Java语言特性系列
Java5的新特性 Java6的新特性 Java7的新特性 Java8的新特性 Java9的新特性 Java10的新特性 Java11的新特性 Java12的新特性 Java13的新特性 Java14的新特性 Java15的新特性 Java16的新特性 Java17的新特性 Java18的新特性
序本文主要讲述一下Java17的新特性
版本号java -versionopenjdk version "17" 2021-09-14OpenJDK Runtime Environment (build 17+35-2724)OpenJDK 64-Bit Server VM (build 17+35-2724, mixed mode, sharing)从version信息可以看出是build 17+35
特性列表JEP 306: Restore Always-Strict Floating-Point Semantics恢复始终执行严格模式的浮点定义，修复25年前英特尔的浮点指令存在的一些问题
JEP 356: Enhanced Pseudo-Random Number Generators引入RandomGenerator及RandomGeneratorFactory提供更好的随机数生成
RandomGenerator generator = RandomGeneratorFactory.all() .filter(RandomGeneratorFactory::isJumpable) .filter(factory -> factory.stateBits() > 128) .findAny() .map(RandomGeneratorFactory::create)// if you need a `JumpableGenerator`:// .map(JumpableGenerator.class::cast) .orElseThrow();JEP 382: New macOS Rendering Pipeline使用Apple Metal API为macOS新增了Java 2D internal rendering pipeline
JEP 391: macOS/AArch64 Port迁移JDK到macOS/AArch64
JEP 398: Deprecate the Applet API for Removal标记Applet API为废弃方便后续移除，具体如下
java.applet.Appletjava.applet.AppletStubjava.applet.AppletContextjava.applet.AudioClipjavax.swing.JAppletjava.beans.AppletInitializerJEP 403: Strongly Encapsulate JDK Internals对JDK内部的api进行更强的封装，是JEP 396: Strongly Encapsulate JDK Internals by Default的后续
JEP 406: Pattern Matching for switch (Preview)引入switch模式匹配的preview版本，instanceof的模式匹配在JDK14作为preview，在JDK15作为第二轮的preview，在JDK16转正
static String formatterPatternSwitch(Object o) { return switch (o) { case Integer i -> String.format("int %d", i); case Long l -> String.format("long %d", l); case Double d -> String.format("double %f", d); case String s -> String.format("String %s", s); default -> o.toString(); };}JEP 407: Remove RMI Activation移除Remote Method Invocation (RMI)，它在JDK15的JEP 385被废弃
JEP 409: Sealed ClassesSealed Classes在JDK15作为preview引入，在JDK16作为第二轮preview，在JDK17转正
package com.example.geometry;public abstract sealed class Shape permits Circle, Rectangle, Square, WeirdShape { ... }public final class Circle extends Shape { ... }public sealed class Rectangle extends Shape permits TransparentRectangle, FilledRectangle { ... }public final class TransparentRectangle extends Rectangle { ... }public final class FilledRectangle extends Rectangle { ... }public final class Square extends Shape { ... }public non-sealed class WeirdShape extends Shape { ... }JEP 410: Remove the Experimental AOT and JIT Compiler移除实验性的java版本的AOT及JIT Compiler，具体移除
jdk.aot — the jaotc tooljdk.internal.vm.compiler — the Graal compilerjdk.internal.vm.compiler.management — Graal's MBean后续要使用可以使用GraalVM
JEP 411: Deprecate the Security Manager for Removal废弃java1.0引入的Security Manager方便后续移除
JEP 412: Foreign Function & Memory API (Incubator)JDK14的JEP 370: Foreign-Memory Access API (Incubator)引入了Foreign-Memory Access API作为incubator，JDK15的JEP 383: Foreign-Memory Access API (Second Incubator)Foreign-Memory Access API作为第二轮incubator，JDK16的JEP 393: Foreign-Memory Access API (Third Incubator)作为第三轮，它引入了Foreign Linker API，JDK17引入Foreign Function & Memory API
JEP 414: Vector API (Second Incubator)JDK16引入了JEP 338: Vector API (Incubator)提供了jdk.incubator.vector来用于矢量计算，JDK17进行改进并作为第二轮的incubator
JEP 415: Context-Specific Deserialization Filters允许应用去配置指定上下文及动态选择的deserialization filters，示例
public class FilterInThread implements BinaryOperator<ObjectInputFilter> { // ThreadLocal to hold the serial filter to be applied private final ThreadLocal<ObjectInputFilter> filterThreadLocal = new ThreadLocal<>(); // Construct a FilterInThread deserialization filter factory. public FilterInThread() {} /** * The filter factory, which is invoked every time a new ObjectInputStream * is created. If a per-stream filter is already set then it returns a * filter that combines the results of invoking each filter. * * @param curr the current filter on the stream * @param next a per stream filter * @return the selected filter */ public ObjectInputFilter apply(ObjectInputFilter curr, ObjectInputFilter next) { if (curr == null) { // Called from the OIS constructor or perhaps OIS.setObjectInputFilter with no current filter var filter = filterThreadLocal.get(); if (filter != null) { // Prepend a filter to assert that all classes have been Allowed or Rejected filter = ObjectInputFilter.Config.rejectUndecidedClass(filter); } if (next != null) { // Prepend the next filter to the