java - eclipse + JNI : Can find library but not method

Question

我正在尝试为库编写 C++ 绑定(bind)，因此为了向您学习，我使用了以下简单的 Java 和 C++ 代码。我正在使用 SWIG。

java代码:

public class App {

    static{
        System.loadLibrary("demo");
    }

    public static void main(String[] args) {

        // TODO Auto-generated method stub
        System.out.println(System.getProperty("java.library.path"));
        printHello("Lars");
    }

    native static void printHello(String name);
}

我的 C++ 代码:

#include <iostream>
#include <string>
#include "demo.hpp"

void printHello(std::string name){
    std::cout << "Hello: "<< name << "\n";
}

我的标题:

void printHello(std::string);

SWIG 的 .i 文件:

%module demo
%include "std_string.i"
%{
  #include <iostream>
  #include <string>
  #include "demo.hpp"
%}
  extern void printHello(std::string);

我运行了 swig -c++ -java demo.i 没有问题。编译:

g++ -c -fPIC demo_wrap.cxx -I/usr/lib64/jvm/java-1.7.0-openjdk-1.7.0/include/ -I/usr/lib64/jvm/java-1.7.0-openjdk-1.7.0/include/linux

并制作了一个共享库并将其移动到/usr/lib

g++ -shared demo_wrap.o -o libdemo.so

但是后来我尝试使用 eclipse 运行我的 java 程序，但我得到了这个错误:

Exception in thread "main" java.lang.UnsatisfiedLinkError: App.printHello(Ljava/lang/String;)V
    at App.printHello(Native Method)
    at App.main(App.java:11)

据我所知，eclipse/java 知道我的库存在，但它无法在库中找到我的函数/方法。我做错了什么吗？或者我遗漏了什么？

提前致谢

编辑:如果 demoJNI.java 的内容可能有帮助

public class demoJNI {
  public final static native void printHello(String jarg1);
}

Demo_wrap.cxx

/* ----------------------------------------------------------------------------
 * This file was automatically generated by SWIG (http://www.swig.org).
 * Version 2.0.10
 * 
 * This file is not intended to be easily readable and contains a number of 
 * coding conventions designed to improve portability and efficiency. Do not make
 * changes to this file unless you know what you are doing--modify the SWIG 
 * interface file instead. 
 * ----------------------------------------------------------------------------- */

#define SWIGJAVA


#ifdef __cplusplus
/* SwigValueWrapper is described in swig.swg */
template<typename T> class SwigValueWrapper {
  struct SwigMovePointer {
    T *ptr;
    SwigMovePointer(T *p) : ptr(p) { }
    ~SwigMovePointer() { delete ptr; }
    SwigMovePointer& operator=(SwigMovePointer& rhs) { T* oldptr = ptr; ptr = 0; delete oldptr; ptr = rhs.ptr; rhs.ptr = 0; return *this; }
  } pointer;
  SwigValueWrapper& operator=(const SwigValueWrapper<T>& rhs);
  SwigValueWrapper(const SwigValueWrapper<T>& rhs);
public:
  SwigValueWrapper() : pointer(0) { }
  SwigValueWrapper& operator=(const T& t) { SwigMovePointer tmp(new T(t)); pointer = tmp; return *this; }
  operator T&() const { return *pointer.ptr; }
  T *operator&() { return pointer.ptr; }
};

template <typename T> T SwigValueInit() {
  return T();
}
#endif

/* -----------------------------------------------------------------------------
 *  This section contains generic SWIG labels for method/variable
 *  declarations/attributes, and other compiler dependent labels.
 * ----------------------------------------------------------------------------- */

