java调用native方法

java调用native方法。

环境:
jdk:11
idea:2024
visual studio:2019
c++:14

步骤

1. 使用IDEA创建java工程

2. 创建NativeCppMethod类

public class NativeCppMethod {
    public native int sayHello();

    public native int plus(int a, int b);

    public native int minus(int a, int b);

    public native int min(int... nums);
}

3. 使用javac -h 生成对应的c++头文件

生成的NativeCppMethod.h

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

#ifndef _Included_NativeCppMethod
#define _Included_NativeCppMethod
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     NativeCppMethod
 * Method:    sayHello
 * Signature: ()I
 */
JNIEXPORT jint JNICALL Java_NativeCppMethod_sayHello
  (JNIEnv *, jobject);

/*
 * Class:     NativeCppMethod
 * Method:    plus
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_NativeCppMethod_plus
  (JNIEnv *, jobject, jint, jint);

/*
 * Class:     NativeCppMethod
 * Method:    minus
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_NativeCppMethod_minus
  (JNIEnv *, jobject, jint, jint);

/*
 * Class:     NativeCppMethod
 * Method:    min
 * Signature: ([I)I
 */
JNIEXPORT jint JNICALL Java_NativeCppMethod_min
  (JNIEnv *, jobject, jintArray);

#ifdef __cplusplus
}
#endif
#endif

4. 使用VisualStudio创建C++动态库

5. 将jdk里的jni.h和jni_md.h头文件,第三步生成的头文件(需要将引入<jni.h>改为"jni.h")拷贝到项目里,创建NativeCppMethod.cpp文件

6. 完成NativeCppMethod.cpp逻辑

#include "NativeCppMethod.h"
#include "jni.h"
#include <iostream>

using namespace std;

JNIEXPORT jint JNICALL Java_NativeCppMethod_sayHello(JNIEnv* env, jobject obj)
{
    cout << "hello world!" << endl;
    return 0;
}

JNIEXPORT jint JNICALL Java_NativeCppMethod_plus(JNIEnv* env, jobject obj, jint a, jint b)
{
    return a + b;
}

JNIEXPORT jint JNICALL Java_NativeCppMethod_minus(JNIEnv* env, jobject obj, jint a, jint b)
{
    return a - b;
}

JNIEXPORT jint JNICALL Java_NativeCppMethod_min(JNIEnv* env, jobject obj, jintArray arr)
{
    jint* jintPtr = env->GetIntArrayElements(arr, NULL);
    jsize len = env->GetArrayLength(arr);

    if (len <= 0) {
        return -1;
    }

    jint min = jintPtr[0];
    for (jint i = 1; i < len; ++i) {
        if (jintPtr[1] < min) {
            min = jintPtr[i];
        }
    }

    return min;
}

7. 编译生成64位release版本动态dll,将dll拷贝到java项目里

8. 编写main函数

public class Main {

    static {
        System.loadLibrary("DllForJavaTest2");
    }

    public static void main(String[] args) {
        NativeCppMethod nativeCppMethod = new NativeCppMethod();
        int a = 10, b = 4, c[] = {1, 2, 3, 6, 7, 4};
        nativeCppMethod.sayHello();
        System.out.println("plus:" + nativeCppMethod.plus(a, b));
        System.out.println("minus:" + nativeCppMethod.minus(a, b));
        System.out.println("min:" + nativeCppMethod.min());
        System.out.println("min:" + nativeCppMethod.min(a));
        System.out.println("min:" + nativeCppMethod.min(a, b));
        System.out.println("min:" + nativeCppMethod.min(c));
    }
}

9. 运行