从Java5到Java12每个版本的新特性(2)

Java5到Java7的新特性见这里:https://www.jianshu.com/p/a051a2f0c3ab

Java8新特性

  • lamda表达式(重磅)
  • 集合的stream操作
  • 提升HashMaps的性能
  • Date-Time Package
  • java.lang and java.util Packages
  • Concurrency

lamda表达式(重磅)

方法引用

/**
 * 静态方法引用:ClassName::methodName
 * 实例上的实例方法引用:instanceReference::methodName
 * 超类上的实例方法引用:super::methodName
 * 类型上的实例方法引用:ClassName::methodName
 * 构造方法引用:Class::new
 * 数组构造方法引用:TypeName[]::new
 * Created by codecraft on 2016-02-05.
 */
public class MethodReference {

    @Test
    public void methodRef(){
        SampleData.getThreeArtists().stream()
                .map(Artist::getName)
                .forEach(System.out::println);
    }

    @Test
    public void constructorRef(){
        ArtistFactory af = Artist::new;
        Artist a = af.create("codecraft","china");
        System.out.println(a);
    }
}

集合的stream操作

/**
 * 主要接口
 * 1,predicate
 * 2,Unary/BinaryOperator:传入参数和返回值必然是同一种数据类型
 * 3,Int/Double/LongFunction/BiFunction:函数接口并不要求传入参数和返回值之间的数据类型必须一样
 * 4,Int/Long/DoubleConsumer/BiConsumer:消费数据
 * 5,Int/Long/DoubleSupplier:生产数据
 *
 * 主要方法:
 * 1,filter
 * 2,map
 * 3,reduce
 * 4,collect
 * 5,peek
 * -Djdk.internal.lambda.dumpProxyClasses
 * Created by codecraft on 2016-02-05.
 */
public class LamdaDemo {

    int[] arr = {4,12,1,3,5,7,9};

    @Test
    public void filter(){
        Arrays.stream(arr).filter((x) -> x%2 !=0).forEach(System.out::println);
    }

    @Test
    public void map(){
        Arrays.stream(arr).map((x) -> x * x).forEach(System.out::println);
    }

    @Test
    public void reduce(){
        Arrays.stream(arr).reduce((x,y) -> x+y).ifPresent(System.out::println);
        System.out.println(Arrays.stream(arr).reduce(-10, (x, y) -> x + y));
    }

    @Test
    public void collect(){
        List list = Arrays.stream(arr).collect(ArrayList::new,ArrayList::add,ArrayList::addAll);
        System.out.println(list);

        Set set = list.stream().collect(Collectors.toSet());
        System.out.println(set);

        Map map = SampleData.getThreeArtists().stream()
                .collect(Collectors.toMap(a -> a.getName(),a -> a));
        System.out.println(map);
    }

    @Test
    public void peek(){
        long count = Arrays.stream(arr).filter(x -> x > 2).peek(System.out::println).count();
        System.out.println(count);
    }

    @Test
    public void average(){
        Arrays.stream(arr).average().ifPresent(System.out::println);
    }

    @Test
    public void sum(){
        System.out.println(Arrays.stream(arr).sum());
    }

    @Test
    public void max(){
        Arrays.stream(arr).max().ifPresent(System.out::println);
    }

    @Test
    public void min(){
        Arrays.stream(arr).min().ifPresent(System.out::println);
    }

    @Test
    public void sorted(){
        Comparator asc = (x,y) -> x.getName().compareTo(y.getName());
        SampleData.getThreeArtists().stream().sorted(asc).forEach(System.out::println);
        SampleData.getThreeArtists().stream().sorted(asc.reversed()).forEach(System.out::println);
        SampleData.getThreeArtists().stream().sorted(Comparator.comparing(Artist::getName)).forEach(System.out::println);
        SampleData.getThreeArtists().stream().sorted(Comparator.comparing(Artist::getName).reversed()).forEach(System.out::println);

        SampleData.getThreeArtists().stream().sorted(Comparator.comparing(Artist::getName).thenComparing(Artist::getNationality)).forEach(System.out::println);
    }

