Java xStream processAnnotations并发

Question

实际上我只想要一个 XStream 实例。所以我有以下类(class):

public class XSteamTool{
    private static XStream xStream = new XStream();

    static{
        xStream.ignoreUnknownElements();
        xStream.registerConverter(new DateConverter(TimeZone.getDefault()));
    }

    public static String objToXml(Object obj){
        xStream.processAnnotations(obj.getClass());
        return xStream.toXML(obj);
    }

    public static <T> T xmlToObj(String xmlString, Class<T> clazz){
        xStream.processAnnotations(clazz);
        return(T)xStream.fromXML(xmlString);
    }
}

但是这在多线程环境下会遇到问题。我发现官方文档中有这样的注释:XStream在配置时不是线程安全的。不幸的是，注释正在定义配置中的更改，现在在处理对象编码时应用该更改
我尝试在 processAnnotations 之前进行同步，看起来不错:

public static String objToXml(Object obj){
    synchronized (obj.getClass()) {
        xStream.processAnnotations(obj.getClass());             
    }
    return xStream.toXML(obj);
}

public static <T> T xmlToObj(String xmlString, Class<T> clazz){
    synchronized (clazz) {
        xStream.processAnnotations(clazz);              
    }
    return(T)xStream.fromXML(xmlString);
}

不知道使用是否正确。如有任何建议，我们将不胜感激。

Answer 1

最后我们决定通过Class共享xStream实例(仅初始化一次xStream，并在多线程环境中重用它):

private static Map<Class<?>, XStream> xStreamMap = Collections.synchronizedMap(new HashMap<Class<?>, XStream>());

private static XStream getXStreamInstance(Class<?> clazz) {
    if (xStreamMap.containsKey(clazz)) {
        return xStreamMap.get(clazz);
    }
    synchronized (clazz) {
        if (xStreamMap.containsKey(clazz)) {
            return xStreamMap.get(clazz);
        }
        XStream xStream = new XStream(new XppDriver(new NoNameCoder()));
        xStream.ignoreUnknownElements();
        xStream.registerConverter(new DateConverter(TimeZone.getDefault()));
        xStream.processAnnotations(clazz);
        xStreamMap.put(clazz, xStream);
        return xStream;
    }
}