guide jdk
The Java Development Kit is an implementation of the Java platform. It provides the Java Virtual Machine (JVM) and the Java Runtime Environment (JRE).
The JDK exists in different editions:
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OpenJDK is a free and open-source edition of the JDK.
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OracleJDK is a commercial edition of the JDK.
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Various alternative JDK editions either commercial (e.g. IBM’s JVM) or open-source.
As Java is evolving and also complex maintaining a JVM requires a lot of energy. Therefore many alternative JDK editions are unable to cope with this and support latest Java versions and according compatibility. Unfortunately OpenJDK only maintains a specific version of Java for a relative short period of time before moving to the next major version. In the end, this technically means that OpenJDK is continuous beta and can not be used in production for reasonable software projects. As OracleJDK changed its licensing model and can not be used for commercial usage even during development, things can get tricky. You may want to use OpenJDK for development and OracleJDK only in production. However, e.g. OpenJDK 11 never released a version that is stable enough for reasonable development (e.g. javadoc tool is broken and fixes are not available of OpenJDK 11 - fixed in 11.0.3 what is only available as OracleJDK 11 or you need to go to OpenJDK 12+, what has other bugs) so in the end there is no working release of OpenJDK 11. This more or less forces you to use OracleJDK what requires you to buy a subscription so you can use it for commercial development. However, there is AdoptOpenJDK that provides forked releases of OpenJDK with bug-fixes what might be an option. Anyhow, as you want to have your development environment close to production, the productively used JDK (most likely OracleJDK) should be preferred also for development.
Until Java 8 compatibility was one of the key aspects for Java version updates (after the mess on the Swing updates with Java2 many years ago). However, Java 9 introduced a lot of breaking changes. This documentation wants to share the experience we collected in devonfw when upgrading from Java 8 to newer versions. First of all we separate runtime changes that you need if you want to build your software with JDK 8 but such that it can also run on newer versions (e.g. JRE 11) from changes required to also build your software with more recent JDKs (e.g. JDK 11 or 12).
This section describes required changes to your software in order to make it run also with versions newer than Java 8.
The first thing that most users hit when running their software with newer Java versions is a ClassNotFoundException like this:
Caused by: java.lang.ClassNotFoundException: javax.xml.bind.JAXBException| Class | GroupId | ArtifactId | Version |
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Further, internal and inofficial APIs (e.g. sun.misc.Unsafe) have been removed.
These are typically not used by your software directly but by low-level 3rd party libraries like asm that need to be updated.
Also simple things like the Java version have changed (from 1.8.x to 9.x, 10.x, 11.x, 12.x, etc.).
Some 3rd party libraries were parsing the Java version in a very naive way making them unable to be used with Java 9+:
Caused by: java.lang.NullPointerException
at org.apache.maven.surefire.shade.org.apache.commons.lang3.SystemUtils.isJavaVersionAtLeast (SystemUtils.java:1626)| GroupId | ArtifactId | Version | Issue |
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If you also want to change your build to work with a recent JDK you also need to ensure that test frameworks and maven plugins properly support this.
Findbugs does not work with Java 9+ and is actually a dead project. The new findbugs is SpotBugs. For maven the new solution is spotbugs-maven-plugin:
<plugin>
<groupId>com.github.spotbugs</groupId>
<artifactId>spotbugs-maven-plugin</artifactId>
<version>3.1.11</version>
</plugin>| GroupId | ArtifactId | Version | Issue |
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We want to give credits and say thanks to the following articles that have been there before and helped us on our way:
This documentation is licensed under the Creative Commons License (Attribution-NoDerivatives 4.0 International).