    @Test
    public void groupBy(){
        Map> rs = SampleData.getThreeArtists().stream().collect(Collectors.groupingBy(Artist::getNationality));
        System.out.println(rs);
    }

    @Test
    public void join(){
        String joinedNames = SampleData.getThreeArtists().stream().map(Artist::getName).collect(Collectors.joining(","));
        System.out.println(joinedNames);
        joinedNames.chars().mapToObj(c -> (char) Character.toUpperCase(c)).forEach(System.out::println);
    }

    @Test
    public void flatMap(){
        Set rs = SampleData.getThreeArtists().stream().flatMap(a -> a.getMembers()).collect(Collectors.toSet());
        rs.stream().forEach(System.out::println);
    }

    @Test
    public void arrStream(){
        Arrays.stream(arr).forEach(System.out::println);
    }

    @Test
    public void then(){
//        IntConsumer out = System.out::println;
//        IntConsumer err = System.err::println;
        IntConsumer out = (x) -> System.out.println("out consume:"+x);
        IntConsumer err = (x) -> System.err.println("err consume:"+x);
//        Arrays.stream(arr).forEach(out.andThen(err));
        Arrays.stream(arr).forEach(err.andThen(out));
    }

    @Test
    public void foreach(){
        List numbers = Arrays.asList(1,2,3,4,5,6);
        numbers.forEach(System.out::println);
    }

    @Test
    public void visitOuterVar(){
        final int num = 2;
        Function fun = (from) -> from * num;
        System.out.println(fun.apply(3));
    }
}

提升HashMaps的性能

当hash冲突时,以前都是用链表存储,在java8里头,当节点个数>=TREEIFY_THRESHOLD - 1时,HashMap将采用红黑树存储,这样最坏的情况下即所有的key都Hash冲突,采用链表的话查找时间为O(n),而采用红黑树为O(logn)。

Date-Time Package

Java 8新增了LocalDate和LocalTime接口,一方面把月份和星期都改成了enum防止出错,另一方面把LocalDate和LocalTime变成不可变类型,这样就线程安全了。

@Test
    public void today(){
        LocalDate today = LocalDate.now();
        System.out.println(today);
    }

    @Test
    public void parseString(){
        // 严格按照ISO yyyy-MM-dd验证,02写成2都不行,当然也有一个重载方法允许自己定义格式
        LocalDate date = LocalDate.parse("2016-02-05");
        System.out.println(date);
    }

    @Test
    public void calculate(){
        LocalDate today = LocalDate.now();
        LocalDate firstDayOfThisMonth = today.with(TemporalAdjusters.firstDayOfMonth());
        System.out.println(firstDayOfThisMonth);

        // 取本月第2天:
        LocalDate secondDayOfThisMonth = today.withDayOfMonth(2);
        System.out.println(secondDayOfThisMonth);

        // 取本月最后一天,再也不用计算是28,29,30还是31:
        LocalDate lastDayOfThisMonth = today.with(TemporalAdjusters.lastDayOfMonth());
        System.out.println(lastDayOfThisMonth);

        // 取下一天:
        LocalDate nextDay = lastDayOfThisMonth.plusDays(1);
        System.out.println(nextDay);

        // 取2015年1月第一个周一,这个计算用Calendar要死掉很多脑细胞:
        LocalDate firstMondayOf2015 = LocalDate.parse("2015-01-01").with(TemporalAdjusters.firstInMonth(DayOfWeek.MONDAY));
        System.out.println(firstMondayOf2015);
    }

    @Test
    public void getTime(){
        LocalTime now = LocalTime.now();
        System.out.println(now);
    }

    @Test
    public void getTimeWithoutMillis(){
        LocalTime now = LocalTime.now().withNano(0);
        System.out.println(now);
    }

    @Test
    public void parseTime(){
        LocalTime zero = LocalTime.of(0, 0, 0); // 00:00:00
        System.out.println(zero);

