在示例程序中找不到JNI_OnLoad_libname [英] Can't find JNI_OnLoad_libname in example program

问题描述

我究竟如何从Java调用本机静态库?我正在使用Java 8.

How exactly do I call native static libraries from Java? I'm using Java 8.

在我看来，我应该能够在具有嵌入式JVM的C ++程序中定义JNI_OnLoad_library，但是当我调用System.loadLibrary时，我的VM一直在崩溃.以下仅打印来自主打招呼".

It looks to me like I should be able to define a JNI_OnLoad_library in a C++ program with an embedded JVM but my VM keeps dying when I call System.loadLibrary. The following only prints "Hello from main".

main.cpp:

#include <jni.h>
#include <iostream>

extern "C" {
    JNIEXPORT jint JNI_OnLoad_hello(JavaVM *vm, void *reserved) {
        std::cout << "Hello World" << std::endl;
        return JNI_VERSION_1_8;
    }
}

int main(int argc, char** argv) {
    JavaVM *jvm;
    JNIEnv *env;
    JavaVMInitArgs vm_args;
    jint error;

    JavaVMOption* options = new JavaVMOption[argc-1];
    for(int i = 0;i < argc-1;i++) {
        options[i].optionString = argv[i+1];
    }

    vm_args.nOptions = argc-1;
    vm_args.options = options;

    vm_args.version = JNI_VERSION_1_8;

    JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args);
    jclass cls = env->FindClass("Main");
    jclass stringCls = env->FindClass("java/lang/String");
    jmethodID mid = env->GetStaticMethodID(cls, "main", "([Ljava/lang/String;)V");
    jobjectArray mainArgs = env->NewObjectArray(0, stringCls, NULL);
    env->CallStaticVoidMethod(cls, mid, mainArgs);
    jvm->DestroyJavaVM();
}

Main.java:

Main.java:

class Main {
    public static void main(String[] args) {
        try {
            System.out.println("Hello from main");
            System.loadLibrary("hello");
            System.out.println("Hello after main");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

推荐答案

通过将--export-dynamic传递给链接器，我终于能够使JVM找到JNI_OnLoad_hello.这允许共享库通过在可执行文件中查找符号来解析它们.同样，System.loadLibrary引发了我怀疑的UnsatisfiedLikeErrors，但是由于某种原因，我不得不使用CheckException和DescribeException在JNI中处理它们.

I was finally able to get the JVM to find JNI_OnLoad_hello by passing --export-dynamic to the linker. This allows shared libraries to resolve symbols by looking for them in the executable. Also, System.loadLibrary was throwing UnsatisfiedLikeErrors like I suspected but for some reason I have to handle them in JNI using CheckException and DescribeException.

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