set a string from c jni to java

Question

I have a problem to set a string from jni to java class,i wrote the jni (in c) , I want to set a string from jni to java i did like this

jclass cls;
jmethodID mid;

/* cls = (*env)->GetObjectClass(env, obj); */
cls = (*env)->FindClass (env,"com/example/lsextractor/LSCore");
jobject objRet = (*env)->AllocObject(env,cls);
jstring estr = (jstring)(*env)->NewStringUTF(env,(char*)"Hello");
mid = (*env)->GetMethodID(env, cls, "setTemplate","(Ljava/lang/String;)V");
(*env)->CallObjectMethod(env,objRet,mid,estr);

return (jint)1;

but this method is not working i cant get the string from my class but i can able to access all other method from my java class i can't set the string from jni to java do have any idea to do this, this is my class

public byte[] getimage()
    {
        return this.Image;
    }
    public void setimage(byte[] rawImg)
    {
         this.Image=rawImg;
    }
    public String getTemplate()
    {
        return this.Template;
    }
    public void setTemplate(String Tmp)
    {
        this.Template = Tmp;
    }
    static
    {
    System.loadLibrary("test"); 
    }

Answer 1

First you should not be using AllocObject since no constructor will be called with that function.

Try this instead:

mid = (*env)->GetMethodID(env, cls, "<init>", "()V");  
jobject objRet = (*env)->NewObject(env, cls, mid);

That will give you an initialized object.

---

Second problem is that you are calling CallObjectMethod

The correct method invocation is:

(*env)->CallVoidMethod(env, objRet, mid, estr);

That is because the Void part of the function is the return type. Your call tried to call a method that returns Object.

---

AllocObject

jobject AllocObject(JNIEnv *env, jclass clazz);

Allocates a new Java object without invoking any of the constructors for the object. Returns a reference to the object.