Java 18 新特性 (EOL)

warning

生命周期结束时间(EOL)： 2023/03/16

官方发布介绍页面：https://openjdk.org/projects/jdk/18/

1. 简单的 Web 服务器

JDK 18 引入了一个简单的 Web 服务器，适用于测试、开发和调试。

import com.sun.net.httpserver.HttpServer;
import java.io.IOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;

public class SimpleWebServer {
    public static void main(String[] args) throws IOException {
        HttpServer server = HttpServer.create(new InetSocketAddress(8000), 0);
        server.createContext("/test", exchange -> {
            String response = "Hello, World!";
            exchange.sendResponseHeaders(200, response.getBytes().length);
            try (OutputStream os = exchange.getResponseBody()) {
                os.write(response.getBytes());
            }
        });
        server.setExecutor(null);
        server.start();
    }
}

2. UTF-8 作为默认字符集

JDK 18 将 UTF-8 设置为默认字符集。

import java.nio.charset.Charset;

public class DefaultCharset {
    public static void main(String[] args) {
        System.out.println(Charset.defaultCharset()); // UTF-8
    }
}

3. Javadoc中新增@snippet标签

JDK 18 支持在 Java API 文档中使用代码片段。

/**
 * This is a sample method.
 * {@snippet :
 * System.out.println("Hello, World!");
 * }
 */
public void sampleMethod() {
    System.out.println("Hello, World!");
}

4. Vector API (第三次孵化器)

引入了 Vector API，允许在 Java 中进行矢量计算。

import jdk.incubator.vector.*;

public class VectorExample {
    public static void main(String[] args) {
        VectorSpecies<Integer> SPECIES = IntVector.SPECIES_256;
        int[] a = {1, 2, 3, 4, 5, 6, 7, 8};
        IntVector va = IntVector.fromArray(SPECIES, a, 0);
        IntVector vb = va.add(1);
        vb.intoArray(a, 0);
        for (int i : a) {
            System.out.println(i); // 2, 3, 4, 5, 6, 7, 8, 9
        }
    }
}

5. Finalization 被标记为即将移除

JDK 18 标记了对象终结机制 (finalization) 为即将移除。

7. Internet 地址解析 SPI

引入了 Internet-Address Resolution SPI，允许自定义主机名解析。

import java.net.InetAddress;
import java.net.spi.InetAddressResolver;
import java.net.spi.InetAddressResolverProvider;
import java.util.List;

public class CustomInetAddressResolverProvider extends InetAddressResolverProvider {
    @Override
    public InetAddressResolver get(InetAddressResolverProvider.Configuration configuration) {
        return new CustomInetAddressResolver();
    }

    private static class CustomInetAddressResolver implements InetAddressResolver {
        @Override
        public List<InetAddress> lookupByName(String host, LookupPolicy lookupPolicy) {
            // Custom host name resolution logic
            return List.of();
        }

        @Override
        public String lookupByAddress(byte[] addr) {
            // Custom address resolution logic
            return null;
        }
    }
}

8. 外部函数和内存API（第二次孵化）

引入了外部函数和内存 API，允许 Java 程序调用本地代码和访问外部内存。

import jdk.incubator.foreign.*;

public class ForeignMemoryAccess {
    public static void main(String[] args) {
        try (MemorySegment segment = MemorySegment.allocateNative(100)) {
            MemoryAccess.setIntAtOffset(segment, 0, 42);
            int value = MemoryAccess.getIntAtOffset(segment, 0);
            System.out.println(value); // 42
        }
    }
}

9. Applet API 被标记为即将移除

Applet API 被标记为即将移除。