JNI intArray
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; }