How do I get the instance of sun.misc.Unsafe?

Question

How do I get the instance of the unsafe class?

I always get the security exception. I listed the code of the OpenJDK 6 implementation. I would like to mess around with

Answer 1

If you use Spring, you can use its class called UnsafeUtils

at org.springframework.objenesis.instantiator.util.UnsafeUtils

public final class UnsafeUtils {
    private static final Unsafe unsafe;

    private UnsafeUtils() {
    }

    public static Unsafe getUnsafe() {
        return unsafe;
    }

    static {
        Field f;
        try {
            f = Unsafe.class.getDeclaredField("theUnsafe");
        } catch (NoSuchFieldException var3) {
            throw new ObjenesisException(var3);
        }

        f.setAccessible(true);

        try {
            unsafe = (Unsafe)f.get((Object)null);
        } catch (IllegalAccessException var2) {
            throw new ObjenesisException(var2);
        }
    }
}

Answer 2

There is another way of doing it you can find in:

http://mishadoff.com/blog/java-magic-part-4-sun-dot-misc-dot-unsafe/

in unsafe source code, you can find:

@CallerSensitive
public static Unsafe getUnsafe() {
    Class<?> caller = Reflection.getCallerClass();
    if (!VM.isSystemDomainLoader(caller.getClassLoader()))
        throw new SecurityException("Unsafe");
    return theUnsafe;
}

you can add your class or jar to bootstrap classpath by using Xbootclasspath, as below:

java -Xbootclasspath:/usr/jdk1.7.0/jre/lib/rt.jar:. com.mishadoff.magic.UnsafeClient

Answer 3

From baeldung.com, we can obtain the instance using reflection:

   Field f =Unsafe.class.getDeclaredField("theUnsafe");
   f.setAccessible(true);
   unsafe = (Unsafe) f.get(null);

Edit

The following is quoted from the description of the project where this code belongs to.

"The implementation of all these examples and code snippets can be found over on GitHub – this is a Maven project, so it should be easy to import and run as it is."