Question

field.setAccessible(false)对非私人字段有什么影响？

我预计会拒绝访问此会员，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();

}

并创建了一个演示：

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

Answer 1

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

值false表示反射对象应强制执行Java语言访问检查。

因此，设置false值并不意味着该字段将无法访问。它只是意味着将强制执行正常的Java访问规则。

因此，public成员将在正常情况下被访问。对于protected成员也是如此（它们可以在同一个包中访问，而在其他包中可以访问）。

field.setAccessible（false）对非私有字段的影响

1 个答案: