Question

How can I make a type which is a MarkupBuilder but has default constructor which is initialized with a StringWriter and overrides toString() to call the toString() on the StringWriter?

The idea is like the following, but of course initializing instance variables before super constructor calls is not allowed:

class StringWriterMarkupBuilder extends MarkupBuilder {
    final def sw = new StringWriter()
    StringWriterMarkupBuilder() {
        super(sw)
    }

    @Override String toString() {
        sw.toString()
    }
}

Answer 1

You could also do this with the metaClass like so:

import groovy.xml.MarkupBuilder

MarkupBuilder createSWMB() {
  new StringWriter().with { sw ->
    new MarkupBuilder( sw ).with { mb ->
      mb.metaClass.toString = { -> sw.toString() }
      mb
    } 
  }
}

MarkupBuilder mb = createSWMB()
mb.root {
  names {
    name( first:'tim', second:'yates' )
  }
}
println mb.toString()