Get Strings used in Java from JNI

Question

JAVA Code

Here is some part of my code that I have written in JAVA, As you can see this is a class called JC_VerificationCandidate that have two String members enrollmentID and seedIndex.

class JC_VerificationCandidate {

    public JCDSM_VerificationCandidate( String enrollmentID, String seedIndex ) {
        this.enrollmentID = enrollmentID;
        this.seedIndex    = seedIndex;
    }

    public String enrollmentID;
    public String seedIndex;
}

Here is main class where I have native method and from where I called that native method.

public class DsmLibraryTest extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {

        JCDSM_VerificationCandidate verificationCandidate[] = {new JCDSM_VerificationCandidate( "tom", "anna" )}; 
        dsm.JDSMVerify( 123456, "http:\\www.test_url.com", bytes, verificationCandidate );

    }

    public native int JDSMVerify(
                   int                         someValue1,
                   String                      someValue2,
                   byte[]                      someValue3,
                   JC_VerificationCandidate    jVerificationCandList[] );
}

As you can see I create array with one object and give it to my function.

JCDSM_VerificationCandidate verificationCandidate[] = {new JCDSM_VerificationCandidate( "tom", "anna" )};

JNI Code

How can I get that two strings enrollmentID, eedIndex that I have set from java application and which are stored in jVerificationCandList ?

JNIEXPORT jint JNICALL Java_com_Dsm_Test_DSM_JDSMVerify( JNIEnv* env, jobject thiz, jint jhDevice, jstring jurlID,
                                                         jbyteArray jInputInfo, jobjectArray jVerificationCandList ) {


}

Solution

The following code should allow you to access the field enrollmentID. Use the JNI String functions to read/manipulate them.

// Load the class
jclass jclass_JCV = env->FindClass(env, "my.package.JC_VerificationCandidate");

jfieldID fid_enrollmentID = env->GetFieldID(env, jclass_JCV, "enrollmentID" , "Ljava/lang/String;");

// Access the first element in the jVerificationCandList array 
jobject jc_v = env->GetObjectArrayElement(env, jVerificationCandList, 0);

// get reference to the string 
jstring jstr = (jstring) env->GetObjectField(env, jc_v, enrollmentID);

// Convert jstring to native string
const char *nativeString = env->GetStringUTFChars(env, jstr, 0);

Comments

[Viktor Apoyan]

const char *nativeString = (*env)->GetStringUTFChars(env, jstr, 0); Okay !!! Thats All !!

[Azeroth2b]

Don't forget to release it later, else you will leak. (*env)->ReleaseStringUTFChars(...)