JNI Hello World不满意链接错误 [英] JNI Hello World Unsatisfied Link Error
问题描述
这是我第一次尝试JNI。我的最终目标是让所有任务当前在一台机器上运行,但需要运行一个简单的例子。当我尝试执行我的主程序时,我不断收到此错误。我提供了简单的Java主程序,生成的头文件和错误。
This is my first attempt at JNI. My ultimate goal is to get all tasks currently running on a machine, but need to get even a simple example running. I keep getting this error when I try to execute my main program. I have supplied my simple Java main program, the header file generated, and the error.
我不知道这个DLL可能依赖什么。它最初引用了我追踪并放入system32(msvcr90.dll)的DLL。
I do not know what this DLL could be dependent on. It was initially referencing a DLL I tracked down and placed into system32 (msvcr90.dll).
这是我用来编译C代码的命令,它生成了DLL,OBJ,LIB,EXP和清单文件。
Here is the command I used to compile the C code as well which produced the DLL, OBJ, LIB, EXP and manifest files.
cl -IC:\Program Files\Java \ _jdk1.6.0 \ include-IC:\Program Files\Java\jdk1.6.0\include \\ \\ win32-MD -LD HelloWorld.c -FeHelloWorld.dll
cl -I"C:\Program Files\Java\jdk1.6.0\include" -I"C:\Program Files\Java\jdk1.6.0\include\win32" -MD -LD HelloWorld.c -FeHelloWorld.dll
class HelloWorld {
private native void print();
public static void main(String[] args) {
new HelloWorld().print();
}
static {
System.load("C:\\temp\\HelloWorld.dll");
}
}
#include <jni.h>
#include <stdio.h>
#include "HelloWorld.h"
JNIEXPORT void JNICALL
Java_HelloWorld_print(JNIEnv *env, jobject obj)
{
printf("Hello World!\n");
return;
}
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class HelloWorld */
#ifndef _Included_HelloWorld
#define _Included_HelloWorld
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: HelloWorld
* Method: print
* Signature: ()V
*/
JNIEXPORT void JNICALL Java_HelloWorld_print
(JNIEnv *, jobject);
#ifdef __cplusplus
}
#endif
#endif
java.lang.UnsatisfiedLinkError: C:\temp\HelloWorld.dll: A dynamic link library (DLL) initialization routine failed
at java.lang.ClassLoader$NativeLibrary.load(Native Method)
at java.lang.ClassLoader.loadLibrary0(Unknown Source)
at java.lang.ClassLoader.loadLibrary(Unknown Source)
at java.lang.Runtime.load0(Unknown Source)
at java.lang.System.load(Unknown Source)
at HelloWorld.<clinit>(HelloWorld.java:7)
Exception in thread "main"
推荐答案
不满意的链接错误可能意味着许多事情都出错了。我会用
The Unsatisfied Link Error can mean many things went wrong. I would use
System.loadLibrary("HelloWorld");
而不是
System.load();
正如TwentyMiles建议的那样。
As TwentyMiles suggested.
此外,在调用程序时,您需要(假设您的DLL与您的类文件位于同一目录中:
Also, when invoking your program you need to (assuming your DLL is on the same directory as your class files:
java -Djava.library.path = .HelloWorld
java -Djava.library.path=. HelloWorld
这是我做的一个简单演示,调用Win32 API函数(MessageBox)
Here's a simple demo I made that calls a Win32 API function (MessageBox)
class CallApi{
private native String showMessageBox(String msg);
private native double getRandomDouble();
static{
try{
System.loadLibrary("CallApi");
System.out.println("Loaded CallApi");
}catch(UnsatisfiedLinkError e){
//nothing to do
System.out.println("Couldn't load CallApi");
System.out.println(e.getMessage());
}
}
public static void main(String args[]){
CallApi api = new CallApi();
double randomNumber = api.getRandomDouble();
String retval = api.showMessageBox("Hello from Java!\n"+
"The native random number: "+randomNumber);
System.out.println("The native string: "+retval);
}
}
生成的头文件
Generated header file
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class CallApi */
#ifndef _Included_CallApi
#define _Included_CallApi
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: CallApi
* Method: showMessageBox
* Signature: (Ljava/lang/String;)Ljava/lang/String;
*/
JNIEXPORT jstring JNICALL Java_CallApi_showMessageBox
(JNIEnv *, jobject, jstring);
/*
* Class: CallApi
* Method: getRandomDouble
* Signature: ()D
*/
JNIEXPORT jdouble JNICALL Java_CallApi_getRandomDouble
(JNIEnv *, jobject);
#ifdef __cplusplus
}
#endif
#endif
C DLL代码
The C DLL code
#include "CallApi.h"
#include <windows.h>
#include <stdlib.h>
#include <time.h>
#pragma comment(lib,"user32.lib")
JNIEXPORT jstring JNICALL Java_CallApi_showMessageBox
(JNIEnv *env, jobject thisObject, jstring js)
{
//first convert jstring to const char for use in MessageBox
const jbyte* argvv = (*env)->GetStringUTFChars(env, js, NULL);
char* argv =(char *) argvv;
//Call MessageBoxA
MessageBox(NULL, argv, "Called from Java!", MB_ICONEXCLAMATION | MB_OK);
return js;
}
JNIEXPORT jdouble JNICALL Java_CallApi_getRandomDouble
(JNIEnv *env, jobject thisObject)
{
double num1;
srand((unsigned)(time(0)));
num1 = ((double)rand()/(double)RAND_MAX);
return num1;
}
编译说明
我使用Visual C ++ express 2008 cl进行编译,删除-ML标志,因为当Java代码尝试调用本机代码时会导致异常:
Compile instructions
I compile with the Visual C++ express 2008 cl, removing the -ML flag since it causes an exception when the Java code tries to call the native code:
cl / I c:\Program Files \ Java \ _ddk1.6.0_10 \ include/ Ic:\ Program Files \ Java @\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ -FeCallApi.dll
cl /I"c:\Program Files\Java\jdk1.6.0_10\include" /I"c:\Program Files\Java\jdk1.6.0_10\include\win32" -LD CallApi.c -FeCallApi.dll
然后,运行代码:
java -Djava.library.path =。 CallApi
java -Djava.library.path=. CallApi
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