presto-main/src/main/java/io/prestosql/sql/planner/planprinter/IoPlanPrinter.java/IoPlanPrinter/print
class IoPlanPrinter:    private String print()
    {
        IoPlanBuilder ioPlanBuilder = new IoPlanBuilder(plan);
        plan.getRoot().accept(new IoPlanVisitor(), ioPlanBuilder);
        return jsonCodec(IoPlan.class).toJson(ioPlanBuilder.build());
    }