        LocalTime mid = LocalTime.parse("12:00:00"); // 12:00:00
        System.out.println(mid);
    }

java.lang and java.util Packages

比如数组的并行排序

public class UtilDemo {

    int[] data = {4,12,1,3,5,7,9};

    @Test
    public void parallelSort(){
        Arrays.parallelSort(data);
        System.out.println(Arrays.toString(data));
    }

    @Test
    public void testCollectPrallel() {
        //[4, 16, 17, 20, 25, 32, 41]
        Arrays.parallelPrefix(data, Integer::sum);
        System.out.println(Arrays.toString(data));
    }
}

比如文件遍历

 @Test
    public void list() throws IOException {
        Files.list(Paths.get(".")).filter(Files::isDirectory).forEach(System.out::println);
    }

    @Test
    public void walk() throws IOException {
        Files.walk(Paths.get("."), FileVisitOption.FOLLOW_LINKS).forEach(System.out::println);
    }

Concurrency

  • StampedLock
public class BankAccountWithStampedLock {

    private final StampedLock lock = new StampedLock();
    private double balance;

    public void deposit(double amount) {
        long stamp = lock.writeLock();
        try {
            balance = balance + amount;
        } finally {
            lock.unlockWrite(stamp);
        }
    }

    public double getBalance() {
        long stamp = lock.readLock();
        try {
            return balance;
        } finally {
            lock.unlockRead(stamp);
        }
    }
}

测试

@Test
    public void bench() throws InterruptedException {
        BankAccountWithStampedLock account = new BankAccountWithStampedLock();
        ExecutorService pool = Executors.newCachedThreadPool();
        List> callables = IntStream.range(1,5)
                .mapToObj(x -> (Callable) () -> {
//                    if (x % 2 == 0) {
//                        return account.getBalance();
//                    } else {
//                        account.deposit(x);
//                        return 0d;
//                    }
                    account.deposit(x);
                    return 0d;
                })
                .collect(Collectors.toList());
        pool.invokeAll(callables).forEach(x -> {
            try {
                System.out.println(x.get());
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (ExecutionException e) {
                e.printStackTrace();
            }
        });
        pool.shutdown();
        System.out.println(account.getBalance());
    }
  • ConcurrentHashMap的stream支持

参考

  • What's New in JDK 8
  • 如何在Java 8中愉快地处理日期和时间

Java9新特性

9版本是过渡版本

Java9 开始,Oracle公司转变方式,每6个月发布一次新版本,Java将更加有活力,其他语言的语法糖或编译器已经很先进、方便,Java不能不开始变革,Oracle希望6个月一个次版本发布,逐步将这个庞大的生态改变,目标是再一次引领时代的未来,来让我们看下9到12版本的变迁吧。

  • Java原生态支持模块化,精简jdk
  • G1成为默认垃圾回收装置
  • Java原生封装方便的操作http协议的工具
  • Jshell,Java开始原生支持交互脚本,或者简称命令行
  • 集合框架进一步优化
  • 提供类的工厂化构建方法
  • 支持docker
    完整的特性详见JDK 9 features,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)
  • JEP 261: Module System
  • JEP 200: The Modular JDK
  • JEP 201: Modular Source Code
  • JEP 282: jlink: The Java Linker
  • JEP 220: Modular Run-Time Images
  • JEP 260: Encapsulate Most Internal APIs

相关解读

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

G1成为默认垃圾回收器

相关JEP:

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

相关解读

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

Unified JVM/GC Logging

相关JEP:

  • JEP 158: Unified JVM Logging
  • JEP 264: Platform Logging API and Service
  • JEP 271: Unified GC Logging

相关解读

  • java9 gc log参数迁移

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)

相关解读

  • java9系列(六)HTTP/2 Client (Incubator)

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

相关JEP

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

相关解读

  • java9系列(一)安装及jshell使用

Convenience Factory Methods for Collections

相关JEP

  • JEP 269: Convenience Factory Methods for Collections

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

相关解读

  • java9系列(四)Process API更新

Stack-Walking API

相关JEP

  • JEP 259: Stack-Walking API

相关解读

  • java9系列(五)Stack-Walking API

Variable Handles

相关JEP

  • JEP 193: Variable Handles

相关解读

  • java9系列(七)Variable Handles

docker方面支持

  • Java SE support for Docker CPU and memory limits
  • Docker CPU limits
  • Experimental support for Docker memory limits
  • Docker memory limits

