Develop Reference

How to know if the process has terminated while processing the inputstream and when should I call process.waitFor() or process.exitValue()?

I am trying to execute commands using Java. So when I try to convert the process Inputstream to string using BufferedReader, the code works if I call process.waitFor() after processing the inputstream to string. But when I try to convert the process input stream using ByteArrayOutputStream to string, the results are not returned if I write process.waitFor() after processing the inputstream to string. It works only process.waitFor is written before inputstream.isavailable(). I don't understand why this is behaving like this? Also I want to know how to determing the buffer array size incase of using ByteArrayStream. I am trying to use isavailable() to know to number of bytes.
``ProcessBuilder pb = new ProcessBuilder();
String cmd = "ls -l /Users/uma/data";
pb.command("bash", "-c",cmd);
try {
Process process = pb.start();
StringBuilder output = new StringBuilder();
BufferedReader reader = new BufferedReader(
new InputStreamReader(process.getInputStream()));
String line;
while ((line = reader.readLine()) != null) {
output.append(line + "\n");
}
intexitVal = process.waitFor();
if (exitVal == 0) {
System.out.println("Success!");
System.out.println(output);
System.exit(0);
} else {
try (final BufferedReader b = new BufferedReader(new InputStreamReader(process.getErrorStream()))) {
String errorline;
if ((errorline = b.readLine()) != null)
System.out.println(errorline);
} catch (final IOException e) {
e.printStackTrace();
}
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
`
``ProcessBuilder pb = new ProcessBuilder();
String cmd = "ls -l /Users/uma/data";
pb.command("bash", "-c",cmd);
try {
Process process = pb.start();
int exitVal = process.waitFor();
InputStream is = process.getInputStream();
ByteArrayOutputStream result = new ByteArrayOutputStream();
byte[] buffer = newbyte[is.available()];
int length;
while ((length = is.read(buffer)) != -1) {
result.write(buffer, 0, length);
}
String output = result.toString();
if (exitVal == 0) {
System.out.println("Success!");
System.out.println(output);
System.exit(0);
} else {
try (final BufferedReader b = new BufferedReader(new InputStreamReader(process.getErrorStream()))) {
String errorline;
if ((errorline = b.readLine()) != null)
System.out.println(errorline);
} catch (final IOException e) {
e.printStackTrace();
}
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}`
How to determine the buffer size? Also when should I call waitFor()?

waitFor() waits for the target process to exit, and returns the exit code given by it. You can use it to wait for the program to stop, before logging any errors or checking the exit code.
As for the buffer size, I recommend using is.readAllBytes() if you just want to get the entire input stream as a byte array. To then convert that to a string, use new String(is.readAllBytes());.
If you just want to stream the content of the input stream into another stream (such as System.out or System.err), use this:
InputStream is = /* get input stream */;
byte[] buffer = new byte[128];
int read;
while((read = is.read(buffer)) != -1) {
System.out.write(buffer, 0, read);
}
This will just write the entire is input stream into System.out, you can configure or change this as you'd like.

How to execute a command after exception

I have a 2d array someArray with some system commands. Let's say I have these commands -
ls
lol (invalid command)
pwd
the second command will trigger an IOException and the third command does not get executed. How do I make sure that the last command will get executed regardless of any exception? Any advice?
for ( int i = 0; i < someArray.length; i++ ) {
try{
ProcessBuilder pb = new ProcessBuilder(someArray[index]);
pb.redirectErrorStream(true);
Process process = pb.start();
InputStream is = process.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String line;
while ( (line = br.readLine()) != null) {
System.out.println(line);
}
br.close();
}catch(IOException e){
System.err.println( "Command not found" );
}
}

Instead of using IOException in the catch use the general class Exception which will catch any kind of Exception thrown
for ( int i = 0; i < someArray.length; i++ ) {
try{
ProcessBuilder pb = new ProcessBuilder(someArray[i]);
pb.redirectErrorStream(true);
Process process = pb.start();
InputStream is = process.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String line;
while ( (line = br.readLine()) != null) {
System.out.println(line);
}
br.close();
} catch (IOException e) {
System.err.println( "Command not found" );
} catch (Exception e) {
System.err.println("Unexpected Exception caught to continue other commands");
e.printStackTrace();
}
}
edit: fixed to report the unexpected error

