Getting ConnectException in linux with Hello World socket program
Hello
i'm running a hello world application that uses sockets ( [found here|http://blog.taragana.com/index.php/archive/understanding-java-simplified-hello-world-for-socket-programming/] ) . I'm running it using a windows machine and a linux machine. When the windows machine is the server, and linux the client, no problem, the application works fine. But when the server is linux and the client is in windows i got a
java.net.ConnectException: Connection timed out: connect
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:352)
in the linux machine i've checked the port being used and it seems to be listening
logan@logan-desktop:~$ netstat --listening |grep 6500
tcp6 0 0 [::]:6500 [::]:* LISTEN
i've also tried changing the port and i got the same error
and i have to say that there is no firewall installed in the linux machine and in the windows machine i disabled the firewall but i'm still getting the same error
what else should i check? or any clue about what could be happening?
thank you in advance
any help would be appreciated
puki_el_pagano wrote:
i'm running a hello world application that uses sockets ( [found here|http://blog.taragana.com/index.php/archive/understanding-java-simplified-hello-world-for-socket-programming/] ) . I'm running it using a windows machine and a linux machine. When the windows machine is the server, and linux the client, no problem, the application works fine. But when the server is linux and the client is in windows i got a
java.net.ConnectException: Connection timed out: connect
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:352)
in the linux machine i've checked the port being used and it seems to be listening
logan@logan-desktop:~$ netstat --listening |grep 6500
tcp6 0 0 [::]:6500 [::]:* LISTEN
i've also tried changing the port and i got the same error
and i have to say that there is no firewall installed in the linux machine Are you absolutely sure?
what else should i check? On the windows box
open a cmd window
C:> telnet linuxbox 6500
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extern "C" {
#endif
* Class: com_myPackage_HelloWorldCaller
* Method: displayHelloWorld
* Signature: ()V
JNIEXPORT void JNICALL Java_com_myPackage_HelloWorldCaller_displayHelloWorld
(JNIEnv *, jobject);
#ifdef __cplusplus
#endif
#endif
The implementation of the native dll function - HelloWorldImp.c -file
* File: HelloWorldImp.c
* Author: mike
* Created on 26. M?rz 2004, 14:34
#include <jni.h>
#include <stdio.h>
#include "com_myPackage_HelloWorldCaller.h"
/* The implementation of the native method
JNIEXPORT void JNICALL Java_com_myPackage_HelloWorldCaller_displayHelloWorld(JNIEnv *env, jobject obj)
printf("Hello world!\n");
return;
Compile the HelloWorldImp.c ? file to a *.dll
On MS Win with Cygwin, the following command builds a dynamic link library HelloWorldImp.dll:
This command is one line without line-breaks.
Check your include because I use the j2sdk1.4.2_04 if you want to do like me than install it.
For j2sdk1.4.2_04:
$ gcc -Wall -mno-cygwin -I/cygdrive/c/j2sdk1.4.2_04/include
-I/cygdrive/c/j2sdk1.4.2_04/include/win32 -shared
HelloWorldImp.c -Wl,--add-stdcall-alias -o HelloWorldImp.dllFor j2sdk1.4.2 as co-installation with NetBeans:
$ gcc -Wall -mno-cygwin -I/cygdrive/c/j2sdk1.4.2/j2sdk1.4.2/include
-I/cygdrive/c/j2sdk1.4.2/j2sdk1.4.2/include/win32 -shared
HelloWorldImp.c -Wl,--add-stdcall-alias -o HelloWorldImp.dll
The used Switches:
-Wall : switches on all warnings
-mno-cygwin : switches off the use of unix-API's, instead of it uses win32-calls
-I<directory> : defines a path to a directory with include *.h-files
-shared : advices the compiler to make shared libraries (*.so for linux and *.dll for win)
-Wl,<option> : Pass an option to the linker (for Wl: l is an L not an 1 and stands for linker)
-Wl,--add-stdcall-alias : pass the switch --add-stdcall-alias to the linker, advices the linker to add standardcalls so the exports have an standard-call alias as well.
