public interface Serializable {
}

public final void writeObject(Object obj) throws IOException {
    if (enableOverride) {
        writeObjectOverride(obj);
        return;
    }
    try {
        writeObject0(obj, false);
    } catch (IOException ex) {
        if (depth == 0) {
            writeFatalException(ex);
        }
        throw ex;
    }
}

private void writeObject0(Object obj, boolean unshared)
    throws IOException
{
    boolean oldMode = bout.setBlockDataMode(false);
    depth++;
    try {
        // handle previously written and non-replaceable objects
        int h;
        if ((obj = subs.lookup(obj)) == null) {
            writeNull();
            return;
        } else if (!unshared && (h = handles.lookup(obj)) != -1) {
            writeHandle(h);
            return;
        } else if (obj instanceof Class) {
            writeClass((Class) obj, unshared);
            return;
        } else if (obj instanceof ObjectStreamClass) {
            writeClassDesc((ObjectStreamClass) obj, unshared);
            return;
        }

        // check for replacement object
        Object orig = obj;
        Class<?> cl = obj.getClass();
        ObjectStreamClass desc;
        for (;;) {
            // REMIND: skip this check for strings/arrays?
            Class<?> repCl;
            desc = ObjectStreamClass.lookup(cl, true);
            if (!desc.hasWriteReplaceMethod() ||
                (obj = desc.invokeWriteReplace(obj)) == null ||
                (repCl = obj.getClass()) == cl)
            {
                break;
            }
            cl = repCl;
        }
        if (enableReplace) {
            Object rep = replaceObject(obj);
            if (rep != obj && rep != null) {
                cl = rep.getClass();
                desc = ObjectStreamClass.lookup(cl, true);
            }
            obj = rep;
        }

        // if object replaced, run through original checks a second time
        if (obj != orig) {
            subs.assign(orig, obj);
            if (obj == null) {
                writeNull();
                return;
            } else if (!unshared && (h = handles.lookup(obj)) != -1) {
                writeHandle(h);
                return;
            } else if (obj instanceof Class) {
                writeClass((Class) obj, unshared);
                return;
            } else if (obj instanceof ObjectStreamClass) {
                writeClassDesc((ObjectStreamClass) obj, unshared);
                return;
            }
        }

        // remaining cases
        if (obj instanceof String) {
            writeString((String) obj, unshared);
        } else if (cl.isArray()) {
            writeArray(obj, desc, unshared);
        } else if (obj instanceof Enum) {
            writeEnum((Enum<?>) obj, desc, unshared);
        } else if (obj instanceof Serializable) {
            writeOrdinaryObject(obj, desc, unshared);
        } else {
            if (extendedDebugInfo) {
                throw new NotSerializableException(
                    cl.getName() + "\n" + debugInfoStack.toString());
            } else {
                throw new NotSerializableException(cl.getName());
            }
        }
    } finally {
        depth--;
        bout.setBlockDataMode(oldMode);
    }
}

private final Object readObject(Class<?> type)
    throws IOException, ClassNotFoundException
{
    if (enableOverride) {
        return readObjectOverride();
    }

    if (! (type == Object.class || type == String.class))
        throw new AssertionError("internal error");

    // if nested read, passHandle contains handle of enclosing object
    int outerHandle = passHandle;
    try {
        Object obj = readObject0(type, false);
        handles.markDependency(outerHandle, passHandle);
        ClassNotFoundException ex = handles.lookupException(passHandle);
        if (ex != null) {
            throw ex;
        }
        if (depth == 0) {
            vlist.doCallbacks();
        }
        return obj;
    } finally {
        passHandle = outerHandle;
        if (closed && depth == 0) {
            clear();
        }
    }
}

private Object readObject0(Class<?> type, boolean unshared) throws IOException {
    boolean oldMode = bin.getBlockDataMode();
    if (oldMode) {
        int remain = bin.currentBlockRemaining();
        if (remain > 0) {
            throw new OptionalDataException(remain);
        } else if (defaultDataEnd) {
            /*
             * Fix for 4360508: stream is currently at the end of a field
             * value block written via default serialization; since there
             * is no terminating TC_ENDBLOCKDATA tag, simulate
             * end-of-custom-data behavior explicitly.
             */
            throw new OptionalDataException(true);
        }
        bin.setBlockDataMode(false);
    }

    byte tc;
    while ((tc = bin.peekByte()) == TC_RESET) {
        bin.readByte();
        handleReset();
    }

    depth++;
    totalObjectRefs++;
    try {
        switch (tc) {
            case TC_NULL:
                return readNull();

            case TC_REFERENCE:
                // check the type of the existing object
                return type.cast(readHandle(unshared));

            case TC_CLASS:
                if (type == String.class) {
                    throw new ClassCastException("Cannot cast a class to java.lang.String");
                }
                return readClass(unshared);

            case TC_CLASSDESC:
            case TC_PROXYCLASSDESC:
                if (type == String.class) {
                    throw new ClassCastException("Cannot cast a class to java.lang.String");
                }
                return readClassDesc(unshared);

            case TC_STRING:
            case TC_LONGSTRING:
                return checkResolve(readString(unshared));

            case TC_ARRAY:
                if (type == String.class) {
                    throw new ClassCastException("Cannot cast an array to java.lang.String");
                }
                return checkResolve(readArray(unshared));

            case TC_ENUM:
                if (type == String.class) {
                    throw new ClassCastException("Cannot cast an enum to java.lang.String");
                }
                return checkResolve(readEnum(unshared));

            case TC_OBJECT:
                if (type == String.class) {
                    throw new ClassCastException("Cannot cast an object to java.lang.String");
                }
                return checkResolve(readOrdinaryObject(unshared));

            case TC_EXCEPTION:
                if (type == String.class) {
                    throw new ClassCastException("Cannot cast an exception to java.lang.String");
                }
                IOException ex = readFatalException();
                throw new WriteAbortedException("writing aborted", ex);

            case TC_BLOCKDATA:
            case TC_BLOCKDATALONG:
                if (oldMode) {
                    bin.setBlockDataMode(true);
                    bin.peek();             // force header read
                    throw new OptionalDataException(
                        bin.currentBlockRemaining());
                } else {
                    throw new StreamCorruptedException(
                        "unexpected block data");
                }

            case TC_ENDBLOCKDATA:
                if (oldMode) {
                    throw new OptionalDataException(true);
                } else {
                    throw new StreamCorruptedException(
                        "unexpected end of block data");
                }

            default:
                throw new StreamCorruptedException(
                    String.format("invalid type code: %02X", tc));
        }
    } finally {
        depth--;
        bin.setBlockDataMode(oldMode);
    }
}

@Data
public class LoginUserInfo implements Serializable {

    private static final long serialVersionUID = 1L;
    
    ...
}

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
        int capacity = calculateCapacity(elementData, size);
        SharedSecrets.getJavaOISAccess().checkArray(s, Object[].class, 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();
        }
    }
}