首先,需要紀錄的是在項目中出現的一個問題,序列化一個內部類,出現NotSerializableException.
解決方法有兩個,第一種方法是最開始自己的處理,使用writeObject和readObject來實現自定義序列化,這個有些
繁雜,需要對每個實例字段進行序列化,不然,當你反序列化時,得到的對象的字段都是默認值,如int=0,string=null.
...
ExpandedBlockStart.gif ContractedBlock.gifpublic class MsgBean implements Serializable dot.gif{
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif /** *//**
InBlock.gif * Comment for <code>serialVersionUID</code>
ExpandedSubBlockEnd.gif */
InBlock.gif private static final long serialVersionUID = 1L;
InBlock.gif
InBlock.gif private int msgType;
InBlock.gif
InBlock.gif private String mName;
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif public String getMName() dot.gif{
InBlock.gif return mName;
ExpandedSubBlockEnd.gif }
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif public void setMName(String name) dot.gif{
InBlock.gif mName = name;
ExpandedSubBlockEnd.gif }
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif public int getMsgType() dot.gif{
InBlock.gif return msgType;
ExpandedSubBlockEnd.gif }
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif public void setMsgType(int msgType) dot.gif{
InBlock.gif this.msgType = msgType;
ExpandedSubBlockEnd.gif }
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif private void writeObject(ObjectOutputStream out) throws IOException dot.gif{
InBlock.gif out.writeObject(getMName());
InBlock.gif out.writeObject(new Integer(getMsgType()));
ExpandedSubBlockEnd.gif }
InBlock.gif
InBlock.gif private void readObject(ObjectInputStream in) throws IOException,
ExpandedSubBlockStart.gif ContractedSubBlock.gif ClassNotFoundException dot.gif{
InBlock.gif setMName((String) in.readObject());
InBlock.gif setMsgType((Integer)in.readObject());
ExpandedSubBlockEnd.gif }
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif public String toString() dot.gif{
InBlock.gif return "The object's class is MsgBean,field:mName=" + mName
InBlock.gif + ",msgType=" + msgType;
ExpandedSubBlockEnd.gif }
ExpandedBlockEnd.gif }
,後來在網上找找,發現只需要將該內部類聲明為static,即可.這是因為內部非靜態類會存在一個隱含的到外部
類的引用(外部類.this),所以當序類化內部類時,會關聯序列化外部類,恰恰外部類沒有實現Serializable接口,就會
出現這個錯誤.下面是改過後的.
ExpandedBlockStart.gif ContractedBlock.gifpublic static class MsgBean implements Serializable dot.gif{
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif /** *//**
InBlock.gif * Comment for <code>serialVersionUID</code>
ExpandedSubBlockEnd.gif */
InBlock.gif private static final long serialVersionUID = 1L;
InBlock.gif
InBlock.gif private int msgType;
InBlock.gif
InBlock.gif private String mName;
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif public String getMName() dot.gif{
InBlock.gif return mName;
ExpandedSubBlockEnd.gif }
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif public void setMName(String name) dot.gif{
InBlock.gif mName = name;
ExpandedSubBlockEnd.gif }
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif public int getMsgType() dot.gif{
InBlock.gif return msgType;
ExpandedSubBlockEnd.gif }
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif public void setMsgType(int msgType) dot.gif{
InBlock.gif this.msgType = msgType;
ExpandedSubBlockEnd.gif }
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif public String toString() dot.gif{
InBlock.gif return "The object's class is MsgBean,field:mName=" + mName
InBlock.gif + ",msgType=" + msgType;
ExpandedSubBlockEnd.gif }
ExpandedBlockEnd.gif }
好了,上面只是題外話.
我們在規劃序列化對象時,一般要考慮序列化的性能,所以對象不能太大,層次也不能太多.從這方面來考慮,
可以選擇序列化完整的一個類,或是只是針對字段來進行序列化.若是用于分布式中數據的傳輸,那應該是後
一種最好了.
