Java SE 11 新增特性
Java SE 11 新增特性
作者：Grey
原文地址：Java SE 11 新增特性
源码
镜像仓库: GitCode：java_new_features
Lambda 类型推断
JDK 10引入了局部变量类型推理（ JEP 286 ）。这简化了代码，因为你不再需要明确说明局部变量的类型，而是可以使用 var 。 JEP 323 将这种语法的使用扩展到Lambda表达式的参数。这里有一个简单的例子。
<pre class="prettyprint hljs swift" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">package git.snippets.jdk11; import java.util.HashMap; import java.util.Map; /** * lambda类型推断 * * @author <a href="mailto:410486047@qq.com">Grey</a> * @date 2021/11/29 * @since 11 */ public class LambdaInfer { public static void main(String[] args) { Map<String, Integer> map = new HashMap<>(2); map.put("hello", 1); map.put("world", 2); map.forEach((var s, var i) -> System.out.println(s + " " + i)); } }</pre>
单命令行运行Java
原先需要 javac ,然后 java
<pre class="hljs nginx" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 0.75em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">javac Hello.java && java Hello</pre>
现在合成一个 java 命令搞定
<pre class="hljs nginx" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 0.75em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">java Hello.java</pre>
同样的
<pre class="hljs gradle" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 0.75em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">java -classpath /home/foo/java Hello.java Bonjour</pre>
等同于如下两条
<pre class="prettyprint hljs groovy" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">javac -classpath /home/foo/java Hello.java java -classpath /home/foo/java Hello Bonjour</pre>
该JEP还提供“shebang”支持。为了减少在命令行上提及 Java 启动器的需要，包含在源文件的第一行。例如：
<pre class="hljs php" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 0.75em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"># !/usr/bin/java --source 11
public class HelloWorld {
...
}</pre>注： --source 11 是必要的，指定了 JDK 的版本。
HTTP 客户端
JDK 9 引入了一个新的 API 来提供支持 HTTP 客户端协议，该API被作为孵化器模块包含在内。孵化器模块旨在提供新的 API，而不会使它们成为Java SE标准的一部分。开发人员可以试用 API 并提供反馈。
HTTP Client API 现在是Java SE 11标准的一部分。JDK 引入了一个新的模块和包: java.net.http 。该 API 可以同步或异步使用。
示例代码如下
<pre class="prettyprint hljs swift" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">package git.snippets.jdk11; import java.io.IOException; import java.net.URI; import java.net.http.HttpClient; import java.net.http.HttpRequest; import java.net.http.HttpResponse; /** * jdk9 中httpclient还在jdk.incubator.httpclient模块中 * * @author <a href="mailto:410486047@qq.com">Grey</a> * @date 2021/11/29 * @since 11 */ public class HttpClientTest { public static void main(String[] args) throws IOException, InterruptedException { HttpClient client = HttpClient.newHttpClient(); URI uri = URI.create("http://httpbin.org/get"); HttpRequest req = HttpRequest.newBuilder(uri).header("accept", "application/json").GET().build(); HttpResponse<String> resp = client.send(req, HttpResponse.BodyHandlers.ofString()); String body = resp.body(); System.out.println(body); } }</pre>
执行后控制台输出
<pre class="prettyprint hljs json" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">{
"args": {},
"headers": {
"Accept": "application/json",
"Content-Length": "0",
"Host": "httpbin.org",
"Http2-Settings": "AAEAAEAAAAIAAAABAAMAAABkAAQBAAAAAAUAAEAA",
"Upgrade": "h2c",
"User-Agent": "Java-http-client/18.0.1",
"X-Amzn-Trace-Id": "Root=1-62fddb2a-7813af3246da12d203c31825"
},
"origin": "211.136.194.3",
"url": "http://httpbin.org/get"
}</pre>移除 Java EE 和 CORBA 模块
随着 JDK 9 中 JPMS 的引入，可以将整体式 rt.jar 文件划分为多个模块。JPMS 的另一个优点是，现在可以创建一个仅包含应用程序所需模块的 Java 运行时，从而大大减小了依赖包的大小。通过明确定义的模块边界，现在可以更轻松地删除 Java API 中过时的部分。
java.se.ee 元模块包括六个模块，这些模块将不再是 Java SE 11 标准的一部分，也不再包含在 JDK 中。受影响的模块包括：
corbatransactionactivationxml.bindxml.wsxml.ws.annotation
自 JDK 9 以来，这些模块已被弃用，并且默认情况下未包含在编译或运行时中。如果您尝试编译或运行一个应用程序，该应用程序在 JDK 9 或 JDK 10 上使用这些模块中的 API 的时候会报错。如果在代码中使用这些模块中的 API，则需要将它们作为单独的模块或库提供。
jdeprscan
JDK提供了 jdeprscan 来检查你的代码是否使用了deprecated的方法.
