JNI调用机制(一)

public class JNITest {
	public native int intFunc(int n); //参数类型为int

	public native boolean booleanFunc(boolean bool);  //参数类型为boolean

	public native String stringFunc(String text);  //参数类型为String

	public native int intArrayFunc(int[] intArray);  //参数类型为int


	public static void main (String[] args) {
		//加载了动态类库，在windows下加载.dll，在Linux下加载.so，决不可加上后缀，要保证JNITest在path路径中

		System.loadLibrary("JNITest"); 
		JNITest jnitest = new JNITest();
		
		int square = jnitest.intFunc(5);
		boolean boolv = jnitest.booleanFunc(true);
		String text = jnitest.stringFunc("Hello JNI");
		int sum = jnitest.intArrayFunc(new int[]{1,2,3,4,5,6,7,8,9,0});

		System.out.println("intFunc: " + square);
		System.out.println("booleanFunc: " + boolv);
		System.out.println("stringFunc: " + text);
		System.out.println("intArrayFunc: " + sum);
	}
}

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class JNITest */

#ifndef _Included_JNITest
#define _Included_JNITest
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     JNITest
 * Method:    intFunc
 * Signature: (I)I
 */
JNIEXPORT jint JNICALL Java_JNITest_intFunc
  (JNIEnv *, jobject, jint);

/*
 * Class:     JNITest
 * Method:    booleanFunc
 * Signature: (Z)Z
 */
JNIEXPORT jboolean JNICALL Java_JNITest_booleanFunc
  (JNIEnv *, jobject, jboolean);

/*
 * Class:     JNITest
 * Method:    stringFunc
 * Signature: (Ljava/lang/String;)Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_JNITest_stringFunc
  (JNIEnv *, jobject, jstring);

/*
 * Class:     JNITest
 * Method:    intArrayFunc
 * Signature: ([I)I
 */
JNIEXPORT jint JNICALL Java_JNITest_intArrayFunc
  (JNIEnv *, jobject, jintArray);

#ifdef __cplusplus
}
#endif
#endif

#include "JNITest.h"
#include <string.h>
/* JNIEnv*：是每个函数都有的参数，代表的是Java环境, 通过这个环境可以调用Java里面的方法;
 *jobject参数: 调用C语言方法的对象, this对象表示当前的对象, jobject 指向在此 Java 代码中实例化的 Java 对象 LocalFunction 的一个句柄，相当于 this 指针即调用JNI方法所在的类;
 *
*/
JNIEXPORT jint JNICALL Java_JNITEST_intFunc(JNIEnv *env, jobject obj, jint num) {

	return num * num;
}

JNIEXPORT jboolean JNICALL Java_JNITEST_booleanFunc(JNIEnv *env, jobject obj, jboolean boolean) {

	return !boolean;
}

JNIEXPORT jstring JNICALL Java_JNITEST_stringFunc(JNIEnv *env, jobject obj, jstring string) {
	//GetStringUTFChars()这个方法，是Java和C/C++之间转换字符串，Java本身应的是双字节字符，而C使用的是单字节字符，故需要转换
	const char* str = (*env)->GetStringUTFChars(env, string, 0);
	char cap[128];
	strcpy(cap, str);
	//ReleaseStringUTFChars()是用来释放对象的, 在Java中有虚拟机进行垃圾回收, 但是在C语言中, 这些对象必须手动回收. 否则可能造成内存泄漏.
	(*env)->ReleaseStringUTFChars(env, string, 0);
	return (*env)->NewStringUTF(env, strupr(cap));
}

JNIEXPORT jint JNICALL Java_JNITEST_intArrayFunc(JNIEnv *env, jobject obj, jintArray array) {
	int i, sum = 0;
	jsize len = (*env)->GetArrayLength(env, array);
	jint *body = (*env)->GetIntArrayElements(env, array, 0);

	for (i = 0; i < len; i++) {
		sum += body[i];
	}
	return sum;
}