继上次分析了java的序列化过程之后，对于serialVersionUID的处理还不是很清晰，今天再看下代码，对serialVersionUID的处理进行了了解，
ObjectOutputStream.java调用writeObject的时候会调用到下面的代码：
这是调用ObjectStreamClass.java的writeNonProxy方法，写入非代理类的元数据信息
在写入类的元数据的时候会把serialVersionUID写入：
[java]
/**
* Writes non-proxy class descriptor information to given output stream.
*/
void writeNonProxy(ObjectOutputStream out) throws IOException {
out.writeUTF(name);
out.writeLong(getSerialVersionUID());
byte flags = 0;
if (externalizable) {
flags |= ObjectStreamConstants.SC_EXTERNALIZABLE;
int protocol = out.getProtocolVersion();
if (protocol != ObjectStreamConstants.PROTOCOL_VERSION_1) {
flags |= ObjectStreamConstants.SC_BLOCK_DATA;
}
} else if (serializable) {
flags |= ObjectStreamConstants.SC_SERIALIZABLE;
}
if (hasWriteObjectData) {
flags |= ObjectStreamConstants.SC_WRITE_METHOD;
}
if (isEnum) {
flags |= ObjectStreamConstants.SC_ENUM;
}
out.writeByte(flags);
out.writeShort(fields.length);
for (int i = 0; i < fields.length; i++) {
ObjectStreamField f = fields[i];
out.writeByte(f.getTypeCode());
out.writeUTF(f.getName());
if (!f.isPrimitive()) {
out.writeTypeString(f.getTypeString());
}
}
}
在读取的时候会做几个部分的校验：
在ObjectInputStream.java的readObject方法时调用ObjectStreamClass.java的readNonProxy方法，
这里会读取suid = Long.valueOf(in.readLong());就是读取serialVersionUID，然后先做第一步校验if (isEnum && suid.longValue() != 0L) 如果是枚举类则serialVersionUID为0.
[java]
void readNonProxy(ObjectInputStream in)
throws IOException, ClassNotFoundException
{
name = in.readUTF();
suid = Long.valueOf(in.readLong());
isProxy = false;
byte flags = in.readByte();
hasWriteObjectData =
((flags & ObjectStreamConstants.SC_WRITE_METHOD) != 0);
hasBlockExternalData =
((flags & ObjectStreamConstants.SC_BLOCK_DATA) != 0);
externalizable =
((flags & ObjectStreamConstants.SC_EXTERNALIZABLE) != 0);
boolean sflag =
((flags & ObjectStreamConstants.SC_SERIALIZABLE) != 0);
if (externalizable && sflag) {
throw new InvalidClassException(
name, "serializable and externalizable flags conflict");
}
serializable = externalizable || sflag;
isEnum = ((flags & ObjectStreamConstants.SC_ENUM) != 0);
if (isEnum && suid.longValue() != 0L) {
throw new InvalidClassException(name,
"enum descriptor has non-zero serialVersionUID: " + suid);
}
int numFields = in.readShort();
if (isEnum && numFields != 0) {
throw new InvalidClassException(name,
"enum descriptor has non-zero field count: " + numFields);
}
fields = (numFields > 0)
new ObjectStreamField[numFields] : NO_FIELDS;
for (int i = 0; i < numFields; i++) {
char tcode = (char) in.readByte();
String fname = in.readUTF();
String signature = ((tcode == 'L') || (tcode == '['))
in.readTypeString() : new String(new char[] { tcode });
try {
fields[i] = new ObjectStreamField(fname, signature, false);
} catch (RuntimeException e) {
throw (IOException) new InvalidClassException(name,
"invalid descriptor for field " + fname).initCause(e);
}
}
computeFieldOffsets();
}
然后下面还会对serialVersionUID进行下一步的验证：同样是在ObjectStreamClass.java的initNo