mp3文件后128字节歌曲信息读写操作

参照网上相关资料，实现向mp3文件后128字节写入指定数据，并读取出来.
项目中为向MP3文件写入歌曲信息，如歌手、专辑、歌名等.
第一步:创建关键类 SongInfo

public class SongInfo {private String TAG = "TAG"; // 文件头1-3
  private String songName = "歌名"; // 歌曲名4-33
  private String artist = "歌手名"; // 歌手名34-63
  private String album = "专辑"; // 专辑名61-93
  private String year = "2007"; // 年94-97
  private String comment = "200"; // 备注98-125       java 放文件大小
  private byte r1, r2, r3; // 三个保留位126，127，128
  private boolean valid; // 是否合法
  public transient String fileName; // 此歌曲对应的文件名,没有封装public SongInfo(byte[] data) {
   if (data.length != 128) {
    throw new RuntimeException("数据长度不合法:" + data.length);
   }
   String tag = "";
   try {
    tag = new String(data, 0, 3);
   } catch (Exception e) { 
    System.out.println("error >> :"+e.getMessage());
    e.printStackTrace();
   }
   
   // 只有前三个字节是TAG才处理后面的字节
   if (tag.equalsIgnoreCase("TAG")) {
    try {
     valid = true;
     songName = new String(data, 3, 30,"UTF-8").trim();
     artist = new String(data, 33, 30,"UTF-8").trim();
     album = new String(data, 63, 30,"UTF-8").trim();
     year = new String(data, 93, 4).trim();
     comment = new String(data, 97, 28).trim();
     r1 = data[125];
     r2 = data[126];
     r3 = data[127];
     
    } catch (Exception e) {
     System.out.println("error 22>> :"+e.getMessage());
     e.printStackTrace();
    }
   } else {
    valid = false;
   }
  }public SongInfo(String tag,String songName,String artist, String album,String fileSize) {
   this.TAG = tag;
   this.songName = songName;
   this.artist = artist;
   this.album = album;
   this.comment = fileSize;
  }  public boolean isValid() {
   return valid;
  }  public  byte[] getBytes() {
   byte[] data = new byte[128];
   try {
    System.arraycopy(TAG.getBytes(), 0, data, 0, 3);
    byte[] temp;
    temp = songName.getBytes("UTF-8");
    
    System.arraycopy(temp, 0, data, 3, temp.length > 30 ? 30 : temp.length);
    temp = artist.getBytes("UTF-8");
    System.arraycopy(temp, 0, data, 33, temp.length > 30 ? 30: temp.length);
    
    temp = album.getBytes("UTF-8");
    System.arraycopy(temp, 0, data, 63, temp.length > 30 ? 30: temp.length);
    
    temp = year.getBytes();
    System.arraycopy(temp, 0, data, 93, temp.length > 4 ? 4 : temp.length);
    
    temp = comment.getBytes();
    System.arraycopy(temp, 0, data, 97, temp.length > 28 ? 28: temp.length);  data[125] = r1;
    data[126] = r2;
    data[127] = r3;
    
   } catch (Exception e) {
    e.printStackTrace();
   }
   return data;
  }public String getArtist() {
   return artist;
  }public void setArtist(String authorName) {
   this.artist = authorName;
  }public String getComment() {
   return comment;
  }public void setComment(String comment) {
   this.comment = comment;
  }public byte getR1() {
   return r1;
  }public void setR1(byte r1) {
   this.r1 = r1;
  }public byte getR2() {
   return r2;
  }public void setR2(byte r2) {
   this.r2 = r2;
  }public byte getR3() {
   return r3;
  }public void setR3(byte r3) {
   this.r3 = r3;
  }public String getSongName() {
   return songName;
  }public void setSongName(String songName) {
   if (songName == null) {
    throw new NullPointerException("歌名不能是null!");
   }
   valid = true;
   this.songName = songName;
  }public String getAlbum() {
   return album;
  }public void setAlbum(String specialName) {
   this.album = specialName;
  }public String getYear() {
   return year;
  }public void setYear(String year) {
   this.year = year;
  }
 }
 第二步: 调用此类实现写MP3文件后128字节数据操作
 public void setSongInfo(String url, String tag, String songName,
    String artist, String album, String fileSize) {
   FileConnection fc = null;
   SongInfo info = null;
   String fileUrl = url;
   OutputStream out = null;
   byte[] buffer = new byte[128];
   try {
    fc = (FileConnection) Connector.open(fileUrl, Connector.READ_WRITE);  if (fc.exists()) {
     info = new SongInfo(tag, songName, artist, album, fileSize);   buffer = info.getBytes();
   out = fc.openOutputStream(fc.fileSize());
   out.write(buffer);
   out.flush();
    }
   } catch (IOException ioe) {
    ioe.printStackTrace();
   } finally {
    try {
     out.close();
     fc.close();
    } catch (IOException e) {
     e.printStackTrace();
    }
   }
  }第三步:读取后128字节内容
 public SongInfo getSongInfo(String url) {
   FileConnection fc = null;
   SongInfo info = null;
   InputStream in = null;
   String songName = "song";
   long songSize = 200;
   String fileUrl = url;
   byte[] buffer = new byte[128];
   try {
    fc = (FileConnection) Connector.open(fileUrl, Connector.READ_WRITE);
    if (fc.exists()) {
     long size = fc.fileSize();   songName = fc.getName();
     songName = songName.substring(0, songName.length() - 4);
     songSize = fc.fileSize();   long byteOffset = size - 128;
   in = fc.openInputStream();
   in.skip(byteOffset);
   in.read(buffer);
    }
    info = new SongInfo(buffer);
    if (info.getSongName().equals("歌名")) {
     info.setSongName(songName);
    }
    if (info.getComment().equals("200")) {
     info.setComment("" + songSize);
    }
    if (info.getAlbum().equals("")) {
     info.setAlbum("未知");
    } } catch (IOException ioe) {
    m_controll.setCurrent(new MessageAlert("warn",
      " getSongInfo error: " + ioe.getMessage() + curURI, disp,
      m_controll));
    ioe.printStackTrace();
   } finally {
    try {
     in.close();
     fc.close();
    } catch (IOException e) {
     e.printStackTrace();
    }
   }
   return info;
  }