文件操作（创建和写）

  String separator = File.separator;
  String filename = "myfile.txt";
  String dir = "mydir1"+separator+"mydir2";
  File f = new File(dir,filename);
  
  if(f.exists()){
   System.out.println("文件名:"+f.getAbsolutePath());
   System.out.println("文件大小:"+f.length());
  }else{
   f.getParentFile().mkdirs();
   try {
    f.createNewFile();
    
   } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   }
  }
  FileWriter writer;
  try {
   writer = new FileWriter(f, true);
   writer.write("xxxxxxxx");
   writer.close();
  } catch (IOException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }