how to redirect stdin to java Runtime.exec?

Question

I want to execute some sql scripts using Java\'s Runtime.exec method. I intend to invoke mysql.exe / mysql.sh and redirect the script file to this process. From the command

Answer 1

Redirection is a functionality of the OS shell/cmd enviroments. To invoke them correctly we should use Runtime.exec(String[]) instead of Runtime.exec(String). Here is the code.

public Result executeCmd(String[] cmds, boolean waitForResult)
{
    Result result = new Result();
    result.output = "";
    try
    {
        for(int i=0;i<cmds.length;i++)
        {
            System.out.println("CMD["+i+"]::"+cmds[i]);
        }
        System.out.println("");
        Process process = null;
        if(cmds.length > 1)
            process=Runtime.getRuntime().exec(cmds);
        else
            process=Runtime.getRuntime().exec(cmds[0]);
        if (waitForResult)
        {
            StreamGobbler errordataReader = new StreamGobbler(process
                    .getErrorStream(), "ERROR");

            StreamGobbler outputdataReader = new StreamGobbler(process
                    .getInputStream(), "OUTPUT");

            errordataReader.start();
            outputdataReader.start();

            int exitVal = process.waitFor();
            errordataReader.join();
            outputdataReader.join();
            result.returnCode = exitVal;
            result.output = outputdataReader.output;
            result.error = errordataReader.output;
        }
    }
    catch (Exception exp)
    {
        result.exp = exp;
        result.returnCode = -1;
    }
    return result;
}

And call this method using

Result result = executeCmd(cmds, true);

where

CMD[0]::cmd
CMD[1]::/c
CMD[2]::.\mysql\bin\mysql --host=<hostname> --port=<portNum> -u <userName>  < .\scripts\create_tables.sql

Answer 2

Exec returns a Process object to you.

Process has getInputStream and getOutputStream methods.

Just use those to grab the input stream and start shoving bytes into it. Don't forget to read the output stream or the process may block.