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电商网站建设免费,软件技术专业介绍公布,网络公关公司联系方式,邵阳小学网站建设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Java19的新特性Java20的新特性Java21的新特性Java22… 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Java19的新特性Java20的新特性Java21的新特性Java22的新特性 序 本文主要讲述一下Java21的新特性 版本号 java -version openjdk version 21 2023-09-19 OpenJDK Runtime Environment (build 2135-2513) OpenJDK 64-Bit Server VM (build 2135-2513, mixed mode, sharing)从version信息可以看出是build 2135 特性列表 JEP 430: String Templates (Preview) 在java21之前字符串拼接或者字符串与表达式组合主要是用StringBuilder、String::format、java.text.MessageFormat不过可读性都不是太好java21引入了StringTemplate(java.lang.StringTemplate)来解决这个问题。 PreviewFeature(featurePreviewFeature.Feature.STRING_TEMPLATES) public interface StringTemplate {ListString fragments();ListObject values();default String interpolate() {return StringTemplate.interpolate(fragments(), values());}default R, E extends Throwable Rprocess(Processor? extends R, ? extends E processor) throws E {Objects.requireNonNull(processor, processor should not be null);return processor.process(this);}static String interpolate(ListString fragments, List? values) {Objects.requireNonNull(fragments, fragments must not be null);Objects.requireNonNull(values, values must not be null);int fragmentsSize fragments.size();int valuesSize values.size();if (fragmentsSize ! valuesSize 1) {throw new IllegalArgumentException(fragments must have one more element than values);}JavaTemplateAccess JTA SharedSecrets.getJavaTemplateAccess();return JTA.interpolate(fragments, values);}ProcessorString, RuntimeException STR StringTemplate::interpolate;ProcessorStringTemplate, RuntimeException RAW st - st;PreviewFeature(featurePreviewFeature.Feature.STRING_TEMPLATES)FunctionalInterfacepublic interface ProcessorR, E extends Throwable {R process(StringTemplate stringTemplate) throws E;static T ProcessorT, RuntimeException of(Function? super StringTemplate, ? extends T process) {return process::apply;}PreviewFeature(featurePreviewFeature.Feature.STRING_TEMPLATES)public sealed interface Linkage permits FormatProcessor {MethodHandle linkage(ListString fragments, MethodType type);}} }StringTemplate是个接口它定义了fragments、values、interpolate、process方法同时提供了interpolate、process方法的默认实现同时内置了两个processor分别是STR和RAW他们的区别在于RAW可以获取到StringTemplate类型STR则是StringTemplate执行了interpolate方法之后的结果获得到的是最终结果String其基本语法就是用{}来包含变量或者表达式 RAW示例 Testpublic void testRaw() {int x 10;int y 20;StringTemplate st RAW.{x} {y} {x y};ListString fragments st.fragments();ListObject values st.values();log.info(fragments:{}, values:{}, st:{}, fragments, values, st.interpolate());}输出fragments:[, , , ], values:[10, 20, 30], st:10 20 30 STR示例 Testpublic void testStr() {String name Joan;String info STR.My name is {name};System.out.println(info);}输出My name is Joan 也支持方法调用和表达式 Testpublic void testStrExpression() {String filePath tmp.dat;File file new File(filePath);String msg STR. The file { filePath } { file.exists() ? does : does not } exist ;System.out.println(msg);}最后输出The file tmp.dat does not exist 对于还有格式化需求的提供了java.util.FMT Testpublic void testFmt() {record Rectangle(String name, double width, double height) {double area() {return width * height;}}Rectangle[] zone new Rectangle[] {new Rectangle(Alfa, 17.8, 31.4),new Rectangle(Bravo, 9.6, 12.4),new Rectangle(Charlie, 7.1, 11.23),};String table FMT.Description Width Height Area%-12s{zone[0].name} %7.2f{zone[0].width} %7.2f{zone[0].height} %7.2f{zone[0].area()}%-12s{zone[1].name} %7.2f{zone[1].width} %7.2f{zone[1].height} %7.2f{zone[1].area()}%-12s{zone[2].name} %7.2f{zone[2].width} %7.2f{zone[2].height} %7.2f{zone[2].area()}{ .repeat(28)} Total %7.2f{zone[0].area() zone[1].area() zone[2].area()};System.out.println(table);}也可以自定义processor Testpublic void testCustomProcessor() {var MYJSON StringTemplate.Processor.of((StringTemplate st) - com.alibaba.fastjson.JSON.parseObject(st.interpolate()));String name Joan Smith;String phone 555-123-4567;String address 1 Maple Drive, Anytown;JSONObject doc MYJSON.