Java 25: New Features, Migration & Real-World Examples (Complete Guide)
With the release of Java 25 (LTS), many developers and enterprises are evaluating whether to upgrade. This guide walks you through the new language features, JVM improvements, migration strategy, and practical usage examples — especially targeting backend & Spring-based applications.
- Overview of major new Java 25 features (language + JVM)
- Code examples using new syntax & APIs
- Migration checklist from Java 17/21 to Java 25
- Real-world use case: integrating new features in a Spring Boot + JPA application
- Performance / backward-compatibility considerations & best practices
1. What’s New in Java 25 — At a Glance
- Enhanced pattern matching & primitive matching — more expressive
switch, simplified type checks - Compact source file + shorter main method syntax — write less boilerplate
- Record enhancements & sealed hierarchies improvements — better modelling of domain data
- JVM improvements: startup, memory, GC tuning, native image support improvements
- Improved concurrency support — lightweight threads (“virtual threads”) matured for production
- New Collection APIs & Stream enhancements — concise, expressive data handling
- Improved foreign function support & I/O APIs (if applicable) — safer, faster external integrations
2. Code Examples — New Syntax & Language Features
2.1. Compact Source + Simplified Main
// File: Main.java
public class Main {
public static void main(String[] args) {
System.out.println("Hello from Java 25!");
}
}
→ With compact source (Java 25 feature), you can write:
public class Main {
public static void main(String[] args) {
System.out.println("Hello from Java 25!");
}
}
Fewer boilerplate imports & setup needed — especially useful for small utilities, scripts, or quick prototypes.
2.2. Enhanced Switch + Pattern Matching
public RecordPoint record Circle(double radius) {}
public RecordPoint record Rectangle(double width, double height) {}
public String describeShape(Object shape) {
return switch (shape) {
case Circle c && c.radius() > 10 -> "Large circle, radius " + c.radius();
case Circle c -> "Circle, radius " + c.radius();
case Rectangle r && r.width() == r.height() -> "Square with side " + r.width();
case Rectangle r -> "Rectangle " + r.width() + "x" + r.height();
default -> "Unknown shape";
};
}
Here we combine switch with pattern matching and conditional guards — much cleaner than traditional if-else chains.
2.3. Record Enhancements & Sealed Hierarchies
public sealed interface PaymentMethod permits CreditCard, PayPal, BankTransfer { }
public record CreditCard(String cardNumber, String cvv) implements PaymentMethod { }
public record PayPal(String email) implements PaymentMethod { }
public record BankTransfer(String accountNumber) implements PaymentMethod { }
public double calculateFee(PaymentMethod pm) {
return switch(pm) {
case CreditCard c -> 2.5; // 2.5% for credit card
case PayPal p -> 1.0;
case BankTransfer b -> 0.5;
};
}
Using sealed + record + pattern-matching switch gives a very expressive, type-safe domain API. Good for modelling DTOs, entities, payments, etc.
2.4. Virtual Threads Example (Concurrency Made Simpler)
import java.util.concurrent.*;
public class VirtualThreadDemo {
public static void main(String[] args) throws Exception {
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(() -> {
// simulate blocking I/O
try { Thread.sleep(1000); } catch (InterruptedException ignored) {}
return 42;
}, executor);
System.out.println("Result: " + f1.join());
}
}
}
Virtual threads (now stable in Java 25) make handling I/O-bound concurrency — like REST calls, DB access — much easier without heavy thread overhead. This can significantly simplify concurrency in Spring Boot or batch apps.
3. Migrating Existing Spring / JPA / Web Apps to Java 25 — Checklist & Best Practices
Upgrading a large codebase requires care. Here’s a checklist to help migrate from Java 17/21 to Java 25 safely:
- ✔ Make sure all dependencies (Spring Boot, libraries, ORM, frameworks) support Java 25.
- ✔ Update build tools (Maven/Gradle) to target Java 25 compliance level.
- ✔ Run full test suite (unit, integration, performance) — virtual threads may change concurrency behavior.
- ✔ Watch out for libraries using internal APIs — JDK strong encapsulation may block some reflective access.
- ✔ If using serialization, reflection, or Java agents — test thoroughly (some JDK internals changed).
- ✔ For production: run load/stress tests to validate GC, startup, memory behavior under Java 25.
JAVA_HOME and build configs flexible — use environment variables so you can rollback if issues arise.
4. Real-World Example: Upgrading a Spring Boot + JPA Service to Java 25
Suppose you have a service built with Spring Boot 2.x / 3.x, using JPA + MySQL / Oracle, REST controllers, maybe some scheduling or batch jobs. Here’s how you can gradually migrate and leverage new Java 25 features — WITHOUT breaking existing functionality.
4.1. pom.xml / Build configuration
<properties>
<java.version>25</java.version>
<maven.compiler.source>25</maven.compiler.source>
<maven.compiler.target>25</maven.compiler.target>
</properties>
Ensure Spring Boot version is compatible (e.g. 3.1+ with Java 25 support), update dependencies accordingly.
4.2. Replace DTO/Entity boilerplate with records & sealed classes
// Old DTO:
public class UserDTO {
private String name;
private String email;
// getters, setters, constructors...
}
// With Java 25:
public record UserDTO(String name, String email) { }
You can safely use `record` for DTOs (not entities) to reduce boilerplate. For JPA entities — continue using traditional classes, as record + JPA still has caveats.
4.3. Use virtual threads for async tasks or blocking I/O
For example, suppose you have a REST endpoint fetching data from a blocking service + DB + external API; switching to virtual threads lets you avoid complex thread-pool configs.
4.4. Use enhanced switch & pattern matching in service logic
public String getUserStatus(User user) {
return switch (user.getRole()) {
case Role.ADMIN -> "Admin privileges";
case Role.USER -> "Regular user";
case null, default -> "Unknown";
};
}
This helps keep code cleaner, easier to maintain, especially in large codebases.
5. Performance & JVM Improvements — What to Expect & Measure
- Faster startup & lower memory footprint — beneficial for microservices or containerized apps
- Better GC & memory management — less overhead under load, especially with many small objects (records, DTOs)
- Concurrency with virtual threads — easier scaling for I/O-bound workloads without heavy thread creation overhead
- Cleaner syntax → easier maintenance, fewer bugs — long-term productivity gains
6. When Not to Upgrade (Yet) — Risks & Caveats
- Third-party libraries may not yet support Java 25 (especially if they use internal JDK APIs or bytecode manipulation).
- Some new features may still be preview/incubator — avoid using them in critical modules unless you’re comfortable updating code when they change.
- Behavior changes in GC, classloading, serialization — could surface bugs in legacy code. Extensive testing required.
- Migration overhead — time & testing cost might outweigh immediate benefit for small/simple applications.
7. Summary & Recommendation
Java 25 brings many compelling improvements — from language syntax to JVM performance and concurrency. For modern backend apps (Spring Boot, microservices, batch, APIs), upgrading can yield:
- Cleaner, more maintainable code (records / enhanced switch / pattern matching)
- Better concurrency model with virtual threads — easier scaling under load
- Potential performance & memory gains — useful for microservices or containerized environments
**But** — only upgrade when:
- Your dependencies support Java 25
- You've thoroughly tested under real-world load
- You're ready to maintain code if preview APIs evolve
If you follow the practices and migration checklist — you can safely adopt Java 25 now and get long-term benefits.