I'm writing a simple program to call a Java function from my C program.
Following is my code:
#include <jni.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <pthread.h>
#include <time.h>
#include <stdlib.h>
JNIEnv* create_vm() {
JavaVM* jvm;
JNIEnv *env;
JavaVMInitArgs vm_args;
JavaVMOption options[1];
options[0].optionString - "-Djava.class.path=/home/chanders/workspace/Samples/src/ThreadPriorityTest";
vm_args.version = JNI_VERSION_1_6;
vm_args.nOptions = 1;
vm_args.options = &options;
vm_args.ignoreUnrecognized = JNI_FALSE;
JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args);
return env;
}
void invoke_class(JNIEnv* env) {
jclass helloWorldClass;
jmethodID mainMethod;
jobjectArray applicationArgs;
jstring applicationArg0;
helloWorldClass = (*env)->FindClass(env, "InvocationHelloWorld");
mainMethod = (*env)->GetStaticMethodID(env, helloWorldClass, "main", "([Ljava/lang/String;)V");
applicationArgs = (*env)->NewObjectArray(env, 1, (*env)->FindClass(env, "java/lang/String"), NULL);
applicationArg0 = (*env)->NewStringUTF(env, "From-C-program");
(*env)->SetObjectArrayElement(env, applicationArgs, 0, applicationArg0);
(*env)->CallStaticVoidMethod(env, helloWorldClass, mainMethod, applicationArgs);
}
int main() {
JNIEnv* env = create_vm();
invoke_class(env);
}
I'm compiling the above program using:
gcc -o invoke -I$JAVA_HOME/include/ -I$JAVA_HOME/include/linux -L$JAVA_HOME/jre/lib/amd64/server/ ThreadPriorityTest.c
and i'm getting the following error:
/tmp/ccllsK5O.o: In function `create_vm': ThreadPriorityTest.c:(.text+0x35): undefined reference to `JNI_CreateJavaVM' collect2: ld returned 1 exit status
I'm not really sure what is causing this problem
UPDATE 1
Included the -ljvm in the command line and then got a undefined reference to FUNCTION_NAME
I'm running it on Rhel 6.2
You've got the path to the Java library (the -L option), but not the library itself. You need to include -ljvm on the link line as well.
Related
I'll start with my code:
#include <jni.h>
int main(int argc, char const *argv[]) {
JavaVMInitArgs args;
JNIEnv *env;
JavaVM *vm;
args.version = JNI_VERSION_1_8;
args.ignoreUnrecognized = JNI_FALSE;
JNI_CreateJavaVM(&vm, (void **)&env, &args);
jclass System;
jclass PrintStream;
jobject out;
jfieldID outID;
jstring someText;
jmethodID println;
someText = (*env)->NewStringUTF(env, "Hello World");
System = (*env)->FindClass(env, "java/lang/System");
PrintStream = (*env)->FindClass(env, "java/io/PrintStream");
outID = (*env)->GetStaticFieldID(env, System, "out", "Ljava/io/PrintStream;");
out = (*env)->GetStaticObjectField(env, System, outID);
println = (*env)->GetMethodID(env, PrintStream, "println", "(Ljava/lang/String;)V");
(*env)->CallVoidMethod(env, out, println, someText);
return 0;
}
I would expect it to print "Hello World" but it does not, instead I get Segmentation fault (core dumped) annoying error. I could not figure out what is wrong with this code, I tried to comment out everything after someText = (*env)->NewStringUTF(env, "Hello World"); and the program didn't crash, I also tried to comment only the someText = (*env)->NewStringUTF(env, "Hello World"); and I worked too. I even changed the println signature to "boolean" and passed 0 to it, program printed "false" as I would expect so I guess this is something wrong with NewStringUTF method.
