引言
Java 17作为Java 17 LTS（长期支持）版本，带来了许多重要的新特性和改进。作为Java开发者，了解和掌握这些新特性对于提升开发效率、优化代码质量和改善应用性能至关重要。本文将深入解析Java 17的三大核心特性：Record类、模式匹配（Pattern Matching）和虚拟线程（Virtual Threads），并通过实际代码示例展示如何在项目中应用这些新特性。
Java 17 核心特性概述
Java 17是在2021年9月发布的长期支持版本，它延续了Java 11和Java 14中的许多重要特性，并在此基础上进行了进一步的完善和优化。与之前的版本相比，Java 17在语言特性、并发编程、性能优化等方面都有显著的提升。
特性亮点
- Record类：简化数据类的创建，减少样板代码
- 模式匹配：提升代码可读性和维护性
- 虚拟线程：优化并发编程体验
- 密封类：增强类型安全和封装性
Record类：简化数据对象创建
什么是Record类
Record类是Java 17中引入的一个新的类类型，它专门用于创建不可变的数据载体类。Record类的设计理念是"数据类"，它自动生成构造函数、getter方法、equals()、hashCode()和toString()等方法，大大减少了样板代码的编写。
Record类的基本语法
// 传统方式创建数据类
public class Person {
private final String name;
private final int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String name() {
return name;
}
public int age() {
return age;
}
@Override
public boolean equals(Object obj) {
// ... 实现
}
@Override
public int hashCode() {
// ... 实现
}
@Override
public String toString() {
// ... 实现
}
}
// 使用Record类的简化方式
public record Person(String name, int age) {
// Record类自动提供所有必需的方法
}
Record类的特性详解
1. 自动实现方法
public record Point(int x, int y) {
// Record类自动提供：
// 1. 所有参数的构造函数
// 2. 所有参数的getter方法
// 3. equals()方法
// 4. hashCode()方法
// 5. toString()方法
}
// 使用示例
public class RecordExample {
public static void main(String[] args) {
Point point1 = new Point(10, 20);
Point point2 = new Point(10, 20);
System.out.println(point1); // Point[x=10, y=20]
System.out.println(point1.equals(point2)); // true
System.out.println(point1.hashCode()); // 123456
}
}
2. 隐式修饰符
public record Student(String name, int age, String email) {
// 所有字段都是public final的
// 所有参数都是public的
// 构造函数是public的
// 所有方法都是public的
// 可以添加自定义方法
public String getFullName() {
return name.toUpperCase();
}
// 可以添加静态方法
public static Student createDefault() {
return new Student("Unknown", 0, "unknown@example.com");
}
}
3. 构造函数和验证
public record BankAccount(String accountNumber, double balance) {
// 验证构造函数
public BankAccount {
if (accountNumber == null || accountNumber.isEmpty()) {
throw new IllegalArgumentException("Account number cannot be null or empty");
}
if (balance < 0) {
throw new IllegalArgumentException("Balance cannot be negative");
}
}
// 可以有多个构造函数
public BankAccount(String accountNumber) {
this(accountNumber, 0.0);
}
// 可以添加自定义方法
public BankAccount deposit(double amount) {
return new BankAccount(accountNumber, balance + amount);
}
public BankAccount withdraw(double amount) {
if (balance < amount) {
throw new IllegalArgumentException("Insufficient funds");
}
return new BankAccount(accountNumber, balance - amount);
}
}
Record类的高级应用
1. 嵌套Record类
public record Address(String street, String city, String zipCode) {
public record Coordinates(double latitude, double longitude) {
public double distanceTo(Coordinates other) {
// 计算距离的复杂逻辑
return 0.0;
}
}
}
public record PersonWithAddress(String name, Address address) {
public String getCity() {
return address.city();
}
}
2. Record类与接口
public interface Shape {
double area();
double perimeter();
}
public record Rectangle(double width, double height) implements Shape {
@Override
public double area() {
return width * height;
}
@Override
public double perimeter() {
return 2 * (width + height);
}
}
Record类的最佳实践
1. 适用场景
// 适合使用Record的场景
public record Coordinates(double lat, double lon) {
// 简单的数据载体
}
public record ApiResponse<T>(boolean success, T data, String message) {
// 泛型数据载体
}
// 不适合使用Record的场景
public record ComplexBusinessObject(String name, int age) {
// 如果需要复杂的业务逻辑，不建议使用Record
public void validate() {
// 复杂的验证逻辑
}
public void process() {
// 复杂的处理逻辑
}
}
2. 性能考虑
// Record类的性能优势
public class PerformanceComparison {
// 传统方式
public static class TraditionalPerson {
private final String name;
private final int age;
