Parser.java 文件源码

/**
 * Given an expression and an optional comparator, build a tree of
 * InputFormats using the comparator to sort keys.
 */
static Node parse(String expr, JobConf job) throws IOException {
  if (null == expr) {
    throw new IOException("Expression is null");
  }
  Class<? extends WritableComparator> cmpcl =
    job.getClass("mapred.join.keycomparator", null, WritableComparator.class);
  Lexer lex = new Lexer(expr);
  Stack<Token> st = new Stack<Token>();
  Token tok;
  while ((tok = lex.next()) != null) {
    if (TType.RPAREN.equals(tok.getType())) {
      st.push(reduce(st, job));
    } else {
      st.push(tok);
    }
  }
  if (st.size() == 1 && TType.CIF.equals(st.peek().getType())) {
    Node ret = st.pop().getNode();
    if (cmpcl != null) {
      ret.setKeyComparator(cmpcl);
    }
    return ret;
  }
  throw new IOException("Missing ')'");
}