使用 XStream 解析 - 空标签和集合

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问题描述

我正在使用 XStream 将 XML 转换为域对象，但遇到了一个问题.省略一些细节，XML 如下所示:

I am using XStream to convert XML into domain objects, and have come by a problem. Omitting a few details, the XML looks like this :

<airport>
    <flights>
        <flight>.....</flight>
        <flight>.....</flight>
        <flight>.....</flight>
    </flights>
</airport>

可以有 0 到 N 个 flight 元素.飞行元素本身包含其他元素.我为机场、航班和航班创建了类，并使用 xstream.alias 函数注册了它们.

There can be 0 to N flight elements. The flight elements themselves contain other elements. I have created classes for airport, flights, and flight and registered them with the xstream.alias function.

xstream = new XStream();
xstream.alias("airport", AirportPojo.class);
xstream.alias("flights", FlightsPojo.class);
xstream.alias("flight", FlightPojo.class);
xstream.useAttributeFor(AirportPojo.class, "flights");
xstream.addImplicitCollection(FlightsPojo.class, "flights", FlightPojo.class);
AirportPojo airportPojo = (AirportPojo) xstream.fromXML(xml);

因此，转换后，这给了我一个包含 FlightsPojo 对象的 AirportPojo 对象，其中包含 FlightPojo 对象的集合.但是，当有 0 个飞行元素时，FlightPojos 的集合似乎是 null.我希望(并且更喜欢)列表被初始化，但其中包含零个元素.我怎么能做到这一点?请记住，我不能使用注释，因为这是一个遗留项目.

So, after converting, this gives me an AirportPojo object containing a FlightsPojo object, containing a collection of FlightPojo objects. However, when there are 0 flight elements it seems that the collection of FlightPojos is null. I would expect (and prefer) the list to be initialized but with zero elements in it. How could I accomplish this? Bear in mind that I cannot use annotations as this is a legacy project.

推荐答案

如何实现自定义转换器?

How about implementing a custom converter?

class FlightsConverter implements Converter {
    @Override
    public boolean canConvert(Class clazz) {
        return clazz.equals(FlightsPojo.class);
    }

    @Override
    public Object unmarshal(HierarchicalStreamReader reader, UnmarshallingContext context) {
        FlightsPojo flightsPojo = new FlightsPojo();
        flightsPojo.setFlights(new ArrayList<FlightPojo>());
        while (reader.hasMoreChildren()) {
            reader.moveDown();
            FlightPojo flightPojo = (FlightPojo) context.convertAnother(flightsPojo, FlightPojo.class);
            flightsPojo.getFlights().add(flightPojo);
            System.out.println(reader.getValue());
            reader.moveUp();
        }
        return flightsPojo;
    }

    @Override
    public void marshal(Object value, HierarchicalStreamWriter writer, MarshallingContext context) {
        // todo...
    }
}

然后像这样挂钩:

    XStream xstream = new XStream();
    xstream.registerConverter(new FlightsConverter());
    xstream.alias("airport", AirportPojo.class);
    xstream.alias("flights", FlightsPojo.class);
    xstream.alias("flight", FlightPojo.class);
    xstream.useAttributeFor(AirportPojo.class, "flights");
    AirportPojo airportPojo = (AirportPojo) xstream.fromXML(xml);

希望这有帮助;)

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