public TraditionalPerson(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() { return name; }
public int getAge() { return age; }
}
// Record方式
public record RecordPerson(String name, int age) {}
// 性能测试代码
public static void performanceTest() {
long start = System.nanoTime();
for (int i = 0; i < 1000000; i++) {
var person = new RecordPerson("John", 30);
// 使用person对象
}
long end = System.nanoTime();
System.out.println("Record time: " + (end - start) + " ns");
}
}
模式匹配（Pattern Matching）：提升代码可读性
模式匹配概述
模式匹配是Java 17中引入的重要语言特性，它允许开发者在类型检查和转换时使用更简洁的语法。模式匹配主要体现在switch表达式和instanceof操作符的改进上。
instanceof操作符的模式匹配
1. 基本语法
// 传统方式
public class InstanceOfExample {
public static String processObject(Object obj) {
if (obj instanceof String) {
String str = (String) obj; // 强制类型转换
return str.toUpperCase();
}
return "Not a string";
}
// 模式匹配方式
public static String processObjectWithPattern(Object obj) {
if (obj instanceof String str) { // 模式匹配
return str.toUpperCase();
}
return "Not a string";
}
}
2. 复杂模式匹配
public class ComplexPatternMatching {
public static String processShape(Object shape) {
return switch (shape) {
case Circle c when c.radius() > 10 -> "Large circle";
case Rectangle r when r.width() > r.height() -> "Wide rectangle";
case Square s when s.side() > 5 -> "Large square";
case null -> "Null shape";
case Shape s -> "Other shape";
default -> "Unknown shape";
};
}
// 嵌套模式匹配
public static String processNested(Object obj) {
if (obj instanceof List<?> list && !list.isEmpty()) {
Object first = list.get(0);
if (first instanceof String str && str.length() > 10) {
return str.substring(0, 10);
}
}
return "Not matching";
}
}
switch表达式的模式匹配
1. 基本用法
public class SwitchPatternExample {
public static String processValue(Object value) {
return switch (value) {
case Integer i when i > 100 -> "Large integer";
case Integer i -> "Small integer";
case String s when s.length() > 10 -> "Long string";
case String s -> "Short string";
case Double d when d > 1000.0 -> "Large double";
case Double d -> "Small double";
case null -> "Null value";
default -> "Unknown type";
};
}
// 处理枚举类型
public enum Status {
ACTIVE, INACTIVE, PENDING, SUSPENDED
}
public static String getStatusMessage(Status status) {
return switch (status) {
case ACTIVE -> "User is active";
case INACTIVE -> "User is inactive";
case PENDING -> "User is pending approval";
case SUSPENDED -> "User is suspended";
};
}
}
2. 复杂对象的模式匹配
public class ComplexSwitchPattern {
public static class Person {
private final String name;
private final int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String name() { return name; }
public int age() { return age; }
}
public static class Employee extends Person {
private final String department;
private final double salary;
public Employee(String name, int age, String department, double salary) {
super(name, age);
this.department = department;
this.salary = salary;
}
public String department() { return department; }
public double salary() { return salary; }
}
public static String processPerson(Object person) {
return switch (person) {
case Person p when p.age() >= 18 -> "Adult: " + p.name();
case Employee e when e.salary() > 50000 -> "High salary employee: " + e.name();
case Employee e -> "Employee: " + e.name();
case null -> "Null person";
default -> "Unknown person type";
};
}
}
模式匹配的最佳实践
1. 性能优化
public class PatternMatchingPerformance {
// 传统方式
public static String processStringTraditional(Object obj) {
if (obj instanceof String) {
String str = (String) obj;
return str.length() > 10 ? str.substring(0, 10) : str;
}
return "";
}
// 模式匹配方式
public static String processStringPattern(Object obj) {
if (obj instanceof String str) {
return str.length() > 10 ? str.substring(0, 10) : str;
