2025 版 Java 学习路线实战指南从入门到精通

# macOS 使用SDKMAN安装
curl -s "https://get.sdkman.io" | bash
source "$HOME/.sdkman/bin/sdkman-init.sh"
sdk install java 21.0.1-librca

# Windows 使用Chocolatey
choco install libericajdk21-full

// 2025版数据类推荐写法
public record User(Long id, String name, LocalDate createTime) {
    // 自动生成所有参数的构造函数、getter、equals、hashCode和toString
    public User {
        // 自定义验证逻辑
        if (name == null || name.isBlank()) {
            throw new IllegalArgumentException("Name cannot be blank");
        }
    }
    
    // 可以添加自定义方法
    public String formattedCreateTime() {
        return createTime.format(DateTimeFormatter.ISO_LOCAL_DATE);
    }
}

// 2025版instanceof模式匹配
Object obj = "Hello";
if (obj instanceof String s && s.length() > 5) {
    System.out.println(s.toUpperCase()); // 直接使用s变量
}

// switch表达式增强
int result = switch (day) {
    case MONDAY, FRIDAY, SUNDAY -> 6;
    case TUESDAY                -> 7;
    case THURSDAY, SATURDAY     -> 8;
    case WEDNESDAY              -> 9;
};

// 两数之和问题（HashMap解法）
public int[] twoSum(int[] nums, int target) {
    Map<Integer, Integer> map = new HashMap<>();
    for (int i = 0; i < nums.length; i++) {
        int complement = target - nums[i];
        if (map.containsKey(complement)) {
            return new int[]{map.get(complement), i};
        }
        map.put(nums[i], i);
    }
    return new int[]{};
}

// 二叉树层序遍历（BFS解法）
public List<List<Integer>> levelOrder(TreeNode root) {
    List<List<Integer>> result = new ArrayList<>();
    if (root == null) return result;
    
    Queue<TreeNode> queue = new LinkedList<>();
    queue.offer(root);
    
    while (!queue.isEmpty()) {
        int levelSize = queue.size();
        List<Integer> currentLevel = new ArrayList<>();
        for (int i = 0; i < levelSize; i++) {
            TreeNode currentNode = queue.poll();
            currentLevel.add(currentNode.val);
            if (currentNode.left != null) queue.offer(currentNode.left);
            if (currentNode.right != null) queue.offer(currentNode.right);
        }
        result.add(currentLevel);
    }
    return result;
}

// 使用Spring Cloud Gateway作为API网关
@SpringBootApplication
@EnableGateway
public class ApiGatewayApplication {
    public static void main(String[] args) {
        SpringApplication.run(ApiGatewayApplication.class, args);
    }
    
    @Bean
    public RouteLocator customRouteLocator(RouteLocatorBuilder builder) {
        return builder.routes()
            .route("user-service", r -> r.path("/api/users/**")
                .uri("lb://user-service"))
            .route("order-service", r -> r.path("/api/orders/**")
                .uri("lb://order-service"))
            .build();
    }
}

// 使用Spring Cloud OpenFeign调用远程服务
@FeignClient(name = "user-service", path = "/api/users")
public interface UserServiceClient {
    @GetMapping("/{id}")
    User getUser(@PathVariable("id") Long id);
}

# 使用Consul作为服务注册与发现中心
spring:
  cloud:
    consul:
      host: localhost
      port: 8500
      discovery:
        service-name: ${spring.application.name}
        instance-id: ${spring.application.name}:${random.value}
        health-check-path: /actuator/health
        health-check-interval: 10s

# 使用Spring Cloud Config配置中心
spring:
  cloud:
    config:
      uri: http://localhost:8888
      name: application
      profile: dev

# deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: user-service
  labels:
    app: user-service
spec:
  replicas: 3
  selector:
    matchLabels:
      app: user-service
  template:
    metadata:
      labels:
        app: user-service
    spec:
      containers:
      - name: user-service
        image: registry.example.com/user-service:v1.0.0
        ports:
        - containerPort: 8080
        env:
        - name: SPRING_PROFILES_ACTIVE
          value: prod
        resources:
          requests:
            memory: "512Mi"
            cpu: "250m"
          limits:
            memory: "1024Mi"
            cpu: "500m"
        readinessProbe:
          httpGet:
            path: /actuator/health
            port: 8080
          initialDelaySeconds: 30
          periodSeconds: 10

# .github/workflows/maven.yml
name: Java CI with Maven

on:
  push:
    branches: [ main ]
  pull_request:
    branches: [ main ]

jobs:
  build:
    runs-on: ubuntu-latest

    steps:
    - uses: actions/checkout@v4
    - name: Set up JDK 21
      uses: actions/setup-java@v4
      with:
        java-version: '21'
        distribution: 'liberica'
        cache: maven

