Java本地调用（JNI）

Posted 2021-12-29 xhBruce

Java本地调用（JNI）

JNI: Java Native Interface(调用c/c++/其他本地代码,该接口提供了java与os本地代码互相调用的功能。

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1、将调用java文件转化为.h

c/c++中 greeting 方法

class HelloNative 
    public static native void greeting();

javac -h ./ HelloNative.java (javah是1.8及以前版本)

生成 HelloNative.h

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

#ifndef _Included_HelloNative
#define _Included_HelloNative
#ifdef __cplusplus
extern "C" 
#endif
/*
 * Class:     HelloNative
 * Method:    greeting
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_HelloNative_greeting
  (JNIEnv *, jclass);

#ifdef __cplusplus

#endif
#endif

2、调用.h文件实现方法

Java_HelloNative_greeting

#include "HelloNative.h"
#include <stdio.h>

JNIEXPORT void JNICALL Java_HelloNative_greeting(JNIEnv* env, jclass cl)

    printf("Hello Native World!\\n");

1. cl -I “…\\jdk-16.0.1\\include” -I “…\\Java\\jdk-16.0.1\\include\\win32” -LD HelloNative.c -FeHelloNative.dll(需要安装Visual Studio)
2. gcc -mno-cygwin -D __int64=“long long” -I “…\\Java\\jdk-16.0.1\\include” -I “…\\Java\\jdk-16.0.1\\include\\win32” -shared -W1,–add-stdcall-alias -o HelloNative.dll HelloNative.c(windows下载Cygwin)
3. gcc -fPIC -I “…\\Java\\jdk-16.0.1\\include” -I “…\\Java\\jdk-16.0.1\\include\\win32” -shared -o HelloNative.so HelloNative.c(Linux中gcc)

（gcc.exe -I "D:\\Program Files\\Java\\jdk-16.0.1\\include" -I "D:\\Program Files\\Java\\jdk-16.0.1\\include\\win32" -shared -Wl,--add-stdcall-alias -o HelloNative.dll HelloNative.c成功）

Java调用dll库（或so库）

public class Main 
    public static void main(String[] args) 
        HelloNative.greeting();
    
    static 
        System.loadLibrary("HelloNative");
    

javac Main.java
java Main

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注意点

1. 若HelloNative.java属于某个包，如package com.xhbruce;

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

#ifndef _Included_com_xhbruce_HelloNative
#define _Included_com_xhbruce_HelloNative
#ifdef __cplusplus
extern "C" 
#endif
/*
 * Class:     com_xhbruce_HelloNative
 * Method:    greeting
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_com_xhbruce_HelloNative_greeting
  (JNIEnv *, jclass);

#ifdef __cplusplus

#endif
#endif