}
return "";
}
// 多层模式匹配
public static String processComplex(Object obj) {
return switch (obj) {
case String s when s.length() > 100 -> s.substring(0, 100);
case String s -> s;
case Integer i when i > 1000 -> "Large number";
case Integer i -> "Small number";
case List<?> list when list.size() > 10 -> "Large list";
case List<?> list -> "Small list";
default -> "Unknown";
};
}
}
2. 错误处理
public class PatternMatchingErrorHandling {
public static String safeProcess(Object obj) {
try {
return switch (obj) {
case String s -> s.trim();
case Number n -> String.valueOf(n.doubleValue());
case List<?> list -> list.toString();
case null -> "Null value";
default -> "Unknown type";
};
} catch (Exception e) {
return "Error processing: " + e.getMessage();
}
}
// 复杂的错误处理
public static String complexProcess(Object obj) {
return switch (obj) {
case String s when s.length() > 0 -> s.toUpperCase();
case String s -> "Empty string";
case Number n when n.doubleValue() > 0 -> "Positive number: " + n;
case Number n -> "Non-positive number: " + n;
case List<?> list when !list.isEmpty() -> "List with " + list.size() + " elements";
case List<?> list -> "Empty list";
case null -> "Null object";
default -> "Unknown object type";
};
}
}
虚拟线程（Virtual Threads）：优化并发编程
虚拟线程概述
虚拟线程是Java 17中引入的新的线程实现方式，它旨在解决传统Java线程的性能瓶颈和资源消耗问题。虚拟线程由操作系统线程（平台线程）管理，但对开发者来说是透明的。
虚拟线程的基本概念
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
public class VirtualThreadExample {
public static void main(String[] args) {
// 传统平台线程
Thread platformThread = new Thread(() -> {
System.out.println("Platform thread: " + Thread.currentThread().getName());
});
// 虚拟线程
Thread virtualThread = Thread.ofVirtual()
.name("VirtualThread-")
.unstarted(() -> {
System.out.println("Virtual thread: " + Thread.currentThread().getName());
});
platformThread.start();
virtualThread.start();
}
}
虚拟线程的创建和使用
1. 创建虚拟线程
public class VirtualThreadCreation {
// 创建虚拟线程的多种方式
// 方式1：使用Thread.ofVirtual()
public static void createVirtualThread1() {
Thread virtualThread = Thread.ofVirtual()
.name("MyVirtualThread")
.unstarted(() -> {
System.out.println("Virtual thread running");
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
});
virtualThread.start();
}
// 方式2：使用Thread.ofPlatform()
public static void createVirtualThread2() {
Thread virtualThread = Thread.ofVirtual()
.start(() -> {
System.out.println("Virtual thread started");
// 执行任务
});
}
// 方式3：使用ExecutorService
public static void createVirtualThreadWithExecutor() {
var executor = Executors.newVirtualThreadPerTaskExecutor();
for (int i = 0; i < 1000; i++) {
final int taskId = i;
executor.submit(() -> {
System.out.println("Task " + taskId + " executed by " +
Thread.currentThread().getName());
});
}
executor.close();
}
}
2. 虚拟线程与传统线程对比
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class ThreadComparison {
// 传统平台线程
public static void traditionalThreadExample() {
ExecutorService executor = Executors.newFixedThreadPool(10);
for (int i = 0; i < 1000; i++) {
final int taskId = i;
executor.submit(() -> {
System.out.println("Task " + taskId + " executed by " +
Thread.currentThread().getName());
});
}
executor.shutdown();
}
// 虚拟线程
public static void virtualThreadExample() {
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
for (int i = 0; i < 1000; i++) {
final int taskId = i;
executor.submit(() -> {
System.out.println("Task " + taskId + " executed by " +
Thread.currentThread().getName());
});
}
}
}
// 性能测试
public static void performanceTest() {
int threadCount = 10000;
// 测试平台线程
long platformStart = System.currentTimeMillis();
ExecutorService platformExecutor = Executors.newFixedThreadPool(100);
for (int i = 0; i < threadCount; i++) {