    - name: Build with Maven
      run: mvn -B package --file pom.xml

    - name: Test Coverage
      uses: codecov/codecov-action@v4
      with:
        token: ${{ secrets.CODECOV_TOKEN }}

    - name: Build and push Docker image
      uses: docker/build-push-action@v5
      with:
        context: .
        push: true
        tags: registry.example.com/user-service:${{ github.sha }}
        secrets:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

// 使用OkHttp调用OpenAI GPT-4 API
public class OpenAIClient {
    private static final String API_KEY = System.getenv("OPENAI_API_KEY");
    private final OkHttpClient client = new OkHttpClient();
    
    public String generateText(String prompt) throws IOException {
        MediaType JSON = MediaType.get("application/json; charset=utf-8");
        String requestBody = """
            {
                "model": "gpt-4-1106-preview",
                "messages": [{"role": "user", "content": "%s"}],
                "temperature": 0.7
            }
            """.formatted(prompt);
        
        RequestBody body = RequestBody.create(requestBody, JSON);
        Request request = new Request.Builder()
            .url("https://api.openai.com/v1/chat/completions")
            .header("Authorization", "Bearer " + API_KEY)
            .post(body)
            .build();
        
        try (Response response = client.newCall(request).execute()) {
            if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
            JSONObject jsonResponse = new JSONObject(response.body().string());
            return jsonResponse.getJSONArray("choices")
                .getJSONObject(0)
                .getJSONObject("message")
                .getString("content");
        }
    }
}

// 使用Byte Buddy实现Java Agent
public class PerformanceAgent {
    public static void premain(String agentArgs, Instrumentation inst) {
        new AgentBuilder.Default()
            .type(ElementMatchers.nameContains("Service"))
            .transform((builder, typeDescription, classLoader, module) ->
                builder.method(ElementMatchers.any())
                    .intercept(MethodDelegation.to(PerformanceInterceptor.class)))
            .installOn(inst);
    }
}

public class PerformanceInterceptor {
    public static Object intercept(@Origin Method method, @AllArguments Object[] args,
                                   @SuperCall Callable<?> callable) throws Exception {
        long startTime = System.currentTimeMillis();
        try {
            return callable.call();
        } finally {
            long duration = System.currentTimeMillis() - startTime;
            System.out.printf("Method %s.%s took %d ms%n",
                    method.getDeclaringClass().getName(),
                    method.getName(),
                    duration);
        }
    }
}

┌───────────────────────────────────────────────────────────────┐
│                          API Gateway                          │
│  (Spring Cloud Gateway + OAuth2 + Rate Limiting + Circuit Breaker) │
└───────────────────┬─────────────────┬────────────────────────┘
                    │                 │
┌───────────────────┴──┐   ┌───────────┴─────────────────┐
│       用户服务         │   │         商品服务            │
│  (User Service)       │   │  (Product Service)          │
│  - 用户管理            │   │  - 商品管理                 │
│  - 认证授权            │   │  - 库存管理                 │
│  - 会员体系            │   │  - 商品搜索(Elasticsearch)  │
└───────────────────────┘   └───────────┬─────────────────┘
                                        │
┌───────────────────┐   ┌───────────┬──┴─────────────────┐   ┌───────────────────┐
│     订单服务       │   │  支付服务  │     营销服务        │   │     消息服务      │
│  (Order Service)   │   │(Payment   │  (Promotion Service)│   │(Message Service)  │
│  - 订单创建        │   │ Service)  │  - 优惠券系统       │   │ - 邮件通知        │
│  - 订单状态管理    │   │ - 支付处理 │  - 促销活动         │   │ - 短信通知        │
│  - 订单分库分表    │   │ - 退款流程 │  - 价格计算         │   │ - WebSocket推送   │
└───────────────────┘   └───────────┘   └─────────────────┘   └───────────────────┘
                                                                      │
┌───────────────────┐   ┌───────────────────┐   ┌───────────────────┴─────────────────┐
│     数据分析服务   │   │     后台管理系统   │   │                基础设施                │
│  (Data Analytics   │   │  (Admin Portal)   │   │  - 服务注册与发现(Consul/Nacos)      │
│   Service)         │   │  - 运营管理界面   │   │  - 配置中心(Spring Cloud Config)      │
│  - 用户行为分析    │   │  - 数据可视化     │   │  - 服务监控与告警(Grafana+Prometheus)  │
│  - 销售报表        │   │  - 系统设置       │   │  - 分布式日志(ELK)                     │
│  - 推荐系统        │   │                   │   │  - 容器编排(Kubernetes)                │
└───────────────────┘   └───────────────────┘   └───────────────────────────────────────┘