How to run .java file from Runnable

[Alex Teslin]

Hi, I am trying to run .java file/class using exec() method. First, when try to compile in the code below, i get 1 as an exit value. I also would like to run that file - any suggestions please?

    
 
public static void main(String[] args) throws Exception
    {
        try {
            String line;
            Runtime rt = Runtime.getRuntime();
            Process p = rt.exec("javac c://Temp//MainTest.java");
            int exitVal = p.waitFor();
            String osName = System.getProperty("os.name");
            System.out.println(osName);
            System.out.println("Process exitValue: " + exitVal);
            System.out.println("Is it compiled");
            }
         catch(IOException e) {
            System.err.println("Error on exec() method");
            e.printStackTrace();
        }
    }   

[Alex Teslin]

I have just eliminated unnecessary lines here.

    
   public static void main(String[] args) throws Exception
    {
        try {
 
            Runtime rt = Runtime.getRuntime();
            Process p = rt.exec("javac c://Temp//MainTest.java");
            int exitVal = p.waitFor();
            System.out.println("Process exitValue: " + exitVal);
            }
         catch(IOException e) {
            System.err.println("Error on exec() method");
            e.printStackTrace();
        }
    }

[Keith Lynn]

Have you tried this?

public static void main(String[] args) throws Exception
{
try {

Runtime rt = Runtime.getRuntime();

String[] cmd = {"cmd.exe","/c",full path to javac.exe,"c://Temp//MainTest.java"};

Process p = rt.exec(cmd);
int exitVal = p.waitFor();
System.out.println("Process exitValue: " + exitVal);
}
catch(IOException e) {
System.err.println("Error on exec() method");
e.printStackTrace();
}
}

[Alex Teslin]

What "/c" stands for after ("cmd.exe","/c")?

[Keith Lynn]

This is the information given about /c when I do a cmd /?

CMD [/A | /U] [/Q] [/D] [/E :-o	 N | /E :-o	 FF] [/F :-o	 N | /F :-o	 FF] [/V :-o	 N | /V :-o	 FF]
    [[/S] [/C | /K] string]
 
/C      Carries out the command specified by string and then terminates

[Alex Teslin]

I get the same result. Does "Program Files" space could be a problem? That is where my jdk is.

[Keith Lynn]

Possibly.

You can abbreviate it c:\\progra~1\\...

[Alex Teslin]

Thanks Keith,

I tried both to abbreviate to progra~1 and also used "quotes" for that path - still no luck. It must something else.
If i had ixitValue 2 on Windows it would mean "file not found" error. But not sure about 1.

[Ernest Friedman-Hill]

Despite the subject line, this has nothing to do with Runnable or with threads. Moving to "Java in General (Intermediate.)"

[Keith Lynn]

Alex,
Try including this after you call exec.

BufferedReader input = new BufferedReader(new InputStreamReader(p.getErrorStream()));
 
String temp = "";
 
while ((temp = input.readLine())
   System.out.println(temp);
 
input.close();

[Alex Teslin]

Thanks Keith,

I have managed to compile now - the error massage was very helpful and i corrected it.

Now, i am trying to run it. First i am creating another String[] cmd2 with

{"cmd.exe","/c", "c://progra~1//Java//jdk1.5.0_05//bin//java.exe", "c://Temp//Test1//MainTest"};

I am envoking getRutime() again like this:
Runtime rt2 = Runtime.getRuntime();
p = rt2.exec(cmd2);

and error i am getting now is:

java.lang.NoClassDefFoundError: c://Temp//Test1//MainTest
Exception in thread "main"

Now, it seems that compiles OK and if it does why can not find a class file.
Or am i missing with my running code?

Thanks again

[Keith Lynn]

You'll probably need to explicitly set the classpath as part of the command line.

For instance, if your .class file is in c:\\temp, then you could do something like

java -cp c:\\temp ...

Also don't list the full path to the .class file. The CLASSPATH should contain that information.
[ February 24, 2006: Message edited by: Keith Lynn ]

[Ernest Friedman-Hill]

Originally posted by Alex Teslin:

{"cmd.exe","/c", "c://progra~1//Java//jdk1.5.0_05//bin//java.exe", "c://Temp//Test1//MainTest"};
...
java.lang.NoClassDefFoundError: c://Temp//Test1//MainTest

First of all, using the "cmd /c" is not useful here. I imagine that what helped the first time was specifying the full path to javac.exe -- perhaps it's not on your PATH. But just as you don't need to type "cmd /c javac..." at the command line, neither do you need to do it with Runtime.exec().