其他

  • JEP 238: Multi-Release JAR Files

    • java9系列(八)Multi-Release JAR Files
  • JEP 266: More Concurrency Updates

  • JEP 274: Enhanced Method Handles

  • JEP 295: Ahead-of-Time Compilation

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。

doc

  • JDK 9 features
  • Java 9 新特性概述
  • java9系列(一)安装及jshell使用
  • java9系列(二)docker运行java9
  • java9系列(三)模块系统精要
  • java9系列(四)Process API更新
  • java9系列(五)Stack-Walking API
  • java9系列(六)HTTP/2 Client (Incubator)
  • java9系列(七)Variable Handles
  • java9系列(八)Multi-Release JAR Files
  • java9系列(九)Make G1 the Default Garbage Collector
  • java9 opens与exports的区别
  • java9迁移注意事项
  • java9 gc log参数迁移
  • java9 module相关选项解析
  • 使用maven构建java9 service实例
  • 使用示例带你提前了解 Java 9 中的新特性

Java10新特性

10是过渡版本

特性列表

  • 286: Local-Variable Type Inference(重磅)

相关解读: java10系列(二)Local-Variable Type Inference

  • 296: Consolidate the JDK Forest into a Single Repository
  • 304: Garbage-Collector Interface
  • 307: Parallel Full GC for G1
  • 310: Application Class-Data Sharing
  • 312: Thread-Local Handshakes
  • 313: Remove the Native-Header Generation Tool (javah)
  • 314: Additional Unicode Language-Tag Extensions
  • 316: Heap Allocation on Alternative Memory Devices
  • 317: Experimental Java-Based JIT Compiler(重磅)

相关解读: Java10来了,来看看它一同发布的全新JIT编译器

  • 319: Root Certificates

相关解读: OpenJDK 10 Now Includes Root CA Certificates

  • 322: Time-Based Release Versioning

相关解读: java10系列(一)Time-Based Release Versioning

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What's New in JDK 10 - New Features and Enhancements,这里举几个例子。

Optional.orElseThrow()

/Library/Java/JavaVirtualMachines/jdk-10.jdk/Contents/Home/lib/src.zip!/java.base/java/util/Optional.java

  • 源码
    /**
     * If a value is present, returns the value, otherwise throws
     * {@code NoSuchElementException}.
     *
     * @return the non-{@code null} value described by this {@code Optional}
     * @throws NoSuchElementException if no value is present
     * @since 10
     */
    public T orElseThrow() {
        if (value == null) {
            throw new NoSuchElementException("No value present");
        }
        return value;
    }
  • 实例
    @Test
    public void testOrElseThrow(){
        var data = List.of("a","b","c");
        Optional optional = data.stream()
                .filter(s -> s.startsWith("z"))
                .findAny();
        String res = optional.orElseThrow();
        System.out.println(res);
    }

新增了orElseThrow与get相对应

输出

java.util.NoSuchElementException: No value present

    at java.base/java.util.Optional.orElseThrow(Optional.java:371)
    at com.example.FeatureTest.testOrElseThrow(FeatureTest.java:19)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

APIs for Creating Unmodifiable Collections

java9新增的of工厂方法的接口参数是一个个元素,java10新增List.copyOf, Set.copyOf,及Map.copyOf用来从已有集合创建ImmutableCollections

