如何将变量参数传递到XPath表达式中? [英] How to pass variable parameter into XPath expression?

问题描述

我想将参数传递到XPath表达式中.

I want to pass a parameter into an XPath expression.

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

我可以使用XPath 1.0来做到这一点吗? (我尝试过string-join，但它在XPath 1.0中不存在)

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

那我该怎么办呢?

我的XML看起来像

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

我想获得x元素值为val1

我尝试了//a/b/c[x='val1']/y，但是没有用.

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，而该库又使用Jaxen，则需要按照以下三个步骤进行操作健壮的方式:

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 SimpleVariableContext ，然后调用context.setVariableValue("val", "value1")进行分配该变量的值.
• 在您的 BaseXPath 对象上，调用.setVariableContext()传递在您分配的上下文中.
• 在表达式中，使用/a/b/c[x=$val]/y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.

请考虑以下内容:

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:

...which emits as output:

abcd

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