Java学习笔记：从入门到精通（2025更新版）一、Java基础（2025版）1.1 开发环境配置JDK推荐使用LTS版本17或最新版本21，通过SDKMAN!进行多版本管理：

代码语言：bash复制# 安装SDKMAN!

curl -s "https://get.sdkman.io" | bash

source "$HOME/.sdkman/bin/sdkman-init.sh"

# 安装并使用Java 21

sdk install java 21.0.1-tem

sdk use java 21.0.1-temIDE推荐使用IntelliJ IDEA 2025.1或VS Code（需安装Extension Pack for Java）。

1.2 核心语法增强1.2.1 文本块（Java 15+）代码语言：java复制String html = """

Hello, Java 21!

""";1.2.2 模式匹配（Java 17+）代码语言：java复制// 传统写法

if (obj instanceof String) {

String s = (String) obj;

System.out.println(s.length());

}

// 模式匹配写法

if (obj instanceof String s) {

System.out.println(s.length());

}1.2.3 记录类（Java 16+）代码语言：java复制// 传统类

class Point {

private final int x;

private final int y;

public Point(int x, int y) {

this.x = x;

this.y = y;

}

// Getters, equals, hashCode, toString

}

// 记录类

record Point(int x, int y) {}1.2.4 增强的switch（Java 14+）代码语言：java复制int day = 3;

String result = switch (day) {

case 1, 2, 3, 4, 5 -> "Weekday";

case 6, 7 -> "Weekend";

default -> throw new IllegalArgumentException("Invalid day: " + day);

};二、面向对象编程（2025版）2.1 密封类（Java 17+）代码语言：java复制// 限制继承范围

public sealed interface Shape

permits Circle, Rectangle, Square {

double area();

}

final class Circle implements Shape { ... }

final class Rectangle implements Shape { ... }

non-sealed class Square implements Shape { ... }2.2 接口增强代码语言：java复制// Java 8+ 默认方法

public interface MyInterface {

default void defaultMethod() {

System.out.println("Default implementation");

}

// Java 9+ 私有方法

private void privateMethod() {

System.out.println("Private implementation");

}

}三、Java进阶（2025版）3.1 虚拟线程（Java 21+）代码语言：java复制// 传统线程池写法

ExecutorService executor = Executors.newFixedThreadPool(200);

for (int i = 0; i < 1000; i++) {

executor.submit(() -> {

Thread.sleep(Duration.ofSeconds(1));

return "Done";

});

}

// 虚拟线程写法

try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {

IntStream.range(0, 10000).forEach(i -> {

executor.submit(() -> {

Thread.sleep(Duration.ofSeconds(1));

return "Done";

});

});

}3.2 结构化并发（Java 21+）代码语言：java复制// 并行执行多个任务

try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {

Future task1 = scope.fork(() -> fetchUser());

Future task2 = scope.fork(() -> fetchOrderCount());

scope.join(); // 等待所有任务完成

scope.throwIfFailed(); // 处理失败的任务

String user = task1.resultNow();

int count = task2.resultNow();

}3.3 向量API（Java 21+）代码语言：java复制// 传统数组计算

float[] a = new float[1024];

float[] b = new float[1024];

float[] c = new float[1024];

for (int i = 0; i < a.length; i++) {

c[i] = a[i] * b[i] + 42.0f;

}

// 向量API加速计算

VectorSpecies species = FloatVector.SPECIES_PREFERRED;

for (int i = 0; i < a.length; i += species.length()) {

var m = species.indexInRange(i, a.length);

var va = FloatVector.fromArray(species, a, i, m);

var vb = FloatVector.fromArray(species, b, i, m);

var vc = va.mul(vb).add(42.0f);

vc.intoArray(c, i, m);

}四、实用类库与框架（2025版）4.1 HTTP客户端（Java 11+）代码语言：java复制import java.net.URI;

import java.net.http.HttpClient;

import java.net.http.HttpRequest;

import java.net.http.HttpResponse;

import java.time.Duration;

public class HttpClientExample {

public static void main(String[] args) throws Exception {

HttpClient client = HttpClient.newBuilder()

.version(HttpClient.Version.HTTP_2)

.connectTimeout(Duration.ofSeconds(10))

.build();

HttpRequest request = HttpRequest.newBuilder()

.uri(URI.create("https://api.example.com/data"))

.header("Content-Type", "application/json")

.GET()

.build();

client.sendAsync(request, HttpResponse.BodyHandlers.ofString())

.thenApply(HttpResponse::body)

.thenAccept(System.out::println)

.join();

}

}4.2 项目构建（Maven vs Gradle）Gradle Kotlin DSL示例代码语言：kotlin复制// build.gradle.kts

plugins {

application

kotlin("jvm") version "1.9.20"

}

repositories {

mavenCentral()

}

dependencies {

implementation("org.springframework.boot:spring-boot-starter-web:3.2.4")

testImplementation("org.junit.jupiter:junit-jupiter:5.10.2")

}

application {

mainClass.set("com.example.MainKt")

}五、微服务与云原生（2025版）5.1 Spring Boot 3.2+代码语言：java复制// REST API示例

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

import org.springframework.web.bind.annotation.GetMapping;

import org.springframework.web.bind.annotation.PathVariable;

import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication

@RestController

public class UserServiceApplication {

public static void main(String[] args) {

SpringApplication.run(UserServiceApplication.class, args);

}

@GetMapping("/users/{id}")

public User getUser(@PathVariable Long id) {

return new User(id, "John Doe", "john@example.com");

}

record User(Long id, String name, String email) {}

}5.2 容器化与Kubernetes代码语言：yaml复制# Dockerfile示例

FROM eclipse-temurin:21-jre-alpine

WORKDIR /app

COPY target/myapp.jar .