  • List.copyOf源码
    /**
     * Returns an unmodifiable List containing the elements of
     * the given Collection, in its iteration order. The given Collection must not be null,
     * and it must not contain any null elements. If the given Collection is subsequently
     * modified, the returned List will not reflect such modifications.
     *
     * @implNote
     * If the given Collection is an unmodifiable List,
     * calling copyOf will generally not create a copy.
     *
     * @param  the {@code List}'s element type
     * @param coll a {@code Collection} from which elements are drawn, must be non-null
     * @return a {@code List} containing the elements of the given {@code Collection}
     * @throws NullPointerException if coll is null, or if it contains any nulls
     * @since 10
     */
    @SuppressWarnings("unchecked")
    static  List copyOf(Collection coll) {
        if (coll instanceof ImmutableCollections.AbstractImmutableList) {
            return (List)coll;
        } else {
            return (List)List.of(coll.toArray());
        }
    }
  • 实例
    @Test(expected = UnsupportedOperationException.class)
    public void testCollectionCopyOf(){
        List list = IntStream.rangeClosed(1,10)
                .mapToObj(i -> "num"+i)
                .collect(Collectors.toList());
        List newList = List.copyOf(list);
        newList.add("not allowed");
    }

Collectors新增了toUnmodifiableList, toUnmodifiableSet,以及 toUnmodifiableMap方法

    @Test(expected = UnsupportedOperationException.class)
    public void testCollectionCopyOf(){
        List list = IntStream.rangeClosed(1,10)
                .mapToObj(i -> "num"+i)
                .collect(Collectors.toUnmodifiableList());
        list.add("not allowed");
    }

小结

java10最主要的新特性,在语法层面就属于Local-Variable Type Inference,而在jvm方面307: Parallel Full GC for G1以及317: Experimental Java-Based JIT Compiler都比较重磅,值得深入研究。

doc

  • JDK 10 Features
  • Introducing Java SE 10(官方解读)
  • What's New in JDK 10 - New Features and Enhancements(官方细项解读)
  • JDK-8140281 : (opt) add no-arg orElseThrow() as preferred alternative to get()
  • JDK-8177290 : add copy factory methods for unmodifiable List, Set, Map

Java11新特性

11版本是8版本之后第一个长支持的版本,可以考虑从8直接升级到11版本,11版本涵盖了9和10的版本特性,并做了优化。

版本号

java -version
openjdk version "11" 2018-09-25
OpenJDK Runtime Environment 18.9 (build 11+28)
OpenJDK 64-Bit Server VM 18.9 (build 11+28, mixed mode)
  • General-Availability Release版本是基于tag为jdk-11+28的版本编译
  • 从version信息可以看出是build 11+28

特性列表

  • 181: Nest-Based Access Control

相关解读Java Nestmate稳步推进,Specification for JEP 181: Nest-based Access Control
简单的理解就是Class类新增了getNestHost,getNestMembers方法

  • 309: Dynamic Class-File Constants

相关解读Specification for JEP 309: Dynamic Class-File Constants (JROSE EDITS)
jvm规范里头对Constant pool新增一类CONSTANT_Dynamic

  • 315: Improve Aarch64 Intrinsics

对于AArch64处理器改进现有的string、array相关函数,并新实现java.lang.Math的sin、cos、log方法

  • 318: Epsilon: A No-Op Garbage Collector

引入名为Epsilon的垃圾收集器,该收集器不做任何垃圾回收,可用于性能测试、短生命周期的任务等,使用-XX:+UseEpsilonGC开启

  • 320: Remove the Java EE and CORBA Modules(重磅)

将java9标记废弃的Java EE及CORBA模块移除掉,具体如下:(1)xml相关的,java.xml.ws, java.xml.bind,java.xml.ws,java.xml.ws.annotation,jdk.xml.bind,jdk.xml.ws被移除,只剩下java.xml,java.xml.crypto,jdk.xml.dom这几个模块;(2)java.corba,java.se.ee,java.activation,java.transaction被移除,但是java11新增一个java.transaction.xa模块

  • 321: HTTP Client (Standard)(重磅)

相关解读java9系列(六)HTTP/2 Client (Incubator),HTTP Client Examples and Recipes,在java9及10被标记incubator的模块jdk.incubator.httpclient,在java11被标记为正式,改为java.net.http模块。

