JNI

**
需求： 需要通过Java调用C++代码完成对应的操作
**

简单说下方法：
1、首先定义对应的执行类和在类中声明native方法
目前只测试了传入int类型值 的方法调用，其他应该是一样的

public class RecorderHandler {
    public native int intMethod(int n);
    public native boolean booleanMethod(boolean bool);
    public native String stringMethod(String text);
    public native int intArrayMethod(int[] intArray);
    
    public static void main(String[] args) {
        System.loadLibrary("RecorderHandler");
        RecorderHandler recorderHandler = new RecorderHandler();
        int i = recorderHandler.intMethod(9);
        // boolean bool = recorderHandler.booleanMethod(true);
        // String text = recorderHandler.stringMethod("Java");
        // int  sum = recorderHandler.intArrayMethod(new int[]{1,2,3});
        
        System.out.println("intMethod: " + i);
    //  System.out.println("booleanMethod: " + bool);
    //  System.out.println("stringMethod: " + text);
    //  System.out.println("intArrayMethod: " +sum);
    // }
    }
    
}

2、编译生成对应的class文件：

javac RecorderHandler.java
生成对应的class类

3、调用javah命令生成对应的头文件，这个头文件就是需要用C++代码实现的头文件

javah RecorderHandler

生成头文件如下：

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

#ifndef _Included_RecorderHandler
#define _Included_RecorderHandler
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     RecorderHandler
 * Method:    intMethod
 * Signature: (I)I
 */
JNIEXPORT jint JNICALL Java_RecorderHandler_intMethod
  (JNIEnv *, jobject, jint);

/*
 * Class:     RecorderHandler
 * Method:    booleanMethod
 * Signature: (Z)Z
 */
JNIEXPORT jboolean JNICALL Java_RecorderHandler_booleanMethod
  (JNIEnv *, jobject, jboolean);

/*
 * Class:     RecorderHandler
 * Method:    stringMethod
 * Signature: (Ljava/lang/String;)Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_RecorderHandler_stringMethod
  (JNIEnv *, jobject, jstring);

/*
 * Class:     RecorderHandler
 * Method:    intArrayMethod
 * Signature: ([I)I
 */
JNIEXPORT jint JNICALL Java_RecorderHandler_intArrayMethod
  (JNIEnv *, jobject, jintArray);

#ifdef __cplusplus
}
#endif
#endif

4、对头文件进行实现，c++部分实现

#include "RecorderHandler.h"
#include <string.h>
#include<stdio.h>
#include<stdlib.h>
JNIEXPORT jint JNICALL Java_RecorderHandler_intMethod
  (JNIEnv *env, jobject obj, jint num)
{
    return num * num;
}

JNIEXPORT jboolean JNICALL Java_RecorderHandler_booleanMethod
  (JNIEnv *env, jobject obj, jboolean boolean)
{
    return !boolean;
}

JNIEXPORT jstring JNICALL Java_RecorderHandler_stringMethod
  (JNIEnv *env, jobject obj, jstring string)
{
    const char* str = env->GetStringUTFChars(string, 0);
    char cap[128];
    strcpy(cap, str);
    env->ReleaseStringUTFChars(string, 0);
    //return env->NewStringUTF(strdup(cap));
    return NULL;
}

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

    for (i = 0; i < len; ++i)
    {
        sum += body[i];
    }
    env->ReleaseIntArrayElements(array, body, 0);
    return sum;
}

5、对以上文件进行编译：如何编译并且进行链接是最重要的一步
注意： -I是对应的链接库库，文件结尾应该是dylib，因为我的mac系统，mac下面的结尾文件应该是dylib，如果是windows应该是.ddl文件吧，如果是linux上进行编译，应该是.so文件吧

g++ -shared -I /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/include  -I/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/include/darwin -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk/usr/include RecorderHandler.cpp -o libRecorderHandler.dylib

执行完了以后，就会在对应的目录生成：

Paste_Image.png

然后进行执行：因为我编译的时候intMethod传入的是9，又因为是去做乘法，所以 9*9输出结果为81
java RecorderHanlder

Paste_Image.png

mac版本JNI参考
一般参考
Java调用jni绝对路径
jni调用的一些列参考，非常详细，重点看