How to redirect ProcessBuilder's output to a string?

Question

I am using the following code to start a process builder.I want to know how can I redirect its output to a String.

ProcessBuilder pb = new ProcessBuilder(
    System.getProperty("user.dir") + "/src/generate_list.sh", filename);
Process p = pb.start();

I tried using ByteArrayOutputStream but it didn't seem to work.

Answer 1

Read from the InputStream. You can append the output to a StringBuilder:

BufferedReader reader = 
                new BufferedReader(new InputStreamReader(process.getInputStream()));
StringBuilder builder = new StringBuilder();
String line = null;
while ( (line = reader.readLine()) != null) {
   builder.append(line);
   builder.append(System.getProperty("line.separator"));
}
String result = builder.toString();

Answer 2

Using Apache Commons IOUtils you can do it in one line:

ProcessBuilder pb = new ProcessBuilder("pwd");
String output = IOUtils.toString(pb.start().getInputStream(), StandardCharsets.UTF_8);

Answer 3

As of Java 9, we finally have a one liner:

ProcessBuilder pb = new ProcessBuilder("pwd");
Process process = pb.start();

String result = new String(process.getInputStream().readAllBytes());

Answer 4

Java 8 example:

public static String runCommandForOutput(List<String> params) {
    ProcessBuilder pb = new ProcessBuilder(params);
    Process p;
    String result = "";
    try {
        p = pb.start();
        final BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));

        StringJoiner sj = new StringJoiner(System.getProperty("line.separator"));
        reader.lines().iterator().forEachRemaining(sj::add);
        result = sj.toString();

        p.waitFor();
        p.destroy();
    } catch (Exception e) {
        e.printStackTrace();
    }
    return result;
}

Usage:

List<String> params = Arrays.asList("/bin/sh", "-c", "cat /proc/cpuinfo");
String result = runCommandForOutput(params);

I use this exact code and it works well for single or multiple line results. You could add an error stream handler as well.