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field.setAccessible(false)对非私有领域有什么影响？

我预计对此成员的访问会被拒绝，但事实并非如此！

我试图挖掘源代码，但在某些时候（Field#getFieldAccessor(Object)）我忘记了正在发生的事情。

我为这种情况创建了一个特殊的类：

public class DemoObject {

    public Object publicMember = new Object();
    protected Object protectedMember = new Object();
    Object defaultMember = new Object();
    private Object privateMember = new Object();
    public final Object publicfinalMember = new Object();
    protected final Object protectedfinalMember = new Object();
    final Object defaultfinalMember = new Object();
    private final Object privatefinalMember = new Object();

}

并创建了一个Demo：

import java.lang.reflect.Field;

public class MyMain {

    public static void main(final String[] args) {

        DemoObject object = new DemoObject();

        System.out.println("'reflective' member access after field.setAccessible(false)");
        for (Field field : object.getClass().getDeclaredFields()) {
            field.setAccessible(false);
            try {
                System.out.println(field.getName() + ": " + field.get(object));
                // only throws exception for the privateMember and privatefinalMember
            } catch (Exception e) {
                e.printStackTrace();
            }

        }

        System.out.println("'reflective' member access after field.setAccessible(true)");
        for (Field field : object.getClass().getDeclaredFields()) {
            try {
                field.setAccessible(true);
                System.out.println(field.getName() + ": " + field.get(object));
                // throws no exception
            } catch (Exception e) {
                e.printStackTrace();
            }

        }

    }

}

输出：

'reflective' member access after field.setAccessible(false)
publicMember: java.lang.Object@e9bfee2
protectedMember: java.lang.Object@237aaeec
defaultMember: java.lang.Object@4b721a26
java.lang.IllegalAccessException: Class MyMain can not access a member of class DemoObject with modifiers "private"
    at sun.reflect.Reflection.ensureMemberAccess(Unknown Source)
    at java.lang.reflect.AccessibleObject.slowCheckMemberAccess(Unknown Source)
    at java.lang.reflect.AccessibleObject.checkAccess(Unknown Source)
    at java.lang.reflect.Field.doSecurityCheck(Unknown Source)
    at java.lang.reflect.Field.getFieldAccessor(Unknown Source)
    at java.lang.reflect.Field.get(Unknown Source)
    at MyMain.main(MyMain.java:13)
publicfinalMember: java.lang.Object@7c30cd64
protectedfinalMember: java.lang.Object@67fc9fee
defaultfinalMember: java.lang.Object@7a67f797
java.lang.IllegalAccessException: Class MyMain can not access a member of class DemoObject with modifiers "private final"
    at sun.reflect.Reflection.ensureMemberAccess(Unknown Source)
    at java.lang.reflect.AccessibleObject.slowCheckMemberAccess(Unknown Source)
    at java.lang.reflect.AccessibleObject.checkAccess(Unknown Source)
    at java.lang.reflect.Field.doSecurityCheck(Unknown Source)
    at java.lang.reflect.Field.getFieldAccessor(Unknown Source)
    at java.lang.reflect.Field.get(Unknown Source)
    at MyMain.main(MyMain.java:13)
'reflective' member access after field.setAccessible(true)
publicMember: java.lang.Object@e9bfee2
protectedMember: java.lang.Object@237aaeec
defaultMember: java.lang.Object@4b721a26
privateMember: java.lang.Object@424c2849
publicfinalMember: java.lang.Object@7c30cd64
protectedfinalMember: java.lang.Object@67fc9fee
defaultfinalMember: java.lang.Object@7a67f797
privatefinalMember: java.lang.Object@15e8f2a0
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1 回答 1

7

根据AccessibleObject#setAccessible(boolean)方法的文档：

值 false 表示反射对象应该强制执行 Java 语言访问检查。

因此，设置一个false值并不意味着该字段将不可访问。这只是意味着将强制执行正常的 Java 访问规则。

因此，public成员将按正常方式访问。成员也一样protected（它们可以在同一个包中访问，并且可以在其他包中访问）。

于 2013-09-04T18:56:18.510 回答