File file = new File("D://param.properties"); 
        FileInputStream fis = null;
        FileOutputStream fos = null;
        try {
            fis = new FileInputStream(file);
            Properties prop = new Properties();
            prop.load(fis);
            prop.setProperty("key", "3");
            fos = new FileOutputStream(file);
            prop.store(fos, null);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            try {
                fis.close();
                fos.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            
        }