JNI intArray

Posted 2020-10-09 CZM&

JNIDemo.java

public class JNIDemo {
    static {         /* 1. load */
        System.loadLibrary("native"); /* libnative.so */
     }
    public native static int[] hello(int[] a);
    public static void main(String[] args) {
         
         System.out.println("JNIDemo");
         int [] a = {1,2,3};
         int [] b = null;
         int i;
         /* 1. load */
         System.loadLibrary("native"); /* libnative.so */

         /* 2. map hello java<-->c c_hello */

         /* 3. call */
         b = hello(a);
         for(i = 0; i < b.length; i++)
            System.out.println(b[i]);
     } 

}

 

native.c

#include <jni.h>    /* /usr/lib/jvm/java-1.7.0-openjdk-amd64/include/ */
#include <stdio.h>
#include <stdlib.h>

#if 0
 typedef struct {
    char *name;          /* Java里调用的函数名 */
    char *signature;    /* JNI字段描述符, 用来表示Java里调用的函数的参数和返回值类型 */
    void *fnPtr;          /* C语言实现的本地函数 */
} JNINativeMethod;
#endif

jintArray c_hello(JNIEnv *env, jclass cls, jintArray arr)
{
    jint *carr;
    jint *oarr;
    jintArray rarr;

    jint i, sum = 0, n = 0;
    carr = (*env)->GetIntArrayElements(env, arr, NULL);
    if (carr == NULL) {
        return 0; /* exception occurred */
    }

    n = (*env)->GetArrayLength(env, arr);
    oarr = malloc(sizeof(jint) * n);

    if(oarr == NULL)
    {
        (*env)->ReleaseIntArrayElements(env, arr, oarr, 0);
        return 0;
    }    

    for (i=0; i < n; i++) {
        oarr[i]= carr[n - 1 -i];
    }

    (*env)->ReleaseIntArrayElements(env, arr, carr, 0);
    
    /*create jintArray*/
    rarr = (*env)->NewIntArray(env, n);
    if(rarr == NULL)
    {
        return 0;
    }

    (*env)->SetIntArrayRegion(env, rarr, 0, n, oarr);
    free(oarr);
    
    return rarr;
}

static const JNINativeMethod methods[] = {
    {"hello", "([I)[I", (void *)c_hello},
};

/* System.loadLibrary */
JNIEXPORT jint JNICALL
JNI_OnLoad(JavaVM *jvm, void *reserved)
{
    JNIEnv *env;
    jclass cls;

    if ((*jvm)->GetEnv(jvm, (void **)&env, JNI_VERSION_1_4)) {
        return JNI_ERR; /* JNI version not supported */
    }
    cls = (*env)->FindClass(env, "JNIDemo");
    if (cls == NULL) {
        return JNI_ERR;
    }

    /* 2. map hello java<-->c c_hello */
    if((*env)->RegisterNatives(env, cls, methods, 1) < 0)
        return JNI_ERR;
    
    return JNI_VERSION_1_4;
}