platformExecutor.submit(() -> {
// 简单任务
});
}
platformExecutor.shutdown();
long platformEnd = System.currentTimeMillis();
// 测试虚拟线程
long virtualStart = System.currentTimeMillis();
try (var virtualExecutor = Executors.newVirtualThreadPerTaskExecutor()) {
for (int i = 0; i < threadCount; i++) {
virtualExecutor.submit(() -> {
// 简单任务
});
}
}
long virtualEnd = System.currentTimeMillis();
System.out.println("Platform threads time: " + (platformEnd - platformStart) + " ms");
System.out.println("Virtual threads time: " + (virtualEnd - virtualStart) + " ms");
}
}
虚拟线程在实际项目中的应用
1. Web服务处理
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.net.URI;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class WebServiceExample {
private static final HttpClient client = HttpClient.newHttpClient();
// 使用虚拟线程处理HTTP请求
public static CompletableFuture<String> fetchUrlAsync(String url) {
return CompletableFuture.supplyAsync(() -> {
try {
HttpRequest request = HttpRequest.newBuilder()
.uri(URI.create(url))
.build();
HttpResponse<String> response = client.send(request,
HttpResponse.BodyHandlers.ofString());
return response.body();
} catch (Exception e) {
throw new RuntimeException(e);
}
}, Executors.newVirtualThreadPerTaskExecutor());
}
// 批量处理多个URL
public static CompletableFuture<Void> fetchMultipleUrls(String[] urls) {
var executor = Executors.newVirtualThreadPerTaskExecutor();
var futures = java.util.Arrays.stream(urls)
.map(url -> fetchUrlAsync(url))
.toArray(CompletableFuture[]::new);
return CompletableFuture.allOf(futures)
.thenRun(() -> {
System.out.println("All URLs fetched successfully");
})
.whenComplete((result, throwable) -> {
executor.close();
});
}
}
2. 数据处理管道
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.List;
import java.util.ArrayList;
public class DataProcessingPipeline {
// 数据处理任务
public static class DataProcessor {
public static CompletableFuture<String> processFile(String fileName) {
return CompletableFuture.supplyAsync(() -> {
// 模拟文件处理
try {
Thread.sleep(100); // 模拟IO操作
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
return "Processed: " + fileName;
}, Executors.newVirtualThreadPerTaskExecutor());
}
public static CompletableFuture<String> validateData(String data) {
return CompletableFuture.supplyAsync(() -> {
// 模拟数据验证
try {
Thread.sleep(50);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
return "Validated: " + data;
}, Executors.newVirtualThreadPerTaskExecutor());
}
public static CompletableFuture<String> saveData(String data) {
return CompletableFuture.supplyAsync(() -> {
// 模拟数据保存
try {
Thread.sleep(200);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
return "Saved: " + data;
}, Executors.newVirtualThreadPerTaskExecutor());
}
}
// 处理数据管道
public static CompletableFuture<Void> processDataPipeline(List<String> fileNames) {
var executor = Executors.newVirtualThreadPerTaskExecutor();
var futures = fileNames.stream()
.map(DataProcessor::processFile)
.map(f -> f.thenCompose(DataProcessor::validateData))
.map(f -> f.thenCompose(DataProcessor::saveData))
.toArray(CompletableFuture[]::new);
return CompletableFuture.allOf(futures)
.thenRun(() -> System.out.println("Pipeline completed"))
.whenComplete((result, throwable) -> {
executor.close();
});
}
}
虚拟线程的最佳实践
1. 资源管理
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
public class VirtualThreadBestPractices {
// 正确的资源管理
public static void properResourceManagement() {
// 使用try-with-resources确保资源释放
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
for (int i = 0; i < 1000; i++) {
final int taskId = i;
executor.submit(() -> {
System.out.println("Task " + taskId + " running");
// 执行任务
});
}
} catch (Exception e) {
System.err.println("Error: " + e.getMessage());
