JAVA JNA 调用C接口的三种方式

1. 准备一个共享库文件

test.c

#include <stdio.h>
int test(char *input){printf("input:%s\n",input);return 0;
}

libtest.so

[root@node-126 ~]# gcc -fPIC -shared -o libtest.so test.c 
[root@node-126 ~]# ls /root/
anaconda-ks.cfg  libtest.so  node-v6.10.2-linux-x64.tar.xz  original-ks.cfg  spring3  test  test.c

可以看到有test方法

[root@node-126 ~]# nm -D libtest.so 
0000000000201038 B __bss_startw __cxa_finalize
0000000000201038 D _edata
0000000000201040 B _end
0000000000000600 T _finiw __gmon_start__
00000000000004c0 T _initw _ITM_deregisterTMCloneTablew _ITM_registerTMCloneTableU printf
00000000000005d5 T test

2. JNA姿势1—继承Library接口

建个普通maven项目

       <dependency><groupId>net.java.dev.jna</groupId><artifactId>jna</artifactId><version>5.5.0</version></dependency>

package jna;import com.sun.jna.Library;
import com.sun.jna.Native;/*** 接口继承** @author majun* @version 1.0* @since 2023-08-22 22:27*/
public interface MyClibrary extends Library {MyClibrary INSTANTCE = Native.load("/root/libtest.so", MyClibrary.class);int test(String input);
}

测试

import jna.MyClibrary;/*** TODO** @author majun* @version 1.0* @since 2023-03-31 7:44*/
public class Main {public static void main(String[] args) {int test = MyClibrary.INSTANTCE.test("extend Library");System.out.println(test);}
}

使用Linux上的Java运行

3. JNA姿势2—直接NativeLibrary.getInstance

import com.sun.jna.Function;
import com.sun.jna.NativeLibrary;/*** TODO** @author majun* @version 1.0* @since 2023-03-31 7:44*/
public class Main {public static void main(String[] args) {NativeLibrary instance = NativeLibrary.getInstance("/root/libtest.so");Function func = instance.getFunction("test");Object res = func.invoke(Integer.class, new Object[]{"NativeLibrary.getInstance"});System.out.println( res);}
}

3. JNA姿势3—Native方法

mkdir -p /root/jna && cd /root/jna 新建MyNative.java

package jna;
import java.io.IOException;public class MyNative {native int  test(String input) throws IOException;
}

编译并生成头文件（这里java17没找到javah命令，改用java8的，但注意javac ,javah要使用同一个Java版本的）

 /usr/local/jdk1.8.0_111/bin/javac  MyNative.java/usr/local/jdk1.8.0_111/bin/javah -classpath /root/ -jni   jna.MyNative

linux直接编辑实现头文件中的接口：

#include <stdio.h>
#include <jni.h>
#include "jna_MyNative.h"
jint  Java_jna_MyNative_test(JNIEnv *jniEnv, jobject clazz, jstring input){printf("input:%s\n",(char *)input);return 0;
}

编译时注意引入jdk头文件包下的jni.h等

gcc -fPIC -shared -I/usr/lib/jvm/jdk-17-oracle-x64/include -I/usr/lib/jvm/jdk-17-oracle-x64/include/linux -o libtest.so test.c

使用Clion实现头文件的接口：新建C项目，引入jna_MyNative.h，并实现其中的方法

注意
1.使用远程toolchain,cmake编译安装运行，注意cmake版本可能导致include_directories(SYSTEM "/usr/lib/jvm/jdk-17-oracle-x64/include") 同步Linux上jdk的头文件失败，本地无法找到符号，但可以正常运行。
2.jniEnv必须Java调用才会有值。

cmake_minimum_required(VERSION 2.8)
project(untitled1)set(CMAKE_CXX_STANDARD 17)
include_directories(SYSTEM "/usr/lib/jvm/jdk-17-oracle-x64/include")
include_directories(SYSTEM "/usr/lib/jvm/jdk-17-oracle-x64/include/linux")add_executable(testexe main.cpp)
add_library(test SHARED main.cpp jna_MyNative.h)
target_link_libraries(test -I/usr/lib/jvm/jdk-17-oracle-x64/include -I/usr/lib/jvm/jdk-17-oracle-x64/linux)
install(TARGETS test LIBRARY DESTINATION /usr/lib)

Java调用测试

import jna.MyNative;import java.io.IOException;/*** TODO** @author majun* @version 1.0* @since 2023-08-23 23:44*/
public class Main {public static void main(String[] args) throws IOException {System.load("/root/jna/libtest.so");//System.loadLibrary("test");// 自动拼接成libtest.so，默认从/usr/lib,/usr/lib64等路径找MyNative myNative = new MyNative();int test = myNative.test("native");System.out.println(test);}
}

姿势3实现的C接口，Java依旧可以使用姿势1，2的方式来调用，注意函数名为Java_jna_MyNative_test

[root@node-126 lib]# nm -D /usr/lib/libtest.so 
0000000000201070 B __bss_startU __cxa_allocate_exceptionw __cxa_finalizeU __cxa_free_exceptionU __cxa_throw
0000000000201070 D _edata
0000000000201078 B _end
0000000000000b4c T _finiw __gmon_start__U __gxx_personality_v0
0000000000000860 T _initw _ITM_deregisterTMCloneTablew _ITM_registerTMCloneTable
0000000000000a15 T Java_jna_MyNative_testw _Jv_RegisterClasses
0000000000000ac8 T mainU printfU _Unwind_Resume
0000000000000b18 W _ZN7JNIEnv_8ThrowNewEP7_jclassPKc
0000000000000aea W _ZN7JNIEnv_9FindClassEPKcU _ZTIi