How to load AttachProvider (attach.dll) dynamically

Question

I'm using com.sun.tools.attach from jdk's tools.jar and it need an specified java.library.path env pointing to attach.dll at startup to properly instatiate provider such as WindowsAttachProvider. For some reasons I need to dynamic loading one of bundled attach.dll. I'm try to use some like this:

public static void main(String[] args) throws Exception {
    Path bin = Paths.get(System.getProperty("user.dir"),"bin").toAbsolutePath();
    switch (System.getProperty("os.arch")) {
        case "amd64":
            bin = bin.resolve("win64");
            break;
        default:
            bin = bin.resolve("win32");
    }
    // Dynamic setting of java.library.path only seems not sufficient
    System.setProperty("java.library.path", System.getProperty("java.library.path") + File.pathSeparator + bin.toString());
    // So I try to manual loading attach.dll. This is not sufficient too.
    System.load(bin.resolve("attach.dll").toString());
    // I'm using com.sun.tools.attach in my app
    new myApp();
}

If I run this out of jdk (in normall jre) it's report to me:

java.util.ServiceConfigurationError: com.sun.tools.attach.spi.AttachProvider:
Provider sun.tools.attach.WindowsAttachProvider could not be instantiated:
java.lang.UnsatisfiedLinkError: no attach in java.library.path
Exception in thread "main" com.sun.tools.attach.AttachNotSupportedException:
no providers installed
    at com.sun.tools.attach.VirtualMachine.attach(...

How to install attach provider without specifying -Djava.library.path to point attach.dll at startup?

Answer 1

The API you are using is using loadLibrary(String). It seems you cannot successfully pre-empt (cause it to succeed) this by invoking the more explicit load(String) first.

So you must to specify the path in java.library.path.

That System property is set once early in JVM lifecycle and is not modifiable by standard means.

So the conventional solution will be to pass an appropriate java.library.path when you launch the JVM.

Alternatively, you could look into the hacks to change this property after JVM startup using reflection. I have not tried any of these.

For example, see here:

System.setProperty( "java.library.path", "/path/to/libs" );

Field fieldSysPath = ClassLoader.class.getDeclaredField( "sys_paths" );
fieldSysPath.setAccessible( true );
fieldSysPath.set( null, null );

BTW, I would recommend pre-pending your custom path to the existing path, rather than replacing it.