My first java multiline logstash config

logstash.conf

input {
    file {
        add_field => [ 'host', 'localhost' ]
        path => '/tmp/application.log'
        type => 'app'
        codec => 'plain'
	start_position => "beginning"
    }
}

output {
    elasticsearch { 
	index => "logstash-%{+YYYY.MM.dd}"
	host => localhost
    }
    stdout { codec => rubydebug }
}

filter {
    if [type] == 'app' {
 	multiline {
		pattern => '^[^\[]'
	        what => 'previous'  
	}
    }
}