Reading Java log input from shell script execution [closed]

Question

I have a unix shell script, and in it I start a Java application. That Java application logs a handful of information upon startup, and I wonder if it's possible for my script to "read" that log information so that the shell script itself can be read by another Java application?

I'm new to some of this, so there is a big chance it's not possible, but thought I'd ask :)

Answer 1

You can use named pipes to redirect your logs from your java application to a named pipe. And in your another java application you should read the content from the named pipe.

Named pipe definition:

A FIFO, also known as a named pipe, is a special file similar to a pipe but with a name on the filesystem. Multiple processes can access this special file for reading and writing like any ordinary file.

Here is an example:

Creating the named pipe:

mkfifo /home/user/pipe1

Java Application that shows the logs

Assuming that you have this application:

Main.java

public class Main {
   

   public static void main(String[] args) throws Exception {
      System.out.println("Hello From Java!");
      Thread.sleep(5000); //sleep 5 seconds
      System.out.println("Goodbye");
   }

}

And the another java application which read the logs from Main.java

ReadLogs.java

import java.io.*;

public class ReadLogs {
 
static BufferedReader pipeReader;

public static void createBuffer(String namedPipe) throws Exception {
    pipeReader = new BufferedReader(new FileReader(new File(namedPipe)));
} 

public static void process() throws Exception {
   String msg;
    while ((msg = pipeReader.readLine()) != null) {
          System.out.println("Message: "+msg);
    }
}

public static void main(String args[]) throws Exception {
       createBuffer("/home/user/pipe1");
       process();              
       System.out.println("EOF: Finished");
}
}

Redirecting the logs from your java application to named pipe:

java MainApplication > /home/user/pipe1

Finally you will have to read the content of the named pipe running the ReadLogs java application:

java ReadLogs

Note: The Main.java application will redirect each output to the pipe1 only if the content of this one has been read. For example, if you only run java Main > /home/user/pipe1 the program will wait for a process that read the content of pipe1.

You can try the following code for reading pipe1 without using java:

#In the terminal type:
java MainApplication > /home/user/pipe1
#In another terminal or tab:
cat /home/user/pipe1