Can I call Java methods from a C application?

How to Call Java Methods from C Applications

Problem:

It is possible to invoke functions defined in Java code from a C application?

Answer:

Yes, it is possible to call Java methods from C code, but the process is somewhat complex. This approach utilizes reflection and operates in a non-type-safe manner.

Implementation:

The C code creates an instance of the Java Virtual Machine (JVM) from within the C code. If the native code is invoked from Java, creating a VM instance is unnecessary.

Here is an example of how to access a Java method from C :

#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;

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

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

    // Get the class containing the method to be invoked
    jclass clazz = env->FindClass("java/lang/String");

    // Get the method to be called
    jmethodID to_lower = env->GetMethodID(clazz, "toLowerCase", "()Ljava/lang/String;");

    // Invoke the method on the object
    jobject result = env->CallObjectMethod(jstr, to_lower);

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

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

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

    // Destroy the JVM
    vm->DestroyJavaVM();

    return 0;
}

Compilation:

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

Note: It is crucial to handle error codes from the JNI methods to implement proper error management.

The above is the detailed content of Can I call Java methods from a C application?. For more information, please follow other related articles on the PHP Chinese website!