[英]Change static final field in java 12+
This question is strongly related to Change private static final field using Java reflection .这个问题与Change private static final field using Java reflection密切相关。 There, it was asked, how to change a
private static final
variable.在那里,有人询问如何更改
private static final
变量。
However, the answers on that question do not work in Java 12+ as you cannot access private variables of java.lang.reflect.Field
using Reflection.但是,该问题的答案在 Java 12+ 中不起作用,因为您无法使用反射访问
java.lang.reflect.Field
的私有变量。
When you try to do it despite that, you will end up with a stack trace like:尽管如此,当您尝试这样做时,您最终会得到如下堆栈跟踪:
Exception java.lang.NoSuchFieldException: modifiers
at Class.getDeclaredField (Class.java:2412)
at <your call of Field.class.getDeclaredField("modifiers").setAccessible(true)>
Is there any way to change such a constant in those versions?有没有办法在这些版本中改变这样的常数?
I could imagine being possible utilizing JNI/JNA.我可以想象使用 JNI/JNA 是可能的。
You can use Unsafe
.您可以使用
Unsafe
。
public class Example
{
// javac will inline static final Strings, so let's say it's Object
private static final Object changeThis = "xxx";
public static void main(String... args) throws Exception
{
final Field unsafeField = Unsafe.class.getDeclaredField("theUnsafe");
unsafeField.setAccessible(true);
final Unsafe unsafe = (Unsafe) unsafeField.get(null);
System.out.println("before = " + changeThis);
final Field ourField = Example.class.getDeclaredField("changeThis");
final Object staticFieldBase = unsafe.staticFieldBase(ourField);
final long staticFieldOffset = unsafe.staticFieldOffset(ourField);
unsafe.putObject(staticFieldBase, staticFieldOffset, "it works");
System.out.println("after = " + changeThis);
}
}
Result:结果:
before = xxx
after = it works
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