Java 17/21 Features and Migration Guide

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Java continues to evolve, and with the release of Java 17 (a Long-Term Support version) and Java 21, developers gain access to powerful new features and improvements. These versions enhance productivity, performance, and security, making them essential upgrades for modern applications. In this blog, we’ll explore the key features of Java 17 and Java 21 and provide a concise guide to migrating your applications.



Key Features of Java 17

Java 17, released in September 2021, is an LTS version, ensuring long-term stability and support. Here are its standout features:


1. Sealed Classes (JEP 409)

Sealed classes allow you to restrict which classes can extend or implement them, enabling better control over inheritance hierarchies.

java
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public sealed class Shape permits Circle, Square { }
public final class Circle extends Shape { }
public final class Square extends Shape { }


2. Pattern Matching for instanceof (JEP 394)

Simplify type checks and casting with pattern matching:

java
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if (obj instanceof String s) {
    System.out.println(s.toUpperCase());
}


3. Strong Encapsulation of JDK Internals (JEP 403)

Internal JDK APIs are now strongly encapsulated, improving security. Use --add-opens to access them if needed.


4. New macOS Rendering Pipeline (JEP 382)

Java 17 introduces a new rendering pipeline for macOS using the Apple Metal API, enhancing performance and compatibility.

5. Deprecate the Applet API (JEP 398)

The obsolete Applet API is deprecated for removal, aligning with modern web standards.


Key Features of Java 21

Java 21, released in September 2023, builds on Java 17 with even more exciting features:


1. Virtual Threads (JEP 444)

Virtual threads are lightweight threads that simplify concurrent programming, enabling efficient handling of millions of threads.


java
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Thread.startVirtualThread(() -> {
    System.out.println("Hello, Virtual Thread!");
});


2. Sequenced Collections (JEP 431)

New interfaces like SequencedCollection, SequencedSet, and SequencedMap provide consistent methods for accessing the first and last elements of collections.


java
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SequencedCollection<String> list = new ArrayList<>();
list.addFirst("First");
list.addLast("Last");


3. String Templates (Preview) (JEP 430)

String templates simplify string interpolation and formatting:


java
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String name = "Java";
String message = STR."Hello, \{name}!";


4. Record Patterns (JEP 440)

Record patterns extend pattern matching to deconstruct records:


java
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record Point(int x, int y) { }
if (obj instanceof Point(int x, int y)) {
    System.out.println(x + ", " + y);
}


5. Generational ZGC (JEP 439)

The Z Garbage Collector now supports generational memory management, improving performance by separating young and old objects.


Migration Guide: Moving to Java 17/21

Migrating to Java 17 or 21 requires careful planning. Follow these steps:


1. Check Compatibility

  • Use tools like jdeprscan to identify deprecated APIs in your codebase.

  • Ensure your dependencies (e.g., Spring, Hibernate) are compatible with Java 17/21.


2. Update Build Tools

  • Update your build tools (Maven, Gradle) to versions that support Java 17/21.

  • For Maven:

    xml
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    <properties>
    <maven.compiler.source>17</maven.compiler.source>
    <maven.compiler.target>17</maven.compiler.target>
</properties>
    Run HTML


  • For Gradle:

    groovy
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    sourceCompatibility = '17'
targetCompatibility = '17'


3. Adopt New Features

  • Refactor your code to leverage new features like sealed classes, pattern matching, and records.

  • Example: Replace traditional POJOs with records:

    java
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    public record User(String name, int age) { }


4. Test Thoroughly

  • Run comprehensive unit and integration tests to ensure your application works as expected.

  • Use tools like JUnit 5 and Testcontainers for testing.


5. Monitor Performance

  • After migration, monitor your application’s performance using tools like VisualVM, JFR, or Prometheus.

  • Optimize garbage collection settings if necessary.


6. Deploy and Validate

  • Deploy your application to a staging environment and validate its behavior.

  • Gradually roll out the update to production.


Why Migrate to Java 17/21?

  1. Long-Term Support: Java 17 is an LTS version, ensuring stability and security updates for years.

  2. Improved Performance: Features like virtual threads and generational ZGC enhance performance.

  3. Modern Syntax: New language features make your code more concise and readable.

  4. Security: Strong encapsulation and removal of deprecated APIs improve security.


Conclusion

Java 17 and Java 21 bring a wealth of features that can transform how you write and maintain Java applications. By migrating to these versions, you can take advantage of improved performance, modern syntax, and long-term support. Follow the migration guide to ensure a smooth transition, and start exploring the new features today!


Happy coding! 🚀

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