CMD ["java", "-jar", "myapp.jar"]

# Kubernetes部署示例

apiVersion: apps/v1

kind: Deployment

metadata:

name: user-service

spec:

replicas: 3

selector:

matchLabels:

app: user-service

template:

metadata:

labels:

app: user-service

spec:

containers:

- name: user-service

image: myregistry/user-service:1.0.0

ports:

- containerPort: 8080

resources:

requests:

memory: "512Mi"

cpu: "250m"

limits:

memory: "1024Mi"

cpu: "500m"六、响应式编程（2025版）6.1 Reactor框架代码语言：java复制import reactor.core.publisher.Flux;

import reactor.core.publisher.Mono;

import java.time.Duration;

public class ReactiveExample {

public static void main(String[] args) {

// 创建数据流

Flux names = Flux.just("Alice", "Bob", "Charlie")

.delayElements(Duration.ofMillis(500));

// 转换与过滤

Flux filteredNames = names

.filter(name -> name.length() > 4)

.map(String::toUpperCase);

// 订阅并消费

filteredNames.subscribe(

name -> System.out.println("Received: " + name),

error -> System.err.println("Error: " + error),

() -> System.out.println("Completed")

);

// 合并多个Mono

Mono mono1 = Mono.just("Hello");

Mono mono2 = Mono.just("World");

Mono.zip(mono1, mono2)

.map(tuple -> tuple.getT1() + " " + tuple.getT2())

.subscribe(System.out::println);

}

}6.2 Spring WebFlux代码语言：java复制// 响应式REST API

import org.springframework.web.bind.annotation.GetMapping;

import org.springframework.web.bind.annotation.PathVariable;

import org.springframework.web.bind.annotation.RestController;

import reactor.core.publisher.Flux;

import reactor.core.publisher.Mono;

@RestController

public class ProductController {

private final ProductService productService;

public ProductController(ProductService productService) {

this.productService = productService;

}

@GetMapping("/products")

public Flux getAllProducts() {

return productService.findAll();

}

@GetMapping("/products/{id}")

public Mono getProductById(@PathVariable String id) {

return productService.findById(id);

}

}七、函数式编程（2025版）7.1 Stream API增强代码语言：java复制import java.util.List;

import java.util.stream.Stream;

public class StreamExample {

public static void main(String[] args) {

List words = List.of("hello", "world", "java", "stream");

// 传统流操作

words.stream()

.filter(w -> w.length() > 4)

.map(String::toUpperCase)

.forEach(System.out::println);

// 新的takeWhile/dropWhile方法

Stream.of(1, 2, 3, 4, 5, 2, 1)

.takeWhile(n -> n < 5) // [1, 2, 3, 4]

.forEach(System.out::print);

Stream.of(1, 2, 3, 4, 5, 2, 1)

.dropWhile(n -> n < 5) // [5, 2, 1]

.forEach(System.out::print);

}

}7.2 函数式接口与Lambda代码语言：java复制// 自定义函数式接口

@FunctionalInterface

interface TriFunction {

R apply(T t, U u, V v);

}

// 使用示例

TriFunction sum = (a, b, c) -> a + b + c;

int result = sum.apply(1, 2, 3); // 6八、测试技术（2025版）8.1 JUnit 5与Mockito代码语言：java复制import static org.junit.jupiter.api.Assertions.*;

import static org.mockito.Mockito.*;

import org.junit.jupiter.api.Test;

import org.junit.jupiter.api.extension.ExtendWith;

import org.mockito.InjectMocks;

import org.mockito.Mock;

import org.mockito.junit.jupiter.MockitoExtension;

@ExtendWith(MockitoExtension.class)

public class UserServiceTest {

@Mock

private UserRepository userRepository;

@InjectMocks

private UserService userService;

@Test

public void testGetUserById() {

// 模拟存储库行为

when(userRepository.findById(1L))

.thenReturn(new User(1L, "John Doe", "john@example.com"));

// 执行测试

User result = userService.getUserById(1L);

// 验证结果

assertNotNull(result);

assertEquals("John Doe", result.getName());

verify(userRepository, times(1)).findById(1L);

}

}8.2 测试容器代码语言：java复制import org.junit.jupiter.api.Test;

import org.springframework.boot.test.context.SpringBootTest;

import org.springframework.test.context.DynamicPropertyRegistry;

import org.springframework.test.context.DynamicPropertySource;

import org.testcontainers.containers.PostgreSQLContainer;

import org.testcontainers.junit.jupiter.Container;

import org.testcontainers.junit.jupiter.Testcontainers;