No output from Runtime.getRuntime().exec("ls")

ping and date returned output, but it's not returning anything from "ls" or "pwd". What I want to do ultimately is run an SSH command. Any idea what I am missing below?
//Works and shows the output
executeCommand("ping -c 3 " + "google.com");
//Works and shows the output
executeCommand("date");
//Does not work. No output
executeCommand("sudo ls");
//Does not work. No output
executeCommand("ls");
private void executeCommand(String command) {
StringBuffer output = new StringBuffer();
Process p;
try {
p = Runtime.getRuntime().exec(command);
p.waitFor();
BufferedReader reader =
new BufferedReader(new InputStreamReader(p.getInputStream()));
String line = "";
while ((line = reader.readLine())!= null) {
output.append(line + "\n");
}
} catch (Exception e) {
e.printStackTrace();
}
Log.d("Output", "Output: " + output.toString());
}

I have two solutions
first solution (you need Java 7):
...
ProcessBuilder pb = new ProcessBuilder("ls");
pb.redirectOutput(Redirect.INHERIT);
Process p = pb.start();
second solution:
Process p=Runtime.getRuntime().exec("ls");
InputStream is = p.getInputStream();
int c;
StringBuilder commandResponse = new StringBuilder();
while( (c = is.read()) != -1) {
commandResponse.append((char)c);
}
System.out.println(commandResponse);
is.close();

Fetch and store output from a subprocess in Java

I'm working on something that requires me to start to subprocess(command prompt) and execute some commands on it. I need to fetch the output from the subprocess and store it in a file or String.
here's what I have done so far, and it doesn't work:
public static void main(String args[])
{
try
{
Runtime RT = Runtime.getRuntime();
String command = "cmd /c start javap java.lang.String";
File file = new File("write.txt");
Writer output = new BufferedWriter(new FileWriter(file));
BufferedReader br = new(BufferedReader(newInputStreamReader(RT.exec(command).getInputStream()));
String temp = br.readLine();
while(!temp.equals(null))
{
output.write(temp);
temp = br.readLine();
}
output.close();
RT.exec("exit");
}
catch(Exception e)
{
System.out.println(e);
}
}

Start changing this:
new(BufferedReader(newInputStreamReader(
To:
new BufferedReader(new InputStreamReader(
Compile and see if you still have the problem
edit
Also, there is a good reason why you shouldn't catch Exception, you also catch programming errors like a NullPointerException
while( !temp.equals(null)) { //Throws NullPointerExceptin when temp is null
Change it with:
while( temp != null ) { //!temp.equals(null)) {
Finally you don't have to "exit" since you're not inside the cmd really.
Corrected version
This version runs as you intend:
import java.io.*;
class Rt {
public static void main(String args[]) throws Exception {
Runtime RT = Runtime.getRuntime();
String command = "javap java.lang.String" ;
File file = new File("write.txt");
Writer output = new BufferedWriter(new FileWriter(file));
BufferedReader br = new BufferedReader(new InputStreamReader(RT.exec(command).getInputStream()));
String temp = br.readLine();
while( temp != null ) { //!temp.equals(null)) {
output.write(temp);
temp = br.readLine();
}
output.close();
//RT.exec("exit");
}
}
edit
Final remarks:
Since Java 1.5 the preferred way to invoke a command is using ProcessBuilder and it is better if you use an array of strings instead of a single string ( or varargs ).
When you're building your output you can get rid of the file object and pass the file name directly to the filewriter.
While reading the line you can assign and evaluate in the condition.
Java's coding conventions suggest to use the opening brace in the same like.
This would be my version of your code:
class Rt {
public static void main(String args[]) throws Exception {
Writer output = new BufferedWriter(new FileWriter ( "write.txt"));
InputStream in = new ProcessBuilder("javap", "java.lang.String").start().getInputStream();
BufferedReader br = new BufferedReader( new InputStreamReader(in));
String line = null;
while( ( line = br.readLine() ) != null ) {
output.write( line );
}
output.close();
}
}
It might need still some work, but I hope it helps you.

