JDK 20 新特性详解
JDK 20 于 2023年3月21日 正式发布，是 Java 半年发布节奏的第九个非 LTS 版本。JDK 20 是一个过渡性版本 ，主要继续推进 JDK 19 引入的预览和孵化特性，包括 Virtual Threads（第二次预览） 、Scoped Values（孵化） 、Record Patterns（第二次预览） 、Pattern Matching for switch（第四次预览） 、Foreign Function & Memory API（第二次预览） 和 Structured Concurrency（第二次孵化）。所有特性都在为 JDK 21（下一个 LTS）的最终定稿做准备。
目录
- [Virtual Threads 虚拟线程（第二次预览）](#Virtual Threads 虚拟线程（第二次预览）)
- [Scoped Values 作用域值（孵化）](#Scoped Values 作用域值（孵化）)
- [Record Patterns 记录模式（第二次预览）](#Record Patterns 记录模式（第二次预览）)
- [Pattern Matching for switch（第四次预览）](#Pattern Matching for switch（第四次预览）)
- [Foreign Function & Memory API（第二次预览）](#Foreign Function & Memory API（第二次预览）)
- [Structured Concurrency 结构化并发（第二次孵化）](#Structured Concurrency 结构化并发（第二次孵化）)
- 其他重要变更
- [JDK 20 特性总览表](#JDK 20 特性总览表)
1. Virtual Threads 虚拟线程（第二次预览）
1.1 概述
JEP 436 --- Virtual Threads 在 JDK 19（首次预览）后，JDK 20 进行了第二次预览。主要基于早期反馈进行了改进，但没有重大 API 变更。
1.2 代码案例
java
// ============ 1. 创建虚拟线程 ============
// 方式1：Thread.startVirtualThread()
Thread vthread = Thread.startVirtualThread(() -> {
System.out.println("Hello from virtual thread!");
System.out.println("Is virtual: " + Thread.currentThread().isVirtual());
});
vthread.join();
// 方式2：Thread.ofVirtual()
Thread vthread2 = Thread.ofVirtual()
.name("my-virtual-thread")
.start(() -> {
System.out.println("Virtual thread: " + Thread.currentThread().getName());
});
vthread2.join();
// ============ 2. 虚拟线程执行器 ============
// 创建虚拟线程执行器
try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
// 提交大量任务
IntStream.range(0, 100_000).forEach(i -> {
executor.submit(() -> {
Thread.sleep(Duration.ofMillis(100));
return i;
});
});
}
// ============ 3. 高并发 Web 服务器示例 ============
public class VirtualThreadWebServer {
public static void main(String[] args) throws Exception {
try (ServerSocket serverSocket = new ServerSocket(8080)) {
System.out.println("服务器启动: http://localhost:8080");
try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
while (true) {
Socket clientSocket = serverSocket.accept();
executor.submit(() -> handleClient(clientSocket));
}
}
}
}
static void handleClient(Socket socket) {
try (socket) {
BufferedReader reader = new BufferedReader(
new InputStreamReader(socket.getInputStream()));
PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);
String request = reader.readLine();
System.out.println("收到请求: " + request);
// 模拟处理（虚拟线程中阻塞不会占用平台线程）
Thread.sleep(Duration.ofMillis(100));
writer.println("HTTP/1.1 200 OK");
writer.println("Content-Type: text/plain");
writer.println();
writer.println("Hello from Virtual Thread!");
} catch (Exception e) {
e.printStackTrace();
}
}
}
// ============ 4. 虚拟线程与平台线程对比 ============
public class VirtualThreadComparison {
public static void main(String[] args) throws Exception {
int taskCount = 100_000;
// 平台线程（受限于系统资源）
long start1 = System.currentTimeMillis();
try (ExecutorService platform = Executors.newFixedThreadPool(200)) {
for (int i = 0; i < taskCount; i++) {
platform.submit(() -> Thread.sleep(Duration.ofMillis(10)));
}
}
long platformTime = System.currentTimeMillis() - start1;
// 虚拟线程
long start2 = System.currentTimeMillis();
try (ExecutorService virtual = Executors.newVirtualThreadPerTaskExecutor()) {
for (int i = 0; i < taskCount; i++) {
virtual.submit(() -> Thread.sleep(Duration.ofMillis(10)));
}
}
long virtualTime = System.currentTimeMillis() - start2;
System.out.println("平台线程: " + platformTime + "ms");
