解决JNA加载DLL后无法删除的问题：理解NativeLibrary的缓存机制

import java.io.File;
import java.nio.file.Files;
import java.nio.file.Paths;

import com.sun.jna.Library;
import com.sun.jna.Native;
import com.sun.jna.NativeLibrary;

class Filter {

    private static ExtDLLTool DLLUtil;
    final private static String dllPath = "./ExternalDownloader_64.dll";

    static {
        // 第一次加载DLL，JNA会根据dllPath和ExtDLLTool.class的ClassLoader等参数进行缓存
        DLLUtil = (ExtDLLTool) Native.loadLibrary(dllPath, ExtDLLTool.class);
    }

    public static void main(String[] args) throws Exception{

        if (DLLUtil != null) {
            DLLUtil = null; // 释放对DLLUtil的引用
            // 尝试获取NativeLibrary实例进行dispose
            NativeLibrary lib = NativeLibrary.getInstance(dllPath); // 问题所在：可能获取到的是新的实例
            lib.dispose(); // 仅释放了新实例，旧实例可能仍被持有
            Thread.sleep(3000); // 尝试等待，但无效
        }

        File dllFile = new File(dllPath);
        if(dllFile.exists()){
            Files.delete(Paths.get(dllPath)); // 抛出AccessDeniedException
            if(dllFile.exists()){
                System.out.println("Unable to delete dll file, since it hold by jvm");
            }
        }
    }

    private interface ExtDLLTool extends Library {
        String validateNomination(String dloadProps);
    }
}

import java.io.File;
import java.nio.file.Files;
import java.nio.file.Paths;

import com.sun.jna.Library;
import com.sun.jna.Native;
import com.sun.jna.NativeLibrary;

class Filter {

    private static ExtDLLTool DLLUtil;
    final private static String dllPath = "./ExternalDownloader_64.dll";

    static {
        // 首次加载DLL，JNA会根据dllPath和ExtDLLTool.class的ClassLoader等参数进行缓存
        DLLUtil = (ExtDLLTool) Native.loadLibrary(dllPath, ExtDLLTool.class);
    }

    public static void main(String[] args) throws Exception{

        if (DLLUtil != null) {
            DLLUtil = null; // 释放对DLLUtil的引用，允许GC回收
            // 关键修正：在获取NativeLibrary实例时，传入正确的ClassLoader
            // 这样才能确保获取到的是最初加载的那个NativeLibrary实例
            NativeLibrary lib = NativeLibrary.getInstance(dllPath, ExtDLLTool.class.getClassLoader());
            lib.dispose(); // 现在，这个dispose()会正确释放原始的DLL实例
            Thread.sleep(3000); // 给予操作系统足够时间释放文件句柄
        }

        File dllFile = new File(dllPath);
        if(dllFile.exists()){
            try {
                Files.delete(Paths.get(dllPath)); // 尝试删除DLL文件
                System.out.println("DLL file deleted successfully.");
            } catch (java.nio.file.AccessDeniedException e) {
                System.err.println("Failed to delete DLL file: Access Denied. It might still be held by JVM. " + e.getMessage());
            } catch (Exception e) {
                System.err.println("An error occurred during DLL file deletion: " + e.getMessage());
            }
        } else {
            System.out.println("DLL file does not exist or was already deleted.");
        }
    }

    private interface ExtDLLTool extends Library {
        String validateNomination(String dloadProps);
    }
}