How to get the next 15 line after the date with groovy script

I'll anwser myslef since I solved it : 

		writeFile.withWriter { writer ->
			// read the file using a reader 
			readFile.withReader{ reader ->
				while (line = reader.readLine()) {
					
					// if line starts with your comment "'"
					if(line.contains(threadInfo)){
						def lineCount = 0
						while(lineCount  < lineCountMax) {
							def nextLine = reader.readLine()
							// to the current line, and writeit in the result file
							writer << "${nextLine}" << System.properties.'line.separator'
							lineCount ++;
						}
					} 
				}
			}
		}

thx anyaway !