System.out.println("虚拟线程: " + virtualTime + "ms");
// 虚拟线程通常快 10-100 倍
}
}
// ============ 5. 虚拟线程与 synchronized ============
// 注意：虚拟线程在 synchronized 块中阻塞时会固定载体线程
// 推荐使用 ReentrantLock 替代
// 不推荐
void badExample() {
Object lock = new Object();
synchronized (lock) {
Thread.sleep(Duration.ofSeconds(1)); // 固定载体线程
}
}
// 推荐
void goodExample() {
ReentrantLock lock = new ReentrantLock();
lock.lock();
try {
Thread.sleep(Duration.ofSeconds(1)); // 不固定载体线程
} finally {
lock.unlock();
}
}
// ============ 6. 编译与运行 ============
// Virtual threads 是预览特性
// javac --enable-preview --release 20 App.java
// java --enable-preview -cp . App2. Scoped Values 作用域值（孵化）
2.1 概述
JEP 429 --- Scoped Values（作用域值）以孵化形式引入，是 ThreadLocal 的现代替代方案。Scoped Values 是不可变的、可以在线程和虚拟线程之间安全共享的值。
核心优势：
- 不可变（线程安全）
- 自动生命周期管理（作用域结束自动清理）
- 比 ThreadLocal 更高效
- 适合虚拟线程场景
2.2 代码案例
java
// ============ 1. 基础用法 ============
import java.lang.ScopedValue;
// 定义 ScopedValue
static final ScopedValue<String> USER = ScopedValue.newInstance();
// 使用 ScopedValue
void handleRequest() {
// 在作用域内绑定值
ScopedValue.where(USER, "Alice")
.run(() -> {
// 在此作用域内可以访问 USER
System.out.println("User: " + USER.get()); // "Alice"
processRequest();
});
}
void processRequest() {
// 可以访问 USER，无需参数传递
System.out.println("Processing for: " + USER.get());
}
// ============ 2. 返回值 ============
static final ScopedValue<Integer> USER_ID = ScopedValue.newInstance();
int processWithReturn() {
return ScopedValue.where(USER_ID, 42)
.call(() -> {
// 可以返回值
return doWork();
});
}
int doWork() {
int userId = USER_ID.get();
return userId * 2;
}
// ============ 3. 多个 ScopedValue ============
static final ScopedValue<String> USER = ScopedValue.newInstance();
static final ScopedValue<String> REQUEST_ID = ScopedValue.newInstance();
static final ScopedValue<Locale> LOCALE = ScopedValue.newInstance();
void handleComplexRequest() {
ScopedValue.where(USER, "Alice")
.where(REQUEST_ID, "req-123")
.where(LOCALE, Locale.CHINA)
.run(() -> {
System.out.println("User: " + USER.get());
System.out.println("Request: " + REQUEST_ID.get());
System.out.println("Locale: " + LOCALE.get());
});
}
// ============ 4. 嵌套作用域 ============
static final ScopedValue<String> LEVEL = ScopedValue.newInstance();
void nestedExample() {
ScopedValue.where(LEVEL, "outer")
.run(() -> {
System.out.println(LEVEL.get()); // "outer"
ScopedValue.where(LEVEL, "inner")
.run(() -> {
System.out.println(LEVEL.get()); // "inner"
});
System.out.println(LEVEL.get()); // "outer"（恢复）
});
}
// ============ 5. 与虚拟线程配合 ============
static final ScopedValue<String> TRACE_ID = ScopedValue.newInstance();
void concurrentProcessing() {
ScopedValue.where(TRACE_ID, "trace-123")
.run(() -> {
try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
// 虚拟线程会继承 ScopedValue
executor.submit(() -> {
System.out.println("Trace ID: " + TRACE_ID.get());
});
}
});
}
// ============ 6. vs ThreadLocal ============
// ThreadLocal（旧方式）
ThreadLocal<String> threadLocal = new ThreadLocal<>();
threadLocal.set("value");
try {
String value = threadLocal.get();
} finally {
threadLocal.remove(); // 必须手动清理
}
// ScopedValue（新方式）
ScopedValue<String> scopedValue = ScopedValue.newInstance();
ScopedValue.where(scopedValue, "value")
.run(() -> {
String value = scopedValue.get();
// 自动清理，无需手动 remove
});
// ============ 7. 实际应用场景 ============
// 7.1 请求上下文传递
public class RequestContext {
static final ScopedValue<String> USER_ID = ScopedValue.newInstance();