openjdk version "1.8.0_131"
OpenJDK Runtime Environment (build 1.8.0_131-b11)
OpenJDK 64-Bit Server VM (build 25.131-b11, mixed mode)
(gdb) bt
#0 0x00007ffff713b2ff in ?? () from /usr/lib/jvm/java-8-openjdk/jre/lib/amd64/server/libjvm.so
#1 0x00007ffff78955c4 in ?? () from /usr/lib/jvm/java-8-openjdk/jre/lib/amd64/server/libjvm.so
#2 0x00007ffff7507e71 in JNI_CreateJavaVM () from /usr/lib/jvm/java-8-openjdk/jre/lib/amd64/server/libjvm.so
#3 0x0000000000400558 in main (argc=1, argv=0x7fffffffe678) at main.c:11
(gdb) info f
Stack level 0, frame at 0x7fffffffe310:
rip = 0x7ffff713b2ff; saved rip = 0x7ffff78955c4
called by frame at 0x7fffffffe490
Arglist at 0x7fffffffe2c8, args:
Locals at 0x7fffffffe2c8, Previous frame's sp is 0x7fffffffe310
Saved registers:
rbx at 0x7fffffffe2d8, rbp at 0x7fffffffe300, r12 at 0x7fffffffe2e0, r13 at 0x7fffffffe2e8, r14 at 0x7fffffffe2f0,
r15 at 0x7fffffffe2f8, rip at 0x7fffffffe308
after commenting out the NewStringUTF
(gdb) bt
#0 0x00007fffe61082b4 in ?? ()
#1 0x0000000000000246 in ?? ()
#2 0x00007fffe6108160 in ?? ()
#3 0x00007fffffffe0f0 in ?? ()
#4 0x00007fffffffe090 in ?? ()
#5 0x00007ffff78f6748 in ?? () from /usr/lib/jvm/java-8-openjdk/jre/lib/amd64/server/libjvm.so
Backtrace stopped: previous frame inner to this frame (corrupt stack?)
(gdb) info f
Stack level 0, frame at 0x7fffffffde80:
rip = 0x7fffe61082b4; saved rip = 0x246
called by frame at 0x7fffffffde88
Arglist at 0x7fffffffde70, args:
Locals at 0x7fffffffde70, Previous frame's sp is 0x7fffffffde80
Saved registers:
rip at 0x7fffffffde78
After some observations, looks like the function JNI_CreateJavaVM is crashing after NewStringUTF was added, but it's "working" after it's removed. How weird is that?
This is JDK and JRE I am using: https://www.archlinux.org/packages/extra/x86_64/jdk8-openjdk/
I am compiling with this command:
gcc \
-I /usr/lib/jvm/java-8-openjdk/include/ \
-I /usr/lib/jvm/java-8-openjdk/include/linux/ \
-L /usr/lib/jvm/java-8-openjdk/jre/lib/amd64/server/ \
-l jvm \
main.c
And running the file with
export LD_LIBRARY_PATH=/usr/lib/jvm/java-8-openjdk/jre/lib/amd64/server/
./a.out
Next Day
Different code, same problem:
#include <jni.h>
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char const *argv[]) {
JavaVMInitArgs args;
JavaVM *jvm;
JNIEnv *env;
args.version = JNI_VERSION_1_8;
args.ignoreUnrecognized = JNI_FALSE;
printf("%s\n", "Creating VM");
JNI_CreateJavaVM(&jvm, (void **)&env, &args);
printf("%s\n", "VM Was Created");
jclass String = (*env)->FindClass(env, "java/lang/String");
if (String == NULL) {
printf("%s\n", "String was NULL");
exit(1);
}
jmethodID method = (*env)->GetMethodID(env, String, "codePointAt", "(I)I");
if (method == NULL) {
printf("%s\n", "method was NULL");
exit(1);
}
printf("%s\n", "I am finishing here");
(*jvm)->DestroyJavaVM(jvm);
return 0;
}
Compile and run:
$ gcc \
> -I /usr/lib/jvm/java-8-openjdk/include/ \
> -I /usr/lib/jvm/java-8-openjdk/include/linux/ \
> -L /usr/lib/jvm/java-8-openjdk/jre/lib/amd64/server/ \
> -l jvm \
> main.c && ./a.out
Creating VM
Segmentation fault (core dumped)
But if I comment the part of the code:
#include <jni.h>
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char const *argv[]) {
JavaVMInitArgs args;
