Logstash dissect插件日志切割后用convert_datatype转换数据类型问题

大家好：
    我使用logstash的dissect插件进行nginx日志的字段切割，然后用convert_datatype进行日志字段数据类型转换，但是有个问题，request_time和upstream_response_time字段有时候并不一定是浮点类型，有时候却是'-'字符来代替，因此用convert_datatype来将这两个字段转换成float类型时会抛异常，然后将这两个字段的值设置为原先的字符串，即'-'。我想要的结果是当这两个字段是'-'导致数据类型转换失败时，给这两个字段一个默认的数值，即0.00而不是给一个字符串'-'。
以下是运行logstash后抛出的异常（配置文件及示例日志见后面）：

[2017-08-05T22:28:29,551][WARN ][logstash.filters.dissect ] Dissector datatype conversion, value cannot be coerced, key: request_time, value: - [2017-08-05T22:28:29,551][WARN ][logstash.filters.dissect ] Dissector datatype conversion, value cannot be coerced, key: upstream_response_time, value: -

以下是我的nginx日志格式：

$time_local|server_ip|$request | $status | $remote_user | $remote_addr | $http_user_agent | $http_referer | $host | $bytes_sent|$request_time|$upstream_response_time|$upstream_addr|$connection|$connection_requests|$uuid

示例日志（注意request_time和upstream_response_time字段的值是'-'，不是数值类型）：

05/Aug/2017:22:22:33 -0700|54.153.101.30|GET /listing/detail/1864252/MO/St-Louis/www HTTP/1.1|200|-|5.255.250.132|Mozilla/5.0 (compatible; YandexBot/3.0; +http://yandex.com/bots)|-|env1-2.chime.me|76627|-|-|127.0.0.1:10300|4483145|2|38873227-aa0e-412b-b93f-13a7d0e26fb7

 
Logstash 配置文件：

input {

  beats {

    port => 5044

  }

}



filter {

   ruby {

       code => "

            event.timestamp.time.localtime

            tstamp = event.get('@timestamp').to_i

            Time.at(tstamp).strftime('%Y-%m-%d')

        "

   }

   

   dissect {

      mapping => {

         "message" => "%{time_local}|%{server_ip}|%{request}|%{status_code}|%{remote_user}|%{remote_addr}|%{http_user_agent}|%{http_referer}|%{host}|%{bytes_sent}|%{request_time}|%{upstream_response_time}|%{upstream_addr}|%{connection}|%{connection_requests}|%{uuid}"

      }

     convert_datatype => {

       status_code => "int"

       bytes_sent => "int"

       request_time => "float"

       upstream_response_time => "float"

     } 

  }

}



output {

    if [business] == "nginx" and [type] == "access" {

          stdout { codec => rubydebug }

    }

}

当以上面的配置文件运行logstash后得到的结果如下：

{

                   "request" => "GET /listing/detail/1864252/MO/St-Louis/www HTTP/1.1",

               "status_code" => 200,

             "upstream_addr" => "127.0.0.1:10300",

       "connection_requests" => "2",

                    "source" => "/home/ec2-user/nginx/logs/access.log",

                      "type" => "access",

                      "uuid" => "38873227-aa0e-412b-b93f-13a7d0e26fb7",

           "http_user_agent" => "Mozilla/5.0 (compatible; YandexBot/3.0; +http://yandex.com/bots)",

               "remote_user" => "-",

              "request_time" => "-",

                  "@version" => "1",

                      "beat" => {

        "hostname" => "awsuw7-50.opi.com",

            "name" => "awsuw7-50.opi.com",

         "version" => "5.5.1"

    },

                      "host" => "env1-2.chime.me",

                 "server_ip" => "54.153.101.30",

                "connection" => "4483145",

               "remote_addr" => "5.255.250.132",

                    "offset" => 270,

                  "business" => "nginx",

                "input_type" => "log",

                "time_local" => "05/Aug/2017:22:22:33 -0700",

                   "message" => "05/Aug/2017:22:22:33 -0700|54.153.101.30|GET /listing/detail/1864252/MO/St-Louis/www HTTP/1.1|200|-|5.255.250.132|Mozilla/5.0 (compatible; YandexBot/3.0; +http://yandex.com/bots)|-|env1-2.chime.me|76627|-|-|127.0.0.1:10300|4483145|2|38873227-aa0e-412b-b93f-13a7d0e26fb7",

                "bytes_sent" => 76627,

                      "tags" => [

        [0] "beats_input_codec_plain_applied",

        [1] "_dataconversionuncoercible_request_time_float",

        [2] "_dataconversionuncoercible_upstream_response_time_float"

    ],

                "@timestamp" => 2017-08-06T05:28:24.508Z,

              "http_referer" => "-",

    "upstream_response_time" => "-"

}

可以发现request_time和upstream_response_time是原先的'-'字符串，这并不是我想要的，我想在转换失败时给一个默认的数值，比如0.00，而不是字符串。