How to patch an xml file with namespaces using xml-patch and xpath?

Question

I am trying to patch several XML files using XML-patch, more specifically using this library https://github.com/dnault/xml-patch

I can properly patch any xml file that does not contain any namespace declarations. I am patching a logback.xml file and all works properly.

The problem is when I try to patch a web.xml file that looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="3.0" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" metadata-complete="true">

    <display-name>My App</display-name>
...
</web-app>

Using a xml-patch file that looks like this

<diff file="WEB-INF/web.xml">
    <add sel="web-app" >
        <simple>true</simple>
    </add>
</diff>

When I run the patcher, I get this exception:

Caused by: com.github.dnault.xmlpatch.PatchException: no matches for selector "web-app"
    at com.github.dnault.xmlpatch.Patcher.selectNodes(Patcher.java:441)
    at com.github.dnault.xmlpatch.Patcher.add(Patcher.java:252)
    at com.github.dnault.xmlpatch.Patcher.patch(Patcher.java:85)
    at com.github.dnault.xmlpatch.Patcher.patch(Patcher.java:65)
    at com.github.dnault.xmlpatch.CommandLineDriver.main(CommandLineDriver.java:62)

I am fairly confident this has to be a problem with the diff file and namespaces, which I probably have not configured properly.

I have tried adding namespace declarations to the diff file but the error is the same.

Any ideas?

Since you're dealing with namespaces, whats the output if you add a wildcard character in your select expression. Like this : add sel="*/web-app" ? It seems that's the proper way to do it. See examples here : xmlpatch.sourceforge.net/srns.txt — E.Wiest
– E.Wiest, Commented Jul 8, 2020 at 1:22
Hi. I had already tried something like that with no success. Your example results in a this error: no matches for selector "*/web-app" — s1m3n
– s1m3n, Commented Jul 9, 2020 at 6:51
I guess that's because I was talking about the wrong XML patch library. The one available on sourceforge (libxmlpatch), not on Github. Glad you found something that works.:) — E.Wiest
– E.Wiest, Commented Jul 10, 2020 at 0:47

wp78de · Accepted Answer · 2020-07-08 23:20:34Z

1

It looks like this is a confirmed issue of the tool. Howevever, the original poster also mentions a workaround:

So in effect I haver to declare the defaultnamespace twice in order to allow selection and addition of new nodes without having to prefix the added nodes one by one with "cfg:" prefix. See the following example:

Applied to your example, the patch.xml should look something like this.

<diff xmlns:app="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="3.0" metadata-complete="true">
    <add sel="app:web-app">
        <simple>true</simple>
    </add>
</diff>

That way the patching succeeds.

answered Jul 8, 2020 at 23:20

wp78de

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s1m3n Over a year ago

This is quite close, but the added element adds an unwanted "xmlns" attribute to the added <simple /> node: <simple xmlns="">true</simple>

s1m3n · Accepted Answer · 2020-07-09 06:59:19Z

1

There is another way to do it:

<diff file="WEB-INF/web.xml">
    <add sel="/*['web-app'=local-name()]">
        <simple>true</simple>
    </add>
</diff>

This also results in an unwanted but harmless "xmlns" attribute being added:

<simple xmlns="">true</simple>

answered Jul 9, 2020 at 6:59

s1m3n

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