field.setAccessible(false) 对非私有(private)字段有什么影响？
我预计该成员的访问会被拒绝，但事实并非如此!
我试图深入研究源代码，但在某些时候( Field#getFieldAccessor(Object) )我不知道发生了什么。
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
最佳答案
根据 AccessibleObject#setAccessible(boolean) 的文档方法:
A value of false indicates that the reflected object should enforce Java language access checks.
因此，设置 false 值并不意味着该字段不可访问。它只是意味着将强制执行正常的 Java 访问规则。
因此，public 成员将像正常情况一样被访问。对于protected成员也是如此(它们可以在同一个包中访问，并且可以在其他包中访问子类)。
关于java - field.setAccessible(false) 对非私有(private)字段的影响，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/18621604/