如何在Linux上编译JNI应用程序的动态库? [英] How to compile dynamic library for a JNI application on linux?
问题描述
我使用 Ubuntu 10.10
这是我做的。
< Hello.java ::
class Hello {
public native void sayHello ;
static {System.loadLibrary(hellolib); }
public static void main(String [] args){
Hello h = new Hello();
h.sayHello();
}
}
然后我运行下面的命令:
dierre @ cox:〜/ Scrivania / provajni $ javac Hello.java
dierre @ cox:〜/ provajni $ javah -jni Hello
我已经获得 Hello.class
和
Hello.h
。
Hello.h :
/ *不要编辑此文件 - 它是机器生成的* /
#include< jni.h>
/ *类Hello的头部/
#ifndef _Included_Hello
#define _Included_Hello
#ifdef __cplusplus
externC{
#endif
/ *
*类:Hello
*方法:sayHello
*签名:()V
* /
JNIEXPORT void JNICALL Java_Hello_sayHello
(JNIEnv *,jobject);
#ifdef __cplusplus
}
#endif
#endif
然后我创建了 Hello.cpp :
#include< jni .h>
#includeHello.h
#include< iostream>
using namespace std;
JNIEXPORT void JNICALL Java_Hello_sayHello(JNIEnv * env,jobject obj){
cout< 你好,世界! << endl;
return;
}
现在的部分,我想我搞砸了。我是由此指南( 编写动态或共享的对象库部分):
dierre @ cox:〜/ Scrivania / provajni $ gcc -I / usr / lib / jvm / java-6-sun / include-I/ usr / lib / jvm / java-6-sun / include / linux-o hellolib.so -shared -Wl,-soname,hello .so Hello.cpp -static -lc
生成文件 hellolib。所以
但是当我尝试用 java运行它Hello
:
线程main中的异常java.lang.UnsatisfiedLinkError:java.library.path中没有hellolib
java.lang.ClassLoader.loadLibrary(ClassLoader.java:1734)
在java.lang.Runtime.loadLibrary0(Runtime.java:823)
在java.lang.System.loadLibrary(System.java: 1028)
在Hello。< clinit>(Hello.java:4)
找不到主类:Hello。程序将退出。
我甚至尝试过:
LD_LIBRARY_PATH =`pwd`
export LD_LIBRARY_PATH
结果。
我知道我做的事情非常蠢,但我不知道是什么。动态库是使用-shared选项生成的,不是吗?
更新#1
我试过 static {System.load(/ home / dierre / Scrivania / provajni / hellolib.so); }
看看是否有效,但现在:
线程mainjava.lang中的异常。 unsatisfiedLinkError:/home/dierre/Scrivania/provajni/hello.so:/home/dierre/Scrivania/provajni/hello.so:未定义的符号:_ZSt4cout
at java.lang.ClassLoader $ NativeLibrary.load(Native Method)
at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1803)
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1699)
at java.lang.Runtime.load0 (Runtime.java:770)
at java.lang.System.load(System.java:1003)
在Hello。< clinit>(Hello.java:4)
更新#2
好,要解决更新#1 问题我必须使用 g ++
insted of gcc
。仍然无法使用加载
方法。我不能告诉它正确的路径。
解决方案 native库可以由loadLibrary加载有效的名称。例如,lib * XXXX *。因此对于linux系列,你的hellolib.so应该重命名为libhello.so。
顺便说一下,我用jni开发java,我将分离实现和本地界面(.c或.cpp)。
static {
System.loadLibrary(hello); //将加载libhello.so
}
实现头(HelloImpl.h):
#ifndef _HELLO_IMPL_H
#define _HELLO_IMPL_H
#ifdef __cplusplus
extern C{
#endif
void sayHello();
#ifdef __cplusplus
}
#endif
#endif
HelloImpl.cpp:
#includeHelloImpl.h
#include< iostream>
using namespace std;
void sayHello(){
cout<< 你好,世界! << endl;
return;
}
Hello.c(我更喜欢在c中编译jni):
#include< jni.h>
#includeHello.h
#includeHelloImpl.h
JNIEXPORT void JNICALL Java_Hello_sayHello(JNIEnv * env,jobject obj){
sayHello ;
return;
}
最后,我们可以通过以下步骤编译它们:
- compile obj(generate HelloImpl.o)
g ++ -c -I/ opt / java / include
-I/ opt / java / include / linuxHelloImpl.cpp
- 使用.o编译jni
g ++ -I/ opt / java / include
-I/ opt / java / include / linux-o libhello.so -shared
-Wl,-soname,hello.so您好。 c HelloImpl.o -static -lc
在步骤2中,我们使用g ++来编译它。这个非常重要。您可以查看如何混合C和C ++
编译之后,可以使用nm检查函数命名:
$ nm libhello。所以| grep说
00000708 T Java_Hello_sayHello
00000784 t _GLOBAL__I_sayHello
00000718 T sayHello
$ b b
有一个Java_Hello_sayHello标记为T.它应该绝对等于你的本地方法名称。如果一切正常。您可以运行它:
$ java -Djava.library.path =。 Hello
Hello World!
