Question

I need to use openssl in java code. e.g.

$ openssl genrsa -out private.pem 2048

$ openssl pkcs8 -topk8 -in private.pem -outform DER -out private.der -nocrypt

$ openssl rsa -in private.pem -pubout -outform DER -out public.der

Is there any library or method to implement this?

Answer 1

The best way is to use Java library for this actions. I can’t write exact code right now but it isn’t very hard. Look at java.security.KeyPairGenerator and so on. And it will be good experience in understanding of cryptography.

But if you need only to call this three command line, Process.waitFor() call is the answer. You can use this class.

package ru.donz.util.javatools;

import java.io.*;

/**
 * Created by IntelliJ IDEA.
 * User: Donz
 * Date: 25.05.2010
 * Time: 21:57:52
 * Start process, read all its streams and write them to pointed streams.
 */
public class ConsoleProcessExecutor
{
    /**
     * Start process, redirect its streams to pointed streams and return only after finishing of this process
     *
     * @param args        process arguments including executable file
     * @param runtime just Runtime object for process
     * @param workDir working dir
     * @param out         stream for redirecting System.out of process
     * @param err         stream for redirecting System.err of process
     * @throws IOException
     * @throws InterruptedException
     */
    public static void execute( String[] args, Runtime runtime, File workDir, OutputStream out, OutputStream err )
            throws IOException, InterruptedException
    {
        Process process = runtime.exec( args, null, workDir );

        new Thread( new StreamReader( process.getInputStream(), out ) ).start();
        new Thread( new StreamReader( process.getErrorStream(), err ) ).start();

        int rc = process.waitFor();
        if( rc != 0 )
        {
            StringBuilder argSB = new StringBuilder( );
            for( String arg : args )
            {
                argSB.append( arg ).append( ' ' );
            }
            throw new RuntimeException( "Process execution failed. Return code: " + rc + "\ncommand: " + argSB );
        }
    }

}

class StreamReader implements Runnable
{
    private final InputStream in;
    private final OutputStream out;


    public StreamReader( InputStream in, OutputStream out )
    {
        this.in = in;
        this.out = out;
    }

    @Override
    public void run()
    {
        int c;
        try
        {
            while( ( c = in.read() ) != -1 )
            {
                out.write( c );
            }
            out.flush();
        }
        catch( IOException e )
        {
            e.printStackTrace();
        }
    }
}