How do I prevent a Maven mojo parameter from being encoded on write to XML?

Question

I'm writing a custom Maven plugin for building a Flatpak from a Java project. In a Maven mojo I understand we use @Parameter annotations to parse pom.xml file configurations. For example:

pom.xml:

<configuration>
    <param1>VALUE</param1>
</configuration>

In MyMojo.java:

@Parameter
private String param1;

But how would I set a value that includes HTML tags? For example:

<configuration>
    <param1><p>VALUE</p></param1>
</configuration>

Trying this, I get the error:

Basic element 'param1' must not contain child elements.

So I wrap the VALUE in a CDATA block:

<configuration>
    <param1><![CDATA[<p>VALUE</p>]]></param1>
</configuration>

This works up to the point where the MetaInfo object is written to file:

private void writeMetaInfo(MetaInfo metaInfo, Writer writer) throws IOException {
    XmlMapper mapper = new XmlMapper();
    new PrintWriter(writer, true).println("<?xml version=\"1.0\" encoding=\"UTF-8\"?>");
    // metaInfo value is correct before writing - it has <p> not &lt;p>
    mapper.writerWithDefaultPrettyPrinter().writeValue(writer, metaInfo);
}

The result is an XML file with: <param1>VALUE</param1>

...with the leading angle brackets replaced with their entity, <. This doesn't work for the Flatpak MetaInfo file I'm building. It needs the  and .

So it seems to be a problem with the XmlMapper (com.fasterxml.jackson.dataformat.xml.XmlMapper from com.fasterxml.jackson.dataformat:jackson-dataformat-xml:2.20.1).

I found this question which seems to indicate just using the CDATA block should work.

Any ideas?

What do you see when execute your plugin with -X ... should be something about configurations and value passed to your params — Slawomir Jaranowski
– Slawomir Jaranowski, Commented Nov 26 at 23:10
[DEBUG] (s) description = Initial release [DEBUG] (f) releases = [flatpak.maven.plugin.models.Release@799fb45e] [DEBUG] (f) releases = [flatpak.maven.plugin.models.Release@799fb45e]. It's a complex object, a List<Release> each of which has a String field called description. The output shows unencoded p-tags. I've debugged to the point where the XmlMapper writes and , before the write, the release instance has a description without the encoding. — CraigFoote
– CraigFoote, Commented Nov 26 at 23:29
What is the library or fully-qualified name of that XmlMapper class? That said, what you see is the correct behaviour for writing a value with < into XML. If you want something else, then you will need to do more work, so it actually writes an XML fragment instead of a value (how or if you can do so depends on the actual XML library). — Mark Rotteveel
– Mark Rotteveel, Commented Nov 27 at 9:49
Thanks for replying. It's com.fasterxml.jackson.dataformat.xml.XmlMapper from com.fasterxml.jackson.dataformat:jackson-dataformat-xml:2.20.1. But I can try another solution if it helps. Can you point me at some code that writes an XML fragment when it's the value? — CraigFoote
– CraigFoote, Commented Nov 27 at 13:23

Olivier · Accepted Answer · 2025-11-30 08:23:23Z

If you want to embed some XML fragments into the generated document, I don't think that high-level XML mappers are the right tool. I would use a more manual approach. Here is a solution based on the XOM library.

Assuming you have this class:

public class MetaInfo
{
    private String id;
    private String name;
    private String description;

    public String getId()
    {
        return id;
    }

    public void setId(String id)
    {
        this.id = id;
    }

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
    }

    public String getDescription()
    {
        return description;
    }

    public void setDescription(String description)
    {
        this.description = description;
    }
}

You can generate the MetaInfo file like this:

import java.io.*;
import nu.xom.*;

class MetaInfoGenerator
{
    private void addSimpleValue(Element parent, String name, String value)
    {
        Element element = new Element(name);
        element.appendChild(value);
        parent.appendChild(element);
    }

    private void addXmlValue(Element parent, String name, String value) throws ParsingException, IOException
    {
        String xml = String.format("<%s>%s</%s>", name, value, name);
        Document doc = new Builder().build(xml, null);
        parent.appendChild(doc.getRootElement().copy());
    }

    public void createMetaInfo(MetaInfo metaInfo, OutputStream out) throws ParsingException, IOException
    {
        Element root = new Element("component");
        root.addAttribute(new Attribute("type", "desktop-application"));
        addSimpleValue(root, "id", metaInfo.getId());
        addSimpleValue(root, "name", metaInfo.getName());
        addXmlValue(root, "description", metaInfo.getDescription());

        Document doc = new Document(root);
        Serializer serializer = new Serializer(out, "UTF-8");
        serializer.setIndent(4);
        serializer.write(doc);
    }

    public static void main(String[] args) throws ParsingException, IOException
    {
        MetaInfo metaInfo = new MetaInfo();
        metaInfo.setId("com.example.foobar");
        metaInfo.setName("Foo Bar");
        metaInfo.setDescription("<p>An awesome app!</p>");

        new MetaInfoGenerator().createMetaInfo(metaInfo, System.out);
    }
}

Output:

<?xml version="1.0" encoding="UTF-8"?>
<component type="desktop-application">
    <id>com.example.foobar</id>
    <name>Foo Bar</name>
    <description>
        <p>An awesome app!</p>
    </description>
</component>

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