  • 323: Local-Variable Syntax for Lambda Parameters

相关解读New Java 11 Language Feature: Local-Variable Type Inference (var) extended to Lambda Expression Parameters
允许lambda表达式使用var变量,比如(var x, var y) -> x.process(y),如果仅仅是这样写,倒是无法看出写var有什么优势而且反而觉得有点多此一举,但是如果要给lambda表达式变量标注注解的话,那么这个时候var的作用就突显出来了(@Nonnull var x, @Nullable var y) -> x.process(y)

  • 324: Key Agreement with Curve25519 and Curve448

使用RFC 7748中描述的Curve25519和Curve448实现key agreement

  • 327: Unicode 10

升级现有的API,支持Unicode10.0.0

  • 328: Flight Recorder

相关解读Java 11 Features: Java Flight Recorder
Flight Recorder以前是商业版的特性,在java11当中开源出来,它可以导出事件到文件中,之后可以用Java Mission Control来分析。可以在应用启动时配置java -XX:StartFlightRecording,或者在应用启动之后,使用jcmd来录制,比如

$ jcmd  JFR.start
$ jcmd  JFR.dump filename=recording.jfr
$ jcmd  JFR.stop
  • 329: ChaCha20 and Poly1305 Cryptographic Algorithms

实现 RFC 7539的ChaCha20 and ChaCha20-Poly1305加密算法

  • 330: Launch Single-File Source-Code Programs(重磅)

相关解读Launch Single-File Source-Code Programs in JDK 11
有了这个特性,可以直接java HelloWorld.java来执行java文件了,无需先javac编译为class文件然后再java执行class文件,两步合成一步

  • 331: Low-Overhead Heap Profiling

通过JVMTI的SampledObjectAlloc回调提供了一个开销低的heap分析方式

  • 332: Transport Layer Security (TLS) 1.3(重磅)

支持RFC 8446中的TLS 1.3版本

  • 333: ZGC: A Scalable Low-Latency Garbage Collector(Experimental)(重磅)

相关解读JDK11的ZGC小试牛刀,一文读懂Java 11的ZGC为何如此高效

  • 335: Deprecate the Nashorn JavaScript Engine

相关解读Oracle弃用Nashorn JavaScript引擎,Oracle GraalVM announces support for Nashorn migration
废除Nashorn javascript引擎,在后续版本准备移除掉,有需要的可以考虑使用GraalVM

  • 336: Deprecate the Pack200 Tools and API

废除了pack200以及unpack200工具以及java.util.jar中的Pack200 API。Pack200主要是用来压缩jar包的工具,不过由于网络下载速度的提升以及java9引入模块化系统之后不再依赖Pack200,因此这个版本将其移除掉。

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What's New in JDK 11 - New Features and Enhancements以及90 New Features (and APIs) in JDK 11,这里举几个例子。

添加项

  • Collection.toArray(IntFunction)
    @Test
    public void testCollectionToArray(){
        Set names = Set.of("Fred", "Wilma", "Barney", "Betty");
        String[] copy = new String[names.size()];
        names.toArray(copy);
        System.out.println(Arrays.toString(copy));
        System.out.println(Arrays.toString(names.toArray(String[]::new)));
    }

Collection类新增toArray(IntFunction)的default方法,可以直接通过传入IntFunction告知要转换的目标类型

  • String.strip
    @Test
    public void testStrip(){
        String text = "  \u2000a  b  ";
        Assert.assertEquals("a  b",text.strip());
        Assert.assertEquals("\u2000a  b",text.trim());
        Assert.assertEquals("a  b  ",text.stripLeading());
        Assert.assertEquals("  \u2000a  b",text.stripTrailing());
    }

java11对String类新增了strip,stripLeading以及stripTrailing方法,除了strip相关的方法还新增了isBlank、lines、repeat(int)等方法

  • 添加了Google Trust Services GlobalSign Root Certificates
  • 添加了GoDaddy Root Certificates
  • 添加了T-Systems, GlobalSign and Starfield Services Root Certificates
  • 添加了Entrust Root Certificates