static final ScopedValue<String> TRACE_ID = ScopedValue.newInstance();
static final ScopedValue<Locale> LOCALE = ScopedValue.newInstance();
public static void handleRequest(String userId, String traceId, Locale locale, Runnable handler) {
ScopedValue.where(USER_ID, userId)
.where(TRACE_ID, traceId)
.where(LOCALE, locale)
.run(handler);
}
public static String getCurrentUserId() {
return USER_ID.get();
}
public static String getCurrentTraceId() {
return TRACE_ID.get();
}
}
// 使用
RequestContext.handleRequest("user-123", "trace-456", Locale.CHINA, () -> {
System.out.println("User: " + RequestContext.getCurrentUserId());
System.out.println("Trace: " + RequestContext.getCurrentTraceId());
});
// ============ 8. 编译与运行 ============
// Scoped Values 是孵化特性
// javac --add-modules jdk.incubator.concurrent App.java
// java --add-modules jdk.incubator.concurrent App3. Record Patterns 记录模式（第二次预览）
3.1 概述
JEP 432 --- Record Patterns 在 JDK 19（首次预览）后，JDK 20 进行了第二次预览。主要改进了嵌套记录模式的支持。
3.2 代码案例
java
// ============ 1. 基础记录模式 ============
record Point(int x, int y) {}
// 解构记录
void printPoint(Object obj) {
if (obj instanceof Point(int x, int y)) {
System.out.println("x=" + x + ", y=" + y);
}
}
// ============ 2. 嵌套记录模式（JDK 20 改进） ============
record Line(Point start, Point end) {}
record Circle(Point center, double radius) {}
// 嵌套解构
void printShape(Object obj) {
if (obj instanceof Line(Point(var x1, var y1), Point(var x2, var y2))) {
System.out.println("Line: (" + x1 + "," + y1 + ") -> (" + x2 + "," + y2 + ")");
} else if (obj instanceof Circle(Point(var x, var y), var r)) {
System.out.println("Circle: center=(" + x + "," + y + "), radius=" + r);
}
}
// ============ 3. switch 中的记录模式 ============
String describe(Object obj) {
return switch (obj) {
case Point(var x, var y) -> "Point: (" + x + ", " + y + ")";
case Line(Point(var x1, var y1), Point(var x2, var y2)) ->
"Line: (" + x1 + "," + y1 + ") -> (" + x2 + "," + y2 + ")";
case Circle(Point(var x, var y), var r) ->
"Circle: center=(" + x + "," + y + "), radius=" + r;
default -> "Unknown";
};
}
// ============ 4. 带条件的记录模式 ============
String classify(Object obj) {
return switch (obj) {
case Point(var x, var y) when x == 0 && y == 0 -> "原点";
case Point(var x, var y) when x == 0 -> "Y轴上";
case Point(var x, var y) when y == 0 -> "X轴上";
case Point(var x, var y) -> "普通点: (" + x + ", " + y + ")";
default -> "未知";
};
}
// ============ 5. 复杂嵌套 ============
record Rectangle(Point topLeft, Point bottomRight) {}
record Triangle(Point p1, Point p2, Point p3) {}
double calculateArea(Object shape) {
return switch (shape) {
case Rectangle(Point(var x1, var y1), Point(var x2, var y2)) ->
Math.abs((x2 - x1) * (y2 - y1));
case Triangle(Point(var x1, var y1), Point(var x2, var y2), Point(var x3, var y3)) -> {
double area = Math.abs((x1 * (y2 - y3) + x2 * (y3 - y1) + x3 * (y1 - y2)) / 2.0);
yield area;
}
default -> 0.0;
};
}
// ============ 6. 实际应用场景 ============
// 6.1 JSON 处理
sealed interface JsonValue permits JsonString, JsonNumber, JsonBoolean, JsonNull, JsonArray, JsonObject {
}
record JsonString(String value) implements JsonValue {}
record JsonNumber(double value) implements JsonValue {}
record JsonBoolean(boolean value) implements JsonValue {}
record JsonNull() implements JsonValue {}
record JsonArray(List<JsonValue> elements) implements JsonValue {}