The exports of the resulting dll:
If you want to test the exports yourself use : http://ftp.berlios.de/pub/unimatrix-fulda/win-devel/impdef.zip and compile it.
impdef.exe is a small program resulting the dll's EXPORTS to standard-device, screen:
$ impdef HelloWorldImp.dll
EXPORTS
Java_com_myPackage_HelloWorldCaller_displayHelloWorld
Java_com_myPackage_HelloWorldCaller_displayHelloWorld@8On Linux:
Not tested, only a sample copy from an other helping guy's text!
gcc -I../ -o libtestjni.so testjni.c ***many .a and .o here*** -shared -Wl,-soname,libnative.so
-I/usr/java/jdk/include -I/usr/java/jdk/include/linux -static -lc
On Solaris, the following command builds a shared library libhello.so:
Not tested, only a sample copy from an other helping guy's text!
cc -G -I/usr/local/java/include -I/usr/local/java/include/solaris \
HelloWorldImp.c -o libhello.so
On Microsoft Windows, the following command builds a dynamic link library hello.dll using Microsoft Visual C++ 4.0:
Not tested, only a sample copy from an other helping guy's text!
cl -Ic:\java\include -Ic:\java\include\win32
-LD HelloWorldImp.c -Fehello.dll
Set Your Library Path
DOS shell (Windows 95/NT)
On Windows 9x/NT/2000/(XP), the loadLibrary() method searches for DLLs in the same manner as other language environments do.
The java.library.path is the same as the systems %PATH%-variable.
Add the directory where your *.dll-file exists
SET PATH=%PATH%;X:YourDirectory
or copy your *.dll-file to one of the allready in the PATH mounted directories.
UNIX
% setenv LD_LIBRARY_PATH mylibrarypath
where mylibrarypath is the name of the directory that contains libhello.so.
MacOS
The Java runtime searches the JavaSoft Folder in the Extensions folder in the System Folder for shared libraries. Create an alias to your shared library in the JavaSoft Folder.
Execute the code
If it works fine:
$ java com.myPackage.HelloWorldCaller
start to load the library
load should already be done
Hello world!
If the dll is not found you get:
$ java com.myPackage.HelloWorldCaller
start to load the library
Exception in thread "main" java.lang.UnsatisfiedLinkError: no HelloWorldImp in java.library.path
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1491)
at java.lang.Runtime.loadLibrary0(Runtime.java:788)
at java.lang.System.loadLibrary(System.java:834)
at com.myPackage.HelloWorldCaller.<init>(HelloWorldCaller.java:24)
at com.myPackage.HelloWorldCaller.main(HelloWorldCaller.java:34)
The java.library.path is not as he should be see: ?Set Your Library Path?
If the dll is loaded, but the native method is not reachable you get something like:
$ java com.myPackage.HelloWorldCaller
Exception in thread "main" java.lang.UnsatisfiedLinkError: displayHelloWorld
at com.myPackage.HelloWorldCaller.displayHelloWorld(Native Method)
at com.myPackage.HelloWorldCaller.main(HelloWorldCaller.java:25)
Check the Naming of your native methods C-implementation and the generation of standard-calls. -
I found some tutorial on SUN site on how to use JNI. I'm using Eclipse to compije Java and C (via Cygwin) files. Here are complete files:
Hello.java:
class Hello
public native void sayHello();
static
try
System.loadLibrary("hello");
catch(Exception e)
System.out.println("exc");
public static void main(String[] args)
Hello h = new Hello();
h.sayHello ();
}Hello.c:
#include <mingw/_mingw.h> //because there are some types needed for JNI
#include <jni.h>
#include "Hello.h"
#include <stdio.h>
JNIEXPORT void JNICALL Java_Hello_sayHello
(JNIEnv *env, jobject obj)
printf("Hello world!\n");
return;
}Makefile:
hello.dll : Hello.o Hello.def
gcc -g -shared -Wl,--kill-at -o hello.dll Hello.o hello.def
Hello.o : Hello.c Hello.h
gcc -c -g -I"$(JAVA_HOME)\include" -I"$(JAVA_HOME)\include\win32" Hello.c -o Hello.o
Hello.h : Hello.class
javah -jni Hello
clean :
rm Hello.h
rm Hello.o
rm hello.dllHello.def
EXPORTS
Java_Hello_sayHelloEverything goes well, but when I run java program it does nothin (it should print message, but it just exit without any error).I'm sure that it's something stupid, but I cant see what. Can anyone tell me what am I doing wrong?
Thenks.Answer 1: yes, there was no problem. I compiled and started simple 'hello world' program from Cygwin and from WinXP console, and it worked well.
Answer 2: This is weird, I changed code to this:
Hello.java:
public native int getInt();
System.out.println("Returned int is " + h.getInt());Hello.c:
JNIEXPORT jint JNICALL Java_Hello_getInt
(JNIEnv *env, jobject obj)
return 25;
}It does not print anything. I started this program from Cygwin and from WinXP console, and from Eclipse. Only if I debug in Eclipse (step by step) I get:
Returned int is 25and still I don't get Hello string printed (even if I go step by step). It looks like cygwin has some problem with OS. Do you have any idea what to do, I'm a bit confused?
Thank you.
Message was edited by:
zly
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