Execute OS command

E

Earl Lewis

You java gurus probably hate it when a posting starts like this, but
here goes anyway. Sorry, in advance!

Disclaimer: I'm not a java guru. I know how to spell it and I've
written some basic OO stuff. I now have a real problem that I'm trying
to solve but have no idea how best to implement it.

Here's the situation. I have a small java routine (in Oracle) that
executes an operating system command. Here's that code:

import java.io.*;
public class Host {
public static void executeCommand(String command) {
try {
String[] finalCommand;
if (isWindows()) {
finalCommand = new String[4];
// Use the appropriate path for your windows version.
finalCommand[0] = "C:\\windows\\system32\\cmd.exe"; //
Windows XP/2003
//finalCommand[0] = "C:\\winnt\\system32\\cmd.exe"; //
Windows NT/2000
finalCommand[1] = "/y";
finalCommand[2] = "/c";
finalCommand[3] = command;
}
else {
finalCommand = new String[3];
finalCommand[0] = "/bin/sh";
finalCommand[1] = "-c";
finalCommand[2] = command;
}

final Process pr = Runtime.getRuntime().exec(finalCommand);
pr.waitFor();

new Thread(new Runnable(){
public void run() {
BufferedReader br_in = null;
try {
br_in = new BufferedReader(new
InputStreamReader(pr.getInputStream()));
String buff = null;
while ((buff = br_in.readLine()) != null) {
System.out.println("Process out :" + buff);
try {Thread.sleep(100); } catch(Exception e) {}
}
br_in.close();
}
catch (IOException ioe) {
System.out.println("Exception caught printing process
output.");
ioe.printStackTrace();
}
finally {
try {
br_in.close();
} catch (Exception ex) {}
}
}
}).start();

new Thread(new Runnable(){
public void run() {
BufferedReader br_err = null;
try {
br_err = new BufferedReader(new
InputStreamReader(pr.getErrorStream()));
String buff = null;
while ((buff = br_err.readLine()) != null) {
System.out.println("Process err :" + buff);
try {Thread.sleep(100); } catch(Exception e) {}
}
br_err.close();
}
catch (IOException ioe) {
System.out.println("Exception caught printing process
error.");
ioe.printStackTrace();
}
finally {
try {
br_err.close();
} catch (Exception ex) {}
}
}
}).start();
}
catch (Exception ex) {
System.out.println(ex.getLocalizedMessage());
}
}

public static boolean isWindows() {
if
(System.getProperty("os.name").toLowerCase().indexOf("windows") != -1)
return true;
else
return false;
}

};

What I want to do is put a timer in this code that will only allow the
command to attempt to run for a set amount of time, and when that time
elapses the program will decide that the command isn't going to work
and it quits with an error message.

The way I understand the documentation, as the code is written right
now (with the pr.waitFor(); line) it will wait for the process (in
this case an OS command) to complete before the code will continue.
That seems to bear out in my testing so far.

I've seen also in the javadocs where you can call Thread.join(50000);
or something similar, to join the running thread and if it doesn't
complete in the specified time that it will kill the thread. Is this
the right approach to solving this problem? Is the problem even clear?
Any suggestions about how to do this and where to put the suggested
code snippets will be greatly appreciated. Thank you.

Sincerely,

Earl
 
N

Nigel Wade

Earl said:
You java gurus probably hate it when a posting starts like this, but
here goes anyway. Sorry, in advance!

Disclaimer: I'm not a java guru. I know how to spell it and I've
written some basic OO stuff. I now have a real problem that I'm trying
to solve but have no idea how best to implement it.