record JsonObject(Map<String, JsonValue> properties) implements JsonValue {}
String renderJson(JsonValue value) {
return switch (value) {
case JsonString(var s) -> "\"" + s + "\"";
case JsonNumber(var n) -> String.valueOf(n);
case JsonBoolean(var b) -> String.valueOf(b);
case JsonNull() -> "null";
case JsonArray(var elements) ->
"[" + elements.stream()
.map(this::renderJson)
.collect(Collectors.joining(", ")) + "]";
case JsonObject(var properties) ->
"{" + properties.entrySet().stream()
.map(e -> "\"" + e.getKey() + "\": " + renderJson(e.getValue()))
.collect(Collectors.joining(", ")) + "}";
};
}
// 6.2 领域建模
record Order(Long id, Customer customer, List<OrderItem> items, OrderStatus status) {}
record Customer(String name, String email) {}
record OrderItem(String product, int quantity, BigDecimal price) {}
enum OrderStatus { PENDING, PAID, SHIPPED, DELIVERED, CANCELLED }
String summarizeOrder(Order order) {
return switch (order) {
case Order(var id, Customer(var name, var email), var items, var status) ->
String.format("订单 #%d: 客户 %s (%s), %d 件商品, 状态: %s",
id, name, email, items.size(), status);
};
}
// ============ 7. 编译与运行 ============
// Record patterns 是预览特性
// javac --enable-preview --release 20 App.java
// java --enable-preview -cp . App4. Pattern Matching for switch（第四次预览）
4.1 概述
JEP 433 --- Pattern Matching for switch 在 JDK 17（首次预览）、JDK 18（第二次预览）、JDK 19（第三次预览）后，JDK 20 进行了第四次预览。主要改进了与记录模式的交互。
4.2 代码案例
java
// ============ 1. 基础 switch 模式匹配 ============
static String format(Object obj) {
return switch (obj) {
case Integer i -> "整数: " + i;
case String s -> "字符串: " + s.toUpperCase();
case List<?> list -> "列表大小: " + list.size();
case null -> "null";
default -> "未知: " + obj;
};
}
// ============ 2. 带 when 条件 ============
static String classify(Object obj) {
return switch (obj) {
case Integer i when i > 0 -> "正整数: " + i;
case Integer i when i == 0 -> "零";
case Integer i -> "负整数: " + i;
case String s when s.isEmpty() -> "空字符串";
case String s -> "字符串: " + s;
case null -> "null";
default -> "其他";
};
}
// ============ 3. 与记录模式配合 ============
record Point(int x, int y) {}
record Line(Point start, Point end) {}
static String describe(Object obj) {
return switch (obj) {
case Point(var x, var y) -> "Point: (" + x + ", " + y + ")";
case Line(Point(var x1, var y1), Point(var x2, var y2)) ->
"Line: (" + x1 + "," + y1 + ") -> (" + x2 + "," + y2 + ")";
case null -> "null";
default -> "Unknown";
};
}
// ============ 4. 实际应用场景 ============
// 命令处理
sealed interface Command permits StartCommand, StopCommand, StatusCommand, UnknownCommand {
void execute();
}
record StartCommand(String serviceName) implements Command {
@Override
public void execute() { System.out.println("启动: " + serviceName); }
}
record StopCommand(String serviceName) implements Command {
@Override
public void execute() { System.out.println("停止: " + serviceName); }
}
record StatusCommand() implements Command {
@Override
public void execute() { System.out.println("状态查询"); }
}
record UnknownCommand(String input) implements Command {
@Override
public void execute() { System.out.println("未知: " + input); }
}
static void processCommand(Command cmd) {
switch (cmd) {
case StartCommand(var name) when name.isEmpty() ->
System.out.println("服务名不能为空");
case StartCommand(var name) ->
System.out.println("启动服务: " + name);
case StopCommand(var name) when name.isEmpty() ->
System.out.println("服务名不能为空");
case StopCommand(var name) ->