@Testcontainers

@SpringBootTest

public class DatabaseIntegrationTest {

@Container

static PostgreSQLContainer postgres = new PostgreSQLContainer<>("postgres:15-alpine")

.withDatabaseName("testdb")

.withUsername("test")

.withPassword("test");

@DynamicPropertySource

static void configureProperties(DynamicPropertyRegistry registry) {

registry.add("spring.datasource.url", postgres::getJdbcUrl);

registry.add("spring.datasource.username", postgres::getUsername);

registry.add("spring.datasource.password", postgres::getPassword);

}

@Test

void contextLoads() {

// 测试数据库连接

}

}九、数据持久化（2025版）9.1 Spring Data JPA 3.2+代码语言：java复制// 实体类

import jakarta.persistence.Entity;

import jakarta.persistence.GeneratedValue;

import jakarta.persistence.GenerationType;

import jakarta.persistence.Id;

@Entity

public class Product {

@Id

@GeneratedValue(strategy = GenerationType.IDENTITY)

private Long id;

private String name;

private double price;

// getters/setters

}

// 仓库接口

import org.springframework.data.jpa.repository.JpaRepository;

import org.springframework.data.jpa.repository.Query;

import java.util.List;

public interface ProductRepository extends JpaRepository {

List findByNameContaining(String name);

@Query("SELECT p FROM Product p WHERE p.price > :minPrice")

List findByPriceGreaterThan(double minPrice);

}9.2 响应式数据访问（R2DBC）代码语言：java复制// R2DBC响应式仓库

import org.springframework.data.repository.reactive.ReactiveCrudRepository;

import reactor.core.publisher.Flux;

public interface UserRepository extends ReactiveCrudRepository {

Flux findByLastName(String lastName);

}

// 使用示例

@Service

public class UserService {

private final UserRepository userRepository;

public UserService(UserRepository userRepository) {

this.userRepository = userRepository;

}

public Flux getUsersByLastName(String lastName) {

return userRepository.findByLastName(lastName);

}

}十、实战项目：Todo应用（2025版）10.1 项目架构代码语言：txt复制todo-app/

├── todo-backend/ # Spring Boot后端

│ ├── src/

│ │ ├── main/

│ │ │ ├── java/com/example/todo/

│ │ │ │ ├── controller/ # REST控制器

│ │ │ │ ├── service/ # 业务逻辑

│ │ │ │ ├── repository/ # 数据访问

│ │ │ │ ├── entity/ # 实体类

│ │ │ │ └── TodoApplication.java

│ │ │ └── resources/

│ │ │ ├── application.yml # 配置文件

│ │ │ └── static/ # 静态资源

│ │ └── test/

│ │ └── java/com/example/todo/ # 测试类

│ └── pom.xml

└── todo-frontend/ # React前端

├── src/

│ ├── components/ # React组件

│ ├── services/ # API服务

│ ├── App.jsx

│ └── index.jsx

└── package.json10.2 后端核心代码代码语言：java复制// Todo实体

@Entity

public class Todo {

@Id

@GeneratedValue(strategy = GenerationType.IDENTITY)

private Long id;

private String title;

private boolean completed;

// getters/setters

}

// Todo控制器

@RestController

@RequestMapping("/api/todos")

public class TodoController {

private final TodoService todoService;

@GetMapping

public List getAllTodos() {

return todoService.getAllTodos();

}

@PostMapping

public Todo createTodo(@RequestBody Todo todo) {

return todoService.createTodo(todo);

}

@PutMapping("/{id}")

public Todo updateTodo(@PathVariable Long id, @RequestBody Todo todoDetails) {

return todoService.updateTodo(id, todoDetails);

}

@DeleteMapping("/{id}")

public ResponseEntity deleteTodo(@PathVariable Long id) {

todoService.deleteTodo(id);

return ResponseEntity.ok().build();

}

}10.3 前端核心代码（React + Vite）代码语言：jsx复制// TodoList组件

import React, { useState, useEffect } from 'react';

import axios from 'axios';

const TodoList = () => {

const [todos, setTodos] = useState([]);

const [newTodo, setNewTodo] = useState('');

useEffect(() => {

fetchTodos();

}, []);

const fetchTodos = async () => {

const response = await axios.get('/api/todos');

setTodos(response.data);

};

const handleCreateTodo = async () => {

if (!newTodo.trim()) return;

await axios.post('/api/todos', { title: newTodo, completed: false });

setNewTodo('');

fetchTodos();

};

const handleToggleComplete = async (id, completed) => {

await axios.put(`/api/todos/${id}`, { completed });

fetchTodos();

};

return (

);

};

export default TodoList;以上代码示例涵盖了Java 21的最新特性、现代开发工具链以及微服务架构，帮助你快速掌握Java开发的核心技能。建议通过实际项目练习来加深理解，例如构建一个完整的Web应用或微服务系统。

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