符
        int modifiers;
        if(this instanceof Executable) {
            modifiers = ((Executable) this).getModifiers();
        } else {
            modifiers = ((Field) this).getModifiers();
        }
        
        /* class is public and package is exported to caller */
        boolean isClassPublic = Modifier.isPublic(declaringClass.getModifiers());
        
        // 如果declaringClass是public类，且declaringModule模块将pn包导出(exports)给了callerModule模块
        if(isClassPublic && declaringModule.isExported(pn, callerModule)) {
            // 如果当前待访问元素是public，则允许caller访问
            if(Modifier.isPublic(modifiers)) {
                logIfExportedForIllegalAccess(caller, declaringClass);
                return true;
            }
            
            // 如果当前待访问元素是protected-static，且caller类与declaringClass类相同，或是declaringClass类的子类，也允许caller访问
            if(Modifier.isProtected(modifiers) && Modifier.isStatic(modifiers) && isSubclassOf(caller, declaringClass)) {
                logIfExportedForIllegalAccess(caller, declaringClass);
                return true;
            }
        }
        
        // 如果declaringModule模块将pn包(开放)opens给了callerModule模块，允许访问
        if(declaringModule.isOpen(pn, callerModule)) {
            logIfOpenedForIllegalAccess(caller, declaringClass);
            return true;
        }
        
        // 生成异常信息
        if(throwExceptionIfDenied) {
            // not accessible
            String msg = "Unable to make ";
            if(this instanceof Field) {
                msg += "field ";
            }
            
            msg += this + " accessible: " + declaringModule + " does not \"";
            
            if(isClassPublic && Modifier.isPublic(modifiers)) {
                msg += "exports";
            } else {
                msg += "opens";
            }
            
            msg += " " + pn + "\" to " + callerModule;
            
            InaccessibleObjectException e = new InaccessibleObjectException(msg);
            if(printStackTraceWhenAccessFails()) {
                e.printStackTrace(System.err);
            }
            
            throw e;
        }
        
        return false;
    }
    
    /**
     * Returns true if a stack trace should be printed when access fails.
     */
    private static boolean printStackTraceWhenAccessFails() {
        if(!printStackPropertiesSet && VM.initLevel() >= 1) {
            String s = GetPropertyAction.privilegedGetProperty("sun.reflect.debugModuleAccessChecks");
            if(s != null) {
                printStackWhenAccessFails = !s.equalsIgnoreCase("false");
            }
            printStackPropertiesSet = true;
        }
        return printStackWhenAccessFails;
    }
    
    private void logIfOpenedForIllegalAccess(Class<?> caller, Class<?> declaringClass) {
        Module callerModule = caller.getModule();
        Module targetModule = declaringClass.getModule();
        // callerModule is null during early startup
        if(callerModule != null && !callerModule.isNamed() && targetModule.isNamed()) {
            IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
            if(logger != null) {
                logger.logIfOpenedForIllegalAccess(caller, declaringClass, this::toShortString);
            }
        }
    }
    
    private void logIfExportedForIllegalAccess(Class<?> caller, Class<?> declaringClass) {
        Module callerModule = caller.getModule();
        Module targetModule = declaringClass.getModule();
    
        // callerModule is null during early startup
        if(callerModule != null && !callerModule.isNamed() && targetModule.isNamed()) {
            IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
            if(logger != null) {
                logger.logIfExportedForIllegalAccess(caller, declaringClass, this::toShortString);
            }
        }
    }
    
    /**
     * Returns a short descriptive string to describe this object in log messages.
     */
    String toShortString() {
        return toString();
    }
    
    /**
     * Returns the root AccessibleObject; or null if this object is the root.
     *
     * All subclasses override this method.
     */
    AccessibleObject getRoot() {
        throw new InternalError();
    }
    
    // 判断queryClass类是否与ofClass类相同，或为ofClass类的子类
    private boolean isSubclassOf(Class<?> queryClass, Class<?> ofClass) {
        while(queryClass != null) {
            if(queryClass == ofClass) {
                return true;
            }
            
            queryClass = queryClass.getSuperclass();
        }
        
        return false;
    }
    
}