Dubbo-URL、数据包结构

public URL(String protocol, String username, String password, String host, int port, String path, Map<String, String> parameters) {
    if ((username == null || username.length() == 0) 
        && password != null && password.length() > 0) {
        throw new IllegalArgumentException("Invalid url, password without username!");
    }
    this.protocol = protocol;
    this.username = username;
    this.password = password;
    this.host = host;
    this.port = (port < 0 ? 0 : port);
    this.path = path;
    // trim the beginning "/"
    while(path != null && path.startsWith("/")) {
        path = path.substring(1);
    }
    if (parameters == null) {
        parameters = new HashMap<String, String>();
    } else {
        parameters = new HashMap<String, String>(parameters);
    }
    this.parameters = Collections.unmodifiableMap(parameters);
}