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In java, reading file using inputstream after deleting the file

I have a question regarding reading files in java.
Here is the sample code
File path = new File("myfile.txt");
InputStream inputStream = new FileInputStream(file);
BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
file.delete();
String line;
while((line = reader.readLine()) != null) {
System.out.println(line);
}
I create an input stream and try to read it. As they say, its like a pipe, you read values byte by byte.
To speed it up, we can use BufferedReader which can read chunk by chunk.
So, I delete this file before reading.
Now, when i read it, it still reads complete file, even though file is not there.
If inputStream is a pipe, why is it not failing ? Any ideas ?

I'm pretty sure it's because the txt file you are loading from is so small it is fully read on initialization of the buffered reader.

In my opinion, the file still exists in the reader and the inputStream. Deleting the source file won't change anything until you rerun your application.
BufferedReader and InputStream classes are probaly prepared for similar situations like this. It can be useful if the source of the file goes offline during the run.
Correct me if I'm wrong, I'm not a professional programmer.

Java Processbuilder Stream to Python-Script

I have a minor Problem with a small Project I'm trying to do.
I'm trying to use a Java-Program to call a Python-Script.
Java:
ProcessBuilder pb = new ProcessBuilder("python3", "tmp.py");
process = pb.start();
OutputStream stdin = process.getOutputStream();
InputStream stderr = process.getErrorStream();
InputStream stdout = process.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(stdout));
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(stdin));
writer.write("example" + "\n");
String output = reader.readLine();
Python-Script tmp.py (example):
import sys
sys.stdin.readline()
print("Hello World")
It wont terminate, seemingly because sys.sdin.readline() isnt catching any input and if I remove this line it terminates just fine.
(stderror was empty too)
I tried different things to fix this but nothing seems to work.
I would really appreciate any advice. Thanks in advance.
(Update: I tried to modify the Java-Program to access a .jar File instead of a Python-Script but the same error occurs here to. Using the Python Method subprocess.Popen() to access the Script however works just fine.)

Make sure you start python unbuffered with -u flag:
Force the binary layer of the stdout and stderr streams (which is
available as their buffer attribute) to be unbuffered. The text I/O
layer will still be line-buffered if writing to the console, or
block-buffered if redirected to a non-interactive file.
Edit
I recommend reviewing the buffering all the same. The python unbuffered is a common one, but you possibly still have some buffering. Make sure you flush java writer, writer.flush().

IOUtils.copy() hangs when copying big stream?

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?

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();

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.

How do I read and write from an external process in Java?

I want to run PianoBar from a Java GUI (PianoBar is a program that runs Pandora from command line). I thought this would be quick and dirty, but I guess I don't know enough about interaction between programs.
I use ProcessBuilder to launch an instance of PianoBar like so:
private Process createPianoBarProcess() throws IOException {
String[] command = {"CMD", "/C", "pianobar"};
ProcessBuilder probuilder = new ProcessBuilder( command );
probuilder.redirectErrorStream(true);
probuilder.directory(new File("~~location where pianobar.exe is~~"));
Process process = probuilder.start();
return process;
}
After I create the process, I create a BufferedReader to read in the PianoBar output:
Process pianoBar = createPianoBarProcess();
InputStream inS = pianoBar.getInputStream();
InputStreamReader isr = new InputStreamReader(inS);
BufferedReader br = new BufferedReader(isr);
But when I read the output from PianoBar via this reader, it spits out the first line of PianoBar ("Welcome to pianobar (2013.05.19-win32)! Press ? for a list of commands."), then it spits out the next line ("[?] Email:"). Then it just hangs.
Obviously, it is waiting for the user to input their email. But no matter what I try, I can't get my Java program to write the email to the PianoBar process when prompted - it just hangs as soon as it reads out the last character.
Is it possible to do what I am trying to do? I thought it would be an easy thing to look for on the internet, but I haven't been able to find anything. All I want is an easy way to write to the external process when prompted. Seems like this should be easy...

You may use the following code snippet to get working:
String s;
//s = email
BufferedWriter bufferedwriter = new BufferedWriter(new OutputStreamWriter(pianoBar.getOutputStream()));
bufferedwriter.write(s);
bufferedwriter.flush();
Done!
Remember to surround the code block with appropriate try/catch

how to read text file on any machine in java

I am trying to read file,but it is reading only on my machine,it is not working on another machine.Here is my code..
FileInputStream fstream=new FileInputStream("/path of myfile/User.txt");
DataInputStream in = new DataInputStream(fstream);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String str;
while ((str = br.readLine()) != null) {
System.out.println(str);
}
Please help me,how to read file on another machine as well,what changes should I make?

I'm just guessing that you already found a way to share the file, either with HTTP, FTP, SMB or NFS, but you've some problems, perhaps some funny characters appearing in the text. If you don't name the encoding that you want to use, the default one for the machine will be used, and if they have different defaults, you'll run into problems.
Choose an encoding when writing and reading, for example for UTF8 universal encoding, your source should be modified as:
BufferedReader br = new BufferedReader(new InputStreamReader(in, "UTF8"));
When you write your file, of course, you've to use the same encoding, for instance:
FileOutputStream fos = new FileOutputStream("/path of myfile/User.txt");
OutputStreamWriter out = new OutputStreamWriter(fos, "UTF-8");

If you want to read a file that resides on another machine, you have to serve that file using some kind of network server, like an http-server or an smb-server.