Question

I have a impl class which has several methods, they all basically call the script using runtime.exec with different argument list e.g.

public String doExport(String ruleIds, String fileName) throws Exception{
        StringBuffer cmd = new StringBuffer();
        cmd.append(SOME_SCRIPT + " -a export ");
        cmd.append(" -f " );
        cmd.append(fileName);
        cmd.append(" -r " );
        cmd.append(ruleIds);
        cmd.append(" 2>/dev/null");
        return execCmd(cmd.toString());
    }

    public String doImport(String fileName, String user, String iface) throws Exception {
        StringBuffer cmd = new StringBuffer();
        cmd.append(SOME_SCRIPT + " -a import ");
        cmd.append(" -f " );
        cmd.append(fileName);
        cmd.append(" -m " );
        cmd.append("user");
        cmd.append(" -u " );
        cmd.append(user);
        cmd.append(" -I " );
        cmd.append(iface);
        return execCmd(cmd.toString());
    } 
public String setRulesMode(String mode) throws Exception {
        String cmd = SOME_SCRIPT + " -a ";
        return execCmd(cmd.toString());
    }

Is there better way to do this? like encapsulate commands and arguments or more generic way of doing it? I tried to use enum but found it enum is better used when there are static/constant parameter list, so looking for better alaternative.

Answer 1

I ‘d create “CommandBuilder” that wraps ProcessBuilder and is able to compose and run command line.

Please pay attention that your attempt to redirect STDOUt to file will not work. Redirection is a shell feature. You can either run your command via shell (e.g. /bin/sh YOUR COMMAND >YOURFILE on unix or cmd -c YOUR COMMAND >YOURFILE on windows.

Better way is to use Process.setOutputStream() from java. It is portable, easier to debug and maintain. This can be functionality of your CommandBuilder.

EDIT

Here are some tips to the CommandBuilder structure.

public class CommandBuilder {
    public void setPrefix(); // e.g. cmd or /bin/sh But some kind of automatic logic should be implemented too, i.e. cmd for windows, /bin/sh for unix
    public void setCommand(); // for example ping
    public void addArgument(String value);  // e.g. myhost
    public void setInputStream(InputStream in);
    public void setOutputStream(OutputStream in);

    // add appropriate getters.

    public Process exec();
    public int execAndWait(); // returns process status
}