从Java发送XPath变量

Question

我有一个XPath表达式,用于搜索静态值.在此示例中,"test"是该值:

XPathExpression expr = xpath.compile("//doc[contains(., 'test')]/*/text()");

如何传递变量而不是固定字符串？我在Eclipse中使用Java.有没有办法使用Java的值String来声明XPath变量？

Answer 1

您可以定义变量解析器并对表达式求解变量进行评估$myvar,例如:

XPathExpression expr = xpath.compile("//doc[contains(., $myVar)]/*/text()");

有一个相当不错的解释在这里.我之前并没有真正做到这一点,所以我可能会去做一个更完整的例子.

更新:

鉴于这一点,一个好吃的.对于一个非常简单的实现的示例,您可以定义一个类,该类从地图返回给定变量的值,如下所示:

class MapVariableResolver implements XPathVariableResolver {
  // local store of variable name -> variable value mappings
  Map<String, String> variableMappings = new HashMap<String, String>();

  // a way of setting new variable mappings 
  public void setVariable(String key, String value)  {
    variableMappings.put(key, value);
  }

  // override this method in XPathVariableResolver to 
  // be used during evaluation of the XPath expression      
  @Override
  public Object resolveVariable(QName varName) {
    // if using namespaces, there's more to do here
    String key = varName.getLocalPart();
    return variableMappings.get(key);
  }
}

现在,例如,在程序中声明并初始化此解析程序的实例

MapVariableResolver vr = new MapVariableResolver() ;
vr.setVariable("myVar", "text");
...
XPath xpath = factory.newXPath();
xpath.setXPathVariableResolver(vr);

然后,在评估XPath表达式期间XPathExpression expr = xpath.compile("//doc[contains(., $myVar)]/*/text()");,变量$myVar将替换为字符串text.

好问题,我自学了一些有用的东西!