Windows JNI 加载并执行 dll 中的 c++ 代码错误 Z93F725A07423FE1C889F448B33DsfiedLinkError:648B33DsfiedLinkError:6

Question

Answer/Solution: To be clear Jorn Vernee's answer is correct in that when i created my.h file originally i didnt have the package information in the.java class but when my code was executed it did have the package information. The method names in the.h file will end up including the package information in the name.

I've got some C++ code that i use to take a screen shot. I've been attempting to call it from Java using both JNA and JNI and having no luck with either. My ultimate goal is to get the captureScreen method working. I created a getNumber method just as a simple test with no parameters passed in but even it wouldnt work.

Update My application is running as a 64 bit application and my dll is 64 bit. Not sure if that affects the parameters passed in or out.

My current implementation

Java

public class JNIScreenShotTest { 
   static {
  String oldLibraryPath = System.getProperty("java.library.path");
  try{
  //This doesnt work for me it fails on the loadLibrary call and I get an UnsatisfiedLinkError
  //System.setProperty("java.library.path", "C:\\workspace\\com.tdkc.udop\dlls");
  //System.loadLibrary("JNIScreenShot"); 
                               
  //This Manages to load the library without error                         
  System.load("C:\\workspace\\com.tdkc.udop\\dlls\\JNIScreenShot.dll")
  }finally}
      System.setProperty("java.library.path", oldLibraryPath );
  }
 }

  private native void captureScreen(String filePath, int x, int y, int width, int height);

  private native int getNumber();

}

I used javac -h to create my header file from the above class

.h file

    /* DO NOT EDIT THIS FILE - it is machine generated */
    #include <jni.h>
    /* Header for class JNIScreenShot */

    #include "DXGICapture.h"

    #include <stdio.h>
    #include <tchar.h>
    #include <shlobj.h>
    #include <atlconv.h>
    #include <string>

    using namespace std;

    #ifndef _Included_JNIScreenShot
    #define _Included_JNIScreenShot
    #ifdef __cplusplus
    extern "C" {
    #endif
        /*
         * Class:     JNIScreenShot
         * Method:    captureScreen
         * Signature: (Ljava/lang/String;IIII)V
         */
        JNIEXPORT void JNICALL Java_JNIScreenShot_captureScreen
        (JNIEnv*, jobject, jstring, jint, jint, jint, jint);

        /*
     * Class:     JNIScreenShotTest
     * Method:    getNumber
     * Signature: ()I
     */
        JNIEXPORT jint JNICALL Java_JNIScreenShotTest_getNumber
        (JNIEnv*, jobject);

    #ifdef __cplusplus
    }
    #endif
    #endif

C++ file

    // ScreenCapture.cpp : Defines the exported functions for the DLL.
//


#include "JNIScreenShot.h"
#include <iostream>


JNIEXPORT void JNICALL Java_JNIScreenShot_captureScreen
(JNIEnv *env, jobject clz, jstring filePath, jint x, jint y, jint width, jint height) {
    HRESULT hr = S_OK;
    CDXGICapture dxgiCapture;
    jboolean isCopy;
    const char* pszOutputFileName = (env)->GetStringUTFChars(filePath, &isCopy);

    hr = dxgiCapture.Initialize();
    tagScreenCaptureFilterConfig config;

    // set default config
    RtlZeroMemory(&config, sizeof(config));
    config.ShowCursor = 1;
    config.SizeMode = tagFrameSizeMode_AutoSize;

    hr = dxgiCapture.SetConfig(config);
    hr = dxgiCapture.CaptureToFile((LPCTSTR)CA2WEX<>(pszOutputFileName), x, y, width, height);
    if (FAILED(hr))
    {
        printf("Error[0x%08X]: CDXGICapture::CaptureToFile failed.\n", hr);
    }
}

/*
 * Class:     JNIScreenShotTest
 * Method:    getNumber
 * Signature: ()I
 */
JNIEXPORT jint JNICALL Java_JNIScreenShotTest_getNumber
(JNIEnv *env, jobject clz) {
    return 2;
}

My calls from java are as follows

File f = new File("Some file");
int x = some value;
int y = some value;
int width = some value;
int height = some value;

JNIScreenShot jniScreenShot = new JNIScreenShot();
jniScreenShot.(f.getAbsolutePath(), x,y,width,height)

This generates an error java.lang.UnsatisfiedLinkError: com.tdkc.udop.screencapture.jniScreenShot.captureScreen(Ljava/lang/string;IIII)V

At first i thought something in my captureScreen was failing or maybe it was a difference in data types i was passing in. So i created the getNumber method as a test

I get a similar error when calling getNumber() java.lang.UnsatisfiedLinkError: com.tdkc.udop.screencapture.jniScreenShot.getNumber()I

Both of the error messages reference the Signature in the.h file so i know its finding the dll and attempting to call the right method.

Spent some time looking at the UnsatisfiedLinkError but most googled results show that when the library is loading which i've seen plenty of including when trying to use System.loadLibrary() instead of System.load()

It would appear that its finding the methods ok as the error contains the signature defined in my.h file for each method.

At this point i've tried following what seems like a million guides and tutorials on JNI and its been 2 days and i'm lost any help is greatly appreciated.

Answer 1

Judging from your error message:

java.lang.UnsatisfiedLinkError: com.tdkc.udop.screencapture.jniScreenShot.getNumber()I

It seems that your class is in a package. But, the name of your native function doesn't match this:

Java_JNIScreenShotTest_getNumber

The package name should be encoded in the name of the native function as well. From that error message, it looks like the name of your native function should be:

Java_com_tdkc_udop_screencapture_jniScreenShot_getNumber

---

Using -Xlog:library*=trace ( since JDK 15 ) you could see the exact name the VM is using for the lookup. For instance:

[0.211s][info][library] Loaded library C:\Program Files\Java\jdk-15\bin\nio.dll, handle 0x00007ffacf0f0000
...
[0.212s][info][library] Found Java_sun_nio_fs_WindowsNativeDispatcher_initIDs in library with handle 0x00007ffacf0f0000