字符流读取文件

package test;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;


public class IOTest {
    public String getTt(String file){
        StringBuffer str = new StringBuffer();
        BufferedReader reder = null;
        try {
            reder = new BufferedReader(new FileReader("jiao"+file+".txt"));
            String s = null;
            int len =1;
            while((s = reder.readLine())!=null ){
                str.append(s.trim());
            }
            
        } catch (Exception e) {
            e.printStackTrace();
        }    finally{
            try {
                reder.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        if("".equals(str.toString())){
            return null;
        }
        return str.toString();
    }
        
    public static void main(String[] args) {
        IOTest i = new IOTest();
        String s = i.getTt("2");
        System.out.println(s);
    }
}