CODEWITHSUNDEEP
java
rick
rick

Reputation: 931

compiling java file from another java class

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class ExecuteShellComand {

    public static void main(String[] args) {

        ExecuteShellComand obj = new ExecuteShellComand();
        String className = "str.java";
        String command = "javac " + className;
        String output = obj.executeCommand(command);
        System.out.println(output);// prints the output of the executed command
    }

    private String executeCommand(String command) {
        StringBuffer output = new StringBuffer();
        Process p;
        try {
            p = Runtime.getRuntime().exec(command);
            p.waitFor();
            BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));
            String line = "";
            while ((line = reader.readLine()) != null) {
                output.append(line + "\n");
            }

        } catch (Exception e) {
            e.printStackTrace();
        }

        return output.toString();

    }

}

I am trying to compile a Java file (str.java) from another Java class(ExecuteShellComand.java). What I am trying to do is if "str.java" compiles successfully then I want to execute "java str" command, but if the compilation fails then proper stacktrace or errors should be printed. I am storing the stacktrace or the errors in output variable.

But when I execute this code although "str.java" has somes errors in it System.out.println(output) is not printing the errors.

Upvotes: 0

Views: 425

Answers (2)

rdllopes
rdllopes

Reputation: 5120

The Process class tries to mimetize OS process. It means, process keep different output stream for error and normal messages and one stream for input. In UNIX, should be:

wc < file > wc.count 2> wc.error

In Java...

  • abstract InputStream getErrorStream() Gets the error stream of the subprocess.
  • abstract InputStream getInputStream() Gets the input stream of the subprocess.
  • abstract OutputStream getOutputStream()

So, you should use getErrorStream() to get errors..

Refactoring your code:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

public class ExecuteShellComand {

    public static void main(String[] args) {
        ExecuteShellComand obj = new ExecuteShellComand();
        String className = "str.java";
        String command = "javac " + className;
        obj.executeCommand(command);
        System.out.println(obj.output);
        System.out.println(obj.errors);
    }

    private String errors;
    private String output;

    private void executeCommand(String command) {
        Process p;
        try {
            p = Runtime.getRuntime().exec(command);
            p.waitFor();
            errors = readStream(p.getErrorStream());
            output = readStream(p.getInputStream());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private String readStream(InputStream inputStream) throws IOException {
        StringBuffer output = new StringBuffer();
        BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
        String line = "";
        while ((line = reader.readLine()) != null) {
            output.append(line + "\n");
        }
        return output.toString();
    }

}

Upvotes: 1

Sanjeev
Sanjeev

Reputation: 9946

If you want to capture the errors from a command then you shall capture error stream instead of Input stream

So replace

BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));

with

BufferedReader reader = new BufferedReader(new InputStreamReader(p.getErrorStream()));

Upvotes: 1

Related Questions