I want to receive in Java the output from a Linux command line program. I need to read the values line by line, because the utilities are reporting their values once per second and the Java program should not need to wait until the end of execution. It should receive the values every second.
The following small program works fine in the case of the ping command, but not for the perf stat command.
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
public class Main {
Process p;
BufferedReader reader;
public Main(int number) throws IOException {
if (number == 1) {
// does NOT work, blocks on readLine()
p = Runtime.getRuntime().exec("sudo perf stat -e cycles -I 1000 -p 9264"); // change PID to the one to be monitored
}
else if (number == 2) {
// WORKS!
p = Runtime.getRuntime().exec("ping www.google.com");
}
else {
System.out.println("Either 1 or 2...");
System.exit(0);
}
reader = new BufferedReader(new InputStreamReader(p.getInputStream()));
}
public void process() throws IOException {
String res = "";
res = reader.readLine();
System.out.println(res);
}
public static void main (String[] args) throws IOException, InterruptedException {
Main myMain = new Main(Integer.parseInt(args[0]));
while (true) {
myMain.process();
Thread.sleep(1000);
}
}
}
So when running java Main 2 it works correctly, but when invoking java Main 1 it will block on the reader.readLine() call.
What's the difference between the two commands? Also with the command 'ls -l' it works correctly and I receive the values line by line.
EDIT:
The command itself works fine, when I run it directly from the command line. The -I option was introduced in newer kernel versions, it did not exist before (I am using kernel 3.11, Ubuntu).
When using 2>$1 to get also the stderr, it will indeed read a value every second, but it will always read null.
The problem seems to be that perf stat does not use stdout by default, but stderr. See the log-fd option.
So you can either redirect stderr to stdout in the command you use,
Or you capture the input Stream from stderr of the Process
Related
I want to see the CPU and RAM utilisation of a machine , until my java code is running. So I used top command, but I don't know how and when to stop it??
I don't know, how waitFor() can work for me?
I might run my code in a thread, but how do I tell it to wait for this thread to finish execution and stop?
MyCode
import...*;
public class MyCode {
ThreadSubclass thread1 = new ThreadSubclass();
thread1.start();
/*
I want Mycode to Run in parallel while top command stores output of RAM and CPU usage.
Can I write my code here??
When myCode is complete, stop Top command.
*/
System.out.println("0");
Process cmdProc = Runtime.getRuntime().exec("top");
System.out.println("1");
BufferedReader stdoutReader = new BufferedReader(
new InputStreamReader(cmdProc.getInputStream()));
String line;
while ((line = stdoutReader.readLine()) != null) {
// process procs standard output here
System.out.println(line);
}
System.out.println("2");
BufferedReader stderrReader = new BufferedReader(
new InputStreamReader(cmdProc.getErrorStream()));
while ((line = stderrReader.readLine()) != null) {
// process procs standard error here
System.out.println(line);
}
cmdProc = Runtime.getRuntime().exec("Ctrl+C");
}
in another file… ThreadSubclass.java
public class ThreadSubclass extends Thread {
#Override
public void run() {
//Should I write all my code here? I had used fork earlier and it gave me pid, so It was easier for me to run my code inside that if condition of fork pid.
System.out.println("ThreadSubclass is running");
}
}
Current Output:
0
ThreadSubclass is running
1
2
TERM environment variable not set.
Expected OutPut:
0
ThreadSubclass is running
1
2
Top command output
Issues:
If I started "top" command first it didn't goes down to execute other commands.
As shown in this code, when I started Thread first, it shows "TERM environment variable not set."
if possible store it in a text file directly, rather than reading and storing it inside java code.
Process cmdProc = Runtime.getRuntime().exec("top -b > Top.csv");
error =>
top: unknown option '>'
Usage:
top -hv | -bcHiOSs -d secs -n max -u|U user -p pid(s) -o field -w [cols]
I'm using a Raspberry Pi to receive the UID of some RFID cards from a RC522 reader. The python script I'm running is here: https://github.com/mxgxw/MFRC522-python
For various reasons I won't go into, I have to process these IDs in Java.
It seems the most viable solution is to run the python script and read in the result into Java. The problem is, the Python code gives continuous output, i.e. it will print the ID of the card into the console window as and when a card is tapped onto the reader, and will only terminate on a user's command.
