Java JNA 调用不会运行 native 代码，导致应用程序停止

Question

我正在使用 JNA(Java native 访问)从 Java 调用 native 方法到 C。 native 方法 (int funcServer(int param1)) 是一个基本的 unix 套接字监听。但不管我是否做优化的 JNA Direct Mapping或 Interface Mapping , JNA 在我身上停滞不前。即使在函数调用的第一行， native 代码也不会打印任何内容，但不会引发异常。

查看我的最小可行 Java 示例(在 NetBeans IDE 产品版本:8.0.2 Build 201411181905 和 Ubuntu Linux 上运行):

package viableexamplejava;

import com.sun.jna.*; // link jna-4.1.0.jar, jna-platform-4.1.0.jar

/**
 * Test on Ubuntu Linux or with Cygwin on Windows 7.
 */
public class ViableExample {

    /**
     * This library depends on Unix Sockets.
     */
    public interface NativeLibary extends Library {

        public int funcServer(int param1);
    }
    //uncomment for Indirect Mapping
    //private static final NativeLibary myNativeLibrary_;

    public static native int funcServer(int param1);

    static {
        final String windowsLibraryName = "ViableExample.dll";
        final String linuxLibraryName = "libViableExampleNative.so"; // compiled with Netbeans

        if (Platform.isWindows()) {
            System.err.println("Loading Windows dll. 'cygwin1.dll' should be in same directory.");
            //myNativeLibrary_ = (NativeLibary) Native.loadLibrary(windowsLibraryName, NativeLibary.class);
            Native.register(windowsLibraryName);
        } else {
            System.err.println("Loading Linux .so");
            //myNativeLibrary_ = (NativeLibary) Native.loadLibrary(linuxLibraryName, NativeLibary.class);
            Native.register(linuxLibraryName);
        }
    }

    public static void main(String[] args) {
        System.err.println("Hello World from Java");
        //uncomment for Indirect Mapping
        //myNativeLibrary_.funcServer(7);
        funcServer(7); // This never prints.
    }

}

/**
 * Side notes: If the dynamic library cannot be found, this error occurs:
 *
 * Exception in thread "main" java.lang.UnsatisfiedLinkError: Unable to load
 * library 'libViableExampleNative.so': Native library
 * (linux-x86-64/libViableExampleNative.so) not found in resource path
 * ([file:/home/user/Desktop/Dropbox/jna-4.1.0.jar,
 * file:/home/user/Desktop/Dropbox/jna-platform-4.1.0.jar,
 * file:/home/user/NetBeansProjects/ViableExampleJava/build/classes/])
 *
 * at com.sun.jna.NativeLibrary.loadLibrary(NativeLibrary.java:271) at
 * com.sun.jna.NativeLibrary.getInstance(NativeLibrary.java:398) at
 * com.sun.jna.Library$Handler.<init>(Library.java:147) at
 * com.sun.jna.Native.loadLibrary(Native.java:412) at
 * com.sun.jna.Native.loadLibrary(Native.java:391) at
 * viableexamplejava.ViableExample.<clinit>(ViableExample.java:29) Java Result:
 * 1
 * 
 * If this happens, you have to put libViableExample.so into the resource path,
 * in my case into:
 * /home/user/NetBeansProjects/ViableExampleJava/build/classes/
 * 
 * Once it's in there, "Hello World from Java" prints, but nothing else gets
 * printed. "myNativeLibrary_.funcServer(7);" doesn't print anything.
 *
 * Output: 
 * Loading Linux .so 
 * Hello World from Java
 * (The application does not terminate or throw an exception).
 */

这是我使用的 C 代码:

