JavaJNI跨平台构建

我正在使用JNI为C库（.so用于linux，.dll用于windows）编写一个包装器库。我使用g++（GCC）4.8.2 64位在linux Fedora 20 64位上使用Oracle Java 1.7.0_45 64位构建了我的库，我还使用Oracle Java 1.7.0_45 32位（用于windows）和MinGW 32位（i686-w64-mingw32-g++（GCC）4.8.2）为windows构建了这个库（我在linux上构建了windows库）

Linux库工作得很好，但当我在带有WindowsXPSP3的机器上使用WindowsLibrary时，当我尝试打印字节数组时，java代码中会出现NullPointerException

以下是用于构建库的命令：

g++ -Wall -I"$(JAVA_HOME)/include" -I"$(JAVA_HOME)/include/linux" -fPIC -shared com_viking_micex_Micex.cpp -o libmicex.so
i686-w64-mingw32-g++ -Wall -Wl,--add-stdcall-alias -D_WIN32 -I"/media/OS/Program Files/Java/jdk1.7.0_45/include/" -I"/media/OS/Program Files/Java/jdk1.7.0_45/include/win32/" -shared com_viking_micex_Micex.cpp -o micex.dll

这是我的C++代码的一部分：

#define com_viking_micex_Micex_MTE_OK 0L
#ifdef _WIN32
    #include <windows.h>
    typedef HMODULE shared_lib;
    typedef __int32 __int32_t;
#else
    #include <dlfcn.h>
    typedef void* shared_lib;
#endif

typedef struct TMTEMsg_
{
    __int32_t DataLen;
    char Data[1];
} TMTEMsg;

shared_lib load_lib(const char* lib_name) {
# ifdef _WIN32
    return LoadLibraryA(lib_name);
# else //_WIN32
    return dlopen(lib_name, RTLD_LAZY);
# endif //_WIN32
}

void* load_func(shared_lib lib, const char* func_name) {
# ifdef _WIN32
    return (void *)GetProcAddress(lib, func_name);
# else //_WIN32
    return dlsym(lib, func_name);
# endif //_WIN32
}

JNIEXPORT jbyteArray JNICALL Java_com_viking_micex_Micex_structure
  (JNIEnv * env, jobject o, jobject pointer, jint connId, jint version) {
# ifdef _WIN32
    shared_lib mtesrl = (HMODULE) env->GetDirectBufferAddress(pointer);
#else
    shared_lib mtesrl = env->GetDirectBufferAddress(pointer);
#endif

    typedef int (*importFunction)(int, int, TMTEMsg **);
    importFunction Structure = (importFunction) load_func(mtesrl, "MTEStructureEx");

    TMTEMsg *Msg;

    int res = Structure(connId, version, &Msg);
    char tmp[4];
    tmp[3] = (res & 0xff);
    tmp[2] = ((res & 0xff00) >> 8);
    tmp[1] = ((res & 0xff0000) >> 16);
    tmp[0] = ((res & 0xff000000) >> 24);

    if (res != com_viking_micex_Micex_MTE_OK)
    {
        jbyteArray arr = env->NewByteArray(4);
        env->SetByteArrayRegion(arr, 0, 4, (jbyte *) ((char*) (tmp)));
        return arr;
    }
    else
    {
        jbyteArray arr = env->NewByteArray(Msg->DataLen + 4);
        env->SetByteArrayRegion(arr, 0, 4, (jbyte *) ((char*) (tmp)));
        env->SetByteArrayRegion(arr, 4, Msg->DataLen, (jbyte *) ((char*) (Msg->Data)));
        return arr;
    }
}

JNIEXPORT jbyteArray JNICALL Java_com_viking_micex_Micex_openTable
  (JNIEnv * env, jobject o, jobject pointer, jint connId, jstring name, jstring params, jboolean complete) {
# ifdef _WIN32
    shared_lib mtesrl = (HMODULE) env->GetDirectBufferAddress(pointer);
#else
    shared_lib mtesrl = env->GetDirectBufferAddress(pointer);
#endif
    typedef int (*importFunction)(int, char*, char*, int , TMTEMsg **);
    importFunction OpenTable = (importFunction) load_func(mtesrl, "MTEOpenTable");

    TMTEMsg *Msg;

    char *params_ = (char *)env->GetStringUTFChars(params, 0);
    char *name_ = (char *)env->GetStringUTFChars(name, 0);
    int res = OpenTable(connId, name_, params_, complete, &Msg);
    env->ReleaseStringUTFChars(params, params_);
    env->ReleaseStringUTFChars(name, name_);
    char tmp[4];
    tmp[3] = (res & 0xff);
    tmp[2] = ((res & 0xff00) >> 8);
    tmp[1] = ((res & 0xff0000) >> 16);
    tmp[0] = ((res & 0xff000000) >> 24);

    if (res < com_viking_micex_Micex_MTE_OK)
    {
        jbyteArray arr = env->NewByteArray(4);
        env->SetByteArrayRegion(arr, 0, 4, (jbyte *) ((char*) (tmp)));
        return arr;
    }
    else
    {
        jbyteArray arr = env->NewByteArray(Msg->DataLen + 4);
        env->SetByteArrayRegion(arr, 0, 4, (jbyte *) ((char*) (tmp)));
        env->SetByteArrayRegion(arr, 4, Msg->DataLen, (jbyte *) ((char*) (Msg->Data)));
        return arr;
    }
}

首先我调用structure（）方法，它工作得很好（在linux和windows上），然后我调用openTable（），它只在linux上工作。在windows系统上.out.println（a==null）；打印错误，但ByteBuffer buff=ByteBuffer.wrap（a）；抛出NullPointerException。 你知道为什么会这样吗

public class Micex {
    private native byte[] structure(Object pointer, int connId, int version);

    private native byte[] openTable(Object pointer, int connId, String name, String params, boolean complete);

    public boolean structure(int version) {
        ByteBuffer buff = ByteBuffer.wrap(structure(this.mtesrl, this.connId, version));
        buff.order(ByteOrder.LITTLE_ENDIAN);
        ...
    }

    public boolean openTable(int key, TableName name, String params, boolean complete) {
        if (openedTables.containsKey(key)) {
            System.out.printf("Table \"%s\" with key \"%d\" is already opened\n", name.toString(), key);
            return true;
        }

        byte [] a = openTable(this.mtesrl, this.connId, name.toString(), params, complete);
        System.out.println(a == null);
        ByteBuffer buff = ByteBuffer.wrap(a);
        ...
    }
}