在以下情況下向後兼容xstream

Question

我有以下類。

class SimpleDate { 
    private final int year; /* ? */ 
    private final int month; /* 0 ~ 11 */ 
    private final int date; /* 1 ~ 31 */ 
} 

現在，我打算重新分類這個類。

class SimpleDate { 
    private final int year; /* ? */ 
    private final int month; /* 1 ~ 12!!!!! <-- change from 0 based to 1 based */ 
    private final int day; /* 1 ~ 31 */ 
} 

爲了解決變量重命名問題，我將使用別名。

xStream.aliasField("date", SimpleDate.class, "day"); 

但是，我怎麼能知道我在讀一個古老的XML文件，我將+1爲新讀取月份字段，將其從0開始改變基於1？

Answer 1

// Converter used to make sure XStream still able to read old version of XML 
// files. 
private static Converter getSimpleDateConverter() { 
    return new Converter() { 
     @Override 
     public void marshal(Object o, HierarchicalStreamWriter writer, MarshallingContext mc) { 
      SimpleDate simpleDate = (SimpleDate) o; 
      writer.startNode("year"); 
      writer.setValue("" + simpleDate.getYear()); 
      writer.endNode(); 
      writer.startNode("month"); 
      writer.setValue("" + simpleDate.getMonth()); 
      writer.endNode(); 
      writer.startNode("day"); 
      writer.setValue("" + simpleDate.getDay()); 
      writer.endNode(); 
     } 

     @Override 
     public Object unmarshal(HierarchicalStreamReader reader, UnmarshallingContext uc) { 
      Map<String, String> map = new HashMap<String, String>(); 
      while (reader.hasMoreChildren()) { 
       reader.moveDown(); 
       map.put(reader.getNodeName(), reader.getValue()); 
       reader.moveUp(); 
      } 
      // Introduce since version 1.0.6. 
      // We had renamed 'date' field to 'day' field. 
      final boolean isOldVersion = map.containsKey("date"); 
      if (isOldVersion) { 
       final int year = Integer.parseInt(map.get("year")); 
       // We changed 0 based month to 1 based month, to fit into Joda library. 
       final int month = Integer.parseInt(map.get("month")) + 1; 
       final int day = Integer.parseInt(map.get("date")); 
       return new SimpleDate(year, month, day); 
      } else { 
       final int year = Integer.parseInt(map.get("year")); 
       final int month = Integer.parseInt(map.get("month")); 
       final int day = Integer.parseInt(map.get("day")); 
       return new SimpleDate(year, month, day); 
      } 
     } 

     @Override 
     public boolean canConvert(Class type) { 
      return SimpleDate.class.isAssignableFrom(type); 
     } 
    }; 
} 

---

xStream.registerConverter(getSimpleDateConverter()); 

Answer 2

xstream FAQ http://x-stream.github.io/faq.html有關於如何處理不同版本的章節。