Here is an example which should work:
StringBuffer outStream = new StringBuffer();
StringBuffer errStream = new StringBuffer();
Runtime runtime = Runtime.getRuntime();
Process process = null;
try {
process = runtime.exec(command);
} catch (IOException ex) {
ex.printStackTrace();
return;
}
InputStream outIs = process.getInputStream();
MonitorOutputThread sout = new MonitorOutputThread(outIs, outStream);
sout.run();
InputStream errIs = process.getErrorStream();
MonitorOutputThread serr = new MonitorOutputThread(errIs, errStream);
serr.run();
while (sout.isAlive() || serr.isAlive()) {
try {
sleep(100);
} catch (InterruptedException ex) {
ex.printStackTrace();
// ignore
}
}
And the code for MonitorOutputThread
private class MonitorOutputThread extends Thread {
private final InputStream is;
private final StringBuffer output;
public MonitorOutputThread(InputStream is, StringBuffer output) {
this.is = is;
this.output = output;
}
#Override
public void run() {
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String line = null;
try {
while ((line = br.readLine()) != null) {
output.append(line);
output.append(LINE_SEPARATOR);
}
if (output.length() >= 1) {
char lastChar = output.charAt(output.length() - 1);
if (lastChar == '\n') {
output.deleteCharAt(output.length() - 1);
}
}
} catch (IOException ex) {
ex.printStackTrace();
return;
}
}
}
This should catch both the standard output and standard error of the command.

DevDaily has a simple example of how to work with Process class.
See the snippet:
import java.io.*;
public class JavaRunCommand {
public static void main(String args[]) {
String s = null;
try {
// run the Unix "ps -ef" command
// using the Runtime exec method:
Process p = Runtime.getRuntime().exec("ps -ef");
BufferedReader stdInput = new BufferedReader(new
InputStreamReader(p.getInputStream()));
BufferedReader stdError = new BufferedReader(new
InputStreamReader(p.getErrorStream()));
// read the output from the command
System.out.println("Here is the standard output of the command:\n");
while ((s = stdInput.readLine()) != null) {
System.out.println(s);
}
// read any errors from the attempted command
System.out.println("Here is the standard error of the command (if any):\n");
while ((s = stdError.readLine()) != null) {
System.out.println(s);
}
System.exit(0);
}
catch (IOException e) {
System.out.println("exception happened - here's what I know: ");
e.printStackTrace();
System.exit(-1);
}
}
}
or even check this code I've writen some time ago

Writing data to InputStream of grep program invoked in java

I'm trying to process data obtained from a run of diff to an instance of GNU grep in a java program. I've managed to get the output of diff using the Process object's outputStream, but I'm currently having programs sending this data to the standard input of grep (through another Process object created in Java). Running Grep with the input only returns status code 1. What am I doing wrong?
Below is the code I have so far:
public class TestDiff {
final static String diffpath = "/usr/bin/";
public static void diffFiles(File leftFile, File rightFile) {
Runtime runtime = Runtime.getRuntime();
File tmp = File.createTempFile("dnc_uemo_", null);
String leftPath = leftFile.getCanonicalPath();
String rightPath = rightFile.getCanonicalPath();
Process proc = runtime.exec(diffpath+"diff -n "+leftPath+" "+rightPath, null);
InputStream inStream = proc.getInputStream();
try {
proc.waitFor();
} catch (InterruptedException ex) {
}
byte[] buf = new byte[256];
OutputStream tmpOutStream = new FileOutputStream(tmp);
int numbytes = 0;
while ((numbytes = inStream.read(buf, 0, 256)) != -1) {
tmpOutStream.write(buf, 0, numbytes);
}
String tmps = new String(buf,"US-ASCII");
inStream.close();
tmpOutStream.close();
FileInputStream tmpInputStream = new FileInputStream(tmp);
Process addProc = runtime.exec(diffpath+"grep \"^a\" -", null);
OutputStream addProcOutStream = addProc.getOutputStream();
numbytes = 0;
while ((numbytes = tmpInputStream.read(buf, 0, 256)) != -1) {
addProcOutStream.write(buf, 0, numbytes);
addProcOutStream.flush();
}
tmpInputStream.close();
addProcOutStream.close();
try {
addProc.waitFor();
} catch (InterruptedException ex) {
}
int exitcode = addProc.exitValue();
System.out.println(exitcode);
inStream = addProc.getInputStream();
InputStreamReader sr = new InputStreamReader(inStream);
BufferedReader br = new BufferedReader(sr);
String line = null;
int numInsertions = 0;
while ((line = br.readLine()) != null) {
String[] p = line.split(" ");
numInsertions += Integer.parseInt(p[1]);
}
br.close();
}
}
Both leftPath and rightPath are File objects pointing to the files to be compared.

Just a couple of hints, you could:
pipe the output of diff directly into grep: diff -n leftpath rightPath | grep "^a"
read the output file from grep instead of stdin: grep "^a" tmpFile
use ProcessBuilder to get your Process where you can easily avoid a blocking process because you're not reading stderr by using redirectErrorStream