/* template workaround for compilers that cannot correctly implement the C++ standard */
#ifndef SWIGTEMPLATEDISAMBIGUATOR
# if defined(__SUNPRO_CC) && (__SUNPRO_CC <= 0x560)
#  define SWIGTEMPLATEDISAMBIGUATOR template
# elif defined(__HP_aCC)
/* Needed even with `aCC -AA' when `aCC -V' reports HP ANSI C++ B3910B A.03.55 */
/* If we find a maximum version that requires this, the test would be __HP_aCC <= 35500 for A.03.55 */
#  define SWIGTEMPLATEDISAMBIGUATOR template
# else
#  define SWIGTEMPLATEDISAMBIGUATOR
# endif
#endif

/* inline attribute */
#ifndef SWIGINLINE
# if defined(__cplusplus) || (defined(__GNUC__) && !defined(__STRICT_ANSI__))
#   define SWIGINLINE inline
# else
#   define SWIGINLINE
# endif
#endif

/* attribute recognised by some compilers to avoid 'unused' warnings */
#ifndef SWIGUNUSED
# if defined(__GNUC__)
#   if !(defined(__cplusplus)) || (__GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
#     define SWIGUNUSED __attribute__ ((__unused__)) 
#   else
#     define SWIGUNUSED
#   endif
# elif defined(__ICC)
#   define SWIGUNUSED __attribute__ ((__unused__)) 
# else
#   define SWIGUNUSED 
# endif
#endif

#ifndef SWIG_MSC_UNSUPPRESS_4505
# if defined(_MSC_VER)
#   pragma warning(disable : 4505) /* unreferenced local function has been removed */
# endif 
#endif

#ifndef SWIGUNUSEDPARM
# ifdef __cplusplus
#   define SWIGUNUSEDPARM(p)
# else
#   define SWIGUNUSEDPARM(p) p SWIGUNUSED 
# endif
#endif

/* internal SWIG method */
#ifndef SWIGINTERN
# define SWIGINTERN static SWIGUNUSED
#endif

/* internal inline SWIG method */
#ifndef SWIGINTERNINLINE
# define SWIGINTERNINLINE SWIGINTERN SWIGINLINE
#endif

/* exporting methods */
#if (__GNUC__ >= 4) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
#  ifndef GCC_HASCLASSVISIBILITY
#    define GCC_HASCLASSVISIBILITY
#  endif
#endif

#ifndef SWIGEXPORT
# if defined(_WIN32) || defined(__WIN32__) || defined(__CYGWIN__)
#   if defined(STATIC_LINKED)
#     define SWIGEXPORT
#   else
#     define SWIGEXPORT __declspec(dllexport)
#   endif
# else
#   if defined(__GNUC__) && defined(GCC_HASCLASSVISIBILITY)
#     define SWIGEXPORT __attribute__ ((visibility("default")))
#   else
#     define SWIGEXPORT
#   endif
# endif
#endif

/* calling conventions for Windows */
#ifndef SWIGSTDCALL
# if defined(_WIN32) || defined(__WIN32__) || defined(__CYGWIN__)
#   define SWIGSTDCALL __stdcall
# else
#   define SWIGSTDCALL
# endif 
#endif

/* Deal with Microsoft's attempt at deprecating C standard runtime functions */
#if !defined(SWIG_NO_CRT_SECURE_NO_DEPRECATE) && defined(_MSC_VER) && !defined(_CRT_SECURE_NO_DEPRECATE)
# define _CRT_SECURE_NO_DEPRECATE
#endif

/* Deal with Microsoft's attempt at deprecating methods in the standard C++ library */
#if !defined(SWIG_NO_SCL_SECURE_NO_DEPRECATE) && defined(_MSC_VER) && !defined(_SCL_SECURE_NO_DEPRECATE)
# define _SCL_SECURE_NO_DEPRECATE
#endif



/* Fix for jlong on some versions of gcc on Windows */
#if defined(__GNUC__) && !defined(__INTEL_COMPILER)
  typedef long long __int64;
#endif

/* Fix for jlong on 64-bit x86 Solaris */
#if defined(__x86_64)
# ifdef _LP64
#   undef _LP64
# endif
#endif

