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 Key Features

  • Estimating the amount of time and effort to upgrade to Java 16 or 17 may be difficult. However, upgrading is often easier than originally thought.
  • This article and other resources can help solve common Java upgrading challenges.
  • Simply get started, spend some time on the upgrade, and determine where the issues are.
  • Upgrade step-by-step so you can monitor the progress. Your teammates and management can see it as well. That way, everyone is more eager to continue with the upgrade.
  • Various features have been removed from the JDK such as fonts, certificates, tools and API methods. If your application uses one of those features, then you need to resolve it when upgrading to a new version of Java.
  • While upgrading Java can be challenging, it’s often a matter of hours or days. From my experience, the upgrade from Java 11 to Java 17 is easier compared to the upgrade from Java 8 to Java 11. Upgrading your application’s dependencies already resolves most, if not all, of these issues.

LTS releases

This article keeps referring to Java 8, Java 11, and Java 17 as LTS releases. What does that mean? Here’s a quote from the Oracle Java SE support roadmap:

For product releases after Java SE 8, Oracle will designate a release, every three years, as a Long-Term-Support (LTS) release. Java SE 11 is an LTS release. For the purposes of Oracle Premier Support, non-LTS releases are considered a cumulative set of implementation enhancements of the most recent LTS release. Once a new feature release is made available, any previous non-LTS release will be considered superseded. For example, Java SE 9 was a non-LTS release and immediately superseded by Java SE 10 (also non-LTS), Java SE 10 in turn is immediately superseded by Java SE 11. Java SE 11 however is an LTS release, and therefore Oracle Customers will receive Oracle Premier Support and periodic update releases, even though Java SE 12 was released.

What needs to change during a Java upgrade?

Your application contains code you and your team wrote, and it probably contains dependencies also. If something is removed from the JDK, that might break the code, the dependencies, or both. It often helps to make sure those dependencies are up to date to resolve these issues. Sometimes you might have to wait until a framework releases a new version that is compatible with the latest Java version before you begin the upgrade process. This means that you have a good knowledge of the dependencies as part of the preupgrade evaluation process.

Most functionality isn’t removed all at once from the JDK. First, functionality is marked for deprecation. For instance, Java Architecture for XML Binding (JAXB) was marked for deprecation in Java 9 before being removed in Java 11. If you continuously update, then you see the deprecations and you can resolve any use of those features before the functionality is removed. However, if you are jumping straight from Java 8 to Java 17, this feature removal will hit you all at once.

To view the API changes and, for instance, see which methods are removed or added to the String API in a specific Java version, look at The Java Version Almanac, by Marc Hoffmann and Cay Horstmann. 

Multirelease JAR functionality

What if your application is used by customers who still use an old JDK and an upgrade at their site is out of your control? Multirelease JAR functionality, introduced in Java 9 with JEP 238, might be useful because it allows you to package code for multiple Java versions (including versions older than Java 9) inside one JAR file.

As an example, create an Application class (Listing 1) and a Student class (Listing 2) and place them in the folder src/main/java/com/example. The Student class is a class that runs on Java 8.

Listing 1. The Application class

public class Application {

   public static void main(String[] args) {
       Student student = new Student("James ");
       System.out.println("Implementation " + student.implementation());
       System.out.println("Student name James contains a blank: " + student.isBlankName());
   }
}

 

Listing 2. The Student class written for Java 8

public class Student {
   final private String firstName;

   public Student(String firstName) {
       this.firstName = firstName;
   }

   boolean isBlankName() {
       return firstName == null || firstName.trim().isEmpty();
   }

   static String implementation() { return "class"; }
}

 

Next to that, create a Student record (Listing 3) that uses not only records (introduced in Java 14) but also the String.isBlank() method (introduced in Java 11), and place it in the folder src/main/java17/com/example.

Listing 3. A Student record using newer Java features

public record Student(String firstName) {
   boolean isBlankName() {
       return firstName.isBlank();
   }

   static String implementation() { return "record"; }
}

Some configuration is required depending on the build tool you use. A Maven example can be found in my GitHub repository. The example is built on Java 17 and creates the JAR file. When the JAR file is executed on JDK 17 or newer, the Student record is used. When the JAR file is executed on older versions, the Student class is used.

This feature is quite useful, for instance, if new APIs offer better performance, because you can use make use of those APIs for customers who have a recent Java version. The same JAR file can be used for customers with an older JDK, without the performance improvements.

Please be aware that all the implementations, in this case, the Student, should have the same public API to prevent runtime issues. Unfortunately build tools don’t verify the public APIs, but some IDEs do. Plus, with JDK 17 you can use the jar –validate command to validate the JAR file.

Something to be aware of is the preview functionality present in some versions of the JDK. Some bigger features are first released as previews and might result in a final feature in one of the next JDKs. Those preview features are present in both LTS and non-LTS versions of Java. The features are enabled with the enable-preview flag and are turned off by default. If you use those preview features in production code, be aware that they might change between JDK versions, which could result in the need for some debugging or refactoring. 

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More about Java deprecations and feature removals

Before upgrading the JDK, make sure your IDE, build tools, and dependencies are up to date. The Maven Versions Plugin and Gradle Versions Plugin show which dependencies you have and list the latest available version.

Be aware that these tools show only the new version for the artifacts you use—but sometimes the artifact names change, forks are made, or the code moves. For instance, JAXB was first available via javax.xml.bind:jaxb-api but changed to jakarta.xml.bind:jakarta.xml.bind-api after its transition to the Eclipse Foundation. To find such changes, you can use Jonathan Lermitage’s Old GroupIds Alerter plugin for Maven or his plugin for Gradle.

JavaFX. Starting with Java 11, the platform no longer contains JavaFX as part of the specification, and most JDK builds have removed it. You can use the separate JavaFX build from Gluon or add the OpenJFX dependencies to your project.  Continue Reading

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