为什么我收到此错误提前结束文件？

Question

我试图解析XML response,但我失败了.我最初认为xml只是没有在回复中返回,所以我通过直接链接到我的xml文件在线制作了下面的代码.我能够毫无问题地打印XML到屏幕.但是,当我调用我的parse方法时,我得到文件的过早结束.

如果我直接传递URL,它可以工作:

• builder.parse( "");

但是当我传递一个InputStream时失败:

• builder.parse(connection.getInputStream());

    try {
      URL url = new URL(xml);
      URLConnection uc =  url.openConnection();
      HttpURLConnection  connection = (HttpURLConnection )uc;
  
      connection.setDoInput(true);
      connection.setDoOutput(true);
  
      InputStream instream;
      InputSource source;
      //get XML from InputStream
      if(connection.getResponseCode()>= 200){
          connection.connect();       
          instream = connection.getInputStream();         
          parseDoc(instream);     
      }
      else{
          instream = connection.getErrorStream();
      }
  
  
  } catch (MalformedURLException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
  } catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
  } catch (ParserConfigurationException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
  } catch (SAXException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
  }
  
  
  
   static void parseDoc(InputStream instream) throws ParserConfigurationException,
   SAXException, IOException{
  
  
    BufferedReader buff_read = new BufferedReader(new InputStreamReader(instream,"UTF-8"));
      String  inputLine = null;
  
      while((inputLine = buff_read.readLine())!= null){
          System.out.println(inputLine);
      }
  
    DocumentBuilderFactory factory =DocumentBuilderFactory.newInstance();
    factory.isIgnoringElementContentWhitespace();
    DocumentBuilder builder = factory.newDocumentBuilder();
    Document doc = builder.parse(instream);
  }
  

我得到的错误:

    [Fatal Error] :1:1: Premature end of file.
org.xml.sax.SAXParseException: Premature end of file.
    at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(Unknown Source)
    at javax.xml.parsers.DocumentBuilder.parse(Unknown Source)
    at com.ameba.api.network.MainApp.parseDoc(MainApp.java:78)
    at com.ameba.api.network.MainApp.main(MainApp.java:41)

Answer 1

当你这样做,

while((inputLine = buff_read.readLine())!= null){
        System.out.println(inputLine);
    }

你在instream中消耗了所有东西,所以instream是空的.现在,当试图这样做,

Document doc = builder.parse(instream);

解析将失败,因为您已经传递了一个空流.

Answer 2

您收到错误是因为 SAXBuilder 不够智能，无法处理“空白状态”。因此，它至少会查找一个<xml ..>声明，当导致无数据响应时，它会创建您看到的异常，而不是报告空状态。