{name: {name},phone: {phone},address: {address}};System.out.println(doc);}JEP 431: Sequenced Collections java21引入了java.util.SequencedCollection、java.util.SequencedMap来统一各类集合的顺序方法方法 public interface SequencedCollectionE extends CollectionE {SequencedCollectionE reversed();default void addFirst(E e) {throw new UnsupportedOperationException();}default void addLast(E e) {throw new UnsupportedOperationException();}default E getFirst() {return this.iterator().next();}default E getLast() {return this.reversed().iterator().next();}default E removeFirst() {var it this.iterator();E e it.next();it.remove();return e;}default E removeLast() {var it this.reversed().iterator();E e it.next();it.remove();return e;} }SequencedCollection继承了Collection接口同时定义了reversed提供了addFirst、addLast、getFirst、getLast、removeFirst、removeLast的default实现List、SequencedSet接口都继承了SequencedCollection接口 public interface SequencedMapK, V extends MapK, V {SequencedMapK, V reversed();default Map.EntryK,V firstEntry() {var it entrySet().iterator();return it.hasNext() ? new NullableKeyValueHolder(it.next()) : null;}default Map.EntryK,V lastEntry() {var it reversed().entrySet().iterator();return it.hasNext() ? new NullableKeyValueHolder(it.next()) : null;}default Map.EntryK,V pollFirstEntry() {var it entrySet().iterator();if (it.hasNext()) {var entry new NullableKeyValueHolder(it.next());it.remove();return entry;} else {return null;}}default Map.EntryK,V pollLastEntry() {var it reversed().entrySet().iterator();if (it.hasNext()) {var entry new NullableKeyValueHolder(it.next());it.remove();return entry;} else {return null;}}default V putFirst(K k, V v) {throw new UnsupportedOperationException();}default V putLast(K k, V v) {throw new UnsupportedOperationException();}default SequencedSetK sequencedKeySet() {class SeqKeySet extends AbstractMap.ViewCollectionK implements SequencedSetK {CollectionK view() {return SequencedMap.this.keySet();}public SequencedSetK reversed() {return SequencedMap.this.reversed().sequencedKeySet();}public boolean equals(Object other) {return view().equals(other);}public int hashCode() {return view().hashCode();}}return new SeqKeySet();}default SequencedCollectionV sequencedValues() {class SeqValues extends AbstractMap.ViewCollectionV implements SequencedCollectionV {CollectionV view() {return SequencedMap.this.values();}public SequencedCollectionV reversed() {return SequencedMap.this.reversed().sequencedValues();}}return new SeqValues();}default SequencedSetMap.EntryK, V sequencedEntrySet() {class SeqEntrySet extends AbstractMap.ViewCollectionMap.EntryK, Vimplements SequencedSetMap.EntryK, V {CollectionMap.EntryK, V view() {return SequencedMap.this.entrySet();}public SequencedSetMap.EntryK, V reversed() {return SequencedMap.this.reversed().sequencedEntrySet();}public boolean equals(Object other) {return view().equals(other);}public int hashCode() {return view().hashCode();}}return new SeqEntrySet();}
