Question

这是我第一次在网站上发布问题。我一直在寻找一个解决方案，并且可能有一个。但是，我找不到任何可以解决我问题的东西，所以我希望你能帮到我。另外，我不是最好的java，所以这个问题最终可能会变得非常愚蠢。

我正在尝试从网址解析天气xml文件，并且我继续收到XPathExpression错误。

public class WeatherBugAPI {

private XPath xpath = XPathFactory.newInstance().newXPath();


String API_KEY = "A***************";

public void getLiveWeather(String zipcode) throws Exception{
        DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
        builderFactory.setNamespaceAware(true);
        DocumentBuilder builder = builderFactory.newDocumentBuilder();
        URL xml = new
        URL("http://A**********.api.wxbug.net/getLiveCompactWeatherRSS.aspx?acode=A**********&zipcode=" + zipcode);
    try{
        InputStream is = xml.openStream();
        Document document = builder.parse(is);
        XPathExpression expr = xpath.compile("//aws:weather");
        Node node = (Node)xpath.evaluate("//aws:weather", is, XPathConstants.NODE);

        LiveWeather weather = new LiveWeather(xpath, node);
        System.out.println(weather);

    } catch(XPathExpressionException e){
        System.out.println("Failed to parse forcast!");
        e.printStackTrace();
    }
  }
}

我的LiveWeather类的所有各种属性都有类似于下面的类型的语句。（其中有很多人。）

stationZipcode = (String)xpath.evaluate("//aws:city-state/@zipcode", node, XPathConstants.STRING);

最后是堆栈跟踪：

Failed to parse forcast!

javax.xml.transform.TransformerException: Unable to evaluate expression using this context
    at com.sun.org.apache.xpath.internal.XPath.execute(XPath.java:363)
    at com.sun.org.apache.xpath.internal.jaxp.XPathImpl.eval(XPathImpl.java:213)
    at com.sun.org.apache.xpath.internal.jaxp.XPathImpl.evaluate(XPathImpl.java:275)
    at WeatherBugAPI.getLiveWeather(WeatherBugAPI.java:36)
    at test.main(test.java:5)
Caused by: java.lang.RuntimeException: Unable to evaluate expression using this context
    at com.sun.org.apache.xpath.internal.axes.NodeSequence.setRoot(NodeSequence.java:212)
    at com.sun.org.apache.xpath.internal.axes.LocPathIterator.execute(LocPathIterator.java:210)
    at com.sun.org.apache.xpath.internal.XPath.execute(XPath.java:335)
    ... 4 more
---------
java.lang.RuntimeException: Unable to evaluate expression using this context
    at com.sun.org.apache.xpath.internal.axes.NodeSequence.setRoot(NodeSequence.java:212)
    at com.sun.org.apache.xpath.internal.axes.LocPathIterator.execute(LocPathIterator.java:210)
    at com.sun.org.apache.xpath.internal.XPath.execute(XPath.java:335)
    at com.sun.org.apache.xpath.internal.jaxp.XPathImpl.eval(XPathImpl.java:213)
    at com.sun.org.apache.xpath.internal.jaxp.XPathImpl.evaluate(XPathImpl.java:275)
    at WeatherBugAPI.getLiveWeather(WeatherBugAPI.java:36)
    at test.main(test.java:5)
--------------- linked to ------------------
javax.xml.xpath.XPathExpressionException
    at com.sun.org.apache.xpath.internal.jaxp.XPathImpl.evaluate(XPathImpl.java:289)
    at WeatherBugAPI.getLiveWeather(WeatherBugAPI.java:36)
    at test.main(test.java:5)
Caused by: javax.xml.transform.TransformerException: Unable to evaluate expression using this context
    at com.sun.org.apache.xpath.internal.XPath.execute(XPath.java:363)
    at com.sun.org.apache.xpath.internal.jaxp.XPathImpl.eval(XPathImpl.java:213)
    at com.sun.org.apache.xpath.internal.jaxp.XPathImpl.evaluate(XPathImpl.java:275)
    ... 2 more
Caused by: java.lang.RuntimeException: Unable to evaluate expression using this context
    at com.sun.org.apache.xpath.internal.axes.NodeSequence.setRoot(NodeSequence.java:212)
    at com.sun.org.apache.xpath.internal.axes.LocPathIterator.execute(LocPathIterator.java:210)
    at com.sun.org.apache.xpath.internal.XPath.execute(XPath.java:335)
    ... 4 more

我试图包含可能需要的任何信息。感谢高级的帮助，如果已经提出这个问题，请对不起。

Answer 1

您的XPath表达式（//aws:weather）包含未绑定到任何名称空间URI的名称空间前缀（aws）。正如javax.xml.xpath.XPath的Javadoc中所解释的那样，表达式中的QNames是针对使用setNamespaceContext（NamespaceContext nsContext）设置的XPath命名空间上下文解析的。因此，在编译表达式之前，需要使用setNamespaceContext方法来建立名称空间上下文。

Answer 2

如果您正在尝试解析XML文档的架构，则可能需要考虑从架构生成JAXB绑定，这样您就可以将整个XML文档转换为Java对象图。

既然你提到你的Java不是最好的结账这个免费的在线书“用Java处理XML”http://www.ibiblio.org/xml/books/xmljava/

从API提要中解析XML（Java）

2 个答案: