SerialVersionUID
Java在反序列化时，会检查序列化字节流中的SerialVersionUID是否和本地类的SerialVersionUID一致，不一致会抛出InvalidClassException异常
SerialVersionUID有两种生成方法
类中指明：
private static final long serialVersionUID = 1L;ObjectOutputStream#writeObject自动计算类的信息自动生成
调用ObjectOutputStream#writeObject(o)后
ObjectOutputStream#writeClassDescriptor -> ObjectStreamClass#writeNonProxy -> ObjectStreamClass#getSerialVersionUID
void writeNonProxy(ObjectOutputStream out) throws IOException {
out.writeUTF(name);
out.writeLong(getSerialVersionUID()); //...
}
/**
* Return the serialVersionUID for this class. The serialVersionUID
* defines a set of classes all with the same name that have evolved from a
* common root class and agree to be serialized and deserialized using a
* common format. NonSerializable classes have a serialVersionUID of 0L.
*/
public long getSerialVersionUID() {
if (suid == null) {
suid = AccessController.doPrivileged(
new PrivilegedAction<Long>() {
public Long run() {
return computeDefaultSUID(cl);
}
}
);
}
return suid.longValue();
}下面是serialVersionUID的计算方式
private static long computeDefaultSUID(Class<?> cl) {
// 没有实现Serializable，serialVersionUID为0L
if (!Serializable.class.isAssignableFrom(cl) || Proxy.isProxyClass(cl))
{
return 0L;
}
try {
ByteArrayOutputStream bout = new ByteArrayOutputStream();
DataOutputStream dout = new DataOutputStream(bout);
// 类名
dout.writeUTF(cl.getName());
int classMods = cl.getModifiers() &
(Modifier.PUBLIC | Modifier.FINAL |
Modifier.INTERFACE | Modifier.ABSTRACT);
Method[] methods = cl.getDeclaredMethods();
if ((classMods & Modifier.INTERFACE) != 0) {
classMods = (methods.length > 0) ?
(classMods | Modifier.ABSTRACT) :
(classMods & ~Modifier.ABSTRACT);
}
// 类的访问修饰符
dout.writeInt(classMods);
if (!cl.isArray()) {
Class<?>[] interfaces = cl.getInterfaces();
String[] ifaceNames = new String[interfaces.length];
for (int i = 0; i < interfaces.length; i++) {
ifaceNames[i] = interfaces[i].getName();
}
Arrays.sort(ifaceNames);
for (int i = 0; i < ifaceNames.length; i++) {
// 类的接口名
dout.writeUTF(ifaceNames[i]);
}
}
Field[] fields = cl.getDeclaredFields();
MemberSignature[] fieldSigs = new MemberSignature[fields.length];
for (int i = 0; i < fields.length; i++) {
fieldSigs[i] = new MemberSignature(fields[i]);
}
Arrays.sort(fieldSigs, new Comparator<MemberSignature>() {
public int compare(MemberSignature ms1, MemberSignature ms2) {
return ms1.name.compareTo(ms2.name);
}
});
for (int i = 0; i < fieldSigs.length; i++) {
MemberSignature sig = fieldSigs[i];
int mods = sig.member.getModifiers() &
(Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED |
Modifier.STATIC | Modifier.FINAL | Modifier.VOLATILE |
Modifier.TRANSIENT);
if (((mods & Modifier.PRIVATE) == 0) ||
((mods & (Modifier.STATIC | Modifier.TRANSIENT)) == 0))
{
// 非私有或私有非静态、非transient的字段名、访问修饰符、签名
dout.writeUTF(sig.name);
dout.writeInt(mods);
dout.writeUTF(sig.signature);
}
}
// 是否有静态字段
if (hasStaticInitializer(cl)) {
dout.writeUTF("<clinit>");
dout.writeInt(Modifier.STATIC);
dout.writeUTF("()V");
}
Constructor<?>[] cons = cl.getDeclaredConstructors();
MemberSignature[] consSigs = new MemberSignature[cons.length];
for (int i = 0; i < cons.length; i++) {
consSigs[i] = new MemberSignature(cons[i]);
}
Arrays.sort(consSigs, new Comparator<MemberSignature>() {
public int compare(MemberSignature ms1, MemberSignature ms2) {
return ms1.signature.compareTo(ms2.signature);
}
});
for (int i = 0; i < consSigs.length; i++) {
MemberSignature sig = consSigs[i];
int mods = sig.member.getModifiers() &
(Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED |
Modifier.STATIC | Modifier.FINAL |
Modifier.SYNCHRONIZED | Modifier.NATIVE |
Modifier.ABSTRACT | Modifier.STRICT);
if ((mods & Modifier.PRIVATE) == 0) {
// 非私有构造器
dout.writeUTF("<init>");
dout.writeInt(mods);
dout.writeUTF(sig.signature.replace('/', '.'));
}
}
MemberSignature[] methSigs = new MemberSignature[methods.length];
for (int i = 0; i < methods.length; i++) {
methSigs[i] = new MemberSignature(methods[i]);
}
Arrays.sort(methSigs, new Comparator<MemberSignature>() {
public int compare(MemberSignature ms1, MemberSignature ms2) {
int comp = ms1.name.compareTo(ms2.name);
if (comp == 0) {
comp = ms1.signature.compareTo(ms2.signature);
}
return comp;
}
});
for (int i = 0; i < methSigs.length; i++) {
MemberSignature sig = methSigs[i];
int mods = sig.member.getModifiers() &
(Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED |
Modifier.STATIC | Modifier.FINAL |
Modifier.SYNCHRONIZED | Modifier.NATIVE |
Modifier.ABSTRACT | Modifier.STRICT);
if ((mods & Modifier.PRIVATE) == 0) {
// 非私有方法
dout.writeUTF(sig.name);
dout.writeInt(mods);
dout.writeUTF(sig.signature.replace('/', '.'));
}
}
dout.flush();
MessageDigest md = MessageDigest.getInstance("SHA");
byte[] hashBytes = md.digest(bout.toByteArray());
long hash = 0;
for (int i = Math.min(hashBytes.length, 8) - 1; i >= 0; i--) {
hash = (hash << 8) | (hashBytes[i] & 0xFF);
}
return hash;
} catch (IOException ex) {//...}
}计算的内容如下：
类名、类的访问修饰符、类的接口名
非私有或私有非静态、非transient的字段名、访问修饰符、签名
非私有构造器
非私有方法
对这些数据进行SHA1哈希，再进行移位和与或运算
反射调用computeDefaultSUID来计算一个类的SerialVersionUID
Class<?> clazz = Class.forName("java.io.ObjectStreamClass");
Method method = clazz.getDeclaredMethod("computeDefaultSUID", Class.class);
method.setAccessible(true);
Object suid = method.invoke(null, Dog.class);
System.out.println(suid);Last updated