I'm currently using a ProcessBuilder to execute the script, however it seems like it's more suited to run the program and read in the immediate result back to Java (which of course is null if I haven't tapped a card onto the reader). I've tried executing the code in a while(true) loop to continuously start the process - but this doesn't work:
import java.io.*;
public class PythonCaller {
/**
* #param args
* #throws IOException
*/
public static void main(String[] args) throws IOException {
// set up the command and parameter
String pythonScriptPath = "/home/pi/MFRC522-python/Read.py";
String[] cmd = new String[3];
cmd[0] = "sudo";
cmd[1] = "python"; // check version of installed python: python -V
cmd[2] = pythonScriptPath;
// create runtime to execute external command
ProcessBuilder pb = new ProcessBuilder(cmd);
// retrieve output from python script
pb.redirectError();
while(true){
Process p = pb.start();
System.out.println("Process Started...");
BufferedReader in = new BufferedReader(new InputStreamReader(p.getInputStream()));
int ret = new Integer(in.readLine()).intValue();
System.out.println("value is : "+ret);
}
}
}
The output on the console window is blank - no exceptions thrown or println's.
Any help would be massively appreciated!!
Thanks
EDIT - I've surrounded my code in a try/catch to see if there's anything at all being thrown, and it doesn't seem to be the case
I use the following programs to try to reproduce the problem
PythonCaller.java
import java.io.*;
public class PythonCaller {
public static void main(String[] args) throws IOException {
// set up the command and parameter
String pythonScriptPath = "/home/pi/test.py";
String[] cmd = { "python", pythonScriptPath };
// create runtime to execute external command
ProcessBuilder pb = new ProcessBuilder(cmd);
// retrieve output from python script
pb.redirectError();
while(true){
Process p = pb.start();
System.out.println("Process Started...");
BufferedReader in = new BufferedReader(new InputStreamReader(p.getInputStream()));
int ret = new Integer(in.readLine()).intValue();
System.out.println("value is : "+ret);
}
}
}
test.py
uid =(123,456,789,999)
print "Card read UID: "+str(uid[0])+","+str(uid[1])+","+str(uid[2])+","+str(uid[3])
The method pb.redirectError() doesn't modify anything. It returns a value, your codes does nothing with it. (see http://docs.oracle.com/javase/7/docs/api/java/lang/ProcessBuilder.html#redirectError%28%29). What you want is probably redirectErrorStream(boolean redirectErrorStream)
The second line of the python test program is taken directly from "Read.py" (line 44). It causes an error with the java intValue() method. If I replace it with String ret = in.readLine();, the program seems to work.
Since the Process p = pb.start(); is inside the loop, the python subprogram is called repeatedly.
The next step should be to try running the python program manually in a console, see what it does.
(n.b. I had to remove "sudo" and change paths to be able to test on my system, you should have no problems replacing things for your setup).
I've managed to get around it by editing my Python script - it returns null if there's no card on the reader, and the UID if there is.
I'll probably use observer pattern or similar on the Java end to detect when there's a card. Very resource intensive but it'll have to do for now!
I need to execute the less command, with paging, from my Java console application. However, the only method I found to execute external commands is Runtime.getRuntime().exec(), which requires me to write/read input/output via streams. So commands like cat work (and less does in fact act like cat), but I need the paging functionality.
In C, I'd use system(). In Ruby, Kernel.exec does the job.
Is there any way to get this done in Java?
When you execute an external process with Runtime.exec() its standard input and output streams are not connected to the terminal from which you are running the Java program. You can use shell redirection to connect it, but first you need to know what terminal to use. There is no way to find the terminal using the standard API but probably you can find an open source library that does it.
To see that it can be done, this program opens itself in less:
public class Test {
public static void main(String[] args) throws Exception {
Process p = Runtime.getRuntime().exec(
new String[] {"sh", "-c",
"less Test.java < "+args[0] + " > "+args[0]});
System.out.println("=> "+p.waitFor());
}
}
To run it you should use java Test $(tty). The tty program prints the name of the terminal connected to its stdin.
I'm not too sure about the portability of this solution; at least it works on Linux.
List item
The following program will work, initially it prints 10 lines , then press enter it will print next line till end of the file.