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <time.h> 

/**
 * Unix server that sends clients the date and time.
 * Compiled with -shared -std=c99. 
 * Produces "libViableExampleNative.so" when built with Netbeans on Linux.
 */
int funcServer(int param1) {
    printf("\n Hello World from C. This is a Socket Server Example Program \n");
    printf("\n param1: %d \n", param1);
    {
        int listenfd = 0, connfd = 0;
        struct sockaddr_in serv_addr;

        char sendBuff[1025];
        time_t ticks;
        // Just verifying that the C code is running.
        printf("I made it to line %d in file %s\n", __LINE__, __FILE__);
        listenfd = socket(AF_INET, SOCK_STREAM, 0);
        memset(&serv_addr, '0', sizeof (serv_addr));
        memset(sendBuff, '0', sizeof (sendBuff));

        serv_addr.sin_family = AF_INET;
        serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
        serv_addr.sin_port = htons(5000);

        bind(listenfd, (struct sockaddr*) &serv_addr, sizeof (serv_addr));

        printf("I made it to line %d in file %s\n", __LINE__, __FILE__);
        listen(listenfd, 10);

        while (1) {
            connfd = accept(listenfd, (struct sockaddr*) NULL, NULL);

            ticks = time(NULL);
            snprintf(sendBuff, sizeof (sendBuff), "%.24s\r\n", ctime(&ticks));
            write(connfd, sendBuff, strlen(sendBuff));

            close(connfd);
            sleep(1);
        }
    }
    return 0;
}

更新 1

尝试将 .so 放入 jar 文件中，然后从终端运行它(UnsatisfiedLinkError:无法加载库“libViableExampleNative.so”:无法获取 linux-x86-64/libViableExampleNative.so 的 InputStream:

$ zip ./ViableExampleJava.jar ./libViableExampleNative.so 
  adding: libViableExampleNative.so (deflated 73%)

~/NetBeansProjects/ViableExampleJava/dist$ java -jar ./ViableExampleJava.jar 
Loading Linux .so

Exception in thread "main" java.lang.UnsatisfiedLinkError: Unable to load library 'libViableExampleNative.so': Can't obtain InputStream for linux-x86-64/libViableExampleNative.so
    at com.sun.jna.NativeLibrary.loadLibrary(NativeLibrary.java:271)
    at com.sun.jna.NativeLibrary.getInstance(NativeLibrary.java:398)
    at com.sun.jna.Native.register(Native.java:1396)
    at com.sun.jna.Native.register(Native.java:1156)
    at viableexamplejava.ViableExample.<clinit>(ViableExample.java:33)

* 更新 2 *

尝试设置系统属性“jna.library.path”

从终端(不是 Netbeans)运行时的正确输出:

// Set jnaPath to: /home/user/NetBeansProjects/ViableExampleNative/dist/Debug/GNU-Linux-x86

$ java -jar ./ViableExampleJava.jar

Hello World from Java

 Hello World from C. This is a Socket Server Example Program 

 param1: 7 
I made it to line 26 in file ../../Desktop/Dropbox/ViableExample/native/ViableExample.c
I made it to line 37 in file ../../Desktop/Dropbox/ViableExample/native/ViableExample.c

* 更新 3 *

尽管它可以在 Ubuntu Linux 终端上运行，但我的 Windows 版本(带有 Cygwin)失败了。

Answer 1

尝试在 Netbeans 之外运行它。

当我在 netbeans 中运行它时，我看到的最后一件事是:

Loading Linux .so
Hello World from Java

当我从终端运行时:

java -jar target/mavenproject5-1.0-SNAPSHOT.jar
Loading Linux .so
Hello World from Java

 Hello World from C. This is a Socket Server Example Program 

 param1: 7 
I made it to line 27 in file newfile.c
I made it to line 38 in file newfile.c

该程序似乎仍在 Netbeans 中运行，但未显示 C 打印输出。我可以说是因为当 telnet 根本没有运行时会显示:

telnet localhost 5000
Trying 127.0.0.1...
telnet: Unable to connect to remote host: Connection refused

但是当程序在 Netbeans 中运行时运行 telnet 会产生这个:

Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Tue Aug  4 19:46:38 2015
Connection closed by foreign host.