下面來看第一種方法的一個例子
序列化對象
ContractedBlock.giftry dot.gif{
InBlock.gif MsgBean msgBean = new MsgBean();
InBlock.gif msgBean.setMName(this.mName);
InBlock.gif msgBean.setMsgType(msgtype);
InBlock.gif ByteArrayOutputStream bytearrayoutputstream = null;
InBlock.gif ObjectOutputStream objectoutputstream = null;
ExpandedSubBlockStart.gif ContractedSubBlock.gif try dot.gif{
InBlock.gif bytearrayoutputstream = new ByteArrayOutputStream();
InBlock.gif objectoutputstream = new ObjectOutputStream(
InBlock.gif bytearrayoutputstream);
InBlock.gif objectoutputstream.writeObject(msgBean);
InBlock.gif this.channel.send(new Message(null, null, bytearrayoutputstream
InBlock.gif .toByteArray()));
ExpandedSubBlockStart.gif ContractedSubBlock.gif } finally dot.gif{
InBlock.gif if (objectoutputstream != null)
InBlock.gif objectoutputstream.close();
InBlock.gif if (bytearrayoutputstream != null)
InBlock.gif bytearrayoutputstream.close();
ExpandedSubBlockEnd.gif }
ExpandedBlockStart.gif ContractedBlock.gif } catch (Exception e) dot.gif{
InBlock.gif logger.error("Jgroups send msg exception,msgtype=" + msgtype
InBlock.gif + ",mName=" + mName, e);
ExpandedBlockEnd.gif }反序列化
public void receive(Message arg0) {
byte[] buf = arg0.getRawBuffer();
None.gifByteArrayInputStream bytearrayinputstream = null;
None.gif ObjectInputStream objectinputstream = null;
ExpandedBlockStart.gif ContractedBlock.gif try dot.gif{
ExpandedSubBlockStart.gif ContractedSubBlock.gif try dot.gif{
InBlock.gif bytearrayinputstream = new ByteArrayInputStream(buf, arg0
.getOffset(), arg0.getLength());
InBlock.gif objectinputstream = new ObjectInputStream(bytearrayinputstream);
InBlock.gif MsgBean msgBean = (MsgBean) objectinputstream.readObject();
InBlock.gif if (logger.isDebugEnabled())
InBlock.gif logger.debug(msgBean.toString());
ExpandedSubBlockStart.gif ContractedSubBlock.gif } finally dot.gif{
InBlock.gif if (objectinputstream != null)
InBlock.gif objectinputstream.close();
InBlock.gif if (bytearrayinputstream != null)
InBlock.gif bytearrayinputstream.close();
ExpandedSubBlockEnd.gif }
ExpandedBlockStart.gif ContractedBlock.gif } catch (Exception e) dot.gif{
InBlock.gif logger.error("Received message and process exception.", e);
ExpandedBlockEnd.gif }
}
另外一種方法,是在jgroups的demo中看到的,
首先定義了一個公共的序列化接口
None.gifpackage org.jgroups.util;
None.gif
None.gifimport java.io.DataInputStream;
None.gifimport java.io.DataOutputStream;
None.gifimport java.io.IOException;
None.gif
ExpandedBlockStart.gif ContractedBlock.gif/** *//**
InBlock.gif * Implementations of Streamable can add their state directly to the output stream, enabling them to bypass costly
InBlock.gif * serialization
InBlock.gif * @author Bela Ban
InBlock.gif * @version $Id: Streamable.java,v 1.2 2005/07/25 16:21:47 belaban Exp $
ExpandedBlockEnd.gif */
ExpandedBlockStart.gif ContractedBlock.gifpublic interface Streamable dot.gif{
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif /** *//** Write the entire state of the current object (including superclasses) to outstream.
ExpandedSubBlockEnd.gif * Note that the output stream <em>must not</em> be closed */
InBlock.gif void writeTo(DataOutputStream out) throws IOException;
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif /** *//** Read the state of the current object (including superclasses) from instream
ExpandedSubBlockEnd.gif * Note that the input stream <em>must not</em> be closed */
InBlock.gif void readFrom(DataInputStream in) throws IOException, IllegalAccessException, InstantiationException;
ExpandedBlockEnd.gif}然後將需要序列化的類實現這個方法
// $Id: DrawCommand.java,v 1.6 2006/10/09 11:35:46 belaban Exp $
None.gif
None.gifpackage org.jgroups.demos;
None.gif
None.gifimport org.jgroups.util.Streamable;
None.gif
None.gifimport java.io.DataOutputStream;
None.gifimport java.io.IOException;
None.gifimport java.io.DataInputStream;
None.gif
ExpandedBlockStart.gif ContractedBlock.gif/** *//**
InBlock.gif * Encapsulates information about a draw command.
