如何将字符串数组从 C++ 返回到 Java (JNI)

Question

i have a String array on c++ and i need to return it to the Java class. How can i do this?

I have tried this:

string paroleord[app.size()];
jobjectArray ret;
ret = (jobjectArray)env->NewObjectArray(app.size(),env->FindClass("java/lang/String"), 0);
for (int k = 0; k < app.size(); k++)
{
    env->SetObjectArrayElement(ret, k,env->NewStringUTF(paroleord[k]));
}

return ret;

But i have an error because NewStringUTF needs an object as parameter, can you help me please?

Answer 1

If you can survive with Vector or Array you can simply return collection from C++ code.

It will require some "low level" coding, but it's fairly straightforward.

Take a look here:

http://jnicookbook.owsiak.org/recipe-no-045/

as for the String itself, take a look here:

http://jnicookbook.owsiak.org/recipe-No-010/

Also, make sure to convert string to array of characters.

(*env)->NewStringUTF(env, my_string.c_str());

Answer 2

You can use Scapix Java Link C++ JNI library to automatically convert between many C++ and Java types. Here is an example :

#include <scapix/java_api/java/lang/System.h>
#include <scapix/java_api/java/util/Locale.h>
#include <scapix/java_api/java/text/DateFormatSymbols.h>

using namespace scapix::link::java;
using namespace scapix::java_api;

void test1()
{
    // C++ objects are automatically converted to and from corresponding Java types.
    // This works for any type supported by scapix::link::java::convert() interface,
    // which supports many STL types and can be extended for your own types.

    std::string version = java::lang::System::getProperty("java.version");
    std::vector<std::string> languages = java::util::Locale::getISOLanguages();
    std::vector<std::vector<std::string>> zone_strings = java::text::DateFormatSymbols::getInstance()->getZoneStrings();
    std::map<std::string, std::string> properties = java::lang::System::getProperties();
}