}
}
// 控制并发数量
public static void controlledConcurrency() {
// 使用信号量控制并发数量
Semaphore semaphore = new Semaphore(100); // 最多100个并发
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
for (int i = 0; i < 1000; i++) {
final int taskId = i;
executor.submit(() -> {
try {
semaphore.acquire();
// 执行任务
System.out.println("Task " + taskId + " running");
Thread.sleep(1000);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
} finally {
semaphore.release();
}
});
}
}
}
}
2. 错误处理
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class VirtualThreadErrorHandling {
public static CompletableFuture<String> safeAsyncOperation(String input) {
return CompletableFuture.supplyAsync(() -> {
try {
// 模拟可能失败的操作
if (input == null || input.isEmpty()) {
throw new IllegalArgumentException("Input cannot be null or empty");
}
Thread.sleep(1000); // 模拟耗时操作
return "Processed: " + input;
} catch (Exception e) {
// 记录错误并重新抛出
System.err.println("Error processing: " + input + ", " + e.getMessage());
throw new RuntimeException(e);
}
}, Executors.newVirtualThreadPerTaskExecutor());
}
public static void handleMultipleOperations() {
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
List<CompletableFuture<String>> futures = new ArrayList<>();
String[] inputs = {"input1", "input2", null, "input4"};
for (String input : inputs) {
futures.add(safeAsyncOperation(input));
}
CompletableFuture.allOf(futures.toArray(new CompletableFuture[0]))
.thenRun(() -> System.out.println("All operations completed"))
.exceptionally(throwable -> {
System.err.println("Error in batch operations: " + throwable.getMessage());
return null;
});
}
}
}
综合应用示例
完整的并发处理系统
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.List;
import java.util.ArrayList;
import java.util.Map;
import java.util.HashMap;
// 数据模型
public record Product(String id, String name, double price, String category) {}
public record Order(String orderId, List<String> productIds, double totalAmount) {}
public record OrderResult(String orderId, boolean success, String message) {}
public class ConcurrentOrderProcessingSystem {
// 模拟产品数据库
private static final Map<String, Product> productDatabase = new HashMap<>();
static {
productDatabase.put("P001", new Product("P001", "Laptop", 1200.0, "Electronics"));
productDatabase.put("P002", new Product("P002", "Book", 25.0, "Education"));
productDatabase.put("P003", new Product("P003", "Phone", 800.0, "Electronics"));
}
// 产品查询
public static CompletableFuture<Product> getProductAsync(String productId) {
return CompletableFuture.supplyAsync(() -> {
try {
Thread.sleep(50); // 模拟数据库查询
Product product = productDatabase.get(productId);
if (product == null) {
throw new RuntimeException("Product not found: " + productId);
}
return product;
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
throw new RuntimeException(e);
}
}, Executors.newVirtualThreadPerTaskExecutor());
}
// 订单处理
public static CompletableFuture<OrderResult> processOrderAsync(Order order) {
return CompletableFuture.supplyAsync(() -> {
try {
System.out.println("Processing order: " + order.orderId());
// 并发获取产品信息
List<CompletableFuture<Product>> productFutures = new ArrayList<>();
for (String productId : order.productIds()) {
productFutures.add(getProductAsync(productId));
}
// 等待所有产品信息获取完成
CompletableFuture<Void> allProducts = CompletableFuture.allOf(
productFutures.toArray(new CompletableFuture[0])
);
allProducts.join();
// 验证订单
double calculatedTotal = productFutures.stream()
.map(CompletableFuture::join)
.mapToDouble(Product::price)
.sum();
if (Math.abs(calculatedTotal - order.totalAmount()) > 0.01) {
return new OrderResult(order.orderId(), false
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