run program like
java Less $fileName
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.Scanner;
public class Less
{
public static void main(String args[]) throws IOException
{
FileReader reader = new FileReader(args[0]);
BufferedReader buff = new BufferedReader(reader);
String readLine;
int lineCount = 0;
while ((readLine = buff.readLine()) != null)
{
System.out.println(readLine);
lineCount++;
if (lineCount > 10)
{
Scanner scanner = new Scanner(System.in);
scanner.nextLine();
}
}
}
}
I am new to java. I am tasked to write java program to run the command lines. I tested the command line under the DOS prompt since i do not have have access to Linux box yet. it worked fine. See the PROGRAM below for full command line syntax. the job will take 6 input files and generate some output files. Next i tried to create a class to and using getruntime and process to process this job. Even it compiled without error but when i run it just show the cursor blinking... i thought i need to use Thread async technique. please provide some advices since i do not have enough time for the projects. I also would like to implement a call back or return values when the job is done. an example would be greatly appreciated. Thanks
import java.io.*;
public class RunJob {
// public static final String PROGRAM = "c:\\wrk\\java.exe Hello";
//one command line below
public static final String PROGRAM = "c:/java.exe -cp \"wrk/jmp.jar;wrk/colt.jar\" gov.lanl.yadas.reliability.UltimateMissileReliabilityModel 10000 \"wrk/\" x1.dat x2c.dat x3.dat x4.dat x5.dat x6.dat true";
// Set to true to end the loop
static boolean done = false;
public static void main(String argv[]) throws IOException {
BufferedReader is;
String line;
String returnMsg = "Start ";
final Process p = Runtime.getRuntime().exec(PROGRAM);
System.out.println("start");
Thread waiter = new Thread() {
public void run() {
try {
p.waitFor();
} catch (InterruptedException ex) {
System.out.println("InterruptedException");
return;
}
System.out.println("Program terminated!");
done = true;
}
};
waiter.start();
is = new BufferedReader(new InputStreamReader(p.getInputStream()));
while (!done && ((line = is.readLine()) != null))
{
System.out.println(line);
returnMsg = returnMsg + line;
}
System.out.println(returnMsg);
System.out.println("End");
return;
}// main
}
I assume that there is a good reason why you want to run a java program from another java program and not just from a shell script, or by invoking an API - but if not - please reconsider.
As to your problem - if your application produces a lot of output (the one you are running as a process) - your application will hang. The p.waitFor() will halt until the process ends. But if you don't read the information from the InputStream - it will overflow and hang!
Advice #1: put the p.waitFor() at the end.
Advice #2: read this article. If I remember correctly it is the one I read when I had a similar problem. You can also google for "StreamGobbler" - it is a common name for a separate thread that "gobbles" your streams.
Advice #3: Don't forget the ErrorStream - if your application will produce too many errors - that stream will cause the process to hang as well.
trying to execute an script, using this piece of code:
String command = "./myScript.sh";
pb = new ProcessBuilder(command, param1, param2);
pb.directory(directory);
pb.start();
I am not getting any kind of error, but neither the supposed results. Anyway, I tryed to run the same command, direclty in the terminal, and everything working correctly.
Am I missing something??
Thanks in advance
When you start a process (pb.start()) you get back a Process instance. If your script reads input or writes output to stdout or stderr you need to handle this on separate threads using Process.getInputStream(), ...getOutputStream() and getErrorStream(). If you don't do this the process can hang. You also should call Process.waitFor() and then Process.exitValue() to get the return status of the process. If it's a negative number then the system was unable to launch your script.
EDIT: Here is a short simplified example. This is a toy only and will work reliably ONLY under the following conditions:
The script does not require any input
The script does not produce a large amount of output on both stdout and stderr. If it does, then since the program reads all of stdout before stderr, the stderr buffer may fill up and block the process from completing. In a 'real' implementation you would read stdout and stderr in separate threads (hint, wrap the loadStream() method in a class that implements Runnable).
public class PBTest
{
public static void main(String[] args) throws Exception
{
ProcessBuilder pb = new ProcessBuilder("sc","query","wuauserv");
Process p = pb.start();
String output = loadStream(p.getInputStream());
String error = loadStream(p.getErrorStream());
int rc = p.waitFor();
System.out.println("Process ended with rc=" + rc);
System.out.println("\nStandard Output:\n");
System.out.println(output);
System.out.println("\nStandard Error:\n");
System.out.println(error);
}
private static String loadStream(InputStream s) throws Exception
{
BufferedReader br = new BufferedReader(new InputStreamReader(s));
StringBuilder sb = new StringBuilder();
String line;
while((line=br.readLine()) != null)
sb.append(line).append("\n");
return sb.toString();
}
}
The problem was not on the way I called the script, which was right.
But it was inside the script. At first it was:
#!/bin/bash
inputFolder=$1
outputFolder=$2
cd $inputFolder
for file in `ls ` ; do
ffmpeg -i $inputFolder/$file -ar 22050 $outputFolder/$file.mp4
done
But I got ffmpeg command not found, so I changed it to:
#!/bin/bash
inputFolder=$1
outputFolder=$2
cd $inputFolder
for file in `ls ` ; do
/usr/local/bin/ffmpeg -i $inputFolder/$file -ar 22050 $outputFolder/$file.mp4
done
with the hole path. But I have still doubts, why this is necessary, if I have ffmpeg in my path and I cand execute in console direclty form any directory??
If someone can give me an answer, it will be welcome :)