I am using ProcessBuilder in Java to run a Perl script. When I run the Perl script while printing the InputStream of the process, the Java program seems to run for the duration of the Perl script. However if I comment out the getOutPut method in main the Java program terminates very fast and the Perl script does not run at all. Why does this occur?
private final static String SCENARIO = "scen";
/**
* #param args
*/
public static void main(String[] args) {
ProcessBuilder pb = new ProcessBuilder("perl", SCENARIO+".pl");
pb.directory(new File("t:/usr/aman/"+SCENARIO));
try {
Process p = pb.start();
getOutput(p.getInputStream(), true);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
private static List getOutput(InputStream is, boolean print) {
List output = new ArrayList<String>();
BufferedReader reader = new BufferedReader(new InputStreamReader(is));
String s = null;
try {
while ((s = reader.readLine()) != null) {
output.add(s);
if(print){
System.out.println(s);
}
}
is.close();
} catch (IOException e) {
// TODO Auto-generated catch block
//e.printStackTrace();
return null;
}
return output;
}
Likely the OS's output stream buffer for your PERL script process gets filled because nothing is emptying this buffer, and this will kill the process. You need to gobble the output stream for this reason which is what your getOutput method does for you.
Please read the classic reference on this problem: When Runtime.exec() won't. Per this article:
Because some native platforms only provide limited buffer size for standard input and output streams, failure to promptly write the input stream or read the output stream of the subprocess may cause the subprocess to block, and even deadlock.
Related
I would like to run a hidden script file that resides in the current location using process builder. with the following code
// System.out.println("line"+reader.readLine());
ProcessBuilder builder = new ProcessBuilder(shfile.getAbsolutePath());
builder.redirectErrorStream(true);
Process process = builder.start();
BufferedReader br = new BufferedReader(new InputStreamReader(process.getInputStream()));
String output = null;
System.out.println("out"); //===printing this
while (null != (output = br.readLine()))
{
System.out.println("in"); //not printing this
System.out.println(">>"+output);
}
int rs = process.waitFor();
but it hangs in the br.readline()..
but when I run the same script file using the following command in terminal
sh .script.sh
it executes and gives me the expected results
I looked into all the loops in the forum everyone asks to handle input stream and error stream in threads or do a redirect error stream. I have added a redirect error stream but still it hangs.
when i press ctrl+c it prints the initial lines of the output and exits.
Content of my script file
#!/bin/sh
cd /home/ats/cloudripper/lke_factory_asb_v2/lk_assets_factory_release/
sh ./LKE_run_Diablo.sh 0a0e0c3dc893
So how to handle this situation.
Process builder have special API to redirect child process input, output and error streams. See documentation
If you need both child and parent process to use same console you should use INHERIT mode redirection. An example:
public class ChildProcessOutputProxy {
public static void main(String[] args) {
ProcessBuilder builder = new ProcessBuilder("whoami");
builder.redirectOutput(Redirect.INHERIT);
builder.redirectErrorStream(true);
try {
var child = builder.start();
child.waitFor();
} catch (IOException e) {
System.err.println(e.getMessage());
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
}
}
I'm running this java program on a raspberry pi. The program is supposed to run the script "hello_pixy" and scan what it prints out. When I run hello_pixy manually, it prints out lines normally (Via C's printf line). But when I run the program, nothing is printed out and the BufferedReader didn't read any lines.
If I substitute the script for something like "ls", then the BufferedReader reads it and prints it out. Is there a way I can change the "printf"s in C to send to the InputStream (I don't really know C, just enough from Java experience)?
Process process = null;
try {
process = Runtime.getRuntime().exec("sudo .ss/pixy/build/hello_pixy/hello_pixy");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} //for Windows
try {
process.waitFor();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
String line;
String print = "";
try {
while ((line = reader.readLine()) != null) {
print += line;
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("\nCodescan:\n\n" + print);
The code I'm executing is here: https://github.com/De-etz/pixy/blob/master/src/host/hello_pixy/hello_pixy.cpp
You're doing this back to front. You must read all the process's output first, and then call waitFor(). Your way you will probably just deadlock, as the process can't exit until it has produced all its output, and if you're not reading it, it will eventually block.
Notes:
C is not a scripting language, and a compiled program is not a script by definition.
Code that depends on the success of code in a prior try block must be inside that try block. At present you are continuing after exceptions as though they didn't happen. Don't write code like this.
I am trying to execute this command sort --field-separator="," --key=2 /home/dummy/Desktop/sample.csv" -o /home/dummy/Desktop/sample_temp.csv using Java Runtime and ProcessBuilder.
Manually I am able to execute this command in linux, but using Runtime or ProcessBuilder, this command does not execute. It returns with an error code = 2.
Edit:
If I am trying to execute 'ls' command in linux through Java, I get the list of files in the current directory. But, If I try to execute the command 'ls | grep a', an IOException is thrown with error code=2.
Here is the snippet:
public static void main(String[] args) throws IOException {
InputStream is = null;
ByteArrayOutputStream baos = null;
ProcessBuilder pb = new ProcessBuilder("ls | grep a");
try {
Process prs = pb.start();
is = prs.getInputStream();
byte[] b = new byte[1024];
int size = 0;
baos = new ByteArrayOutputStream();
while((size = is.read(b)) != -1){
baos.write(b, 0, size);
}
System.out.println(new String(baos.toByteArray()));
}
catch (IOException e)
{
e.printStackTrace();
}
finally
{
try {
if(is != null) is.close();
if(baos != null) baos.close();
} catch (Exception ex){}
}
}
There could be a range of issue with your code. Hence you did not supply your code I can only guess.
