wheee.groovy

@Grab( 'com.bloidonia:groovy-common-extensions:0.5.5' )
@Grab('com.xlson.groovycsv:groovycsv:1.0')
import static com.xlson.groovycsv.CsvParser.parseCsv
import groovy.transform.*

// A bufferedReader with some output
@InheritConstructors
class SpinnerReader extends BufferedReader {
    private String output = '/-\\|'
    private int offset = 0
    private void update() {
        print "\r${output[ offset ]}"
        System.out.flush()
        offset += 1
        offset %= output.length()
    }
    int read() { update() ; super.read() }
    int read(char[] cbuf, int off, int len) { update() ; super.read( cbuf, off, len ) }
    String readLine() { update() ; super.readLine() }
    void close() {
        print "\r"
        super.close()
    }
}

// Add a method to the metaClass of File
File.metaClass.withSpinnerReader = { Closure cl ->
    // withClosable is from common-extensions
    new SpinnerReader( delegate.newReader() ).withClosable cl
}

// Then, to use it:
new File( 'massiveFile.csv' ).withSpinnerReader { r ->
    parseCsv( r, separator:'\t' ).each { row ->
        // do something
    }
}