Java-按行数分割文本

package First;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;

public class DealFile {
	public static void main(String[] args) throws Exception{
		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		String fileName = in.readLine();
		FileManager source = new FileManager(fileName);
		String head = source.nextWord();
		String word = null;
		int count = 0;
		int n = 0;
		fileName = fileName.substring(0, fileName.length()-4);
		FileWriter w = null;
		while((word = source.nextWord()) != null){
			if(count == 0){
				w = new FileWriter(fileName+n+".csv");
				w.write(head);
			}
			//System.out.println(n + ":" + count);
			w.write(word);
			++count;
			if(count == 100000){
				++n;
				count = 0;
				w.close();
			}
		}
	}
}

class FileManager{
	int pos = 0;
	File f;
	FileReader reader;
	boolean flag = false;

	public FileManager(String filename)throws Exception{
		f = new File(filename);
		reader = new FileReader(f);
	}

	public String nextWord() throws IOException{
		if(flag)
			return null;
		char[] buf = new char[1];
		StringBuffer sb = new StringBuffer();
		int len;
		do{
			len = reader.read(buf);
			sb.append(buf[0]);
		}while('\n' != buf[0] && len != -1);
		if(len == -1)
			flag = true;
		return sb.toString();
	}
}