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JAVA9-12新特性简述

本文是个人在企业内部分享使用的简要大纲，列举了JAVA9-12的重要更新，文章的结构较简单，也不规范，鉴于近期写若干文章时总会忘记一些新特性所处的版本，特将此大纲流copy留用。

一 JAVA9 新特性

1.Java Platform Module System/ Modular Java Application Packaging模块化系统及类加载器分级

2.jshell

3.Multi-Release JAR Files 多版本的jar包

4.Jlink 工具

5.Segmented Code Cache 代码片段缓存

6.Dynamic Linking of Language-Defined Object Models 动态链接语言定义模型

7.Unified JVM Logging 统一JVM日志

8.将G1作为默认垃圾收集器,并deprecated CMS.

9.进程API

10.变量句柄

11.字符串内部实现优化(字符数组变字节数组+编码方式)

12.发布订阅框架

13.集合工厂方法

14.自旋暗示

15.对象序列化数据过滤

16."栈旅行者"

17.Milling Project Coin(鬼知道该怎么翻译).

Allow @SafeVargs on private instance methods. //允许在私有实例方法上标注@SafeVargs注解

Allow effectively final variables to be used as resources in the try-with-resourcesstatement. //try-with-resource 语法支持实际final的变量

Allow the diamond with anonymous classes if the argument type of the inferred type is denotable.//允许对可推荐出类型的匿名内部类使用钻石符号.

Complete the removal, begun in Java SE 8, of the underscore from the set of legal identifier names.//移除java8中已经开始的,以下划线作为完整标识符名称

Add support for private interface methods.//接口中可定义私有方法.

18.扩大的unicode集

19.孵化官方http client.

二 JAVA10

1.局部变量类型推断

2.统一定义的 GC接口.

3.g1垃圾收集器的并行full gc

4.应用类数据共享

5.thread local 握手

6.扩展unicode语言标签.

三. JAVA11

1.unicode10支持

2.标准化java9中孵化的http客户端

demo:同步式编程

public void get(String uri) throws Exception {

HttpClient client = HttpClient.newHttpClient();
    HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create(uri))
            .build();
    HttpResponse<String> response =
            client.send(request, HttpResponse.BodyHandlers.ofString());

    System.out.println(response.body());
}

demo:响应式编程

public CompletableFuture<String> getCompletableFuture(String uri) {

HttpClient client = HttpClient.newHttpClient();
    HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create(uri))
            .build();

    return client.sendAsync(request, HttpResponse.BodyHandlers.ofString())
            .thenApply(HttpResponse::body);
}

demo:响应式编程-并发

public void testConcurrentRequests(){

HttpClient client = HttpClient.newHttpClient();
    List<String> urls = List.of("http://www.baidu.com","http://www.alibaba.com/","http://www.tencent.com");
    List<HttpRequest> requests = urls.stream()
            .map(url -> HttpRequest.newBuilder(URI.create(url)))
            .map(reqBuilder -> reqBuilder.build())
            .collect(Collectors.toList());

    List<CompletableFuture<HttpResponse<String>>> futures = requests.stream()
            .map(request -> client.sendAsync(request, HttpResponse.BodyHandlers.ofString()))
            .collect(Collectors.toList());
    futures.stream()
            .forEach(e -> e.whenComplete((resp,err) -> {
                if(err != null){
                    err.printStackTrace();
                }else{
                    System.out.println(resp.body());
                    System.out.println(resp.statusCode());
                }
            }));
    CompletableFuture.allOf(futures
            .toArray(CompletableFuture<?>[]::new))
            .join();
}

注：以上代码是分享时从网上转来的，因为此文是从内部wiki粘过来，出处已忘。接下来打算发一篇CompletableFuture有关的文章，最近对响应式编程的兴趣更加深刻了。

3.Collection.toArray(IntFunction) Default 方法

4.编译器线程的懒分配

5.体验版zgc大杀器(缺少类和元数据卸载)

6.Epsilon GC no-op 体验版

7.少代价的堆分析工具jvmti

8.nests, an access-control context ,省去编译器插入accessibility-broadening bridge methods

9.一些属性变事实的只读.java.home, user.home, user.dir, user.name等

10.Reference类不再支持克隆

11.使用classpath进行编译运行时,默认解析的模块策略变更:root模块集在此版本变更为所有可见的导出api的系统模块,唯一可见的改变是java.se模块不在默认解析.

12.SelectableChannel可以在select操作正在进行中注册.

13.DatagramChannel.send Throws AlreadyConnectedException Instead of IllegalArgumentException