移除项

  • 移除了com.sun.awt.AWTUtilities
  • 移除了sun.misc.Unsafe.defineClass,使用java.lang.invoke.MethodHandles.Lookup.defineClass来替代
  • 移除了Thread.destroy()以及 Thread.stop(Throwable)方法
  • 移除了sun.nio.ch.disableSystemWideOverlappingFileLockCheck、sun.locale.formatasdefault属性
  • 移除了jdk.snmp模块
  • 移除了javafx,openjdk估计是从java10版本就移除了,oracle jdk10还尚未移除javafx,而java11版本则oracle的jdk版本也移除了javafx
  • 移除了Java Mission Control,从JDK中移除之后,需要自己单独下载
  • 移除了这些Root Certificates :Baltimore Cybertrust Code Signing CA,SECOM ,AOL and Swisscom

废弃项

  • 废弃了Nashorn JavaScript Engine
  • 废弃了-XX+AggressiveOpts选项
  • -XX:+UnlockCommercialFeatures以及-XX:+LogCommercialFeatures选项也不再需要
  • 废弃了Pack200工具及其API

小结

  • java11是java改为6个月发布一版的策略之后的第一个LTS(Long-Term Support)版本(oracle版本才有LTS),这个版本最主要的特性是:在模块方面移除Java EE以及CORBA模块,在JVM方面引入了实验性的ZGC,在API方面正式提供了HttpClient类。
  • 从java11版本开始,不再单独发布JRE或者Server JRE版本了,有需要的可以自己通过jlink去定制runtime image

doc

  • JDK11
  • JDK11 Features
  • Introducing Java SE 11(官方解读)
  • JDK 11 Release Notes(官方细项解读)
  • What is new in Java 11 ?
  • Java Nestmate稳步推进
  • Specification for JEP 181: Nest-based Access Control
  • Specification for JEP 309: Dynamic Class-File Constants (JROSE EDITS)
  • Java 11 Features: Java Flight Recorder
  • java9系列(六)HTTP/2 Client (Incubator)
  • Java 11: Standardized HTTP Client API
  • java.net.http javadoc
  • HTTP Client Examples and Recipes
  • New Java 11 Language Feature: Local-Variable Type Inference (var) extended to Lambda Expression Parameters
  • JDK11的ZGC小试牛刀
  • 一文读懂Java 11的ZGC为何如此高效
  • Oracle弃用Nashorn JavaScript引擎
  • Oracle GraalVM announces support for Nashorn migration
  • JDK 11: New Default Collection Method toArray(IntFunction)
  • 90 New Features (and APIs) in JDK 11
  • APIs To Be Removed from Java 11
  • Java 11 String API Updates

Java12新特性

12版本也是一个过渡版本

  • 支持原生字符串,ts/js等语言早已支持,java再不支持就说不过去了,不过这个语法真的是方便,我预言Java12以后模版引擎将成为过去式。
  • 转译支持
  • 边距处理

原生字符串支持

Java中书写多行字符串和特殊转义字符时非常不方便和不直观,Java 12将会引入原生字符串(Raw String Literals)解决这一问题。

Java 12之前的写法:

String html = "\n" + " \n" + 
" 

Hello World.

\n" + " \n" + "\n";

Java 12的写法:

String html = `   

Hello World.

`;

转义支持(Escapes)

为了原生字符串中使用转义字符,String class中增加了两个方法:

public String unescape() 
public String escape()

以下结果都返回true:

boolean b0 = `\n`.equals("\\n"); boolean b1 = `\n`.unescape().equals("\n"); boolean b2 = `\n`.length == 2; boolean b3 = `\n`.unescape().length == 1;

边距管理(Margin Management)

为了处理多行字符串左边距的问题,String class中增加了两个方法:

public String align() 
public String indent(int n)

align方法用来去掉开头和结尾的空白行,保持每行的相对缩进。

indent方法用来控制每行开头增加或减少几个空格,n为正数时增加,n为负数时减少。

通常会组合两者使用,align().indent(n),所以另外提供了一个组合方法:

public String align(int n)
其他特性见参考:https://openjdk.java.net/projects/jdk/12/

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