Copying InputStream to OutputStream halts unless I also write to System.out

Copying InputStream to OutputStream halts unless I also write to System.out

By : user7455107
Date : November 21 2020, 03:00 PM
fixed the issue. Will look into that further As EJP suggested, I split the copying of the streams into separate threads via an executor, then I make sure to close them upon completion of the spawned process:
code :
public int runModule(OutputStream moduleOut, int argShowRange, List<String> arguments) throws IOException {

    int status = -1;
    Logger logger = Util.getOutputStreamLogger(moduleOut);
    logger.info("Starting module {}", getModuleName());

    ProcessBuilder exec = new ProcessBuilder();
    if (configureEnvironment(exec.environment(), moduleOut)) {

        List<String> command = getExecutable();

        logger.info("With PYTHONPATH: {}", exec.environment().get("PYTHONPATH"));
        logger.info("In: {}", getWorkingDirectory());
        logger.info("Executing: {}", StringUtils.join(command, " "));
        Process proc = exec.start();

        try (InputStream procOut = proc.getInputStream(); InputStream procErrOut = proc.getErrorStream()) {
            copy(procOut, moduleOut);
            copy(procErrOut, moduleOut);
            LOGGER.debug("Waiting for process to finish");
            status = proc.waitFor();
            LOGGER.debug("Closing streams");
            logger.info("The process finished with exit code: {}", status);
        } catch (InterruptedException e) {
            LOGGER.warn("The thread was interrupted", e);
    } else {
        logger.info("Module configuration failed");

    return status;

public void copy(final InputStream in, final OutputStream out) throws IOException {
    executor.execute(() -> {
        try {
            byte[] buffer = new byte[4096];
            int n = 0;
            while ((n = in.read(buffer)) != -1) {
                out.write(buffer, 0, n);
        } catch (IOException e) {
            LOGGER.error("Ya done goofed", e);

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Easy way to write contents of a Java InputStream to an OutputStream

Easy way to write contents of a Java InputStream to an OutputStream

By : bobmcleod
Date : March 29 2020, 07:55 AM
seems to work fine Java 9
Since Java 9, InputStream provides a method called transferTo with the following signature:
code :
public long transferTo(OutputStream out) throws IOException
when write of OutputStream write bytes(internally), then why read of InputStream returns int?

when write of OutputStream write bytes(internally), then why read of InputStream returns int?

By : mohanraj
Date : March 29 2020, 07:55 AM
I wish did fix the issue. Read returns an int so that it can also indicate the end of the stream, as -1. If the signature were
code :
byte read()
Better way of copying InputStream to OutputStream

Better way of copying InputStream to OutputStream

By : Serry Abdelrahman
Date : March 29 2020, 07:55 AM
will help you You can't get away without a buffer with streams, unless you want to copy a byte at a time, which isn't efficient unless you know there are buffered streams in the stack for both input and output.
You can't use ByteBuffers with streams. You can use them with channels, and you can get channels from streams, but all you're doing is adding extra layers over the streams API. You're better off confronting it direct, as below. In the case of network streams, the performance is dominated by the network, not by the code, in any case.
code :
while ((count = in.read(buffer)) > 0)
    out.write(buffer, 0, count);
Java: Write to OutputStream and then use it as InputStream

Java: Write to OutputStream and then use it as InputStream

By : mümin gök
Date : March 29 2020, 07:55 AM
may help you . I want to get a file from a remote storage as an InputStream without saving it to the local File System. The remote storage provides a Java API with a method that takes an OutputStream and dumps the file data into it. , Two options:
Java inputstream/outputstream write to file with same name

Java inputstream/outputstream write to file with same name

By : sh.F
Date : March 29 2020, 07:55 AM
will help you If you'd prefer not to use the popular temporary-file approach, then you can always just read in the whole file, then write back to it afterwards.
Here's a straight-forward implementation.
code :
public static void addRootTag(File xml) throws IOException {
    final List<String> lines = new ArrayList<>();;
    try (Scanner in = new Scanner(xml)) {
        while (in.hasNextLine())

    try (PrintStream out = new PrintStream(xml)) {
        for (String line : lines) {
            // indentation, if you want
            out.print("    ");
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