"vietnamese_stop": {
          "type":       "stop",
          "stopwords_path": "${fess.dictionary.path}vi/stopwords.txt"
        },
        "truncate10_filter" : {
          "type" : "truncate",
          "length" : 10
        },
        "truncate20_filter" : {
          "type" : "truncate",
          "length" : 20
        },
        "alphanum_word_filter" : {
          "type" : "alphanum_word",