Handling Java command line arguments in the format “cat file.txt | java YourMainClass”

Question

I've never used java from the terminal before, and I certainly have never coded for it. My question is simple: How do I intake a file when the calling format is

cat  file.txt  |  java  YourMainClass

I have the rest of the code up and running swimmingly, I just need to take the given file name into my main method.

Answer 1

Since the cat command displays the contents of the file, you need to use the System.in buffer to capture the data coming in from that command. You can use a BufferedReader pointing to System.in to loop through the data and process it.

Look at this Example

public class ReadInput {
    public static void main(String[] args) throws IOException {
    BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
        String x = null;  
        while( (x = input.readLine()) != null ) {    
            System.out.println(x); 
        }    
    }
}  

Answer 2

As you are looking to read from System.in as the output from cat , you could do:

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

String line;
while ((line = br.readLine()) != null) {
   // use line...
}