Question

这是JNI代码。

Java代码：

public class Sample1 {

    public native String stringMethod(String text);

    public static void main(String[] args)
    {
       System.loadLibrary("Sample1");
       Sample1 sample = new Sample1();

       String  text   = sample.stringMethod("world");

       System.out.println("stringMethod: " + text);    
   }
}

stringMethod函数的Cpp方法：

JNIEXPORT jstring JNICALL Java_Sample1_stringMethod
   (JNIEnv *env, jobject obj, jstring string) {

 const char *name = env->GetStringUTFChars(string, NULL);//Java String to C Style string
 char msg[60] = "Hello ";
 jstring result;

 strcat(msg, name);
 env->ReleaseStringUTFChars(string, name);
 puts(msg);
 result = env->NewStringUTF(msg); // C style string to Java String
 return result;    
 }

运行我的java代码时。我得到了下面的结果。

stringMethod: world

但是我用“Hello”添加了字符串“world”。我也在这里返回附加的字符串。但为什么我只得到“世界”而不是“Hello World”。真的我对这段代码感到困惑。我该怎么做才能得到附加字符串的结果？

Answer 1

这应该是这样做的方式....

JNIEXPORT jstring JNICALL Java_Sample1_stringMethod
   (JNIEnv *env, jobject obj, jstring string) {

 const char *name = (*env).GetStringUTFChars(env,string, NULL);
 char msg[60] = "Hello ";
 jstring result;

 strcat(msg, name);  
 (*env).ReleaseStringUTFChars(env,string, name);   
 puts(msg);            
 result = (*env).NewStringUTF(env,msg); 
 return result;        
 }

Answer 2

there are several ways but the best i got by converting const char * to c++ string 
and then to jbyteArray, and its easy to conversion of byteArray to UTF-8 on java 
side.

C++ side:
const char* string = propertyValue;
std::string str = string;

jbyteArray array = env->NewByteArray(str.length());
env->SetByteArrayRegion(array,0,str.length(),(jbyte*)str.c_str());


return array;

java/kotlin side:

String((array), Charset.defaultCharset()))

jstring在JNI程序中返回

2 个答案: