How jni deliver a string array?

Question

How to deliver a string array?

I post the code:

xx.cpp

JNIEXPORT jstring JNICALL Hello_Native(JNIEnv *env, jobject obj,jstring string)
{
    const char *str = env->GetStringUTFChars(string, 0);
    return env->NewStringUTF( "Hello from JNI !");
}
static JNINativeMethod gMethods[] = {
   {"JniHello",const_cast<char*>("(Ljava/lang/jsting)Ljava/lang/jsting;"),(void*)Hello_Native}

xx.java

public native static String JniHello(String text);

System always prompt it has the problem when declare JniHello in gMethods and the parameter is not right.

Pavel Zdenek · Accepted Answer · 2013-01-30 11:31:25Z

2

stop using wrong manual names for JNICALL functions. javah will generate it for you correctly. If your Java name is JniHello in class MyHello and your package is com.hello , JNICALL function must be Java_com_hello_MyHello_JniHello. It can't be Hello_Native, you have made it up.
then of course this correct function name must be used in the last member of JNINativeMethod struct
there is no such class as java/lang/jsting. There is not even a java/lang/jstring if i add the missing r for you. You are asked for the JAVA signature, not JNI. So it must be java/lang/String.
ADDED (thanks @EJP): stop using wrong manual strings for JNI signatures and use the output of javap -s instead

Your code has one more problem: when used GetStringUTFChars, you must also call `ReleaseStringUTFChars' before returning, otherwise you have a leak. But you will find this yourself sooner or later.

edited Jan 30, 2013 at 11:31

answered Jan 29, 2013 at 14:17

Pavel Zdenek

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3 Comments

user207421 Over a year ago

Good advice. I would add 'stop using wrong manual strings for JNI signatures and use the output of javap -s instead'. That would solve (3). +1

user207421 Over a year ago

I prefer the 'stop using' wording that agrees with your own point 1.

Pavel Zdenek Over a year ago

@EJP i wanted to avoid sounding too strong. But for no apparent reason besides vague humanistic feeling, i admit.

cox · Accepted Answer · 2013-08-31 09:33:00Z

1

const_cast("(Ljava/lang/jsting)Ljava/lang/jsting;") spell error, should be const_cast("(Ljava/lang/jsting)Ljava/lang/jstring;")

jsting ==> jstring

answered Aug 31, 2013 at 9:33

cox

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cox · Accepted Answer · 2013-08-31 09:39:05Z

Copy some android source code to help you(JNI):


static jobject osNetworkSystem_getHostByNameImpl(JNIEnv* env, jclass clazz,
        jstring nameStr, jboolean preferIPv6Addresses) {

}

static void osNetworkSystem_setInetAddressImpl(JNIEnv* env, jobject obj,
        jobject sender, jbyteArray address) {

}

static jobject osNetworkSystem_inheritedChannelImpl(JNIEnv* env, jobject obj) {

}

/*
 * JNI registration.
 */
static JNINativeMethod gMethods[] = {
    /* name, signature, funcPtr */
    { "getHostByNameImpl",                 "(Ljava/lang/String;Z)Ljava/net/InetAddress;",                              (void*) osNetworkSystem_getHostByNameImpl                  },
    { "setInetAddressImpl",                "(Ljava/net/InetAddress;[B)V",                                              (void*) osNetworkSystem_setInetAddressImpl                 },
    { "inheritedChannelImpl",              "()Ljava/nio/channels/Channel;",                                            (void*) osNetworkSystem_inheritedChannelImpl               },
};

int register_org_apache_harmony_luni_platform_OSNetworkSystem(JNIEnv* env) {
    return jniRegisterNativeMethods(env,
            "org/apache/harmony/luni/platform/OSNetworkSystem",
            gMethods,
            NELEM(gMethods));
}

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