如何使用JNA处理Java内部内存访问

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英文:

How can i handle a Java internal memory access using JNA

问题

以下是翻译好的内容：

C代码部分：

  1. extern int APIENTRY LSGetDocData(
  2.     short          hConnect,
  3.     HWND           hWnd,
  4.     unsigned long  *NrDoc,
  5.     LPSTR          FilenameFront,
  6.     LPSTR          FilenameBack,
  7.     LPSTR          Reserved1,      // not used must be NULL         
  8.     LPSTR          Reserved2,      // not used must be NULL
  9.     LPHANDLE       *FrontImage,
  10.     LPHANDLE       *BackImage,
  11.     LPHANDLE       *Reserved3,     // not used must be NULL
  12.     LPHANDLE       *Reserved4,     // not used must be NULL
  13.     LPSTR          CodelineSW,
  14.     LPSTR          CodelineHW,
  15.     LPSTR          BarCode,
  16.     LPSTR          CodelinesOptical,
  17.     short          *DocToRead,
  18.     long           *NrPrinted,
  19.     LPVOID         Reserved5,      // not used must be NULL
  20.     LPVOID         Reserved6);

Java方法部分：

  1. public int LSGetDocData(
  2.     short hConnect, 
  3.     int hWnd, 
  4.     long[] NrDoc, 
  5.     String FilenameFront, 
  6.     String FilenameBack, 
  7.     String Reserved1, 
  8.     String Reserved2, 
  9.     int[] FrontImage, 
  10.     int[] RearImage,
  11.     int[] FrontImage2, 
  12.     int[] RearImage2, 
  13.     StringBuffer CodelineSW, 
  14.     StringBuffer CodelineHW, 
  15.     StringBuffer Barcode, 
  16.     StringBuffer CodelinesOptical, 
  17.     short[] DocToRead, 
  18.     long[] NrPrinted,
  19.     int Reserved5,
  20.     int Reserved6);
  22. public int lSGetDocData(long[] nrDoc, int[] frontImage, int[] rearImage, StringBuffer micrHW, StringBuffer barcode, StringBuffer micrSW, StringBuffer codeLineOptical) {    
  23.         return LsApi.call.LSGetDocData(hConnect[0], hWnd, 
  24.             nrDoc, "imageF", "ImageR", null, null, 
  25.             frontImage, rearImage, null, null,
  26.             micrSW, micrHW, barcode, codeLineOptical,
  27.             new short[0], new long[0], 0, 0);
  28. }

错误部分：

  1. Exception in thread "StartCapture" java.lang.Error: Invalid memory access
  2. 	at com.sun.jna.Native.invokeInt(Native Method)
  3. 	at com.sun.jna.Function.invoke(Function.java:426)
  4. 	at com.sun.jna.Function.invoke(Function.java:361)
  5. 	at com.sun.jna.Library$Handler.invoke(Library.java:265)
  6. 	at com.sun.proxy.$Proxy2.LSGetDocData(Unknown Source)

这段代码在使用 IBM Java 1.6 32 位版本时完美运行，但我们想要使用 Oracle Java 1.8 32 位版本，却出现了这个错误。

英文:

the c code is

  1. extern int APIENTRY LSGetDocData(
  2.     short          hConnect,
  3.     HWND           hWnd,
  4.     unsigned long  *NrDoc,
  5.     LPSTR          FilenameFront,
  6.     LPSTR          FilenameBack,
  7.     LPSTR          Reserved1,      // not used must be NULL         
  8.     LPSTR          Reserved2,      // not used must be NULL
  9.     LPHANDLE       *FrontImage,
  10.     LPHANDLE       *BackImage,
  11.     LPHANDLE       *Reserved3,     // not used must be NULL
  12.     LPHANDLE       *Reserved4,     // not used must be NULL
  13.     LPSTR          CodelineSW,
  14.     LPSTR          CodelineHW,
  15.     LPSTR          BarCode,
  16.     LPSTR          CodelinesOptical,
  17.     short          *DocToRead,
  18.     long           *NrPrinted,
  19.     LPVOID         Reserved5,      // not used must be NULL
  20.     LPVOID         Reserved6);