}SequencedMap接口继承了Map接口它定义了reversed方法同时提供了firstEntry、lastEntry、pollFirstEntry、pollLastEntry、putFirst、putLast、sequencedKeySet、sequencedValues、sequencedEntrySet方法的默认实现 此次版本的变动
List现在有作为其直接的超级接口SequencedCollectionDeque现在有作为其直接的超级接口SequencedCollectionLinkedHashSet另外实现SequencedSet接口SortedSet现在有作为其直接的超级接口SequencedSetLinkedHashMap另外实现SequencedMap接口SortedMap现在有作为它的直接超级接口SequencedMap 另外Collections还提供了工厂方法用于返回不可变类型 Collections.unmodifiableSequencedCollection(sequencedCollection) Collections.unmodifiableSequencedSet(sequencedSet) Collections.unmodifiableSequencedMap(sequencedMap)JEP 439: Generational ZGC ZGC分代回收无疑是一个重磅的GC特性ZGC之前的版本不支持分代回收此次支持分代回收的话可以更方便地对年轻代进行收集提高GC性能。目前是分代与非分代都支持使用分代则通过-XX:UseZGC-XX:ZGenerational开启后续版本将会把分代设置为默认的而-XX:-ZGenerational用于开启非分代最后将会废除非分代的支持届时ZGenerational参数也就没有作用了。 JEP 440: Record Patterns JDK19的JEP 405: Record Patterns (Preview)将Record的模式匹配作为第一次preview JDK20的JEP 432: Record Patterns (Second Preview)作为第二次preview 此次在JDK21则作为正式版本发布使用示例如下 record Point(int x, int y) {}// As of Java 21 static void printSum(Object obj) {if (obj instanceof Point(int x, int y)) {System.out.println(xy);} }enum Color { RED, GREEN, BLUE } record ColoredPoint(Point p, Color c) {} record Rectangle(ColoredPoint upperLeft, ColoredPoint lowerRight) {} // As of Java 21 static void printUpperLeftColoredPoint(Rectangle r) {if (r instanceof Rectangle(ColoredPoint ul, ColoredPoint lr)) {System.out.println(ul.c());} }static void printColorOfUpperLeftPoint(Rectangle r) {if (r instanceof Rectangle(ColoredPoint(Point p, Color c),ColoredPoint lr)) {System.out.println©;} }JEP 441: Pattern Matching for switch 在JDK14JEP 305: Pattern Matching for instanceof (Preview)作为preview 在JDK15JEP 375: Pattern Matching for instanceof (Second Preview)作为第二轮的preview 在JDK16JEP 394: Pattern Matching for instanceof转正 JDK17引入JEP 406: Pattern Matching for switch (Preview) JDK18的JEP 420: Pattern Matching for switch (Second Preview)则作为第二轮preview JDK19的JEP 427: Pattern Matching for switch (Third Preview)作为第三轮preview JDK20的JEP 433: Pattern Matching for switch (Fourth Preview)作为第四轮preview 而此次JDK21将Pattern Matching for switch作为正式版本发布示例如下 // Prior to Java 21 static String formatter(Object obj) {String formatted unknown;if (obj instanceof Integer i) {formatted String.format(int %d, i);} else if (obj instanceof Long l) {formatted String.format(long %d, l);} else if (obj instanceof Double d) {formatted String.format(double %f, d);} else if (obj instanceof String s) {formatted String.format(String %s, s);}return formatted; }// As of Java 21 static String formatterPatternSwitch(Object obj) {return switch (obj) {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 - obj.toString();}; }// As of Java 21 static void testFooBarNew(String s) {switch (s) {case null - System.out.println(Oops);case Foo, Bar - System.out.println(Great);default - System.out.println(Ok);} }// As of Java 21 static void testStringEnhanced(String response) {switch (response) {case null - { }case y, Y - {System.out.println(You got it);}case n, N - {System.out.println(Shame);}case String swhen s.equalsIgnoreCase(YES) - {System.out.println(You got it);}case String swhen s.equalsIgnoreCase(NO) - {System.out.println(Shame);}case String s - {System.out.println(Sorry?);}} }// As of Java 21 static void exhaustiveSwitchWithBetterEnumSupport(CardClassification c) {switch © {case Suit.CLUBS - {System.out.println(Its clubs);}case Suit.DIAMONDS - {System.out.println(Its diamonds);}case Suit.HEARTS - {System.out.println(Its hearts);}case Suit.SPADES - {System.out.println(Its spades);}case Tarot t - {System.out.println(Its a tarot);}} }// As of Java 21 sealed interface Currency permits Coin {} enum Coin implements Currency { HEADS, TAILS } static void goodEnumSwitch1(Currency c) {switch © {case Coin.HEADS - { // Qualified name of enum constant as a labelSystem.out.println(Heads);}case Coin.TAILS - {System.out.println(Tails);}} }static void goodEnumSwitch2(Coin c) {switch © {case HEADS - {System.out.println(Heads);}case Coin.TAILS - { // Unnecessary qualification but allowedSystem.out.println(Tails);}} }// As of Java 21 static void testNew(Object obj) {switch (obj) {case String s when s.length() 1 - …case String s - ……} }JEP 442: Foreign Function Memory API (Third Preview) Foreign Function Memory (FFM) API包含了两个incubating API 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 (JEP 389) FFM API在JDK 17的JEP 412: Foreign Function Memory API (Incubator)作为incubator引入 FFM API在JDK 18的JEP 419: Foreign Function Memory API (Second Incubator)作为第二轮incubator JDK19的JEP 424: Foreign Function Memory API (Preview)则将FFM API作为preview API JDK20的JEP 434: Foreign Function Memory API (Second Preview)作为第二轮preview JDK21则作为第三轮的preview使用示例 .javac –release 21 –enable-preview …java –enable-preview …// 1. Find foreign function on the C library path Linker linker Linker.nativeLinker(); SymbolLookup stdlib linker.defaultLookup(); MethodHandle radixsort linker.downcallHandle(stdlib.find(radixsort), …); // 2. Allocate on-heap memory to store four strings String[] javaStrings { mouse, cat, dog, car }; // 3. Use try-with-resources to manage the lifetime of off-heap memory try (Arena offHeap Arena.ofConfined()) {// 4. Allocate a region of off-heap memory to store four pointersMemorySegment pointers offHeap.allocateArray(ValueLayout.ADDRESS, javaStrings.length);// 5. Copy the strings from on-heap to off-heapfor (int i 0; i javaStrings.length; i) {MemorySegment cString offHeap.allocateUtf8String(javaStrings[i]);pointers.setAtIndex(ValueLayout.ADDRESS, i, cString);}// 6. Sort the off-heap data by calling the foreign functionradixsort.invoke(pointers, javaStrings.length, MemorySegment.NULL, \0);// 7. Copy the (reordered) strings from off-heap to on-heapfor (int i 0; i javaStrings.length; i) {MemorySegment cString pointers.getAtIndex(ValueLayout.ADDRESS, i);javaStrings[i] cString.getUtf8String(0);} } // 8. All off-heap memory is deallocated here assert Arrays.equals(javaStrings,new String[] {car, cat, dog, mouse}); // trueJEP 443: Unnamed Patterns and Variables (Preview) Unnamed Patterns and Variables支持用_来替代没有使用的变量声明比如 r instanceof Point _ r instanceof ColoredPoint(Point(int x, int _), Color ) if (r instanceof ColoredPoint(, Color c)) { … c … } switch (b) {case Box(RedBall _), Box(BlueBall _) - processBox(b);case Box(GreenBall ) - stopProcessing();case Box() - pickAnotherBox(); } int acc 0; for (Order _ : orders) {if (acc LIMIT) { … acc …} } while (q.size() 3) {var x q.remove();var _ q.remove();var _ q.remove(); … new Point(x, 0) … }JEP 444: Virtual Threads 在JDK19https://openjdk.org/jeps/425作为第一次preview 在JDK20JEP 436: Virtual Threads (Second Preview)作为第二次preview此版本java.lang.ThreadGroup被永久废弃 在JDK21版本Virtual Threads正式发布与之前版本相比这次支持了threadlocal然后也可以通过Thread.Builder来创建而且也支持threaddump(jcmd pid Thread.dump_to_file -formatjson file) 使用示例 void handle(Request request, Response response) {var url1 …var url2 …try (var executor Executors.newVirtualThreadPerTaskExecutor()) {var future1 executor.submit(() - fetchURL(url1));var future2 executor.submit(() - fetchURL(url2));response.send(future1.get() future2.get());} catch (ExecutionException | InterruptedException e) {response.fail(e);} }String fetchURL(URL url) throws IOException {try (var in url.openStream()) {return new String(in.readAllBytes(), StandardCharsets.UTF_8);} }一般用Executors.newVirtualThreadPerTaskExecutor()是想通过池化技术来减少对象创建开销不过由于虚拟线程相比平台线程更为廉价因而不再需要池化如果需要控制虚拟线程数则可以使用信号量的方式因而提供了Thread.Builder来直接创建虚拟线程示例如下 Thread thread Thread.ofVirtual().name(duke).unstarted(runnable); Thread.startVirtualThreadRunnable JEP 445: Unnamed Classes and Instance Main Methods (Preview) 未命名的类和实例main方法这个特性可以简化hello world示例方便java新手入门示例如下 static void main(String[] args) {System.out.println(static main with args);}static void main() {System.out.println(static main without args);}void main(String[] args) {System.out.println(main with args);}void main() {System.out.println(main with without args);}javac –release 21 –enable-preview Main.javajava –enable-preview Main 其中main方法选择的优先顺序是static的优于非static的然后有args的优于没有args的 JEP 446: Scoped Values (Preview) Scoped Values在JDK20的JEP 429: Scoped Values (Incubator)作为Incubator 此次在JDK21作为preview版本 ScopedValue是一种类似ThreadLocal的线程内/父子线程传递变量的更优方案。ThreadLocal提供了一种无需在方法参数上传递通用变量的方法InheritableThreadLocal使得子线程可以拷贝继承父线程的变量。但是ThreadLocal提供了set方法变量是可变的另外remove方法很容易被忽略导致在线程池场景下很容易造成内存泄露。ScopedValue则提供了一种不可变、不拷贝的方案即不提供set方法子线程不需要拷贝就可以访问父线程的变量。具体使用如下 class Server {public final static ScopedValueUser LOGGED_IN_USER ScopedValue.newInstance();private void serve(Request request) {// …User loggedInUser authenticateUser(request);ScopedValue.where(LOGGED_IN_USER, loggedInUser).run(() - restAdapter.processRequest(request));// …} }通过ScopedValue.where可以绑定ScopedValue的值然后在run方法里可以使用方法执行完毕自行释放可以被垃圾收集器回收 JEP 448: Vector API (Sixth 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incubatorJEP 414: Vector API (Second Incubator) JDK18的JEP 417: Vector API (Third Incubator)进行改进并作为第三轮的incubator JDK19的JEP 426:Vector API (Fourth Incubator)作为第四轮的incubator JDK20的JEP 438: Vector API (Fifth Incubator)作为第五轮的incubator 而JDK21则作为第六轮的incubator使用示例如下 static final VectorSpeciesFloat SPECIES FloatVector.SPECIES_PREFERRED;void vectorComputation(float[] a, float[] b, float[] c) {int i 0;int upperBound SPECIES.loopBound(a.length);for (; i upperBound; i SPECIES.length()) {// FloatVector va, vb, vc;var va FloatVector.fromArray(SPECIES, a, i);var vb FloatVector.fromArray(SPECIES, b, i);var vc va.mul(va).add(vb.mul(vb)).neg();vc.intoArray(c, i);}for (; i a.length; i) {ci * -1.0f;} }JEP 449: Deprecate the Windows 32-bit x86 Port for Removal 废弃了对Windows 32-bit x86 (x86-32)的移植以便后续版本删除 JEP 451: Prepare to Disallow the Dynamic Loading of Agents 对将代理动态加载到正在运行的 JVM 中时发出警告后续版本将不允许动态加载agent。 在 JDK 9 及更高版本中可以通过-XX:-EnableDynamicAgentLoading禁止动态加载agent。 在 JDK 21 中允许动态加载agent但 JVM 会在发生时发出警告。例如 WARNING: A {Java,JVM TI} agent has been loaded dynamically (file:/u/bob/agent.jar) WARNING: If a serviceability tool is in use, please run with -XX:EnableDynamicAgentLoading to hide this warning WARNING: If a serviceability tool is not in use, please run with -Djdk.instrument.traceUsage for more information WARNING: Dynamic loading of agents will be disallowed by default in a future release若要允许工具动态加载agent而不发出警告用户必须在命令行上使用-XX:EnableDynamicAgentLoading JEP 452: Key Encapsulation Mechanism API Key Encapsulation Mechanism(KEM)是一种现代加密技术它使用非对称或公钥加密来保护对称密钥。传统的方法是使用公钥加密一个随机生成的对称密钥但这需要填充并且可能难以证明安全。相反KEM利用公钥的属性派生一个相关的对称密钥这不需要填充。 