只是一个简单的问题:是否可以从c / c ++调用Java函数?
是的,你可以,但是它有点令人费解,并且以反射/非类型安全的方式工作(示例使用的C ++ API比C版本更干净)。在这种情况下,它将从C代码中创建Java VM的实例。如果首先从Java调用你的本机调用,则无需构造VM实例
#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(); }
编译(在Ubuntu上):
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
注意:为了实现正确的错误处理,应检查每种方法的返回代码(为方便起见,我将其忽略了)。例如
str = env->GetStringUTFChars(jstr, NULL); if (str == NULL) { return; /* out of memory */ }