and my Java method is

  1. public int LSGetDocData(
  2.     short hConnect, 
  3.     int hWnd, 
  4.     long[] NrDoc, 
  5.     String FilenameFront, 
  6.     String FilenameBack, 
  7.     String Reserved1, 
  8.     String Reserved2, 
  9.     int[] FrontImage, 
  10.     int[] RearImage,
  11.     int[] FrontImage2, 
  12.     int[] RearImage2, 
  13.     StringBuffer CodelineSW, 
  14.     StringBuffer CodelineHW, 
  15.     StringBuffer Barcode, 
  16.     StringBuffer CodelinesOptical, 
  17.     short[] DocToRead, 
  18.     long[] NrPrinted,
  19.     int Reserved5,
  20.     int Reserved6);
  22. public int lSGetDocData(long[] nrDoc, int[] frontImage, int[] rearImage, StringBuffer micrHW, StringBuffer barcode, StringBuffer micrSW, StringBuffer codeLineOptical) {    
  23.         return LsApi.call.LSGetDocData(hConnect[0], hWnd, 
  24.             nrDoc, "imageF", "ImageR", null, null, 
  25.             frontImage, rearImage, null, null,
  26.             micrSW, micrHW, barcode, codeLineOptical,
  27.             new short[0], new long[0], 0, 0);
  28. }

the error is

  1. Exception in thread "StartCapture" java.lang.Error: Invalid memory access
  2. 	at com.sun.jna.Native.invokeInt(Native Method)
  3. 	at com.sun.jna.Function.invoke(Function.java:426)
  4. 	at com.sun.jna.Function.invoke(Function.java:361)
  5. 	at com.sun.jna.Library$Handler.invoke(Library.java:265)
  6. 	at com.sun.proxy.$Proxy2.LSGetDocData(Unknown Source)

This code works perfectly using IBM Java 1.6 32 bits... but we want to use Oracle Java 1.8 32 bits and we get this error.

答案1

得分: 1

您的类型映射不正确，IBM JDK 可能以与 Oracle 不同的方式处理某些对象（数组、StringBuffer）的内存指针，使这些不正确的映射似乎能够工作。

一些具体的注意事项：

  • 在Java中，long 是64位的，但在C中，long 可能是32位或64位。您提到您正在使用32位的JRE，但没有提到操作系统的位数。NativeLong 可以处理这种差异。
  • HWND 在JNA中被映射为扩展HANDLE，而HANDLE的大小与指针相同。在32位系统上，int 可以工作，但为了可移植性，应该使用HWND。
  • 类似地，LPHANDLE 被映射为HANDLEByReference，这是指向指针大小值的指针。
  • JNA处理String 到C字符串的映射，但我不确定关于StringBuffer。这可能是问题的根源。
  • JNA不太好地处理大小为0的数组。我怀疑new short[0] 或 new long[0] 可能会引起问题，因为您定义了一个指向空分配的指针。原生代码是否尝试在这里写入内容？

总之，在32位（或任何位数的Windows）上，long * 映射是错误的，或者在64位上，HWND 和 LPHANDLE 的映射可能是错误的（取决于指针大小）。StringBuffer 的映射可能有问题。0大小的数组不能被写入（所以也许在这里使用 null 是合适的）。

英文:

Your type mappings are not correct, and it is possible that the IBM JDK handled pointers to memory for some objects (arrays, StringBuffers) in a different manner than Oracle, permitting these incorrect mappings to appear to work.

Some specific notes:

  • long in Java is 64 bits, but long can be 32-bits or 64-bits in C. You state you're using a 32-bit JRE but not what the operating system bitness is. NativeLong can handle this difference.
  • HWND is mapped in JNA, extending HANDLE, which is pointer-sized. On 32-bit systems, int works, but you should use HWND for portability.
  • similarly, LPHANDLE is mapped to HANDLEByReference, a pointer to a pointer-sized value.
  • JNA Handles the mapping of String to C Strings, but I'm not sure about StringBuffer. This could be a source of the problem.
  • JNA does not handle 0-sized arrays well. I suspect the new short[0] or new long[0] may be causing problems, as you're defining a pointer to an empty allocation. Does the native code attempt to write something here?

In summary, on 32-bit (or any bitness of Windows) the long * mapping is wrong, or on 64-bit the HWND and LPHANDLE mappings are probably wrong (depending on pointer size). The StringBuffer mappings might be suspect. And 0-size arrays cannot be written to (so perhaps null is appropriate there).

huangapple
  • 本文由 发表于 2020年8月29日 04:18:42
  • 转载请务必保留本文链接：https://go.coder-hub.com/63640391.html
  • java
  • java-8
  • jna
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