此次新增了javax.crypto.KEM、javax.crypto.KEMSpi package javax.crypto;public class DecapsulateException extends GeneralSecurityException;public final class KEM {public static KEM getInstance(String alg)throws NoSuchAlgorithmException;public static KEM getInstance(String alg, Provider p)throws NoSuchAlgorithmException;public static KEM getInstance(String alg, String p)throws NoSuchAlgorithmException, NoSuchProviderException;public static final class Encapsulated {public Encapsulated(SecretKey key, byte[] encapsulation, byte[] params);public SecretKey key();public byte[] encapsulation();public byte[] params();}public static final class Encapsulator {String providerName();int secretSize(); // Size of the shared secretint encapsulationSize(); // Size of the key encapsulation messageEncapsulated encapsulate();Encapsulated encapsulate(int from, int to, String algorithm);}public Encapsulator newEncapsulator(PublicKey pk)throws InvalidKeyException;public Encapsulator newEncapsulator(PublicKey pk, SecureRandom sr)throws InvalidKeyException;public Encapsulator newEncapsulator(PublicKey pk, AlgorithmParameterSpec spec,SecureRandom sr)throws InvalidAlgorithmParameterException, InvalidKeyException;public static final class Decapsulator {String providerName();int secretSize(); // Size of the shared secretint encapsulationSize(); // Size of the key encapsulation messageSecretKey decapsulate(byte[] encapsulation) throws DecapsulateException;SecretKey decapsulate(byte[] encapsulation, int from, int to,String algorithm)throws DecapsulateException;}public Decapsulator newDecapsulator(PrivateKey sk)throws InvalidKeyException;public Decapsulator newDecapsulator(PrivateKey sk, AlgorithmParameterSpec spec)throws InvalidAlgorithmParameterException, InvalidKeyException;}它主要是提供了newEncapsulator、newDecapsulator方法使用示例如下 // Receiver side KeyPairGenerator g KeyPairGenerator.getInstance(ABC); KeyPair kp g.generateKeyPair(); publishKey(kp.getPublic());// Sender side KEM kemS KEM.getInstance(ABC-KEM); PublicKey pkR retrieveKey(); ABCKEMParameterSpec specS new ABCKEMParameterSpec(…); KEM.Encapsulator e kemS.newEncapsulator(pkR, specS, null); KEM.Encapsulated enc e.encapsulate(); SecretKey secS enc.key(); sendBytes(enc.encapsulation()); sendBytes(enc.params());// Receiver side byte[] em receiveBytes(); byte[] params receiveBytes(); KEM kemR KEM.getInstance(ABC-KEM); AlgorithmParameters algParams AlgorithmParameters.getInstance(ABC-KEM); algParams.init(params); ABCKEMParameterSpec specR algParams.getParameterSpec(ABCKEMParameterSpec.class); KEM.Decapsulator d kemR.newDecapsulator(kp.getPrivate(), specR); SecretKey secR d.decapsulate(em);// secS and secR will be identicalJEP 453: Structured Concurrency (Preview) 在JDK19的JEP 428: Structured Concurrency (Incubator)作为第一次incubator 在JDK20的JEP 437: Structured Concurrency (Second Incubator)作为第二次incubator 此次在JDK21则作为preview使用示例如下 Response handle() throws ExecutionException, InterruptedException {try (var scope new StructuredTaskScope.ShutdownOnFailure()) {SupplierString user scope.fork(() - findUser());SupplierInteger order scope.fork(() - fetchOrder());scope.join() // Join both subtasks.throwIfFailed(); // … and propagate errors// Here, both subtasks have succeeded, so compose their resultsreturn new Response(user.get(), order.get());} }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 21 Release Notes这里举几个例子。 