How to display the contents of a .txt file on cmd window using Java?

问题

I am working on a project and I want to display the contents of a .txt file on the CMD window. I wrote this piece of code to open a demo.txt file on cmd but it does not work. The "path" variable contains the location where the demo.txt file is placed (as you can see obviously).

public static void main(String[] args){
    try{
        String path = "C:\\Users\\Hp\\Documents\\NetBeansProject\\Project\\build\\classes\\";
        //cmd command to open open the txt file on cmd window
        String command = ("type " + path + "\\demo.txt");
        //executing this command on cmd using java
        Process process = Runtime.getRuntime().exec(command);
        }catch(IOException e){
            e.printStackTrace();
        }

This code produces the following output:

Don't mind the cringey or faulty code as I'm still a beginner in Java programming.

回答1:

The executable that displays a CMD window (as you refer to it in your question) is:

C:\Windows\System32\conhost.exe

Use class java.lang.ProcessBuilder to launch conhost.exe

ProcessBuilder pb = new ProcessBuilder("conhost.exe");
Process proc = pb.start();

When you run this java code a CMD window will be displayed.
Note that you can't type commands into this window because its standard input is your java program and not the keyboard. However you can send commands to the window from your java code. You simply write to the output stream of the Process instance.

First get the output stream of the Process

OutputStream os = proc.getOutputStream();

Then write your desired commands to the output stream.

I used the [Windows] start command to open a separate window – which you can interact with – and ran your desired command in that window. And finally, I closed the window that I opened via conhost.exe. As a result, the window opened by the start command remains open and the java program terminates.

Here is the entire code.

import java.io.IOException;
import java.io.OutputStream;

public class Script {

    public static void main(String[] args) throws IOException, InterruptedException {
        ProcessBuilder pb = new ProcessBuilder("conhost.exe");
        Process proc = pb.start(); // throws java.io.IOException
        OutputStream os = proc.getOutputStream();
        os.write("start /D C:\\Users\\Hp\\Documents\\NetBeansProject\\Project\\build\\classes type demo.txt".getBytes()); // throws java.io.IOException
        os.write(System.lineSeparator().getBytes()); // throws java.io.IOException
        os.write("exit".getBytes()); // throws java.io.IOException
        os.write(System.lineSeparator().getBytes()); // throws java.io.IOException
        os.flush(); // throws java.io.IOException
        int status = proc.waitFor(); // throws java.lang.InterruptedException
        System.out.println("Exit status = " + status);
    }
}

回答2:

The "type" command is only valid within CMD.EXE so CMD.EXE must be launched. Unfortunately CMD.EXE won't launch as a new window - it is running in background with it's input / output streams available to the Process class returned.

So you need to make CMD run a second CMD "start type blah.txt" to see a new window! This would do it - though I don't recommend this approach at all:

Path file = Path.of(path, "demo.txt");
String[] command = new String[]{"CMD.EXE", "/c", "start", "type", file.toString()};
Runtime.getRuntime().exec(command);

来源：https://stackoverflow.com/questions/63244536/how-to-display-the-contents-of-a-txt-file-on-cmd-window-using-java

标签

java

cmd

file-handling

java-io