JavaVM *jvm;
JNIEnv *env;
args.version = JNI_VERSION_1_8;
args.ignoreUnrecognized = JNI_FALSE;
printf("%s\n", "Creating VM");
JNI_CreateJavaVM(&jvm, (void **)&env, &args);
printf("%s\n", "VM Was Created");
jclass String = (*env)->FindClass(env, "java/lang/String");
if (String == NULL) {
printf("%s\n", "String was NULL");
exit(1);
}
/*jmethodID method = (*env)->GetMethodID(env, String, "codePointAt", "(I)I");
if (method == NULL) {
printf("%s\n", "method was NULL");
exit(1);
}*/
printf("%s\n", "I am finishing here");
(*jvm)->DestroyJavaVM(jvm);
return 0;
}
Compile and run:
$ gcc \
> -I /usr/lib/jvm/java-8-openjdk/include/ \
> -I /usr/lib/jvm/java-8-openjdk/include/linux/ \
> -L /usr/lib/jvm/java-8-openjdk/jre/lib/amd64/server/ \
> -l jvm \
> main.c && ./a.out
Creating VM
VM Was Created
I am finishing here
So, for me, it works as expected:
> gdb ./main
...
(gdb) run
Starting program: ..../issue/main
[New Thread 0x1403 of process 2600]
[New Thread 0x1503 of process 2600]
warning: unhandled dyld version (15)
Hello World
[Inferior 1 (process 2600) exited normally]
(gdb)
However, I have slightly different env. macOS and I use Oracle's JDK.
Maybe you can try installing debug info and check what exactly happens inside JDK?
This question already has answers here:
Calling C# method within a Java program
(2 answers)
Closed 7 years ago.
I need to call C# function from java and to this I have created the following.
I have a create a java header file Authenticator.h , here is the code:
#include <jni.h>
/* Header for class Authenticator */
#ifndef _Included_Authenticator
#define _Included_Authenticator
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: Authenticator
* Method: authenticate
* Signature: (Ljava/lang/String;Ljava/lang/String;)Z
*/
JNIEXPORT jboolean JNICALL Java_Authenticator_authenticate
(JNIEnv *, jobject, jstring, jstring);
#ifdef __cplusplus
}
#endif
#endif
I have then create a C# function that Authenticate
namespace SharpAuthenticator
{
public class Authenticator
{
public bool Authenticate(String username,String password)
{
return username == "user" && password == "login";
}
}
}
Then I am trying to call the C# function from C++(project to create a dll) using the code below;
String^ toString(const char *str)
{
int len = (int)strlen(str);
array<unsigned char>^ a = gcnew array<unsigned char>(len);
int i = 0;
while (i < len)
{
a[i] = str[i];
i++;
}
return Encoding::UTF8->GetString(a);
}
bool authenticate(const char *username, const char *password)
{
SharpAuthenticator::Authenticator::Authenticate(toString(username), toString(password));
}
JNIEXPORT jboolean JNICALL Java_Authenticator_authenticate
(JNIEnv *env, jobject c, jstring name, jstring pass)
{
jboolean result;
jboolean isCopyUsername;
const char * username = env->GetStringUTFChars(name, &isCopyUsername);
jboolean isCopypassword;
const char * password = env->GetStringUTFChars(pass, &isCopypassword);
result = authenticate(username, password);
env->ReleaseStringUTFChars(name, username);
env->ReleaseStringUTFChars(pass, password);
return result;
}
And finnally create a dll that i need to call from java. The dll is created and I load it well in java but I get this error log in java. What could I be Missing.
