List list = new ArrayList();
            String[] strread =new String[8];
            String str ="";
            str =gpid+","+gpname+","+gpcomment+","+update+","+operator+","+"0";
            String s ="";
            try {
                File out = new File("D:/redsun/groupinfo.txt");
                File in = new File("D:/redsun/groupinfo.txt");
                BufferedWriter output = new BufferedWriter(new FileWriter(out));//在这又把.Txt文件都清空了
                output.write(str);
                output.flush();
                output.newLine();
                output.close();
                BufferedReader input = new BufferedReader(new FileReader(in));
                while((s = input.readLine())!=null){
                    strread =s.split(",");
                    if("0".equals(strread[5])){
                    list.add(strread[1]);
                    }
                }    
                input.close();
                
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } 
            return list;
        }

BufferedWriter output = new BufferedWriter(new FileWriter(out,true));//

------解决方案--------------------
改成
output.append(str);

------解决方案--------------------
Java code

BufferedReader input = new BufferedReader(new FileReader(in));   //在这里又清空了

------解决方案--------------------
探讨

FileWriter 
public FileWriter(File file, 
                  boolean append) 
           throws IOException在给出 File 对象的情况下构造一个 FileWriter 对象。如果第二个参数为 true，则将字节写入文件末尾处，而不是写入文件开始处。  

参数： 
file - 要写入数据的 File 对象 
append - 如果为 true，则将字节写入文件末尾处，而不是写入文件开始处  


Java codeBufferedWriter output = new BufferedWrit…


------解决方案--------------------
没必要开两个内容一样的文件对象

------解决方案--------------------
一楼的解法有点麻烦，我试了试
二楼的是正解

------解决方案--------------------

Java code

import java.io.*;
import java.util.ArrayList;

import java.util.List;

import java.util.Iterator;


public class WriteFile {

    /**
     * @param args
     */
    private String gpid="00031";
    private String gpname="xmlbook";
    private String gpcomment="this is good book for readers";
    private String update="2008-03-26";
    private String operator = "add + ";
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        List<String> output = new WriteFile().writeEndFile();
        Iterator<String> item = output.iterator();
        while(item.hasNext()){
            System.out.println(item.next());
        }

    }
    public List<String> writeEndFile(){
        ArrayList<String> list = new ArrayList<String>();
        String[] strread =new String[8];
        String str ="";
        str =gpid+","+gpname+","+gpcomment+","+update+","+operator+","+"0";
        String s ="";
        try {
            File out = new File("D:/redsun/groupinfo.txt");
            FileOutputStream output = new FileOutputStream(out,true);//在这又把.Txt文件都清空了
            output.write(str.getBytes());
            output.flush();
            output.close();
            System.out.println("File writing has done!!");
            File in = new File("D:/redsun/groupinfo.txt");
            BufferedReader input = new BufferedReader(new FileReader(in));
            
            while((s = input.readLine())!=null){
                strread =s.split(",");
                if("0".equals(strread[strread.length-1])){
                    list.add(strread[1]);
                }
            }    
            input.close();
            
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } 
        return list;
    }
}