InBlock.gif * Used by the {@link Draw} and other demos.
InBlock.gif *
ExpandedBlockEnd.gif */
ExpandedBlockStart.gif ContractedBlock.gifpublic class DrawCommand implements Streamable dot.gif{
InBlock.gif static final byte DRAW=1;
InBlock.gif static final byte CLEAR=2;
InBlock.gif byte mode;
InBlock.gif int x=0;
InBlock.gif int y=0;
InBlock.gif int r=0;
InBlock.gif int g=0;
InBlock.gif int b=0;
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif public DrawCommand() dot.gif{ // needed for streamable
ExpandedSubBlockEnd.gif }
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif DrawCommand(byte mode) dot.gif{
InBlock.gif this.mode=mode;
ExpandedSubBlockEnd.gif }
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif DrawCommand(byte mode, int x, int y, int r, int g, int b) dot.gif{
InBlock.gif this.mode=mode;
InBlock.gif this.x=x;
InBlock.gif this.y=y;
InBlock.gif this.r=r;
InBlock.gif this.g=g;
InBlock.gif this.b=b;
ExpandedSubBlockEnd.gif }
InBlock.gif
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif public void writeTo(DataOutputStream out) throws IOException dot.gif{
InBlock.gif out.writeByte(mode);
InBlock.gif out.writeInt(x);
InBlock.gif out.writeInt(y);
InBlock.gif out.writeInt(r);
InBlock.gif out.writeInt(g);
InBlock.gif out.writeInt(b);
ExpandedSubBlockEnd.gif }
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif public void readFrom(DataInputStream in) throws IOException, IllegalAccessException, InstantiationException dot.gif{
InBlock.gif mode=in.readByte();
InBlock.gif x=in.readInt();
InBlock.gif y=in.readInt();
InBlock.gif r=in.readInt();
InBlock.gif g=in.readInt();
InBlock.gif b=in.readInt();
ExpandedSubBlockEnd.gif }
InBlock.gif
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif public String toString() dot.gif{
InBlock.gif StringBuffer ret=new StringBuffer();
ExpandedSubBlockStart.gif ContractedSubBlock.gif switch(mode) dot.gif{
InBlock.gif case DRAW: ret.append("DRAW(" + x + ", " + y + ") [" + r + '|' + g + '|' + b + ']');
InBlock.gif break;
InBlock.gif case CLEAR: ret.append("CLEAR");
InBlock.gif break;
InBlock.gif default:
InBlock.gif return "<undefined>";
ExpandedSubBlockEnd.gif }
InBlock.gif return ret.toString();
ExpandedSubBlockEnd.gif }
InBlock.gif
ExpandedBlockEnd.gif}序列化
ContractedBlock.gifpublic void sendClearPanelMsg() dot.gif{
InBlock.gif int tmp[]=new int[1]; tmp[0]=0;
InBlock.gif DrawCommand comm=new DrawCommand(DrawCommand.CLEAR);
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif try dot.gif{
InBlock.gif byte[] buf=Util.streamableToByteBuffer(comm);
InBlock.gif channel.send(new Message(null, null, buf));
ExpandedSubBlockEnd.gif }
ExpandedSubBlockStart.gif ContractedSubBlock.gif catch(Exception ex) dot.gif{
InBlock.gif System.err.println(ex);
ExpandedSubBlockEnd.gif }
ExpandedBlockEnd.gif }
反序列化
public void receive(Message msg) dot.gif{
InBlock.gif byte[] buf=msg.getRawBuffer();
ExpandedSubBlockStart.gif ContractedSubBlock.gif if(buf == null) dot.gif{
InBlock.gif System.err.println("received null buffer from " + msg.getSrc() + ", headers: " + msg.getHeaders());