JDK 10 到 JDK 11 所有涉及调整的API清单
举几个例子， String 类中增加了很多有用的 API。
<pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">package git.snippets.jdk11; /** * String 新增API * * @author <a href="mailto:410486047@qq.com">Grey</a> * @date 2021/11/29 * @see String * @since 11 */ public class StringNewAPI { public static void main(String[] args) { isBlankTest(); linesTest(); repeatTest(); stripTest(); } // 按行打印 private static void linesTest() { String abcd = "\na\nb\tc\td"; abcd.lines().forEach(System.out::println); } // String.isBlank() private static void isBlankTest() { String blank = " "; System.out.println(blank.isBlank()); } static void repeatTest() { String repeat = "abcd"; // repeat(n) 表示复制几次 String repeat3 = repeat.repeat(3); System.out.println(repeat3); } //trim 只能去除半角空格，而 strip 是去除各种空白符。 static void stripTest() { String a = " bbbd a "; String b = a.strip(); System.out.println(b); System.out.println(a); String strip = " 我是 "; // 去前面空白字符，如全角空格，TAB System.out.println("==" + strip.stripLeading() + "=="); // 去后面空白字符，如全角空格，TAB System.out.println("==" + strip.stripTrailing() + "=="); } }</pre>
File 中增加了一些 API，比如 Files.writeString 和 Files.readString
<pre class="prettyprint hljs java" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">package git.snippets.jdk11; import java.io.IOException; import java.nio.file.Files; import java.nio.file.Path; /** * File增强API * * @author <a href="mailto:410486047@qq.com">Grey</a> * @date 2021/11/29 * @since */ public class FileNewAPI { public static void main(String[] args) throws IOException { testFile(); } static void testFile() throws IOException { // 创建临时文件 Path path = Files.writeString(Files.createTempFile("test", ".txt"), "hello world,你好，世界"); System.out.println(path); // 读取文件 // String ss = Files.readString(Path.of("file.json")); String s = Files.readString(path); System.out.println(s); } }</pre>
Optional 和 Predicate 相关 API 增强
<pre class="prettyprint hljs swift" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">package git.snippets.jdk11; import java.util.Arrays; import java.util.List; import java.util.Objects; import java.util.Optional; import java.util.function.Predicate; import java.util.stream.Collectors; /** * Optional用法 * * @author <a href="mailto:410486047@qq.com">Grey</a> * @date 2021/11/19 * @since 11 */ public class OptionalAndPredicateTest { public static void main(String[] args) { Optional<String> helloOptional = Optional.of("Hello"); Optional<String> emptyOptional = Optional.empty(); helloOptional.ifPresent(s -> System.out.println(s.length())); emptyOptional.ifPresent(s -> System.out.println(s.length())); List<String> lines = Arrays.asList("a", " ", "", null, "b"); List<String> ans = lines.stream().filter(Objects::nonNull).filter(Predicate.not(String::isBlank)).collect(Collectors.toList()); System.out.println(ans); } }</pre>#Java##Java开发##Java工程师##java#
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