Question

我尝试使用XPath检索包含大量数据的XML文件中的属性值。我想在XML文件中搜索特定属性，并返回相应的属性。

我的代码目前给出了表达式错误，我猜这意味着我的表达错误。

private String getPrivateID(String platformNo)
{

    String platformTag = null;

    try
    {
        InputStream is = getResources().openRawResource(R.raw.platform);
        InputSource inputSrc = new InputSource(is);

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

        String expression = String.format("//Platform[@PlatformNo=%s]/@PlatformTag", 
            platformNo);
        NodeList nodes = (NodeList) xpath.evaluate(expression, 
            inputSrc, XPathConstants.NODESET);

        platformTag = xpath.evaluate(expression, nodes);

        return platformTag;

    }
    catch (Exception e)
    {
        return null;
    }
}

我的XML是这样的：

<JPPlatforms>
  <Platform PlatformTag="2980" PlatformNo="47280" Name="AGHS" 
       BearingToRoad="2.6606268e+002" RoadName="Avonside Dr">
    <Position Lat="-4.352447905000000e+001" Long="1.726611665000000e+002"/>
  </Platform>
  <Platform PlatformTag="1219" PlatformNo="28142" Name="Addington Village" 
       BearingToRoad="3.2193924e+002" RoadName="Lincoln Rd">
    <Position Lat="-4.354269524000000e+001" Long="1.726134222000000e+002"/>
  </Platform>
  <Platform PlatformTag="1220" PlatformNo="44108" Name="Addington Village" 
       BearingToRoad="1.4198888e+002" RoadName="Lincoln Rd">
    <Position Lat="-4.354386705000000e+001" Long="1.726111654000000e+002"/>
  </Platform>
  <Platform PlatformTag="2940" PlatformNo="45477" Name="Aidanfield Dr near Bibiana St" 
       BearingToRoad="2.1811232e+002" RoadName="Aidanfield Dr">
    <Position Lat="-4.356581921000000e+001" Long="1.725743414000000e+002"/>
  </Platform>
  <Platform PlatformTag="2941" PlatformNo="47192" Name="Aidanfield Dr near Bibiana St" 
       BearingToRoad="3.8112324e+001" RoadName="Aidanfield Dr">
    <Position Lat="-4.356595693000000e+001" Long="1.725742336000000e+002"/>
  </Platform>
<JPPlatforms>

我哪里出错了？提前谢谢！

Answer 1

xpath

//Platform[@PlatformNo=%s]/@PlatformTag

提取属性，而您尝试评估NODESET。由于您只需要返回单个标量值，请尝试：

String platformTag = (String) xpath.evaluate(expression, inputSrc, XPathConstants.STRING);

您也可以考虑使用引号转义该数字：

//Platform[@PlatformNo='%s']/@PlatformTag

使用XPath搜索和检索XML中的属性

1 个答案: