如何将可变参数传递给 XPath 表达式? [英] How to pass variable parameter into XPath expression?

问题描述

我想将参数传递给 XPath 表达式.

I want to pass a parameter into an XPath expression.

(//a/b/c[x=?],myParamForXAttribute)

我可以用 XPath 1.0 做到这一点吗?(我尝试了 string-join 但它在 XPath 1.0 中没有)

Can I do this with XPath 1.0 ? (I tried string-join but it is not there in XPath 1.0)

那我该怎么做呢?

我的 XML 看起来像

My XML looks like

<a>
 <b>
  <c>
   <x>val1</x>
   <y>abc</y>
  </c>
  <c>
   <x>val2</x>
   <y>abcd</y>
  </c>
</b>
</a>

我想获得 元素值，其中 x 元素值为 val1

I want to get <y> element value where x element value is val1

我尝试了 //a/b/c[x='val1']/y 但没有奏效.

I tried //a/b/c[x='val1']/y but it did not work.

推荐答案

鉴于您使用的是 Axiom XPath 库，而后者又使用 Jaxen，您需要按照以下三个步骤彻底完成此操作稳健的方式:

Given that you're using the Axiom XPath library, which in turn uses Jaxen, you'll need to follow the following three steps to do this in a thoroughly robust manner:

• 创建一个 SimpleVariableContext，并调用 context.setVariableValue("val", "value1") 为该变量赋值.
• 在您的 BaseXPath 对象上，调用 .setVariableContext() 传入您分配的上下文.
• 在表达式中，使用 /a/b/c[x=$val]/y 来引用该值.

• Create a SimpleVariableContext, and call context.setVariableValue("val", "value1") to assign a value to that variable.
• On your BaseXPath object, call .setVariableContext() to pass in the context you assigned.
• Inside your expression, use /a/b/c[x=$val]/y to refer to that value.

考虑以下事项:

package com.example;

import org.apache.axiom.om.OMElement;
import org.apache.axiom.om.impl.common.AxiomText;
import org.apache.axiom.om.util.AXIOMUtil;
import org.apache.axiom.om.xpath.DocumentNavigator;
import org.jaxen.*;

import javax.xml.stream.XMLStreamException;

public class Main {

    public static void main(String[] args) throws XMLStreamException, JaxenException {
        String xmlPayload="<parent><a><b><c><x>val1</x><y>abc</y></c>" +
                                        "<c><x>val2</x><y>abcd</y></c>" +
                          "</b></a></parent>";
        OMElement xmlOMOBject = AXIOMUtil.stringToOM(xmlPayload);

        SimpleVariableContext svc = new SimpleVariableContext();
        svc.setVariableValue("val", "val2");

        String xpartString = "//c[x=$val]/y/text()";
        BaseXPath contextpath = new BaseXPath(xpartString, new DocumentNavigator());
        contextpath.setVariableContext(svc);
        AxiomText selectedNode = (AxiomText) contextpath.selectSingleNode(xmlOMOBject);
        System.out.println(selectedNode.getText());
    }
}

...作为输出发出:

abcd

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