thread filter, if any // Initially this is the static JVM-wide filter passed from the OIS constructor // Append the filter to reject all UNDECIDED results filter = ObjectInputFilter.Config.merge(next, filter); filter = ObjectInputFilter.Config.rejectUndecidedClass(filter); } return filter; } else { // Called from OIS.setObjectInputFilter with a current filter and a stream-specific filter. // The curr filter already incorporates the thread filter and static JVM-wide filter // and rejection of undecided classes // If there is a stream-specific filter prepend it and a filter to recheck for undecided if (next != null) { next = ObjectInputFilter.Config.merge(next, curr); next = ObjectInputFilter.Config.rejectUndecidedClass(next); return next; } return curr; } } /** * Apply the filter and invoke the runnable. * * @param filter the serial filter to apply to every deserialization in the thread * @param runnable a Runnable to invoke */ public void doWithSerialFilter(ObjectInputFilter filter, Runnable runnable) { var prevFilter = filterThreadLocal.get(); try { filterThreadLocal.set(filter); runnable.run(); } finally { filterThreadLocal.set(prevFilter); } }}// Create a FilterInThread filter factory and set var filterInThread = new FilterInThread(); ObjectInputFilter.Config.setSerialFilterFactory(filterInThread); // Create a filter to allow example.* classes and reject all others var filter = ObjectInputFilter.Config.createFilter("example.*;java.base/*;!*"); filterInThread.doWithSerialFilter(filter, () -> { byte[] bytes = ...; var o = deserializeObject(bytes); });细项解读上面列出的是大方面的特性，除此之外还有一些api的更新及废弃，主要见JDK 17 Release Notes，这里举几个例子。
添加项DatagramSocket Can Be Used Directly to Join Multicast Groups (JDK-8237352)更新了java.net.DatagramSocket用于支持joining multicast groups
Console Charset API (JDK-8264208)java.io.Console新增了方法用于返回console的charset
JDK Flight Recorder Event for Deserialization (JDK-8261160)JDK Flight Recorder新增了jfr.Deserialization实现
Unified Logging Supports Asynchronous Log Flushing (JDK-8229517)引入了-Xlog:async参数用于异步日志，以及-XX:AsyncLogBufferSize=<bytes>用于控制buffer的大小
移除项Removal of sun.misc.Unsafe::defineAnonymousClass (JDK-8243287)移除sun.misc.Unsafe::defineAnonymousClass方法
废弃项Deprecate 3DES and RC4 in Kerberos (JDK-8139348)废弃了Kerberos的des3-hmac-sha1及rc4-hmac这两个encryption types
Deprecate the Socket Implementation Factory Mechanism (JDK-8235139)废弃了如下几个工厂
static void ServerSocket.setSocketFactory(SocketImplFactory fac)static void Socket.setSocketImplFactory(SocketImplFactory fac)static void DatagramSocket.setDatagramSocketImplFactory(DatagramSocketImplFactory fac)已知问题TreeMap.computeIfAbsent Mishandles Existing Entries Whose Values Are null (JDK-8259622)TreeMap.computeIfAbsent方法针对null的处理与规范有偏差
Segmentation Fault Error on 9th and 10th Generation Intel® Core™ Processors (JDK-8263710)当运行在9th and 10th Generation Intel® Core™ Processors时会有Segmentation Fault Error
其他事项Updated List of Capabilities Provided by JDK RPMs (JDK-8263575)xml-commons-api, jaxp_parser_impl, 以及java-fonts已经从OracleJDK/OracleJRE RPMs移除
New Implementation of java.nio.channels.Selector on Microsoft Windows (JDK-8266369)对windows的java.nio.channels.Selector API采用了更具可扩展的方式实现，原来的实现没有被移除，可以使用-Djava.nio.channels.spi.SelectorProvider=sun.nio.ch.WindowsSelectorProvider来继续使用
Parallel GC Enables Adaptive Parallel Reference Processing by Default (JDK-8204686)针对Parallel GC默认开启了-XX:ParallelRefProcEnabled
URLClassLoader No Longer Throws Undocumented IllegalArgumentException From getResources and findResources (JDK-8262277)URLClassLoader的getResources、findResources不再抛出文档未定义的IllegalArgumentException
小结Java17主要有如下几个特性
JEP 306: Restore Always-Strict Floating-Point SemanticsJEP 356: Enhanced Pseudo-Random Number GeneratorsJEP 382: New macOS Rendering PipelineJEP 391: macOS/AArch64 PortJEP 398: Deprecate the Applet API for RemovalJEP 403: Strongly Encapsulate JDK InternalsJEP 406: Pattern Matching for switch (Preview)JEP 407: Remove RMI ActivationJEP 409: Sealed ClassesJEP 410: Remove the Experimental AOT and JIT CompilerJEP 411: Deprecate the Security Manager for RemovalJEP 412: Foreign Function & Memory API (Incubator)JEP 414: Vector API (Second Incubator)JEP 415: Context-Specific Deserialization FiltersdocJDK 17 FeaturesJDK 17 Release NotesJDK 17 Release NotesJava SE deprecated-listThe arrival of Java 17!Java 17 and IntelliJ IDEABetter Random Number Generation in Java 17