Here's the situation. I have a small java routine (in Oracle) that
executes an operating system command. Here's that code:

import java.io.*;
public class Host {
public static void executeCommand(String command) {
try {
String[] finalCommand;
if (isWindows()) {
finalCommand = new String[4];
// Use the appropriate path for your windows version.
finalCommand[0] = "C:\\windows\\system32\\cmd.exe"; //
Windows XP/2003
//finalCommand[0] = "C:\\winnt\\system32\\cmd.exe"; //
Windows NT/2000
finalCommand[1] = "/y";
finalCommand[2] = "/c";
finalCommand[3] = command;
}
else {
finalCommand = new String[3];
finalCommand[0] = "/bin/sh";
finalCommand[1] = "-c";
finalCommand[2] = command;
}

final Process pr = Runtime.getRuntime().exec(finalCommand);
pr.waitFor();

new Thread(new Runnable(){
public void run() {
BufferedReader br_in = null;
try {
br_in = new BufferedReader(new
InputStreamReader(pr.getInputStream()));
String buff = null;
while ((buff = br_in.readLine()) != null) {
System.out.println("Process out :" + buff);
try {Thread.sleep(100); } catch(Exception e) {}
}
br_in.close();
}
catch (IOException ioe) {
System.out.println("Exception caught printing process
output.");
ioe.printStackTrace();
}
finally {
try {
br_in.close();
} catch (Exception ex) {}
}
}
}).start();

new Thread(new Runnable(){
public void run() {
BufferedReader br_err = null;
try {
br_err = new BufferedReader(new
InputStreamReader(pr.getErrorStream()));
String buff = null;
while ((buff = br_err.readLine()) != null) {
System.out.println("Process err :" + buff);
try {Thread.sleep(100); } catch(Exception e) {}
}
br_err.close();
}
catch (IOException ioe) {
System.out.println("Exception caught printing process
error.");
ioe.printStackTrace();
}
finally {
try {
br_err.close();
} catch (Exception ex) {}
}
}
}).start();
}
catch (Exception ex) {
System.out.println(ex.getLocalizedMessage());
}
}

public static boolean isWindows() {
if
(System.getProperty("os.name").toLowerCase().indexOf("windows") != -1)
return true;
else
return false;
}

};

What I want to do is put a timer in this code that will only allow the
command to attempt to run for a set amount of time, and when that time
elapses the program will decide that the command isn't going to work
and it quits with an error message.

The way I understand the documentation, as the code is written right
now (with the pr.waitFor(); line) it will wait for the process (in
this case an OS command) to complete before the code will continue.
That seems to bear out in my testing so far.

I've seen also in the javadocs where you can call Thread.join(50000);
or something similar, to join the running thread and if it doesn't
complete in the specified time that it will kill the thread. Is this
the right approach to solving this problem? Is the problem even clear?
Any suggestions about how to do this and where to put the suggested
code snippets will be greatly appreciated. Thank you.

Sincerely,

Earl
Click to expand...

I believe there is a flaw in the logic in the above program.

You call Process.waitFor() before you start the threads which read the process's
standard output/error channels. If the process generates a lot of output, such
that either the output or error channel fills and blocks the process, the
waitFor() will not return. The threads to read that output, which should
prevent the process from blocking, haven't been started yet. Start the threads
to read the process output *before* you invoke Process.waitFor().

This may prevent you from needing to terminate if the process doesn't complete
in a fixed time.
 
