IOUtils.copy() hangs when copying big stream?

Question

I want to parse content of some file by srcML parser which is an external windows program. I'm doing this in a following way:

String command = "src2srcml.exe --language java";
Process proc = Runtime.getRuntime().exec(command);

InputStream fileInput = Files.newInputStream(file)
OutputStream procOutput = proc.getOutputStream();

IOUtils.copy(fileInput, procOutput);

IOUtils.copy() is from Commons IO 2.4 library.

When my file is small (several KB) everything works fine. However, when I try to copy some relatively big file (~72 KB) my program hangs.

Moreover, when I execute the parser 'manually' in cmd:

src2srcml.exe --language Java < BigFile.java

everything works fine, too.

Any ideas why this is happening?

Answer 1

You should buffer the OutputStream:

OutputStream procOutput = proc.getOutputStream();
BufferedOutputStream bos = new BufferedOutputStream(procOutput);
IOUtils.copy(fileInput, bos);

Moreover, why don't you simply redirect fileInput as the process InputStream?

 ProcessBuilder pb = new ProcessBuilder(command);
 pb.redirectInput(file);
 Process proc = pb.start();
 proc.waitFor();

Answer 2

The problem is most likely that you are not consuming the output of the external program in a separate thread. you need to start a separate thread to consume the output so that the external program does not get blocked.