解析Java架构中的性能优化和扩展性设计

// 避免多重循环
for (int i = 0; i < list.size(); i++) {
    for (int j = 0; j < list.get(i).size(); j++) {
        // do something
    }
}

// 优化后的代码
for (List<Integer> sublist : list) {
    for (int num : sublist) {
        // do something
    }
}

// 错误的查询语句
String sql = "SELECT * FROM users WHERE name LIKE '%" + keyword + "%'";

// 优化后的查询语句
String sql = "SELECT * FROM users WHERE name LIKE ?"; 
PreparedStatement stmt = conn.prepareStatement(sql);
stmt.setString(1, "%" + keyword + "%");
ResultSet rs = stmt.executeQuery();

// 使用内存缓存
Map<String, Object> cache = new HashMap<>();
Object data = cache.get(key);
if (data == null) {
    // 从数据库或其他外部资源中获取数据
    data = getDataFromDB();
    cache.put(key, data);
} 

// 模块A接口定义
public interface ModuleA {
    void methodA();
}

// 模块A实现类
public class ModuleAImpl implements ModuleA {
    public void methodA() {
        // do something
    }
}

// 使用模块A
ModuleA moduleA = new ModuleAImpl();
moduleA.methodA();

// 服务接口定义
public interface UserService {
    User getUserById(int id);
}

// 服务实现类
public class UserServiceImpl implements UserService {
    public User getUserById(int id) {
        // 从数据库中根据ID查询用户信息
        return userDao.getUserById(id);
    }
}

// 服务消费者
public class UserConsumer {
    private UserService userService;

    public void setUserService(UserService userService) {
        this.userService = userService;
    }

    public void doSomething() {
        // 调用远程服务
        User user = userService.getUserById(1);
        // do something with user
    }
}

// 负载均衡器
public class LoadBalancer {
    private List<Server> serverList;

    public void addServer(Server server) {
        serverList.add(server);
    }

    public Server getServer() {
        // 根据负载均衡算法选择一台服务器
        return selectedServer;
    }
}

// 服务器
public class Server {
    public void handleRequest() {
        // 处理请求
    }
}