What’s New in Java 18: A Developer’s Guide

Date: March 15, 2022

Category: Java Language & Platform Updates

While not a long-term support (LTS) release, Java 18 delivered some interesting improvements and previews that laid important groundwork for future versions. For many teams still on Java 11 or just moving to Java 17, Java 18 may have flown under the radar—but if you’re building modern Java web applications or APIs, there are a few things worth knowing.

Let’s take a look at what Java 18 brought to the table.

---

1. UTF-8 as the Default Charset (JEP 400)

This is arguably the most immediately relevant change for most web developers.

What changed?

Before Java 18, the default charset was platform-dependent (e.g., windows-1252 on Windows). That meant code behavior could change depending on where it was run. In Java 18, UTF-8 is now the default charset across all platforms.

Why it matters

This makes your Java applications more predictable and portable. It’s a big win for API development, microservices, and anything involving text data. You can now safely rely on UTF-8 without manually setting file.encoding.

Charset defaultCharset = Charset.defaultCharset(); // Now returns UTF-8

---

2. Simple Web Server (JEP 408)

Java 18 introduced a minimal HTTP static file server, available via CLI and the Java API. It’s intended for local development and educational use, not production, but it’s surprisingly useful.

✅ Use Cases:

• Serve frontend assets (HTML, JS, CSS) from a Java project
• Preview generated files (e.g., docs or reports)
• Build quick REST API stubs or demo UIs
• Run in a container for basic health checks or static hosting

---

🛠️ How to Use It

🧪 CLI Usage (Quickest Way)

From any directory:

jwebserver

It serves static files from the current directory on port 8000.

Customize Port and Directory:

jwebserver --port 8081 --directory ./public

Additional Options:

• --bind-address: Set a specific network interface
• --mime-type: Add custom content types
• --browse: Automatically open in a browser

💡 Example:

If you run:

jwebserver --directory ./docs --port 3000

And you have a file docs/index.html, just open http://localhost:3000 in your browser.

---

🧩 Programmatic API

You can also use it in Java code via:

com.sun.net.httpserver.HttpServer

Example – Serve static files in your app:

HttpServer server = HttpServer.create(new InetSocketAddress(8080), 0);
HttpHandler handler = HttpHandlers.ofFile(Path.of("index.html"));
server.createContext("/", handler);
server.start();

This allows you to embed a quick HTTP server directly in test tools, demos, or internal utilities—without needing Spring Boot or a servlet container.

☝️ This isn’t designed to replace full-featured frameworks like Jetty or Spring Boot—it’s meant to reduce boilerplate for small dev tasks.

---

🔐 Security and Limits

• No HTTPS support
• No dynamic routing or API logic
• No authentication
• Cannot serve directories above the working directory

Use only in safe, local dev environments.

---

🚀 Why It Matters

For many developers—especially those building with Spring or other Java frameworks—the setup for even a trivial file server can be overkill.

Now you can:

• Share a folder with teammates via HTTP
• Test a static UI without deploying to Tomcat or Nginx
• Run a mini server as part of an integration test

It also aligns Java more closely with other modern ecosystems:

• Python: python -m http.server
• Node.js: npx serve
• Go: http.FileServer

---

📌 Summary

Feature	Description
Port default	8000
Command	jwebserver
Secure?	No (HTTP only)
Java API available?	Yes (HttpServer class)
Production use?	❌ No
Dev use?	✅ Perfect for local demos

---

3. Code Snippets in JavaDoc (JEP 413)

JavaDoc has long supported code examples via the @code and @example tags in comments, but these were… well, not great. They were:

• Non-compilable (easy to get out-of-sync)
• Hard to maintain (no structure or validation)
• Lacking formatting (indented plain text)

JEP 413 fixes that by introducing structured, validated code snippets inside JavaDoc using a new @snippet tag.

---

✅ Why It Matters

This change bridges the gap between documentation and real, working code. Now you can:

• Include real examples in your API docs
• Highlight best practices
• Let tools validate the code during the build
• Avoid misleading or outdated documentation

If you’re building libraries in Spring, Jakarta EE, or custom SDKs, this is a big deal for developer experience.