System.out.println("停止服务: " + name);
case StatusCommand s ->
System.out.println("查询所有服务状态");
case UnknownCommand(var input) ->
System.out.println("未知命令: " + input);
}
}
// ============ 5. 编译与运行 ============
// Pattern matching for switch 是预览特性
// javac --enable-preview --release 20 App.java
// java --enable-preview -cp . App5. Foreign Function & Memory API（第二次预览）
5.1 概述
JEP 434 --- Foreign Function & Memory API 在 JDK 19（首次预览）后，JDK 20 进行了第二次预览。主要改进了 API 的稳定性和性能。
5.2 代码案例
java
// ============ 1. 调用 C 标准库函数 ============
import java.lang.invoke.*;
import jdk.incubator.foreign.*;
import static jdk.incubator.foreign.ValueLayout.*;
Linker linker = Linker.nativeLinker();
SymbolLookup stdlib = linker.defaultLookup();
// 查找 strlen 函数
MethodHandle strlen = linker.downcallHandle(
stdlib.lookup("strlen").orElseThrow(),
FunctionDescriptor.of(JAVA_LONG, ADDRESS)
);
// 调用
try (MemorySegment str = SegmentAllocator.implicitAllocating().allocateUtf8String("Hello")) {
long length = (long) strlen.invoke(str);
System.out.println("长度: " + length); // 5
}
// ============ 2. 操作堆外内存 ============
try (MemorySegment segment = MemorySegment.allocateNative(1024)) {
MemoryAddress base = segment.baseAddress();
VarHandle intHandle = JAVA_INT.varHandle();
intHandle.set(base, 0L, 42);
int value = (int) intHandle.get(base, 0L);
System.out.println("值: " + value); // 42
}
// ============ 3. 结构体布局 ============
MemoryLayout pointLayout = MemoryLayout.structLayout(
JAVA_INT.withName("x"),
JAVA_INT.withName("y")
);
try (MemorySegment segment = MemorySegment.allocateNative(pointLayout)) {
VarHandle xHandle = pointLayout.varHandle(MemoryLayout.PathElement.groupElement("x"));
VarHandle yHandle = pointLayout.varHandle(MemoryLayout.PathElement.groupElement("y"));
MemoryAddress base = segment.baseAddress();
xHandle.set(base, 0L, 10);
yHandle.set(base, 0L, 20);
System.out.println("x = " + xHandle.get(base, 0L)); // 10
System.out.println("y = " + yHandle.get(base, 0L)); // 20
}
// ============ 4. 编译与运行 ============
// 孵化 API 需要额外参数
// javac --add-modules jdk.incubator.foreign App.java
// java --add-modules jdk.incubator.foreign App6. Structured Concurrency 结构化并发（第二次孵化）
6.1 概述
JEP 437 --- Structured Concurrency（结构化并发）在 JDK 19（首次孵化）后，JDK 20 进行了第二次孵化。主要改进了 API 的稳定性和性能。
6.2 代码案例
java
// ============ 1. 基础结构化并发 ============
import java.util.concurrent.*;
// 传统方式
void traditionalApproach() throws Exception {
ExecutorService executor = Executors.newFixedThreadPool(2);
try {
Future<String> userFuture = executor.submit(() -> fetchUser());
Future<List<Order>> ordersFuture = executor.submit(() -> fetchOrders());
String user = userFuture.get();
List<Order> orders = ordersFuture.get();
} finally {
executor.shutdown();
}
}
// 结构化并发
void structuredApproach() throws Exception {
try (var scope = new StructuredTaskScope<Object>()) {
Subtask<String> userTask = scope.fork(() -> fetchUser());
Subtask<List<Order>> ordersTask = scope.fork(() -> fetchOrders());
scope.join();
String user = (String) userTask.get();
List<Order> orders = (List<Order>) ordersTask.get();
}
}
// ============ 2. 错误处理 ============
void structuredErrorHandling() {
try (var scope = new StructuredTaskScope<Object>()) {
Subtask<String> task1 = scope.fork(() -> riskyOperation1());
Subtask<String> task2 = scope.fork(() -> riskyOperation2());
scope.join();
String result1 = (String) task1.get();
String result2 = (String) task2.get();
