如何將大型XML文件轉換爲對象的流式樣java8

Question

Hy， 我有一個非常大的XML文件（100GB），其中包含foo列表，我想將它轉換爲類似於他們的流到java 8的對象：

任何想法的lib或代碼示例？

開頭：

<foos> 
    <foo>...</foo> 
    <foo>...</foo> 
</foos> 

末：

Stream<Foo> foosStream = ????("foo.xml") 
streamFoos.forEach(foo->foo.doFooStuffs()); 

編輯： @Pierre感謝你，這裏是你的解決方案的實施：

try { 
      XMLEventReader reader = XMLInputFactory.newInstance(). 
        createXMLEventReader(stream); 
      final Unmarshaller unmarshaller = JAXBContext.newInstance(XXXXX.class).createUnmarshaller(); 

      Iterator<XXXXX> it = new XmlIterator<>(reader, unmarshaller, "xxxxxx"); 
      return StreamSupport.stream(Spliterators.spliteratorUnknownSize(it, Spliterator.ORDERED), false); 
     } catch (XMLStreamException e1) { 
      logger.error("XMLStreamException", e1); 
     } catch (JAXBException e) { 
      logger.error("JAXBException", e); 
     } 

和

public class XmlIterator<T> implements Iterator<T> { 

    private final Logger logger = LoggerFactory.getLogger(this.getClass()); 

    XMLEventReader reader; 

    XMLEvent event; 

    Unmarshaller unmarshaller; 
    String name; 

    public XmlIterator(XMLEventReader reader, Unmarshaller unmarshaller, String name) { 
     this.reader = reader; 
     this.unmarshaller = unmarshaller; 
     this.name = name; 
     try { 
      reader.next(); 
      this.event = reader.peek(); 
     } catch (XMLStreamException e) { 
      logger.error("", e); 
      event = null; 
     } 
    } 

    @Override 
    public boolean hasNext() { 
     try { 
      while (event != null && !(event.isStartElement() && name.equals(event.asStartElement().getName().getLocalPart()))) { 
       Object a = reader.next(); 
       event = reader.peek(); 
      } 
      return event != null; 

     } catch (XMLStreamException e) { 
      logger.error("", e); 
      event = null; 
     } 
     return event != null; 
    } 

    @Override 
    public T next() { 
     try { 
      T next = ((JAXBElement<T>) unmarshaller.unmarshal(reader)).getValue(); 
      event = reader.peek(); 
      return next; 
     } catch (JAXBException e) { 
      logger.error("error during unmarshalling ", e); 
      return null; 
     } catch (XMLStreamException e) { 
      logger.error("error during stream ", e); 
      return null; 
     } 
    } 
} 

Answer 1

• 創建斯塔克斯事件閱讀https://docs.oracle.com/javase/tutorial/jaxp/stax/example.html讀取XML文件

• 每次看到標籤「富」的時間（使用https://docs.oracle.com/javase/7/docs/api/javax/xml/stream/XMLEventReader.html#peek()），使用Stax的閱讀器解析，建立自己的對象Foo

  Foo readFoo(XMLEventReader xmlIn) throws XMLStreamException { 
      (...) 
      return foo; 
  } 
  

• 實現了一個java.util.Iterator，它將使用前面的函數返回'next（）'Foo

• 將此迭代器轉換爲str eam How to create a Java 8 Stream from an iterator?