java - JNI- FindClass函数返回null

我有一个使用 shell 脚本和Eclipse编译的简单Java类(“MainX”)。当我调用env-> FindClass(“MainX”)函数时，从脚本生成的MainX.class文件返回null，而从eclipse生成的MainX.class文件返回该类，然后执行runMainX函数。

生成的MainX.class文件与JNI C++可执行文件位于同一文件夹中。

MainX.java

public class MainX {
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        System.out.println(new MainX().runMainX());
    }

    public String runMainX(){
        return ("0.789");
    }
}

JNIBinding.cpp

#define USER_CLASSPATH "."
....
....

JNIEnv* createVM (JavaVM **jvm)
{
    JNIEnv *env;                     /* pointer to native method interface */
    JavaVMInitArgs vm_args;              /* JDK/JRE 6 VM initialization arguments */
    JavaVMOption* options = new JavaVMOption[1]; //holds various JVM optional settings

    options[0].optionString = const_cast<char*>("-Djava.class.path="USER_CLASSPATH);
    vm_args.version = JNI_VERSION_1_6;       //version of Java platform
    vm_args.nOptions = 1;
    vm_args.options = options;
    vm_args.ignoreUnrecognized = false;
    /* load and initialize a Java VM, return a JNI interface * pointer in env */
    long status = JNI_CreateJavaVM(jvm, (void**)&env, &vm_args);

    if (status == JNI_ERR){
       cout << "Fail: Unable to load JVM \t Exit" << endl;
    }
    else if (status == JNI_OK){
    cout << "CreateVM:\t\tJVM loaded successfully!" << endl ;
    }

    delete options;
    return env;
}

....
....

float invokeMainX(JavaVM **jvm, JNIEnv *env){

    jclass    mainClass ; //Returns a class object from a fully-qualified name, or NULL if the class cannot be found.
    jmethodID classConstructor; //Returns the method ID for an instance (nonstatic) method of a class
    jobject   classObject;  //Constructs a new java object
    jmethodID methodid;

    float outcome = 0;

    mainClass = env->FindClass("MainX");    //Returns a class object from a fully-qualified name, or NULL if the class cannot be found.
    if (mainClass==0) return 0;
         classConstructor = env->GetMethodID(mainClass, "<init>", "()V"); //Returns the method ID for an instance (nonstatic) method of a class
    if (classConstructor==0) return -1;
         classObject = env->NewObject(mainClass, classConstructor); //Constructs a new java object
    if (classObject==0) return -2;
         methodid = env->GetMethodID(mainClass, "runMainX", "()Ljava/lang/String;");
    if (methodid==0) return -3;
            jstring result = (jstring)env->CallObjectMethod(classObject, methodid); //returns the result of the calling method, an object

....
....
}

有人可以解释一下为什么会这样吗？

感谢您的帮助。

任何想法？？？预先感谢

最佳答案

从JNI Documentation中获取FindClass:

name: a fully-qualified class name (that is, a package name, delimited by "/",
      followed by the class name).

So assuming the class is in the package your.package.name, I guess you'll have to replace

mainClass = env->FindClass("MainX");

与

mainClass = env->FindClass("your/package/name/MainX");

希望这可以帮助!