} catch (Exception e) {
// scope 关闭时自动取消所有未完成的任务
System.out.println("错误: " + e.getMessage());
}
}
// ============ 3. 超时控制 ============
void withTimeout() throws Exception {
try (var scope = new StructuredTaskScope<Object>()) {
Subtask<String> task1 = scope.fork(() -> slowOperation1());
Subtask<String> task2 = scope.fork(() -> slowOperation2());
scope.joinUntil(Instant.now().plusSeconds(5));
if (task1.state() == Subtask.State.SUCCESS) {
String result = (String) task1.get();
}
}
}
// ============ 4. 实际应用场景 ============
// 4.1 并发数据获取
class UserProfile {
String name;
List<Order> orders;
List<Notification> notifications;
}
UserProfile loadUserProfile(Long userId) throws Exception {
try (var scope = new StructuredTaskScope<Object>()) {
Subtask<String> nameTask = scope.fork(() -> fetchUserName(userId));
Subtask<List<Order>> ordersTask = scope.fork(() -> fetchOrders(userId));
Subtask<List<Notification>> notificationsTask = scope.fork(() -> fetchNotifications(userId));
scope.join();
UserProfile profile = new UserProfile();
profile.name = (String) nameTask.get();
profile.orders = (List<Order>) ordersTask.get();
profile.notifications = (List<Notification>) notificationsTask.get();
return profile;
}
}
// 4.2 竞速模式
String race() throws Exception {
try (var scope = new StructuredTaskScope<String>()) {
Subtask<String> task1 = scope.fork(() -> queryServer1());
Subtask<String> task2 = scope.fork(() -> queryServer2());
Subtask<String> task3 = scope.fork(() -> queryServer3());
scope.joinUntil(Instant.now().plusSeconds(5));
if (task1.state() == Subtask.State.SUCCESS) {
return task1.get();
} else if (task2.state() == Subtask.State.SUCCESS) {
return task2.get();
} else if (task3.state() == Subtask.State.SUCCESS) {
return task3.get();
}
throw new TimeoutException("All tasks failed");
}
}
// ============ 5. 编译与运行 ============
// Structured Concurrency 是孵化特性
// javac --add-modules jdk.incubator.concurrent App.java
// java --add-modules jdk.incubator.concurrent App7. 其他重要变更
7.1 其他改进
java
// ============ 1. 性能改进 ============
// 1. G1 GC 改进
// - 更好的并行标记
// - 改进的内存回收
// 2. ZGC 改进
// - 更低的暂停时间
// - 更好的内存归还
// ============ 2. 安全改进 ============
// 1. 改进了 TLS 1.3 实现
// 2. 增强了证书路径验证
// 3. 改进了 PKCS#12 密钥库处理
// ============ 3. 国际化 ============
// 升级到 Unicode 15.0
// 改进了 CLDR 数据8. JDK 20 特性总览表
| 序号 | 特性 | JEP | 类型 | 重要性 |
|---|---|---|---|---|
| 1 | Virtual Threads 虚拟线程（第二次预览） | JEP 436 | 并发 | ★★★★★ |
| 2 | Scoped Values 作用域值（孵化） | JEP 429 | 并发 | ★★★★☆ |
| 3 | Record Patterns 记录模式（第二次预览） | JEP 432 | 语言 | ★★★★★ |
| 4 | Pattern Matching for switch（第四次预览） | JEP 433 | 语言 | ★★★★☆ |
| 5 | Foreign Function & Memory API（第二次预览） | JEP 434 | API | ★★★★☆ |
| 6 | Structured Concurrency 结构化并发（第二次孵化） | JEP 437 | 并发 | ★★★★★ |
附录：预览特性状态追踪
| 特性 | JDK 12-16 | JDK 17 | JDK 18 | JDK 19 | JDK 20 | JDK 21 |
|---|---|---|---|---|---|---|
| Pattern Matching switch | 预览 | 预览 | 第二次预览 | 第三次预览 | 第四次预览 | 正式 |
| Record Patterns | --- | --- | --- | 预览 | 第二次预览 | 正式 |
| Virtual Threads | --- | --- | --- | 预览 | 第二次预览 | 正式 |
| Structured Concurrency | --- | --- | --- | 孵化 | 第二次孵化 | 孵化 |
| Scoped Values | --- | --- | --- | --- | 孵化 | 孵化 |
总结 ：JDK 20 是一个过渡性版本，主要继续推进 JDK 19 引入的预览和孵化特性。Virtual Threads 和 Structured Concurrency 共同构成了 Java 并发编程的未来方向；Record Patterns 让模式匹配更加强大；Scoped Values 为 ThreadLocal 提供了现代替代方案。所有特性都在为 JDK 21（下一个 LTS）的最终定稿做准备。JDK 20 虽然是非 LTS 版本，但其引入的虚拟线程和结构化并发特性将对 Java 生态系统产生深远影响。