InBlock.gif return;
ExpandedSubBlockEnd.gif }
InBlock.gif
ExpandedSubBlockStart.gif ContractedSubBlock.gif try dot.gif{
InBlock.gif DrawCommand comm=(DrawCommand)Util.streamableFromByteBuffer(DrawCommand.class, buf, msg.getOffset(), msg.getLength());
ExpandedSubBlockStart.gif ContractedSubBlock.gif switch(comm.mode) dot.gif{
InBlock.gif case DrawCommand.DRAW:
InBlock.gif if(panel != null)
InBlock.gif panel.drawPoint(comm);
InBlock.gif break;
InBlock.gif case DrawCommand.CLEAR:
InBlock.gif clearPanel();
InBlock.gif break;
InBlock.gif default:
InBlock.gif System.err.println("***** received invalid draw command " + comm.mode);
InBlock.gif break;
ExpandedSubBlockEnd.gif }
ExpandedSubBlockEnd.gif }
ExpandedSubBlockStart.gif ContractedSubBlock.gif catch(Exception e) dot.gif{
InBlock.gif e.printStackTrace();
ExpandedSubBlockEnd.gif }
ExpandedBlockEnd.gif }
上面兩個方法用到的兩個util類的方法
None.gif dot.gif dot.gif
None.gif private static final ByteArrayOutputStream out_stream=new ByteArrayOutputStream(512);
None.gif dot.gif dot.gif
ExpandedBlockStart.gif ContractedBlock.gif public static byte[] streamableToByteBuffer(Streamable obj) throws Exception dot.gif{
InBlock.gif byte[] result=null;
ExpandedSubBlockStart.gif ContractedSubBlock.gif synchronized(out_stream) dot.gif{
InBlock.gif out_stream.reset();
InBlock.gif DataOutputStream out=new DataOutputStream(out_stream);
InBlock.gif obj.writeTo(out);
InBlock.gif result=out_stream.toByteArray();
InBlock.gif out.close();
ExpandedSubBlockEnd.gif }
InBlock.gif return result;
ExpandedBlockEnd.gif }
None.gif
ExpandedBlockStart.gif ContractedBlock.gifpublic static Streamable streamableFromByteBuffer(Class cl, byte[] buffer, int offset, int length) throws Exception dot.gif{
InBlock.gif if(buffer == null) return null;
InBlock.gif Streamable retval=null;
InBlock.gif ByteArrayInputStream in_stream=new ByteArrayInputStream(buffer, offset, length);
InBlock.gif DataInputStream in=new DataInputStream(in_stream); // changed Nov 29 2004 (bela)
InBlock.gif retval=(Streamable)cl.newInstance();
InBlock.gif retval.readFrom(in);
InBlock.gif in.close();
InBlock.gif if(retval == null)
InBlock.gif return null;
InBlock.gif return retval;
ExpandedBlockEnd.gif }
None.gif dot.gif dot.gif
就是這麼多了.
寫到這裡,突然想到,是否java默認的序列化,也就是只將實例字段進行序列化,類結構等等應該不會也序列化的.
那麼這樣,上面兩種方法實際上區別不大(第一種是我這種懶惰的人比較喜歡的,^_^).
不過默認的序列化,即使只將實例字段進行序列化,應該也要帶上字段的名稱等信息吧,這樣的話,序列後的字節數應該還是比第二種多.
補充
看了一下jdk關于ObjectOutputStream中的注釋,了解到,默認的序列化,也沒有將整個類的代碼都序列化,而是序列
化可變的數據等等,下面是jdk的一部份內容:
对象的默认序列化机制写入的内容是：对象的类，类签名，以及非瞬态和非静态字段的值。其他对象的引用（瞬态和静态字段除外）也会导致写入那些对象。可使用引用共享机制对单个对象的多个引用进行编码，这样即可将对象的图形还原为最初写入它们时的形状。
writeObject 方法负责写入特定类的对象状态，以便相应的 readObject 方法可以还原它。该方法本身不必与属于对象的超类或子类的状态有关。状态是通过使用 writeObject 方法或使用 DataOutput 支持的用于基本数据类型的方法将各个字段写入 ObjectOutputStream 来保存的。
基本数据（不包括 serializable 字段和 externalizable 数据）以块数据记录的形式写入 ObjectOutputStream 中。块数据记录由头部和数据组成。块数据部分包括标记和跟在部分后面的字节数。连续的基本写入数据被合并在一个块数据记录中。块数据记录的分块因子为 1024 字节。每个块数据记录都将填满 1024 字节，或者在终止块数据模式时被写入。调用 ObjectOutputStream 方法 writeObject、defaultWriteObject 和 writeFields 最初只是终止所有现有块数据记录。
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