>>704
こんな感じでいいかな？
import java.io.*;
import java.util.*;

public class Test{
public static void main(String args[]){
BufferedReader br;
String line, tmp, data[];
HashMap map = new HashMap();

try{
br = new BufferedReader(new FileReader("テキストファイルＡ"));
while((line = br.readLine()) != null){
data = line.split(",");
map.put(data[0], data[1]);
}
br.close();

br = new BufferedReader(new FileReader("テキストファイルＢ"));
while((line = br.readLine()) != null){
tmp = (String)map.get(line);
if(tmp != null)
System.out.println(line + "," + tmp);
}
}catch(Exception e){
e.printStackTrace();
}
}
}