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本文主要是介绍 Java 9语言新特性 。

• 特性列表
  • 模块系统JPMS(重磅)
  • G1成为默认垃圾回收器
  • Unified JVM/GC Logging
  • HTTP/2 Client(Incubator)
  • jshell: The Java Shell (Read-Eval-Print Loop)
  • Convenience Factory Methods for Collections
  • Process API Updates
  • Stack-Walking API
  • Variable Handles
  • docker方面支持
  • 其他
• 小结
• 参考文章

本文主要讲述一下Java9的新特性

特性列表

完整的特性详见JDK 9 features (opens new window)，这里列几个相对重要的：

模块系统JPMS(重磅)

相关的规范及JEP:

• Java Platform Module System (JSR 376) (opens new window)
• JEP 261: Module System (opens new window)
• JEP 200: The Modular JDK (opens new window)
• JEP 201: Modular Source Code (opens new window)
• JEP 282: jlink: The Java Linker (opens new window)
• JEP 220: Modular Run-Time Images (opens new window)
• JEP 260: Encapsulate Most Internal APIs (opens new window)

相关解读

• java9系列(三)模块系统精要 (opens new window)
• java9 opens与exports的区别 (opens new window)
• java9迁移注意事项 (opens new window)
• java9 module相关选项解析 (opens new window)

G1成为默认垃圾回收器

相关JEP:

• JEP 248: Make G1 the Default Garbage Collector (opens new window)
• JEP 291: Deprecate the Concurrent Mark Sweep (CMS) Garbage Collector (opens new window)
• JEP 278: Additional Tests for Humongous Objects in G1 (opens new window)

相关解读

• java9系列(九)Make G1 the Default Garbage Collector (opens new window)

Unified JVM/GC Logging

相关JEP:

• JEP 158: Unified JVM Logging (opens new window)
• JEP 264: Platform Logging API and Service (opens new window)
• JEP 271: Unified GC Logging (opens new window)

相关解读

• java9 gc log参数迁移 (opens new window)

HTTP/2 Client(Incubator)

支持HTTP2，同时改进httpclient的api，支持异步模式。

相关JEP

• JEP 110: HTTP/2 Client (Incubator) (opens new window)

相关解读

• java9系列(六)HTTP/2 Client (Incubator) (opens new window)

jshell: The Java Shell (Read-Eval-Print Loop)

相关JEP

• JEP 222: jshell: The Java Shell (Read-Eval-Print Loop) (opens new window)

相关解读

• java9系列(一)安装及jshell使用 (opens new window)

Convenience Factory Methods for Collections

相关JEP

• JEP 269: Convenience Factory Methods for Collections (opens new window)

以前大多使用Guava类库集合类的工厂，比如

Lists.newArrayList(1,2,3,4,5);
Sets.newHashSet(1,2,3,4,5);
Maps.newHashMap();

注意，上面这种返回的集合是mutable的

现在java9可以直接利用jdk内置的集合工厂，比如

List.of(1,2,3,4,5);
Set.of(1,2,3,4,5);
Map.of("key1","value1","key2","value2","key3","value3");

注意，jdk9上面这种集合工厂返回的是immutable的

Process API Updates

相关JEP

• JEP 102: Process API Updates (opens new window)

相关解读

• java9系列(四)Process API更新 (opens new window)

Stack-Walking API

相关JEP

• JEP 259: Stack-Walking API (opens new window)

相关解读

• java9系列(五)Stack-Walking API (opens new window)

Variable Handles

相关JEP

• JEP 193: Variable Handles (opens new window)

相关解读

• java9系列(七)Variable Handles (opens new window)

docker方面支持

• Java SE support for Docker CPU and memory limits (opens new window)
• Docker CPU limits (opens new window)
• Experimental support for Docker memory limits (opens new window)
• Docker memory limits (opens new window)

其他

• JEP 238: Multi-Release JAR Files (opens new window)
  • java9系列(八)Multi-Release JAR Files (opens new window)
• JEP 266: More Concurrency Updates (opens new window)
• JEP 274: Enhanced Method Handles (opens new window)
• JEP 295: Ahead-of-Time Compilation (opens new window)

小结

java9大刀阔斧，重磅引入了模块化系统，自身jdk的类库也首当其冲模块化。新引入的jlink可以精简化jdk的大小，外加Alpine Linux的docker镜像，可以大大减少java应用的docker镜像大小，同时也支持了Docker的cpu和memory限制(Java SE 8u131及以上版本开始支持)，非常值得使用。

参考文章

• https://segmentfault.com/a/1190000013620826