How do I get live input/output of a Java program started with C#-CodePudding

I have a C# program that needs to execute a Java program, however, when executing Java applications, no output is shown. I would also need this output to be live, as well as input.

Take this sample code:

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("Executing \"echo test\":");
        EchoRedirectDemo();
        Console.WriteLine("Executing \"java -version\":");
        JavaRedirectDemo();
    }

    static void JavaRedirectDemo()
    {
        ProcessStartInfo processStartInfo = new ProcessStartInfo("java")
        {
            Arguments = "-version",
            RedirectStandardOutput = true,
            RedirectStandardError = true,
            RedirectStandardInput = true
        };

        Process process = Process.Start(processStartInfo);

        process.WaitForExit();
        
        Console.WriteLine(process.StandardOutput.ReadToEnd());
    }
    
    static void EchoRedirectDemo()
    {
        ProcessStartInfo processStartInfo = new ProcessStartInfo("echo")
        {
            Arguments = "test",
            RedirectStandardOutput = true,
            RedirectStandardError = true,
            RedirectStandardInput = true
        };

        Process process = Process.Start(processStartInfo);

        process.WaitForExit();
        
        Console.WriteLine(process.StandardOutput.ReadToEnd());
    }
}

It will run echo test just fine and redirect the in/out/err, but there will be no in/out/err on the java -v command, as seen below:

Executing "echo test":
test

Executing "java -version":

Any idea about how to fix this issue?

CodePudding user response：

java -version will output the version info on STDERR, not STDOUT. This would require you to use something like Console.WriteLine(process.StandardError.ReadToEnd()); in your C# program.

However, java --version (note the double dash) output the version info on STDOUT. Thus, i would recommend to use this instead of java -version.

(This is also described in Java's online documentation about the commandline parameters at https://docs.oracle.com/en/java/javase/13/docs/specs/man/java.html)

CodePudding user response：

CliWrap can simplify this for you.

using System.Text;
using System;
using CliWrap;
using System.Threading.Tasks;

namespace proj
{
   public class Program
    {
        public static async Task Main(string[] args)
        {
            var stdOutBuffer = new StringBuilder();
            var stdErrBuffer = new StringBuilder();

            var result = await Cli.Wrap("java")
            .WithArguments("-version")
            .WithWorkingDirectory("/")
            .WithStandardOutputPipe(PipeTarget.ToStringBuilder(stdOutBuffer))
            .WithStandardErrorPipe(PipeTarget.ToStringBuilder(stdErrBuffer))
            .ExecuteAsync();

            var stdOut = stdOutBuffer.ToString(); 
            var stdErr = stdErrBuffer.ToString();
            Console.WriteLine(stdOut);
            Console.WriteLine(stdErr);

        }
    }
}

OUTPUT

java version "1.8.0_301"
Java(TM) SE Runtime Environment (build 1.8.0_301-b09)
Java HotSpot(TM) 64-Bit Server VM (build 25.301-b09, mixed mode)