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (0xe0434352), pid=9708, tid=7756
#
# JRE version: 7.0-b147
# Java VM: Java HotSpot(TM) Client VM (21.0-b17 mixed mode, sharing windows-x86 )
# Problematic frame:
# C [KERNELBASE.dll+0x812f]
#
# Failed to write core dump. Minidumps are not enabled by default on client versions of Windows
First of all lets create a C# file like this:
using System;
public class Test{
public Test(){}
public String ping(){
return "C# is here.";
}
}
Then compile this with command below:
csc.exe /target:module Test.cs
You can find csc.exe in install path of .NET framework. After that create java file:
public class Test{
public native String ping();
public static void main(String[] args){
System.load("/path/to/dll");
System.out.println("Java is running.");
Test t = new Test();
System.out.println("Trying to catch C# " + r.ping());
}
}
javac Test.java This generates a Test.class.
javah -jni Test This generates a Test.h file which will be included in
C++ code.
After that we need to create our C++ file:
#include "stdafx.h"
#include "JAVA/Test.h"
#include "MCPP/Test.h"
#pragma once
#using <mscorlib.dll>
#using "Test.netmodule"
JNIEXPORT jstring JNICALL Java_Test_ping(JNIEnv *env, jobject obj){
Test^ t = gcnew Test();
String^ ping = t->ping();
char* str = static_cast<char*>((System::Runtime::InteropServices::Marshal::StringToHGlobalAnsi(ping)).ToPointer());
char cap[128];
strcpy_s(cap, str);
return env->NewStringUTF(cap);
}
Finally:
c:\>java Test
I hope this helps you. A basic example to use function C# in Java.
Sources:
https://www.quora.com/How-common-is-the-problem-of-calling-C-methods-from-Java-Do-many-developers-come-across-such-necessity
I am writing a small C program using Cygwin that launches a Java Virtual Machine (libraries I am using require POSIX environment). So far, I have been able to get it to work as long as I place all of my classes in the same folder as the executable. However, I want to specify an actual JAR file that contains the application I want to run. This does not seem to work though, FindClass simply returns a null. I've narrowed it down to a problem with the classpath setting, like I said, because I can extract my jar file in the same directory as the executable and it will work. Here is a subset of my code:
I've loosely been following this guide: http://www.inonit.com/cygwin/jni/invocationApi/
int main( int argc, char *argv[] )
{
void* jvmDllHandle;
JNIEnv* jenv;
JavaVM* jvm;
JavaVMInitArgs args;
JavaVMOption options[1];
jclass cls;
jmethodID mainMethod;
jobjectArray appArgs;
jstring arg0;
assert( cygwin_internal( CW_SYNC_WINENV ) != 1UL );
jvmDllHandle = LoadLibrary( "c:\\Path\\To\\Application\\jre\\bin\\server\\jvm.dll" );
createJavaVM = dlsym( jvmDllHandle, "JNI_CreateJavaVM" );
args.version = JNI_VERSION_1_6;
args.nOptions = 1;
options[0].optionString = "-Djava.class.path=c:\\Path\\To\\Application\\TheJarFile.jar";
args.options = options;
args.ignoreUnrecognized = JNI_FALSE;
createJavaVM( &jvm, (void **) &jenv, &args );
cls = (*jenv)->FindClass( jenv, "some/package/MainClass" );
assert( cls != NULL ); // This fails.
/// Omitted...
return 0;
}
Tried using -classpath and -cp
int main( int argc, char *argv[] )
{
void* jvmDllHandle;
JNIEnv* jenv;
JavaVM* jvm;
JavaVMInitArgs args;
JavaVMOption options[1];
jclass cls;
jmethodID mainMethod;
jobjectArray appArgs;
jstring arg0;
assert( cygwin_internal( CW_SYNC_WINENV ) != 1UL );
jvmDllHandle = LoadLibrary( "c:\\Path\\To\\Application\\jre\\bin\\server\\jvm.dll" );
createJavaVM = dlsym( jvmDllHandle, "JNI_CreateJavaVM" );
args.version = JNI_VERSION_1_6;
args.nOptions = 1;
options[0].optionString = "-classpath c:\\Path\\To\\Application\\TheJarFile.jar";
args.options = options;
args.ignoreUnrecognized = JNI_FALSE;
createJavaVM( &jvm, (void **) &jenv, &args );
cls = (*jenv)->FindClass( jenv, "some/package/MainClass" );
assert( cls != NULL ); // This fails.
