#DBCP database properties
username=root
dontencry=YES
password=root
driverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/gcra

    public void modifyFile(String fileName, String key, String value){
        OptProperties op = new OptProperties();
        
        File file = op.getFileFromBasePath(fileName);
        RandomAccessFile raf = null;
        //position
        long oldPos = 0;
        long newPos = 0;
        
        String lineStr = "";
        try {
            raf = new RandomAccessFile(file, "rw");
            oldPos = raf.getFilePointer();
            lineStr = raf.readLine();
            newPos = raf.getFilePointer();
            while(lineStr != null){
                //key = "password"
                if(lineStr.contains(key)){
                    //将读取位置设置到oldPos
                    raf.seek(oldPos);                    
                    System.out.println(oldPos);                    
                    raf.write(value.getBytes());
                    //raf.write(value.getBytes(), (int)(oldPos+1), (int)(newPos-oldPos));
                    break;
                }
                oldPos = raf.getFilePointer();
                lineStr = raf.readLine();
                newPos = raf.getFilePointer();
            }
            
            /*for(int i=0; i<7; i++){
                System.out.println(raf.readLine() + ", " + raf.getFilePointer());
            }*/
            
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally{
            if(raf != null){
                try {
                    raf.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

raf.seek(oldPos);
改为
raf.seek(oldPos + key.length() + 1);    //+1是因为有个等号

------解决方案--------------------

如果文件完全没有改变就不是因为位置的问题
没有抛异常吗？
另外，检查下你的value变量传入的对不对