Java implementation of process_result_set for improving performance of creating row hashes from a ResultSet

gistfile1.java

package com.msp;

import java.math.BigDecimal;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Time;
import java.sql.Timestamp;

import org.jruby.Ruby;
import org.jruby.RubyArray;
import org.jruby.RubyHash;
import org.jruby.RubyModule;
import org.jruby.RubyString;
import org.jruby.RubySymbol;
import org.jruby.anno.JRubyMethod;
import org.jruby.exceptions.RaiseException;
import org.jruby.javasupport.JavaEmbedUtils;
import org.jruby.runtime.Block;
import org.jruby.runtime.ThreadContext;
import org.jruby.runtime.builtin.IRubyObject;

public class DatasetUtils {

  private static IRubyObject BIG_DECIMAL = null;
  private static RubyModule LAZY_DATE = null;

  /**
   * Run this method only once during init to add the method in
   * @param runtime
   */
  public static void patchModule(RubyModule module) {
    BIG_DECIMAL = module.getRuntime().getClass("BigDecimal");
    LAZY_DATE = module.getRuntime().getClassFromPath("MSP::LazyDate");
    module.defineAnnotatedMethods(DatasetUtils.class);
  }

  /**
   * Attempt at speeding up the conversion process from a JDBC result set in to
   * a Sequel row
   */
  @JRubyMethod(name="process_result_set", required = 1)
  public static void processResultSet(ThreadContext context, IRubyObject recv, IRubyObject r_rs, Block block) throws SQLException {
    Ruby runtime = context.getRuntime();
    try {

      ResultSet rs = (ResultSet) r_rs.toJava(ResultSet.class);
      ResultSetMetaData md = rs.getMetaData();

      int cc = md.getColumnCount();
      IRubyObject[] labels = new RubySymbol[cc];
      for (int i = 0; i < cc; i++) {
        String label = md.getColumnLabel(i + 1);
        labels[i] = recv.callMethod(context, "output_identifier", JavaEmbedUtils.javaToRuby(runtime, label));
      }

      // Adapters have to set this as sequel uses it to get schema information about tables
      recv.getInstanceVariables().setInstanceVariable("@columns",
          RubyArray.newArrayNoCopyLight(runtime, labels));

      while (rs.next()) {
        // populate the hash
        RubyHash hash = new RubyHash(runtime);
        for (int i = 0; i < cc; i++) {
          Object obj = rs.getObject(i + 1);
          if (obj instanceof java.sql.Date || obj instanceof Timestamp || obj instanceof Time) {
            obj = LAZY_DATE.callMethod(context, "new", JavaEmbedUtils.javaToRuby(runtime, obj));
          } else if (obj instanceof BigDecimal) {
            obj = BIG_DECIMAL.callMethod(context, "new", RubyString.newUnicodeString(runtime, obj.toString()));
          } else {
            obj = JavaEmbedUtils.javaToRuby(runtime, obj);
          }
          // FIXME - support more types, see sequel/dataset/jdbc - convert_type
          hash.put(labels[i], obj);
        }

        // pass the hash to our block
        block.call(context, new IRubyObject[] {hash});
      }
    } catch (SQLException e) {
      throw RaiseException.createNativeRaiseException(runtime, e);
    }
  }

}