如何访问Java方法在C ++应用程序

问题描述：

只是一个简单的问题：
是否有可能调用从C Java函数/ C ++？

Just a simple question: Is it possible to call a java function from c/c++ ?

答

当然可以，但它是一个有点令人费解，并在反射/非类型安全的工作方式（例如使用C ++ API，它是一个小更清洁比C版本）。在这种情况下，从C code内创建Java虚拟机的一个实例。如果你的母语所谓首次被从Java叫那么就没有必要建立一个虚拟机实例

Yes you can, but it is a little convoluted, and works in a reflective/non type safe way (example uses the C++ api which is a little cleaner than the C version). In this case it creates an instance of the Java VM from within the C code. If your native called is first being called from Java then there is no need to construct a VM instance

#include<jni.h>
#include<stdio.h>

int main(int argc, char** argv) {

    JavaVM *vm;
    JNIEnv *env;
    JavaVMInitArgs vm_args;
    vm_args.version = JNI_VERSION_1_2;
    vm_args.nOptions = 0;
    vm_args.ignoreUnrecognized = 1;

    // Construct a VM
    jint res = JNI_CreateJavaVM(&vm, (void **)&env, &vm_args);

    // Construct a String
    jstring jstr = env->NewStringUTF("Hello World");

    // First get the class that contains the method you need to call
    jclass clazz = env->FindClass("java/lang/String");

    // Get the method that you want to call
    jmethodID to_lower = env->GetMethodID(clazz, "toLowerCase",
                                      "()Ljava/lang/String;");
    // Call the method on the object
    jobject result = env->CallObjectMethod(jstr, to_lower);

    // Get a C-style string
    const char* str = env->GetStringUTFChars((jstring) result, NULL);

    printf("%s\n", str);

    // Clean up
    env->ReleaseStringUTFChars(jstr, str);

    // Shutdown the VM.
    vm->DestroyJavaVM();
}

要编译（在Ubuntu）：

To compile (on Ubuntu):

g++ -I/usr/lib/jvm/java-6-sun/include \ 
    -I/usr/lib/jvm/java-6-sun/include/linux \ 
    -L/usr/lib/jvm/java-6-sun/jre/lib/i386/server/ -ljvm jnitest.cc

请注意：从每一种方法的返回code应该以落实正确的错误处理进行检查（我忽略了这个方便）。例如。

Note: that the return code from each of these methods should be checked in order to implement correct error handling (I've ignored this for convenience). E.g.

str = env->GetStringUTFChars(jstr, NULL);
if (str == NULL) {
    return; /* out of memory */
}

如何访问Java方法在C ++应用程序

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