XPathExpression没有在适当的上下文中评估？

Question

我正在尝试从USGS解析一些XML.

这是一个例子

"parameterCd"参数列出了我想要的3项数据.我可能会或可能不会全部回来.

我在使用javax库的Android上执行此操作.

在我的代码中,我最初检索0-3 ns1:timeSeries节点.这很好用.我当时想要做的是,在单个timeSeries节点的上下文中,检索ns1:variable和ns1:values节点.

所以在我的代码下面我有:

expr = xpath.compile("//ns1:variable");
NodeList variableNodes = (NodeList) expr.evaluate(timeSeriesNode, XPathConstants.NODESET);

我希望只返回一个节点,因为评估应该发生在我传入的单个timeSeriesNode的上下文中(根据文档).但是,它会返回文档的所有ns1:variable节点.

我错过了什么吗？

这是相关部分......

XPathFactory factory = XPathFactory.newInstance();
XPath xpath = factory.newXPath();
xpath.setNamespaceContext(new InstantaneousValuesNamespaceContext());
XPathExpression expr;
NodeList timeSeriesNodes = null;
InputStream is = new ByteArrayInputStream(sourceXml.getBytes());
try {
    expr = xpath.compile("//ns1:timeSeries");
    timeSeriesNodes = (NodeList) expr.evaluate(new InputSource(is), XPathConstants.NODESET);

    for(int timeSeriesIndex = 0;timeSeriesIndex < timeSeriesNodes.getLength(); timeSeriesIndex++){
        Node timeSeriesNode = timeSeriesNodes.item(timeSeriesIndex);
        expr = xpath.compile("//ns1:variable");
        NodeList variableNodes = (NodeList) expr.evaluate(timeSeriesNode, XPathConstants.NODESET);

        // Problem here. I've got all the variables, not the individual one I want.
        for(int variableIndex = 0; variableIndex < variableNodes.getLength(); variableIndex++){
            Node variableNode = variableNodes.item(variableIndex);
            expr = xpath.compile("//ns1:valueType");
            NodeList valueTypeNodes = (NodeList) expr.evaluate(variableNode, XPathConstants.NODESET);
        }
    }
} catch (XPathExpressionException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

Answer 1

尝试改变

//ns1:variable

至

.//ns1:variable

尽管正如文档所说,表达式是在当前节点的上下文中进行评估的,但是//特殊的(除非修改)总是意味着"从根目录搜索整个文档".通过输入.,你强制你想要的意思,'从这一点向下搜索整个树'.