/// Omitted...
return 0;
}
How am I specifying the classpath incorrectly?
On x86-64, the Oracle Windows JDK headers define jint as long. This is 32 bits with Microsoft compilers (which the Oracle JDK is written for) but 64 bits with Cygwin gcc. Since JavaVMInitArgs contains some fields of this type, its binary layout is changed by this discrepancy.
I worked around this by providing a local jni.h header:
#include "stdint.h"
#define __int64 int64_t
#define long int32_t
#include "jni_md.h"
#undef long
#include_next "jni.h"
I'm including only jni_md.h within the scope of the long redefinition because it doesn't include any other headers, whereas jni.h includes a couple of standard headers which we would not want to be affected as well.
To ensure this is always included ahead of the Oracle header, use the -I compiler option to add its directory to the #include path.
Recently I'm learning JNI to execute C code. Of course I did basic examples that were on the web. Now Im trying to load a C library that makes dynamic library loading (dlopen). But Im fighthing with an error. Im posting my Java code, C ++ code and the error.
My Java Class
/**
*
* #author glassfish
*/
public class MediationJniWeb {
public String library ;
static {
System.loadLibrary("-core-web");
}
/**
*
* #param library name of mediation core library [32]
* #param method name of method to be executed [128]
* #param parameters parameters of method [10240]
* [partype1,value1,...,valuen]...[partypen,value1,..,valuen]
* #return
*/
private native String execute();
public static void main(String args[]) {
//new MediationJniWeb().callToFunction(null, null, null) ;
MediationJniWeb jniWeb = new MediationJniWeb();
jniWeb.library = "libtest.so" ;
System.out.println(jniWeb.execute());
}
}
I generate .class file with
javac MediationJniWeb
and I generate .h File with
javah -jni MediationJniWeb
my MediationJniWeb.h file is
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class MediationJniWeb */
#ifndef _Included_MediationJniWeb
#define _Included_MediationJniWeb
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: MediationJniWeb
* Method: execute
* Signature: ()Ljava/lang/String;
*/
JNIEXPORT jstring JNICALL Java_MediationJniWeb_execute
(JNIEnv *, jobject);
#ifdef __cplusplus
}
#endif
#endif
and my MediationJniWEb.cpp file
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
#include <dlfcn.h>
#include <iostream>
#include "MediationJniWeb.h"
using namespace std ;
typedef void (*test)(string);
/*
* Class: MediationJniWeb
* Method: execute
* Signature: ()Ljava/lang/String;
*/
JNIEXPORT jstring JNICALL Java_MediationJniWeb_execute
(JNIEnv * env, jobject obj){
const char * str_library ;
jfieldID fid_library ;
jstring jstr_library ;
jboolean isCopy ;
jclass cls = env->GetObjectClass( obj) ;
fid_library = env->GetFieldID( cls,"library", "Ljava/lang/String;");
jstr_library = ( jstring )env->GetObjectField( obj,fid_library);
str_library = env->GetStringUTFChars( jstr_library, &isCopy) ;
void* handle = dlopen(str_library, RTLD_NOW); // open libtest.so
if ( 0 == handle ) {
cout << "failed to load 'libtest.so'. " << dlerror () <<endl;
exit(1);
}
test t = (test)dlsym(handle, "_Z8testfuncSs"); // run default method
if ( 0 == t ) {
cout << "failed to load 'testfunc()'." << endl;
exit(1);
}
t("Hello, World!");
dlclose(handle);
/*
*/
return env->NewStringUTF( str_library); // I just return library name just for fun
}
}
I compile with
g++ -shared -fpic -I//include/ -I//include/linux/ MediationJniWeb.cpp -o lib-core-web.so MediationJniWeb.cpp -ldl
this generate lib-core-web.so file. Then I copy this to $HOME/lib and I configure
LD_LIBRARY_PATH=$HOME/lib
Now I create my library libtest.so that is going to be executed by lib-core-web.so
I create file for shared libray mylib.cpp
#include <iostream>
#include <string>
using namespace std;
void testfunc(string s)
{
cout << s << endl;
}
I compile this that is going to work as a shared library with
g++ -shared -fpic -o libtest.so mylib.cpp
This command generates libtest.so file.. and also, I copy it to $HOME/lib
That's all I do to call from JNI to a C++ library to load a dynamic library.
when I execute MediationJniWeb java class I'm having this error
failed to load. libtest.so: cannot open shared object file: No such
file or directory
What do I have to do with libtest.so ?? where do I have to put it ?
I have on mind that configuring only LD_LIBRARY_PATH variable with right path, JVM should know where to find all needed libraries to be loaded.
Please help with your comments and let me know where my mistakes are.
Thanks in advance !
A simple thing I have done
instead of
jniWeb.library = "libtest.so"
library parameter to be loaded I declared
jniWeb.library = "/home/myuser/lib/libtest.so"
And it worked !
I'm getting a "error LNK1104: cannot open file {path}\jvm.lib" when trying tocompile a VS C++/CLI (managed) project. It's very simple and my goal is to call some Java methods in pre-existing java libs - here is the code I'm using:
// This is the main DLL file.
#include "stdafx.h"
#include <jni_md.h>
#include <jni.h>
#include "JBridge.h"
#pragma once
using namespace System;
namespace JBridge
{
public ref class JniBridge
{
// TODO: Add your methods for this class here.
public:
void HelloWorldTest()
{
System::Console::WriteLine("Hello Worldl from managed C++!");
}
JNIEnv* create_vm(JavaVM ** jvm)
{
JNIEnv *env;
JavaVMInitArgs vm_args;
JavaVMOption options;
//Path to the java source code
options.optionString = "-Djava.class.path=D:\\Java Src\\TestStruct";
vm_args.version = JNI_VERSION_1_6; //JDK version. This indicates version 1.6
vm_args.nOptions = 1;
vm_args.options = &options;
vm_args.ignoreUnrecognized = 0;
int ret = JNI_CreateJavaVM(jvm, (void**)&env, &vm_args);
if(ret < 0)
printf("\nUnable to Launch JVM\n");
return env;
}
};
}
I've verified the file does exist in the path location and I've added it to the project properties for the include dir and the linker property pages.
Update
Got the jvm.lib to be linked with a bit more fiddling.
Compilation causes following errors during build:
Error 1 error LNK2028: unresolved token (0A00000A) "extern "C" long __stdcall JNI_CreateJavaVM(struct JavaVM_ * *,void * *,void *)" (?JNI_CreateJavaVM##$$J212YGJPAPAUJavaVM_##PAPAXPAX#Z) referenced in function "struct JNIEnv_ * __cdecl create_vm(struct JavaVM_ * *)" (?create_vm##$$FYAPAUJNIEnv_##PAPAUJavaVM_###Z) c:\Temp\CLRTest\JBridge\JBridge\JBridge.obj JBridge
Error 2 error LNK2019: unresolved external symbol "extern "C" long __stdcall JNI_CreateJavaVM(struct JavaVM_ * *,void * *,void *)" (?JNI_CreateJavaVM##$$J212YGJPAPAUJavaVM_##PAPAXPAX#Z) referenced in function "struct JNIEnv_ * __cdecl create_vm(struct JavaVM_ * *)" (?create_vm##$$FYAPAUJNIEnv_##PAPAUJavaVM_###Z) c:\Temp\CLRTest\JBridge\JBridge\JBridge.obj JBridge
Error 3 error LNK1120: 2 unresolved externals c:\temp\CLRTest\JBridge\Debug\JBridge.dll JBridge
Work around was to dynamically load the JVM by using LoadLibrary("path/to/jvm"); and then invoking the native functions.