I'm using Ubuntu 10.10
So that's what I did.
Hello.java:
class Hello {
public native void sayHello();
static { System.loadLibrary("hellolib"); }
public static void main(String[] args){
Hello h = new Hello();
h.sayHello();
}
}
Then I ran the follwing commands:
dierre@cox:~/Scrivania/provajni$ javac Hello.java
dierre@cox:~/Scrivania/provajni$ javah -jni Hello
I've obtained Hello.class
and Hello.h
.
Hello.h:
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class Hello */
#ifndef _Included_Hello
#define _Included_Hello
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: Hello
* Method: sayHello
* Signature: ()V
*/
JNIEXPORT void JNICALL Java_Hello_sayHello
(JNIEnv *, jobject);
#ifdef __cplusplus
}
#endif
#endif
Then I created Hello.cpp:
#include <jni.h>
#include "Hello.h"
#include <iostream>
using namespace std;
JNIEXPORT void JNICALL Java_Hello_sayHello (JNIEnv *env, jobject obj) {
cout << "Hello World!" << endl;
return;
}
And now the part where I think I screwed up. I was inspired by this guide (Compile the Dynamic or Shared Object Library section):
dierre@cox:~/Scrivania/provajni$ gcc -I"/usr/lib/jvm/java-6-sun/include" -I"/usr/lib/jvm/java-6-sun/include/linux" -o hellolib.so -shared -Wl,-soname,hello.so Hello.cpp -static -lc
that generates the file hellolib.so
But when I try to run it with java Hello
I have this error:
Exception in thread "main" java.lang.UnsatisfiedLinkError: no hellolib in java.library.path
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1734)
at java.lang.Runtime.loadLibrary0(Runtime.java:823)
at java.lang.System.loadLibrary(System.java:1028)
at Hello.<clinit>(Hello.java:4)
Could not find the main class: Hello. Program will exit.
I even tried this:
LD_LIBRARY_PATH=`pwd`
export LD_LIBRARY_PATH
with no results.
I know I'm doing something extremely stupid but I can't figure out what it is. The dynamic lib is generated with the -shared option, isn't it?
Update #1
I tried static { System.load("/home/dierre/Scrivania/provajni/hellolib.so"); }
to see if that worked but now:
Exception in thread "main" java.lang.UnsatisfiedLinkError: /home/dierre/Scrivania/provajni/hello.so: /home/dierre/Scrivania/provajni/hello.so: undefined symbol: _ZSt4cout
at java.lang.ClassLoader$NativeLibrary.load(Native Method)
at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1803)
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1699)
at java.lang.Runtime.load0(Runtime.java:770)
at java.lang.System.load(System.java:1003)
at Hello.<clinit>(Hello.java:4)
Update #2
Ok, to solve the Update #1 problem I had to use g++
insted of gcc
, obviously. Still having trouble to use the load
method though. I can't seem to tell it the right path.
解决方案 Native library can be loaded by loadLibrary with a valid name. By example, lib*XXXX*.so for linux family, your hellolib.so should rename to libhello.so.
By the way, I develop java with jni, I will separate the implementation and native interface (.c or .cpp).
static {
System.loadLibrary("hello"); // will load libhello.so
}
The implementation header(HelloImpl.h):
#ifndef _HELLO_IMPL_H
#define _HELLO_IMPL_H
#ifdef __cplusplus
extern "C" {
#endif
void sayHello ();
#ifdef __cplusplus
}
#endif
#endif
HelloImpl.cpp:
#include "HelloImpl.h"
#include <iostream>
using namespace std;
void sayHello () {
cout << "Hello World!" << endl;
return;
}
Hello.c (I prefer to compile jni in c):
#include <jni.h>
#include "Hello.h"
#include "HelloImpl.h"
JNIEXPORT void JNICALL Java_Hello_sayHello (JNIEnv *env, jobject obj) {
sayHello();
return;
}
Finally, we can compile them in some steps:
- compile obj (generate HelloImpl.o)
g++ -c -I"/opt/java/include"
-I"/opt/java/include/linux" HelloImpl.cpp
- compile jni with .o
g++ -I"/opt/java/include"
-I"/opt/java/include/linux" -o libhello.so -shared
-Wl,-soname,hello.so Hello.c HelloImpl.o -static -lc
in step 2, we use g++ to compile it. This is very important. yor can see How to mix C and C++
After compilation, you can check the function naming with nm:
$ nm libhello.so |grep say
00000708 T Java_Hello_sayHello
00000784 t _GLOBAL__I_sayHello
00000718 T sayHello
There is a Java_Hello_sayHello marked T. It should extactly equal to your native method name. If everything is ok. you can run it:
$ java -Djava.library.path=. Hello
Hello World!
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