E

Earl Lewis

Earl said:
You java gurus probably hate it when a posting starts like this, but
here goes anyway. Sorry, in advance!
Click to expand...
Disclaimer: I'm not a java guru. I know how to spell it and I've
written some basic OO stuff. I now have a real problem that I'm trying
to solve but have no idea how best to implement it.
Click to expand...
Here's the situation. I have a small java routine (in Oracle) that
executes an operating system command. Here's that code:
Click to expand...
import java.io.*;
public class Host {
public static void executeCommand(String command) {
try {
String[] finalCommand;
if (isWindows()) {
finalCommand = new String[4];
// Use the appropriate path for your windows version.
finalCommand[0] = "C:\\windows\\system32\\cmd.exe"; //
Windows XP/2003
//finalCommand[0] = "C:\\winnt\\system32\\cmd.exe"; //
Windows NT/2000
finalCommand[1] = "/y";
finalCommand[2] = "/c";
finalCommand[3] = command;
}
else {
finalCommand = new String[3];
finalCommand[0] = "/bin/sh";
finalCommand[1] = "-c";
finalCommand[2] = command;
}
Click to expand...
final Process pr = Runtime.getRuntime().exec(finalCommand);
pr.waitFor();
Click to expand...
new Thread(new Runnable(){
public void run() {
BufferedReader br_in = null;
try {
br_in = new BufferedReader(new
InputStreamReader(pr.getInputStream()));
String buff = null;
while ((buff = br_in.readLine()) != null) {
System.out.println("Process out :" + buff);
try {Thread.sleep(100); } catch(Exception e) {}
}
br_in.close();
}
catch (IOException ioe) {
System.out.println("Exception caught printing process
output.");
ioe.printStackTrace();
}
finally {
try {
br_in.close();
} catch (Exception ex) {}
}
}
}).start();
Click to expand...
new Thread(new Runnable(){
public void run() {
BufferedReader br_err = null;
try {
br_err = new BufferedReader(new
InputStreamReader(pr.getErrorStream()));
String buff = null;
while ((buff = br_err.readLine()) != null) {
System.out.println("Process err :" + buff);
try {Thread.sleep(100); } catch(Exception e) {}
}
br_err.close();
}
catch (IOException ioe) {
System.out.println("Exception caught printing process
error.");
ioe.printStackTrace();
}
finally {
try {
br_err.close();
} catch (Exception ex) {}
}
}
}).start();
}
catch (Exception ex) {
System.out.println(ex.getLocalizedMessage());
}
}
Click to expand...
public static boolean isWindows() {
if
(System.getProperty("os.name").toLowerCase().indexOf("windows") != -1)
return true;
else
return false;
}

What I want to do is put a timer in this code that will only allow the
command to attempt to run for a set amount of time, and when that time
elapses the program will decide that the command isn't going to work
and it quits with an error message.
Click to expand...
The way I understand the documentation, as the code is written right
now (with the pr.waitFor(); line) it will wait for the process (in
this case an OS command) to complete before the code will continue.
That seems to bear out in my testing so far.
Click to expand...
I've seen also in the javadocs where you can call Thread.join(50000);
or something similar, to join the running thread and if it doesn't
complete in the specified time that it will kill the thread. Is this
the right approach to solving this problem? Is the problem even clear?
Any suggestions about how to do this and where to put the suggested
code snippets will be greatly appreciated. Thank you.

Earl
Click to expand...

I believe there is a flaw in the logic in the above program.

You call Process.waitFor() before you start the threads which read the process's
standard output/error channels. If the process generates a lot of output, such
that either the output or error channel fills and blocks the process, the
waitFor() will not return. The threads to read that output, which should
prevent the process from blocking, haven't been started yet. Start the threads
to read the process output *before* you invoke Process.waitFor().

This may prevent you from needing to terminate if the process doesn't complete
in a fixed time.

--
Nigel Wade, System Administrator, Space Plasma Physics Group,
University of Leicester, Leicester, LE1 7RH, UK
E-mail : (e-mail address removed)
Phone : +44 (0)116 2523548, Fax : +44 (0)116 2523555
Click to expand...


You may well be right. I can tell you that the code 'works' for the
requirements I've had
to date. Up to this point I've only used this for OS commands that
return some sort of
output almost immediately. Now I'm trying to use it to execute a
ping. For security reasons
many hosts are disallowing ping/icmp and subsequently ping will just
sit there waiting for
a reply. That's why I need to only allow this to run for some fixed
period of time before
it is forcibly terminated and returns an error.

I'll try your suggestion and see if I can get the results I want.
Thanks.

Earl
 
G

Gordon Beaton

Now I'm trying to use it to execute a ping. For security reasons
many hosts are disallowing ping/icmp and subsequently ping will just
sit there waiting for a reply. That's why I need to only allow this
to run for some fixed period of time before it is forcibly
terminated and returns an error.
Click to expand...

Perhaps the easiest solution in this case would be to specify a
timeout as part of the ping command itself (read the documentation).

Exactly how does disallowing icmp improve security?

/gordon

--
 

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