java 如何在 xpath 表达式中使用逻辑运算符
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How to use logical operator in xpath expression
提问by user2121
i wrote the beloww code to retrive the value of the attribuet vin the element tagby specifyin the latand lonvalues as shown below.
i think my mistake is related to the how i use the && operator in the xpath expression, because when i used
我编写了下面的代码，通过在和 中指定值来检索v元素中属性的值，如下所示。我认为我的错误与我在 xpath 表达式中使用 && 运算符的方式有关，因为当我使用taglatlon
String expr0 = "//node[@lat='53.334062']/following-sibling::tag[1]/@v";
i receive the expected value, but when i uesd the below posted expression, the system crashs
我收到了预期值，但是当我使用下面发布的表达式时，系统崩溃了
but at run time, the program crashs and shows the below error message.
但在运行时，程序崩溃并显示以下错误消息。
code:
代码：
String expr0 = "//node[@lat='53.334062' && @lon='8.841545']/following-sibling::tag[1]/@v";
xPath.compile(expr0);
String s = (String) xPath.evaluate(expr0, document, XPathConstants.STRING);
System.out.println(s);
xml:
xml:
<?xml version='1.0' encoding='utf-8' ?>
<osm>
<node id="25779111" lat="53.0334062" lon="8.8461545"/>
<node id="25779112" lat="53.0338904" lon="8.846314"/>
<node id="25779119" lat="53.0337395" lon="8.8489255"/>
<tag k="maxspeed" v="30"/>
<tag k="maxspeed:zone" v="yes"/>
<node id="25779114" lat="53.334062" lon="8.841545"/>
<node id="25779117" lat="53.038904" lon="8.84614"/>
<node id="25779110" lat="53.033795" lon="8.489255"/>
<tag k="maxspeed" v="32"/>
<tag k="maxspeed:zone" v="yes"/>
</osm>
error:
错误：
Exception in thread "main" javax.xml.transform.TransformerException: Zus?tzliche ungültige Tokens: '&&', '[', '@', 'lon', '=', ''8.841545'', ']', '/', 'following-sibling', '::', 'tag', '[', '1', ']', '/', '@', 'v'
at com.sun.org.apache.xpath.internal.compiler.XPathParser.error(Unknown Source)
at com.sun.org.apache.xpath.internal.compiler.XPathParser.initXPath(Unknown Source)
at com.sun.org.apache.xpath.internal.XPath.<init>(Unknown Source)
at com.sun.org.apache.xpath.internal.XPath.<init>(Unknown Source)
at com.sun.org.apache.xpath.internal.jaxp.XPathImpl.compile(Unknown Source)
回答by Ian Roberts
The Boolean "and" operator in XPath is the word and, not &&(specification)
XPath 中的布尔“与”运算符是单词and, not &&（规范）
String expr0 = "//node[@lat='53.334062' and @lon='8.841545']/following-sibling::tag[1]/@v";
Alternatively you can use two predicates:
或者，您可以使用两个谓词：
String expr0 = "//node[@lat='53.334062'][@lon='8.841545']/following-sibling::tag[1]/@v";
This has the same effect - predicates apply from left to right so the first predicate filters the set of all nodeelements to just those that have @lat='53.334062', the second filters thatset to just those that have @lon='8.841545'.
这有相同的效果-谓词从左至右适用，所以第一个谓词筛选集合所有的node元素，只是那些有@lat='53.334062'，第二过滤器是集只是那些有@lon='8.841545'。