The output file needs to be already created
The ',' field separator does not need the quotes around it (see code below)
So after these 2 issues (both making the program exit with '2'), this code actually works:
import java.io.IOException;
import java.util.Arrays;
public class Test {
public static void main(String[] args) throws IOException, InterruptedException {
ProcessBuilder pb = new ProcessBuilder(Arrays.asList("sort", "--field-separator=,", "--key=2", "/tmp/sample.csv", "-o",
"/tmp/sample_temp.csv"));
Process p = pb.start();
int returnCode = p.waitFor();
System.out.println(returnCode);
}
}
Will print '0' and will sort the file correctly.
For the 'ls | grep' issue, read this great article: http://www.javaworld.com/article/2071275/core-javahen-runtime-exec---won-t/core-java/when-runtime-exec---won-t.html
The article basically explains that the Runtime.exec (and the ProcessBuilder wrapper) is for running processes and not a Shell (the ls | grep you are trying are actually 2 processes in Linux communicating with each other thru stdout/in).
I am able to execute that manually. And error code 2 means Misuse of Shell BuiltIns
I see in your example you are only invoking "ls", not "/usr/bin/ls" (or something like that).
When you execute manually you have the luxury of PATH environment variable which is not availabled to the process you create.
Use "which ls" to discover the location of 'ls' on your target system. For your code to be portable you will have to make it a configurable option.
this is the way to execute any bash commands like sort, ls, cat (with sub-options). Please find the snippet:
private String executeCommand(String command) {
StringBuffer output = new StringBuffer();
Process p;
try {
p = Runtime.getRuntime().exec("script.sh");
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();
}
return output.toString();
}
In the exec() method, I passed a shell script which contains the bash command within it. That linux command will be executed and you can carry on with the next task. Hope this was helpful.
I am new to this kind of integration of java with Unix.
what i am trying to do is
String command="passwd";
Runtime rt=Runtime.getRuntime();
try {
Process pc=rt.exec(command);
try {
pc.waitFor();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
BufferedReader buf = new BufferedReader(new InputStreamReader(pc.getInputStream()));
String line = "";
while ((line=buf.readLine())!=null) {
System.out.println(line);
}
BufferedReader buf1 = new BufferedReader(new InputStreamReader(pc.getErrorStream()));
String line1 = "";
while ((line1=buf1.readLine())!=null) {
System.out.println("Error--"+line1);
}
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
System.out.println("IOException---"+e1.getMessage());
}
now when i am trying to pass the "passwd" command the Unix environment goes to suspended mode.
I want to know how can i pass the old password ,new password and confirm new password to the shell using the java code.
You need to pass it in using the confusing named Process.getOutputStream(). From the doc:
Gets the output stream of the subprocess. Output to the stream is
piped into the standard input stream of the process represented by
this Process object
Note that you need to capture the processes stdout/err simultaneously to avoid blocking. See this answer for more details.
There is a utility called expect. If u installed u can pass argument for any thing. So construct as string execute by
String ConstructedCommand;
Process p=Runtime.getRuntime().exec(ConstructedCommand);
This link will be deserve your need. http://linux.die.net/man/1/expect
i wanted to read the output-stream of a c-Application in my Java program. iremoted (available here: Link) is a C-Application that puts out seperate lines like "0x19 pressed" if a button on my Apple Remote is pressed. If i start the iremoted program everything is doing well and these separate lines are shown on my screen everytime I pressed a button.
Now I wanted to read the output-stream of the c-application in my Java application to process inputs of the Apple Remote in Java projects.
Unfortunately i don't know why no input is regocnized?
I tried it with a simple HelloWorld.c program and my program responded as intended in this case (prints out HelloWorld).
Why doensn't it work with the iremoted program?
public class RemoteListener {
public void listen(String command) throws IOException {
String line;
Process process = null;
try {
process = Runtime.getRuntime().exec(command);
} catch (Exception e) {
System.err.println("Could not execute program. Shut down now.");
System.exit(-1);
}
Reader inStreamReader = new InputStreamReader(process.getInputStream());
BufferedReader in = new BufferedReader(inStreamReader);
System.out.println("Stream started");
while((line = in.readLine()) != null) {
System.out.println(line);
}
in.close();
System.out.println("Stream Closed");
}
public static void main(String args[]) {
RemoteListener r = new RemoteListener();
try {
r.listen("./iremoted"); /* not working... why?*/
// r.listen("./HelloWorld"); /* working fine */
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
stdout is buffered and it's not automatically flushed if you are not writing to screen. Add:
fflush(stdout);
after:
printf("%#lx %s\n", (UInt32)event.elementCookie,
(event.value == 0) ? "depressed" : "pressed");
iremoted is likely writing to stderr if a hello world program works. You would want the error stream in that case. I'm not sure how this works for your hello world case - I think you're doing the wrong thing here:
new InputStreamReader(process.getInputStream());
should be
new InputStreamReader(process.getOutputStream());
or
new InputStreamReader(process.getErrorStream());