#include <jni.h>
#include <stdlib.h>
#include <string.h>


/* Support for throwing Java exceptions */
typedef enum {
  SWIG_JavaOutOfMemoryError = 1, 
  SWIG_JavaIOException, 
  SWIG_JavaRuntimeException, 
  SWIG_JavaIndexOutOfBoundsException,
  SWIG_JavaArithmeticException,
  SWIG_JavaIllegalArgumentException,
  SWIG_JavaNullPointerException,
  SWIG_JavaDirectorPureVirtual,
  SWIG_JavaUnknownError
} SWIG_JavaExceptionCodes;

typedef struct {
  SWIG_JavaExceptionCodes code;
  const char *java_exception;
} SWIG_JavaExceptions_t;


static void SWIGUNUSED SWIG_JavaThrowException(JNIEnv *jenv, SWIG_JavaExceptionCodes code, const char *msg) {
  jclass excep;
  static const SWIG_JavaExceptions_t java_exceptions[] = {
    { SWIG_JavaOutOfMemoryError, "java/lang/OutOfMemoryError" },
    { SWIG_JavaIOException, "java/io/IOException" },
    { SWIG_JavaRuntimeException, "java/lang/RuntimeException" },
    { SWIG_JavaIndexOutOfBoundsException, "java/lang/IndexOutOfBoundsException" },
    { SWIG_JavaArithmeticException, "java/lang/ArithmeticException" },
    { SWIG_JavaIllegalArgumentException, "java/lang/IllegalArgumentException" },
    { SWIG_JavaNullPointerException, "java/lang/NullPointerException" },
    { SWIG_JavaDirectorPureVirtual, "java/lang/RuntimeException" },
    { SWIG_JavaUnknownError,  "java/lang/UnknownError" },
    { (SWIG_JavaExceptionCodes)0,  "java/lang/UnknownError" }
  };
  const SWIG_JavaExceptions_t *except_ptr = java_exceptions;

  while (except_ptr->code != code && except_ptr->code)
    except_ptr++;

  jenv->ExceptionClear();
  excep = jenv->FindClass(except_ptr->java_exception);
  if (excep)
    jenv->ThrowNew(excep, msg);
}


/* Contract support */

#define SWIG_contract_assert(nullreturn, expr, msg) if (!(expr)) {SWIG_JavaThrowException(jenv, SWIG_JavaIllegalArgumentException, msg); return nullreturn; } else


#include <string>


  #include <iostream>
  #include <string>
  #include "demo.hpp"


#ifdef __cplusplus
extern "C" {
#endif

SWIGEXPORT void JNICALL Java_demoJNI_printHello(JNIEnv *jenv, jclass jcls, jstring jarg1) {
  std::string arg1 ;

  (void)jenv;
  (void)jcls;
  if(!jarg1) {
    SWIG_JavaThrowException(jenv, SWIG_JavaNullPointerException, "null string");
    return ;
  } 
  const char *arg1_pstr = (const char *)jenv->GetStringUTFChars(jarg1, 0); 
  if (!arg1_pstr) return ;
  (&arg1)->assign(arg1_pstr);
  jenv->ReleaseStringUTFChars(jarg1, arg1_pstr); 
  printHello(arg1);
}


#ifdef __cplusplus
}
#endif

Answer 1

事实证明，我对 SWIG 正在做的事情有误解。也许，你也是。

SWIG 的目的是自动为 C/C++ 库构建包装器。它不是 javah 的替代品。通过 SWIG，您从 C 或 C++ 代码开始，然后接收自动生成的 C++ 和 Java 代码。这样，您就可以在您的项目中使用这些包装器 Java 类(在您的例子中为 demoJNI)。您没有在 Java 代码中声明 native 方法。您通过包装 Java 类和包装 C/C++ 代码(Demo_wrap.cxx 和 demoJNI.java)与您的 C++ 库通信。

SWIG 文档明确指出，它不是将 Java 代码连接到几个 native 函数的正确工具。它的设计目标是使用复杂的 API、Java、Python 和许多其他高级语言自动包装大型 C++ 项目。