xml-patch

Java implementation of RFC 5261: An XML Patch Operations Framework Utilizing XPath Selectors

Also compatible with RFC 7351 patch documents.

Featuring Gradle and Ant integration.

Maven Coordinates

<dependency>
  <groupId>com.github.dnault</groupId>
  <artifactId>xml-patch</artifactId>
  <version>0.3.1</version>
</dependency>

You can also download the JAR if you want to run the patcher from the command line.

Introduction

So you're interested in patching some XML documents? Here's a quick illustration of why RFC 5261 XML patches are the way to go.

Original document:

<example>
    <patchTool url="https://en.wikipedia.org/wiki/Regular_expression"/>
    <greeting>Hello sorrow</greeting>
</example>

RFC 5261 patch:

<diff>
    <replace sel="example/patchTool/@url">https://tools.ietf.org/html/rfc5261</replace>
    <add pos="before" sel="example/greeting"><valediction>Goodbye sorrow</valediction>
    </add>
    <replace sel="example/greeting/text()">Hello XML patch</replace>
</diff>

Result of applying the patch to the original document:

<example>
    <patchTool url="https://tools.ietf.org/html/rfc5261" />
    <valediction>Goodbye sorrow</valediction>
    <greeting>Hello XML patch</greeting>
</example>

Check out RFC 5261 for more examples and a detailed explanation of the patch language.

Multi-Patch

RFC 5261 is great for patching one document at a time. If you need to patch many documents, it may be convienient to bundle related patches into a 'multi-patch' document that can target multiple, specific files.

Original file 'pets.xml':

<pets>
    <pet type="dog" name="Frankie"/>
    <pet type="cat" name="Lucy"/>
</pets>

Original file 'stores.xml':

<stores>
    <store name="Pets R Us"/>
</stores>

Multi-patch:

<diffs>
    <diff file="pets.xml">
        <remove sel="//pet[@name='Lucy']"/>
    </diff>

    <diff file="stores.xml">
        <add sel="stores">
            <store name="Paw Pals"/>
        </add>
    </diff>
</diffs>

As you can see, a multi-patch bundles zero or more RFC 5261 diff elements into a single document. Each diff element has a file attribute specifying a relative path to the file targeted by the patch.

If your project configuration is spread across multiple XML files (web.xml, log4j.xml, foo.xml, etc.) then a multi-patch is a convenient way to patch all of these files at once.

Multi-Patch Composition

Multi-patches may include other multi-patches. This is useful if your project has multiple configurations that share some common patches.

Multipatch file 'common-multi-patch.xml':

<diffs>
    <diff file="config.xml">
        <!-- apply common patches here -->
    </diff>
</diffs>

Multipatch file 'testing-multi-patch.xml':

<diffs>
    <include file="common-multi-patch.xml"/>

    <diff file="config.xml">
        <!-- apply patches for testing environment -->
    </diff>
</diffs>

Multipatch file 'production-multi-patch.xml':

<diffs>
    <include file="common-multi-patch.xml"/>

    <diff file="config.xml">
        <!-- apply patches for production environment -->
    </diff>
</diffs>

Using the patch tool

The xml-patch library may invoked from the command line, or from build tools like Gradle or Ant.

Gradle

XML patching is implemented using Gradle's built-in support for custom filters. Any task implementing CopySpec can be augmented to perform XML patching.

File 'build.gradle':

buildscript {
    repositories {
        jcenter()
    }
 
    dependencies {
        classpath "com.github.dnault:xml-patch:0.2.0"
    }
}
 
import com.github.dnault.xmlpatch.filter.XmlPatch
import com.github.dnault.xmlpatch.filter.multi.XmlMultiPatch
import com.github.dnault.xmlpatch.filter.multi.XmlPatchSpec
 
apply plugin: 'java'
 
ext {
    patchDir = "config/xml-patches"
}
 
// Copy a directory, selectively applying a single-target patch.
//
// Use this single-target technique if you're only patching a few documents
// and don't require multi-patch composition.
//
task singleTargetPatchExample(type: Copy) {
    inputs.dir patchDir
 
    from "src/main/example-documents"
    into "${buildDir}/patched"
 
    // Use one 'filesMatching' statement for each file you want to patch.
 
    filesMatching("**/patch-me.xml") {
        // Single-target patches use the 'XmlPatch' filter.
        filter(XmlPatch, patch: "${patchDir}/single/first-patch.xml")
    }
 
    filesMatching("**/patch-me-twice.xml") {
        // Multiple filters may be applied in sequence.
        filter(XmlPatch, patch: "${patchDir}/single/first-patch.xml")
        filter(XmlPatch, patch: "${patchDir}/single/second-patch.xml")
    }
}
 
 
// Augment the standard 'processResources' task to apply a multi-patch
// to classpath resources. The same technique could be applied to the 'war' task
// to patch webapp documents.
//
// Use this multi-patch technique if you're patching many documents or want
// to take advantage of multi-patch composition.
//
processResources {
    inputs.dir patchDir
 
    // To apply a multi-patch, first create a patch specification.
    def resourcesPatch = new XmlPatchSpec("${patchDir}/multi/resources-multi-patch.xml")
 
    filesMatching("**/*.xml") {
        // Multi-patches use the 'XMlMultiPatch' filter.
        // The filter will only process the file if the 'path' specified here
        // matches the 'file' attribute of a <diff> in the multi-patch document.
        filter(XmlMultiPatch, spec: resourcesPatch, path: it.path)
    }
 
    // Optionally assert that each file targeted by the patch was seen by the filter.
    doLast {
        resourcesPatch.done()
    }
}

Command Line

You'll need the JAR for this. You can grab it from the download link in the Maven Coordinates section above.

Apply an RFC 5261 patch:

java -jar xml-patch-<version>.jar <input file> <patch file> <output file>

A dash (-) may be used to indicate standard input / output.

Credits

This library includes the following software, repackaged to avoid dependency conflicts:

Apache Commons IO (Apache License 2.0) Copyright 2002-2012 The Apache Software Foundation

dnault / xml-patch