另外,由于对相同级别的Level实例来说,它必须是单例的,因而Log4J对序列化和反序列化做了一些处理。
即它的三个成员都是transient,真正序列化和反序列化的代码自己写,并且加入readResolve()方法的支持,以保证反序列化出来的相同级别的Level实例是相同的实例。
这样处理序列化和反序列化跟必须是单例的有什么关系?
public boolean isGreaterOrEqual(Level level) {
return this.level >= level.level;
}
public static Level toLevel(int level) {
return toLevel(level, DEBUG);
}
public static Level toLevel(int level, Level defaultLevel) {
switch(level) {
case OFF_INT: return OFF;
case FATAL_INT: return FATAL;
case ERROR_INT: return ERROR;
case WARN_INT: return WARN;
case INFO_INT: return INFO;
case DEBUG_INT: return DEBUG;
case TRACE_INT: return TRACE;
case ALL_INT: return ALL;
}
return defaultLevel;
}
private void readObject(final ObjectInputStream input) throws IOException, ClassNotFoundException {
input.defaultReadObject();
level = input.readInt();
syslogEquivalent = input.readInt();
levelStr = input.readUTF();
if(levelStr == null) {
levelStr = "";
}
}
private void writeObject(final ObjectOutputStream output) throws IOException {
output.defaultWriteObject();
output.writeInt(level);
output.writeInt(syslogEquivalent);
output.writeUTF(levelStr);
}
private Object readResolve() throws ObjectStreamException {
if(this.getClass() == Level.class) {
return toLevel(level);
}
return this;
}