jaxb2-maven-plugin 2.4 and Java 11

I decided to investigate how to use jaxb2-maven-plugin 2.4 with Java 11. It’s still not easy to make these things working together but this time I was more lucky (see my previous attempt with Java 10) and here is a ready-to-use receipt how to do it!

Versions

Java version:

$ java --version
openjdk 11.0.2 2019-01-15
OpenJDK Runtime Environment 18.9 (build 11.0.2+9)
OpenJDK 64-Bit Server VM 18.9 (build 11.0.2+9, mixed mode)

Maven version:

$ mvn --version
Apache Maven 3.5.2
Maven home: /usr/share/maven
Java version: 11.0.2, vendor: Oracle Corporation
Java home: .../jdk-11.0.2
Default locale: pl_PL, platform encoding: UTF-8
OS name: "linux", ..., family: "unix"

pom.xml

With Java 11 (most likely the same would work with Java 10) we need to explicitly add dependencies required to have working JAXB, because many things were removed from Java in version 11:

• project dependecies: JAXB API, JAXB runtime, javax.activation package
• jaxb2-maven-plugin dependencies: xjc, javax.activation package

Moreover we need to explicitly declare some Maven plugins to make sure we’re using latest versions of these plugins which are ready for Java 11.

Please note the <sources> tag in configuration section for jaxb2-maven-plugin. It consists of 2 elements. One is the path to the desired XSD (src/main/xsd/your-file.xsd) – change it according to your requirements. The other element (src/main/xsd/dummy.xsd) is a workaround for some strange issue jaxb2-maven-plugin has when working with Java 11.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>...</groupId>
    <artifactId>...</artifactId>
    <version>...</version>
    <packaging>jar</packaging>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>11</maven.compiler.source>
        <maven.compiler.target>11</maven.compiler.target>
    </properties>

    <dependencies>
        ...
        <dependency>
            <groupId>javax.xml.bind</groupId>
            <artifactId>jaxb-api</artifactId>
            <version>2.3.0</version>
        </dependency>        
        <dependency>
            <groupId>org.glassfish.jaxb</groupId>
            <artifactId>jaxb-runtime</artifactId>
            <version>2.3.2</version>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>com.sun.activation</groupId>
            <artifactId>jakarta.activation</artifactId>
            <version>1.2.1</version>
            <scope>runtime</scope>
        </dependency>        
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.0</version>
                <configuration>
                    <release>11</release>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.22.0</version>
                <configuration>
                    <argLine>--illegal-access=permit</argLine>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>jaxb2-maven-plugin</artifactId>
                <version>2.4</version>
                <executions>
                    <execution>
                        <id>xjc</id>
                        <goals>
                            <goal>xjc</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <sources>
                        <source>src/main/xsd/dummy.xsd</source>
                        <source>src/main/xsd/your-file.xsd</source>
                    </sources>
                    <packageName>your.package</packageName>
                </configuration>
                <dependencies>
                    <dependency>
                        <groupId>org.glassfish.jaxb</groupId>
                        <artifactId>jaxb-xjc</artifactId>
                        <version>2.3.2</version>
                    </dependency>
                    <dependency>
                        <groupId>com.sun.activation</groupId>
                        <artifactId>jakarta.activation</artifactId>
                        <version>1.2.1</version>
                    </dependency>
                </dependencies>
            </plugin>
        </plugins>
    </build>
</project>

Note that without the line 70 (<source>src/main/xsd/dummy.xsd</source>) the build will fail with the following error:

[ERROR] Failed to execute goal org.codehaus.mojo:jaxb2-maven-plugin:2.4:xjc (xjc) on project ...: Prefix '' is already bound to '' -> [Help 1]

dummy.xsd

As far as I know the content of this file is just:

<xs:schema id="Dummy" xmlns:xs="http://www.w3.org/2001/XMLSchema"> 
    <xs:element name="Dummy"> 
        <xs:complexType> 
            <xs:sequence> 
                <xs:element name="test"/> 
            </xs:sequence> 
        </xs:complexType> 
    </xs:element> 
</xs:schema>

You need to put this file into src/main/xsd folder.

And now things are working!!! 🙂 Run maven and make use of model classes generated from XSD file.

The only difference comparing to case when using Java 8 is that now we see these warning messages as the very first lines printed when executing mvn package command:

WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by com.google.inject.internal.cglib.core.$ReflectUtils$1 (file:/usr/share/maven/lib/guice.jar) to method java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain)
WARNING: Please consider reporting this to the maintainers of com.google.inject.internal.cglib.core.$ReflectUtils$1
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

My guess is this is not dangerous and it will be solved by newer Maven release.