首先我们必须承认，Java 8 是一个里程碑式的版本，这个相信大多数Java程序员都认同，其中最知名的是 Streams & Lambda ，这让 Functional Programming 成为可能，让 Java 换发新的活力。这也是即便 Oracle 不在支持 Java 8 的更新，各个云厂商还是积极支持，站点为 https://adoptopenjdk.net/ ，可以让 Java 8 能继续保留非常长的时间。

var 关键字(局部变量类型推导) Local-Variable Type Inference

---

Map<String, List<Map<String,Object>>>  store = new ConcurrentHashMap<String, List<Map<String,Object>>>();
        Map<String, List<Map<String,Object>>>  store = new ConcurrentHashMap<>();
        Map<String, List<Map<String,Object>>>  store = new ConcurrentHashMap<String, List<Map<String,Object>>>();
  //lambda
  BiFunction<String, String, String> function1 = (var s1, var s2) -> s1 + s2;
        System.out.println(function1.apply(text1, text2));

sudo cp bin/confd /usr/local/bin
confd

ProcessHandle

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ProcessHandle ph =  ProcessHandle.of(89810).get();
System.out.println(ph.info());

Collection factory methods

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Set<Integer> ints = Set.of(1, 2, 3);
List<String> strings = List.of("first", "second");

String 类的新 API

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HTTP 2支持

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 HttpClient client = HttpClient.newHttpClient();
        HttpRequest req =
                HttpRequest.newBuilder(URI.create("https://httpbin.org/ip"))
                        .header("User-Agent", "Java")
                        .GET()
                        .build();
        HttpResponse<String> resp = client.send(req, HttpResponse.BodyHandlers.ofString());
        System.out.println(resp.body());

Text Block(JDK 13)

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String jsonText = "{\"id\": 1, \"nick\": \"leijuan\"}";

//language=json
  String cleanJsonText = """
        {"id": 1, "nick": "leijuan"}""";

    //language=html
    String textBlock = """
    <span >Hello %s</span>""";
    System.out.println(textBlock.formatted(nick));

Switch 提升

---

  //legacy
    switch (DayOfWeek.FRIDAY) {
        case MONDAY: {
            System.out.println(1);
            break;
        }
        case WEDNESDAY: {
            System.out.println(2);
            break;
        }
        default: {
            System.out.println("Unknown");
        }
    }
    //Arrow labels
    switch (DayOfWeek.FRIDAY) {
        case MONDAY, FRIDAY, SUNDAY -> System.out.println(6);
        case TUESDAY -> System.out.println(7);
        case THURSDAY, SATURDAY -> System.out.println(8);
        case WEDNESDAY -> System.out.println(9);
    }

    //Yielding a value
    int i2 = switch (DayOfWeek.FRIDAY) {
        case MONDAY, FRIDAY, SUNDAY -> 6;
        case TUESDAY -> 7;
        case THURSDAY, SATURDAY -> 8;
        case WEDNESDAY -> 9;
        default -> {
            yield 10;
        }
    };

---

<dependency>
            <groupId>com.github.bsideup.jabel</groupId>
            <artifactId>jabel-javac-plugin</artifactId>
            <version>0.2.0</version>
 </dependency>

然后调整一下 maven 的 compiler plugin，将 source 设置为你想要的 Java 版本，如 13 ， target 和 release 设置为 8 就可以啦。  IntelliJ IDEA 会自动识别，也不需要调整。

<plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>13</source>
                    <target>8</target>
                    <release>8</release>
                </configuration>
</plugin>

这样你就可以愉快地使用介绍的特性啦。

总结

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参考

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雷卷，阿里巴巴资深技术专家，GitHub ID @linux-china。

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