Java序列化

public class User implements Serializable {
    private String userName;
    private String password;
    private Integer id;

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    @Override
    public String toString() {
        return "User{" +
                "userName='" + userName + '\'' +
                ", password='" + password + '\'' +
                ", id=" + id +
                '}';
    }
}

//ArrayList
 private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException{
        // Write out element count, and any hidden stuff
        int expectedModCount = modCount;
        s.defaultWriteObject();
        // Write out size as capacity for behavioural compatibility with clone()
        s.writeInt(size);
        // Write out all elements in the proper order.
        for (int i=0; i<size; i++) {
            s.writeObject(elementData[i]);
        }
        if (modCount != expectedModCount) {
            throw new ConcurrentModificationException();
        }
    }
    /**
     * Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
     * deserialize it).
     */
    private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        elementData = EMPTY_ELEMENTDATA;
        // Read in size, and any hidden stuff
        s.defaultReadObject();
        // Read in capacity
        s.readInt(); // ignored
        if (size > 0) {
            // be like clone(), allocate array based upon size not capacity
            ensureCapacityInternal(size);
            Object[] a = elementData;
            // Read in all elements in the proper order.
            for (int i=0; i<size; i++) {
                a[i] = s.readObject();
            }
        }

    }

   if (externalizable) {
                        cons = getExternalizableConstructor(cl);
    } else {
                        cons = getSerializableConstructor(cl); 
    ...

    /**
     * Returns public no-arg constructor of given class, or null if none found.
     * Access checks are disabled on the returned constructor (if any), since
     * the defining class may still be non-public.
     */
    private static Constructor<?> getExternalizableConstructor(Class<?> cl) {
        try {
            Constructor<?> cons = cl.getDeclaredConstructor((Class<?>[]) null);
            cons.setAccessible(true);
            return ((cons.getModifiers() & Modifier.PUBLIC) != 0) ?
                cons : null;
        } catch (NoSuchMethodException ex) {
            return null;
        }
    }

stream:
  magic version contents

contents:
  content
  contents content

content:
  object
  blockdata

object:
  newObject
  newClass
  newArray
  newString
  newEnum
  newClassDesc
  prevObject
  nullReference
  exception
  TC_RESET

newClass:
  TC_CLASS classDesc newHandle

classDesc:
  newClassDesc
  nullReference
  (ClassDesc)prevObject      // an object required to be of type
                             // ClassDesc

superClassDesc:
  classDesc

newClassDesc:
  TC_CLASSDESC className serialVersionUID newHandle classDescInfo
  TC_PROXYCLASSDESC newHandle proxyClassDescInfo
classDescInfo:
  classDescFlags fields classAnnotation superClassDesc 

className:
  (utf)

serialVersionUID:
  (long)

classDescFlags:
  (byte)                  // Defined in Terminal Symbols and
                            // Constants

proxyClassDescInfo:
  (int)<count> proxyInterfaceName[count] classAnnotation
      superClassDesc
proxyInterfaceName:
  (utf)
fields:
  (short)<count>  fieldDesc[count]

fieldDesc:
  primitiveDesc
  objectDesc

primitiveDesc:
  prim_typecode fieldName

objectDesc:
  obj_typecode fieldName className1

fieldName:
  (utf)

className1:
  (String)object             // String containing the field's type,
                             // in field descriptor format
classAnnotation:
  endBlockData
  contents endBlockData      // contents written by annotateClass

prim_typecode:
  `B'       // byte
  `C'       // char
  `D'       // double
  `F'       // float
  `I'       // integer
  `J'       // long
  `S'       // short
  `Z'       // boolean

obj_typecode:
  `[`   // array
  `L'       // object

newArray:
  TC_ARRAY classDesc newHandle (int)<size> values[size]

newObject:
  TC_OBJECT classDesc newHandle classdata[]  // data for each class

classdata:
  nowrclass                 // SC_SERIALIZABLE & classDescFlag &&
                            // !(SC_WRITE_METHOD & classDescFlags)
  wrclass objectAnnotation  // SC_SERIALIZABLE & classDescFlag &&
                            // SC_WRITE_METHOD & classDescFlags
  externalContents          // SC_EXTERNALIZABLE & classDescFlag &&
                            // !(SC_BLOCKDATA  & classDescFlags
  objectAnnotation          // SC_EXTERNALIZABLE & classDescFlag&& 
                            // SC_BLOCKDATA & classDescFlags

nowrclass:
  values                    // fields in order of class descriptor

wrclass:
  nowrclass

objectAnnotation:
  endBlockData
  contents endBlockData     // contents written by writeObject
                            // or writeExternal PROTOCOL_VERSION_2.

blockdata:
  blockdatashort
  blockdatalong

blockdatashort:
  TC_BLOCKDATA (unsigned byte)<size> (byte)[size]

blockdatalong:
  TC_BLOCKDATALONG (int)<size> (byte)[size]

endBlockData   :
  TC_ENDBLOCKDATA

externalContent:          // Only parseable by readExternal
  ( bytes)                // primitive data
    object

externalContents:         // externalContent written by 
  externalContent         // writeExternal in PROTOCOL_VERSION_1.
  externalContents externalContent

newString:
  TC_STRING newHandle (utf)
  TC_LONGSTRING newHandle (long-utf)

newEnum:
  TC_ENUM classDesc newHandle enumConstantName
enumConstantName:
  (String)object
prevObject
  TC_REFERENCE (int)handle

nullReference
  TC_NULL

exception:
  TC_EXCEPTION reset (Throwable)object         reset 

magic:
  STREAM_MAGIC

version
  STREAM_VERSION

values:          // The size and types are described by the
                 // classDesc for the current object

newHandle:       // The next number in sequence is assigned
                 // to the object being serialized or deserialized

reset:           // The set of known objects is discarded
                 // so the objects of the exception do not
                 // overlap with the previously sent objects 
                 // or with objects that may be sent after 
                 // the exception