Java/Java SE 9: What's New, Release History & Support Lifecycle

What Is New in Java 9

Java 9 is a major release centered around the Java Platform Module System (JPMS), which fundamentally changes how applications are structured and deployed. Alongside this, it delivers a new HTTP client, improved APIs, and a collection of new tools for developers.

How does the Module System change Java development?

The Java Platform Module System (JPMS), also known as Project Jigsaw, introduces a new level of abstraction above packages. It allows you to declare explicit dependencies and define which packages are publicly accessible, enforcing strong encapsulation.

In practice, this means you can create a module-info.java file to define your module's name, its required dependencies, and the packages it exports. This solves long-standing issues like the brittle classpath and JAR hell.

module com.example.myapp {
    requires java.sql;
    requires com.example.mylibrary;
    exports com.example.myapp.api;
}

This modularization also enabled the restructuring of the JDK itself into modules, leading to the creation of smaller, customized runtime images using the jlink tool.

What new tools are available for developers?

Java 9 shipped with jshell, the first official REPL (Read-Eval-Print Loop) for Java. It lets you quickly test code snippets, expressions, and APIs without compiling a full class, which is fantastic for prototyping and learning.

The HTTP/2 Client API was introduced as an incubator module (jdk.incubator.http), providing a modern, non-blocking alternative to the old HttpURLConnection. It supports HTTP/2 and WebSocket out of the box.

Multi-Release JAR Files

This feature allows a single JAR file to contain different versions of class files tailored for different Java versions. You can have Java 9-specific code in a META-INF/versions/9 directory while maintaining backward compatibility.

Which API improvements should I start using?

The Process API received significant upgrades for managing native operating system processes. You can now easily get the PID, command line arguments, and children of a process, which was notoriously difficult before.

New convenience methods were added to core interfaces. The Stream API got takeWhile, dropWhile, and iterate overloads for more expressive filtering. The Optional class gained methods like ifPresentOrElse and or for better handling of empty values.

List<String> result = stream
    .takeWhile(s -> s.length() < 5)
    .collect(Collectors.toList());

Java 9 also included the reactive streams API in the java.util.concurrent package, providing a standard for asynchronous stream processing with backpressure.

What security enhancements were implemented?

Support for the Datagram Transport Layer Security (DTLS) protocol was added, enabling secure communication for datagram-based applications. The SHA-3 family of cryptographic hash algorithms is now available for use.

A crucial change was the disabling of SSLv3 and TLS 1.0 for FTPS implementations to align with modern security standards. Certificates signed with the SHA-1 hash algorithm were also deprecated and disabled by default for TLS connections.