Take C++ program output as Java input

Question

I have a situation where I'm looking my Java program to run as BASH script which is turn will run a C++ program.

I am looking to take the output of the C++ program (plain text strings printed to terminal) as input to the Java program.

My first attempt was using the following code to read in input from the terminal, but I wasn't sure how to convert it from user input to automatically taking the C++ input.

Console c;
c = System.console();
if (c == null) {
  System.out.println("No console.");
  System.exit(1);
}
String data = c.readLine();

I then tried using InputStreamReader along with redirecting the output of the C++ program:

Java code:

BufferedReader input = null;
try {
  input = new BufferedReader(new InputStreamReader(System.in));
  String htmlLine = null;
  while ((htmlLine = input.readLine()) != null) {
    System.out.println(htmlLine);
  }
}

Command to redirect output:

java -jar program.jar arg1 arg2 arg3 < ./runActivities.sh

However the result of that is that it just prints the contents of runActivities.sh to the terminal.

Matthias · Accepted Answer · 2015-05-29 08:06:27Z

5

Looks like you have all the Java and C++ code already in place. The missing puzzle piece seems to be the shell redirection. You should consult the manual of the shell you are using and look for redirection. In case you are using bash shell the redirection should look like this:

$ ./runActivities.sh | java -jar program.jar arg1 arg2 arg3

edited May 29, 2015 at 8:06

answered May 29, 2015 at 7:55

Matthias

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2 Comments

Colin747 Over a year ago

That worked thanks! Didn't think it'd be something so simple.

Colin747 Over a year ago

I just need it running at initial start up.

Krzysztof Cichocki · Accepted Answer · 2015-05-29 07:59:48Z

1

You could use Runtime.getRuntime().exec("yourCommand") function from java, it will return a Process object which has an input, output and err streams, You can use those Streams to send and receive data to and from your Porcess.

    Process p = Runtime.getRuntime().exec("yourCommand");
    InputStream is = p.getInputStream();
    // you con now read from inputStream, it is the output of your programm in C++

answered May 29, 2015 at 7:59

Krzysztof Cichocki

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1 Comment

Matthias Over a year ago

Since the command to execute is a shell script this stackoverflow may be helpful, too: stackoverflow.com/questions/17142573/…

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