Second, the argument to java.exe is not the path to a file. It is the name of a class, including its package name. "C:\" is never an appropriate part of that argument to java.exe.

Third, the doubled forward slashes are both unnecessary and inappropriate.

Assuming MainTest is in the default package, you could do something like

rt2.exec("c:/progra~1/Java/jdk1.5.0_05/bin/java.exe -cp c:/Temp/Test1 MainTest");

or if it's in the package "Test1" then you'd want to do

rt2.exec("c:/progra~1/Java/jdk1.5.0_05/bin/java.exe -cp c:/Temp Test1.MainTest");

[Alex Teslin]

Keith,

I have tried many different ways - still no luck.
I will put my code here and hopefully for last time now.

 
public static void main(String args[]) throws Exception
    {
        try {
            String line;
            Runtime rt = Runtime.getRuntime();
            String[] cmd = { 
                "cmd.exe","/c", "c://progra~1//Java//jdk1.5.0_05//bin//javac.exe", "c://Temp//Test1.java"
            };
             String[] cmd2 = { 
                "cmd.exe","/c", "c://progra~1//Java//jdk1.5.0_05//bin//java.exe", "c://Temp//Test1"
            };
            Process p = rt.exec(cmd);
            
            Runtime rt2 = Runtime.getRuntime();
            p = rt2.exec(cmd2);
                        
            BufferedReader input = new BufferedReader(new InputStreamReader(p.getErrorStream()));
            String temp = "";
            while((temp = input.readLine()) != null) {
                System.out.println(temp);
            }
            input.close();
   

I will be greatfull if you let me know what is wrong with it

[Keith Lynn]

Try this.

public static void main(String args[]) throws Exception
    {
        try {
            String line;
            Runtime rt = Runtime.getRuntime();
            String[] cmd = { 
                "cmd.exe","/c", "c://progra~1//Java//jdk1.5.0_05//bin//javac.exe", "c://Temp//Test1.java"
            };
             String[] cmd2 = { 
                "cmd.exe","/c", "c://progra~1//Java//jdk1.5.0_05//bin//java.exe", "-cp","c://Temp","Test1"
            };
            Process p = rt.exec(cmd);
            
            Runtime rt2 = Runtime.getRuntime();
            p = rt2.exec(cmd2);
                        
            BufferedReader input = new BufferedReader(new InputStreamReader(p.getErrorStream()));
            String temp = "";
            while((temp = input.readLine()) != null) {
                System.out.println(temp);
            }
            input.close();

[ February 24, 2006: Message edited by: Keith Lynn ]

[Ernest Friedman-Hill]

Originally posted by Alex Teslin:

I will be greatfull if you let me know what is wrong with it

My message has some important stuff -- you may not have read it yet. Another thing that that your compilation will almost certainly not have finished when you start the second process. You need to call p.waitFor() after starting the compilation and wait for it to return before you proceed.

[Alex Teslin]

I have eliminated Double slashes - it was wrong.
I also deleted cmd.exe and c/ - it works now without them.

But when i try not to pass the classpath of the MainTest to java.exe as an argument - it does no work. Well it does not work either way. But by passing as an argument it completes the try block. Without the argument after the compilation jumps to Exception.

Keith, with your code still would not work.

[Alex Teslin]

I also called p.waitFor() just after compilation.

[Keith Lynn]

Alex,
Here is an example showing how you can do what you want. Remember that when you run a program through exec, the Process does not put its output on standard out nor does it put its errors on standard err. You have to read those streams.

import java.io.*;
 
public class InterpretProgram {
 
   public static String readStream(InputStream stream) {
      String output = "";
 
      try {
         BufferedReader input = new BufferedReader(new InputStreamReader(stream));
 
         String temp = "";
 
         while ((temp = input.readLine()) != null)
            output += temp + "\n";
 
         input.close();
      } catch (IOException ie) {
      }
 
      return(output);
   }
 
   public static void main(String[] args) {
      try {
         String[] cmd = {"cmd.exe",
                         "/c",
                         "c:\\progra~1\\java\\jdk1.5.0_05\\bin\\java.exe",
                         "-classpath",
                         "c:\\temp",
                         "Test1"};
 
         Process p = Runtime.getRuntime().exec(cmd);
 
         System.out.println("Output: " + readStream(p.getInputStream()));
 
         System.out.println("Errors: " + readStream(p.getErrorStream()));
      } catch (IOException ie) {
      }
   }
 
}

[Alex Teslin]

Thank you for your example Keith,
The problem i had was precisely that, that I was expecting to get printouts on standard output not knowing that the program was running.

Thanks for your help