添加项 Math.clamp() and StrictMath.clamp() Methods (JDK-8301226)New String indexOf(int,int,int) and indexOf(String,int,int) Methods to Support a Range of Indices (JDK-8302590)New splitWithDelimiters() Methods Added to String and java.util.regex.Pattern (JDK-8305486)System.exit() and Runtime.exit() Logging (JDK-8301627)The java.net.http.HttpClient Is Now AutoCloseable (JDK-8267140)New StringBuilder and StringBuffer repeat Methods (JDK-8302323)Last Resort G1 Full GC Moves Humongous Objects (JDK-8191565) 移除项 Removed SECOM Trust System’s RootCA1 Root Certificate (JDK-8295894)java.io.File’s Canonical Path Cache Is Removed (JDK-8300977)Removal of the java.compiler System Property (JDK-8041676)The java.lang.Compiler Class Has Been Removed (JDK-8205129)Remove the JAR Index Feature (JDK-8302819)Removal of G1 Hot Card Cache (JDK-8225409)Obsolete Legacy HotSpot Parallel Class Loading Workaround Option -XX:EnableWaitForParallelLoad Is Removed (JDK-8298469)The MetaspaceReclaimPolicy Flag has Been Obsoleted (JDK-8302385) 废弃项 Deprecate GTK2 for Removal (JDK-8280031)Deprecate JMX Subject Delegation and the JMXConnector.getMBeanServerConnection(Subject) Method for Removal (JDK-8298966) 重要bug修复 Error Computing the Amount of Milli- and Microseconds between java.time.Instants (JDK-8307466)Disallow Extra Semicolons Between “import” Statements (JDK-8027682) 已知问题 JVM May Crash or Malfunction When Using ZGC and Non-Default ObjectAlignmentInBytes (JDK-8312749)Validations on ZIP64 Extra Fields (JDK-8313765)java.util.regex.MatchResult Might Throw StringIndexOutOfBoundsException on Regex Patterns Containing Lookaheads and Lookbehinds (JDK-8132995)JVM May Hang When Using Generational ZGC if a VM Handshake Stalls on Memory (JDK-8311981) 其他事项 ObjectInputStream::readObject() Should Handle Negative Array Sizes without Throwing NegativeArraySizeExceptions (JDK-8306461)File::listRoots Changed to Return All Available Drives on Windows (JDK-8208077)Thread.sleep(millis, nanos) Is Now Able to Perform Sub-Millisecond Sleeps (JDK-8305092)FileChannel.transferFrom Extends File if Called to Transfer Bytes to the File (JDK-8303260)Clarification of the Default Charset Initialization with file.encoding (JDK-8300916)java.util.Formatter May Return Slightly Different Results on double and float (JDK-8300869)JVM TI ThreadStart and ThreadEnd Events Not Sent for Virtual Threads (JDK-8307399)Add final Keyword to Some Static Methods (JDK-8302696) 小结 Java21主要有如下几个特性 JEP 430: String Templates (Preview)JEP 431: Sequenced CollectionsJEP 439: Generational ZGCJEP 440: Record PatternsJEP 441: Pattern Matching for switchJEP 442: Foreign Function Memory API (Third Preview)JEP 443: Unnamed Patterns and Variables (Preview)JEP 444: Virtual ThreadsJEP 445: Unnamed Classes and Instance Main Methods (Preview)JEP 446: Scoped Values (Preview)JEP 448: Vector API (Sixth Incubator)JEP 449: Deprecate the Windows 32-bit x86 Port for RemovalJEP 451: Prepare to Disallow the Dynamic Loading of AgentsJEP 452: Key Encapsulation Mechanism APIJEP 453: Structured Concurrency (Preview) 其中JEP 439: Generational ZGC及JEP 444: Virtual Threads应属于重磅级的特性而JEP 430: String Templates (Preview)、JEP 431: Sequenced Collections、JEP 440: Record Patterns及JEP 441: Pattern Matching for switch则在语言表达力层面上有了增强 另外java21是继JDK 17之后最新的长期支持(LTS)版本将获得至少8年的支持。 doc JDK 21 FeaturesJDK 21 Release NotesConsolidated JDK 21 Release NotesJava SE 21 deprecated-listThe Arrival of Java 21JDK 21 G1/Parallel/Serial GC changesJava 21, the Next LTS Release, Delivers Virtual Threads, Record Patterns and Pattern MatchingJDK 21 and JDK 22: What We Know So FarJava 21 New Features: “The ZGC is generational and will further improve performance for suitable applications”Java 21 is Available Today, And It’s Quite the Update