Question

Hello everyone don’t know why this code works on windows but not on linux so if anyone sees something wrong with this or another way of doing this I would really appreciate some guidance thanks for your time.

Process p = Runtime.getRuntime().exec(linuxCommand);
int cont=0,retorno=p.waitFor();
try {
     synchronized (this) {
     while (retorno!=0 && conteo<10000){
         retorno=p.waitFor();
         System.out.println("cont++);
     }
    if (retorno == 0) {
        ans = true;
        logger.info("Return Value: " + ans);
    }else{
        ans = false;
        logger.info("Return Value: " + ans);
    }
 }

} catch (InterruptedException e) {
    e.printStackTrace();
}

Objective: create *1_Output.txt* from the info contained in *1_Input.txt*,

MyObjectT resides in /var/xp/client/a/h/n/test
MyObjectT will call several classes in /var/xp/client/a/h/n/clases/z1, and eventually READ the content of 1_Output.txt so it can return ans(true/false)

PROBLEM

• on windows: the flow when to fast it did not wait for the 1_Output.txt file to be created so there was nothing to read, with current code that was solved. (p.waitFor() eventually return 0 and everyone is happy)
• Linux : p.waitFor() never returns 0 the flow ends and nothing

linuxCommand is a parsed String that represent a java command to be executed in linux

notice that if I paste this command as it is in the command shell it would run ok with no warning or error . I donw think “ play an important role here. linuxCommand->
/opt/jdk/jdk1.6.0_22/bin/java -classpath “/var/xp/client/a/h/n/clases/z1″:”/var/xp/client/a/h/n/test” MyObjectT /m:Param21 /f:”/var/xp/client/a/h/n/IOFile/1_Input.txt” /o:”/var/xp/client/a/h/n/IOFile/1_Output.txt”

so what confuses me is that if use getErrorStream() to track down some errors an I get this

Exception in thread "main" java.lang.NoClassDefFoundError: MyObjectT 
Caused by: java.lang.ClassNotFoundException: MyObjectT 
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Could not find the main class: MyObjectT.  Program will exit.

any help, its much appreciated thank again

lol Im sorry for the variable name in spanish retorno=return but at the time I translated I did not stop and think about the return ajajjaajajajaj :=)

Answer 1

There’s a few things in play, simultaneously. First, you’ve got multiple programs running — this one and the one that you’re spawning — and the errors in that program are causing troubles here.

First, the linuxCommand:

/opt/jdk/jdk1.6.0_22/bin/java -classpath
"/var/xp/client/a/h/n/clases/z1":"/var/xp/client/a/h/n/test"
MyObjectT /m:Param21 /f:"/var/xp/client/a/h/n/IOFile/1_Input.txt"
/o:"/var/xp/client/a/h/n/IOFile/1_Output.txt"

I’ve arbitrarily line-wrapped it. Depending upon how you’ve defined this string in your program, you may need to escape all those " marks in this string. (If you just print this using System.out.println(), what does it look like?)

Probably the better approach is to use a slightly different form of exec(), one that takes an array of strings instead of a single string. This way you can break the parameters as the program requires without worrying about proper shell quoting. It’d look something like this (untested) chunk:

String linuxCommand[] = {"/opt/jdk/jdk1.6.0_22/bin/java",
                         "-classpath",
                         "/var/xp/client/a/h/n/clases/z1:/var/xp/client/a/h/n/test",
                         "MyObjectT",
                         "/m:Param21",
                         "/f:/var/xp/client/a/h/n/IOFile/1_Input.txt",
                         "/o:/var/xp/client/a/h/n/IOFile/1_Output.txt"};
Process p = Runtime.getRuntime().exec(linuxCommand);

You did say you’ve run this command by hand in a shell to confirm it works, but those /i, /o, etc. feel very awkward on a Unix-alike platform. Are you confident that format works as expected on Linux?