logstash.conf

input {
  generator {
    count => 1
    lines => [
      "qid=ABCD1 first",
      "qid=XYZ2 first",
      "qid=ABCD1 second",
      "qid=XYZ2 second",
      "qid=ZZZZ first",
      "qid=ABCD1 third"
    ]
  }
}

filter {
  kv { }
  multiline {
    # Group by 'qid'
    stream_identity => "%{qid}"

    # Any lines
    pattern => ""
    what => next
  }
}

output {
  stdout { codec => json_lines }
}

result.txt

% bin/logstash -f test.conf
{"message":"qid=ABCD1 first\nqid=ABCD1 second\nqid=ABCD1 third","@version":"1","@timestamp":"2015-01-19T20:01:21.386Z","host":"Macintosh.local","sequence":0,"qid":"ABCD1","tags":["multiline"]}
{"message":"qid=XYZ2 first\nqid=XYZ2 second","@version":"1","@timestamp":"2015-01-19T20:01:21.387Z","host":"Macintosh.local","sequence":0,"qid":"XYZ2","tags":["multiline"]}
{"message":"qid=ZZZZ first","@version":"1","@timestamp":"2015-01-19T20:01:21.392Z","host":"Macintosh.local","sequence":0,"qid":"ZZZZ","tags":["multiline"]}