---

✨ What’s New with @snippet

Here’s an example:

/**
 * Reads a file into a string.
 * 
 * @snippet :
 * Path path = Path.of("example.txt");
 * String content = Files.readString(path);
 */
public String readExample() { ... }

Notice how the @snippet tag is followed by a colon (:) and inline code. This creates a formatted, syntax-highlighted block in the generated HTML docs.

---

🔧 Advanced Usage

You can also include snippets from external source files, using the file and region attributes.

1. Extracted Snippet from a File

/**
 * @snippet file=MyExample.java region=loadFile
 */

Then, in MyExample.java:

// @start region=loadFile
Path path = Path.of("example.txt");
String content = Files.readString(path);
// @end

This makes it easier to reuse actual code in docs—keeping docs and logic in sync.

---

💡 Benefits for Teams

• 🔒 Avoids Stale Docs – Your JavaDoc examples can now be checked for compilation
• 🔍 Improves Clarity – Devs reading your API can learn how to use it with real context
• 🧪 IDE Friendly – IDEs like IntelliJ and Eclipse display enhanced docs
• 🔄 Easier Refactoring – Snippets update automatically if included from source files

---

🧠 Pro Tip for Framework Maintainers

If you’re writing a Spring Boot starter, Hibernate module, or internal API layer—use @snippet to document usage patterns that are:

• Correct (compile-checked)
• Maintainable
• Developer-friendly

This reduces support overhead, increases confidence, and makes your docs feel more alive.

---

🔍 Tooling Support

As of Java 18:

• The javadoc tool supports @snippet
• Snippets are included in HTML output
• Syntax highlighting is enabled (via HTML/CSS)
• Compilation checks can be enabled using --enable-preview (if needed)

You may need to wait for full IDE support or plug-in tooling depending on your setup.

---

📌 Summary

Feature	Description
Tag introduced	@snippet
Use cases	Examples, tutorials, API usage patterns
Validated?	✅ Yes (with external file inclusion)
Inline & external?	✅ Both supported
IDE aware?	Partial (as of 2025), improving
Java version	Java 18+

---

🛠️ Final Thought

Code that lives in docs but doesn’t compile is a trap. @snippet makes your documentation smarter, safer, and far more useful—especially when building for other developers.

---

4. Incubator & Preview Features

Though not production-ready, Java 18 previewed several forward-looking features:

Pattern Matching for switch (Preview – JEP 420)

This preview makes switch smarter and safer. Instead of using instanceof with casting, you can match and bind directly:

static String format(Object obj) {
    return switch (obj) {
        case Integer i -> "int " + i;
        case String s -> "string " + s;
        default -> "unknown";
    };
}

This improves both readability and type safety.

⚠️ Not enabled by default. You must use --enable-preview at compile and run time.

---

Vector API (Third Incubator – JEP 417)

This incubator API gives developers access to SIMD (Single Instruction, Multiple Data) hardware for high-performance operations on arrays and math-heavy code.

Not your everyday web dev tool—but useful in domains like cryptography, image processing, or ML.

---

Foreign Function & Memory API (Second Incubator – JEP 419)

Replaces JNI with a safer and more performant way to interoperate with native code. This is important if you’re working with C libraries, memory-mapped files, or performance-critical integrations.

---

Summary

Java 18 may not have made huge headlines, but it pushed the platform in the right direction—cleaner defaults, better tooling, smarter pattern matching, and gradual evolution toward high-performance and native-friendly Java.

What to keep in mind as a web developer:

• UTF-8 by default will save you headaches.
• jwebserver is a neat trick to keep in your toolbox.
• Pattern matching for switch is the beginning of cleaner control flow in Java.
• Preview features are optional, but worth exploring if you’re targeting Java 19 or beyond.

Next up in the series, we’ll look at Java 19 and 20, which bring exciting changes like virtual threads (Project Loom) and more.