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import java.time.LocalDate; |
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import java.util.ArrayList; |
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import java.util.Comparator; |
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import java.util.List; |
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import java.util.regex.Pattern; |
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// ─────────────────────────────────────────────
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// 策略接口
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// ─────────────────────────────────────────────
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interface ParseStrategy { |
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boolean supports(String url); |
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Article parse(String url); |
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String getName(); |
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default int getPriority() { return 100; } |
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} |
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// ─────────────────────────────────────────────
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// 策略实现1：GitHub 专属（priority=10）
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// ─────────────────────────────────────────────
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class GithubParseStrategy implements ParseStrategy { |
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@Override |
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public boolean supports(String url) { |
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return url != null && url.matches("^https?://(www\\.)?github\\.com/.*"); |
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} |
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@Override |
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public Article parse(String url) { |
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String path = url.replaceFirst("https?://(www\\.)?github\\.com/", ""); |
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String[] parts = path.split("/"); |
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String owner = parts.length > 0 ? parts[0] : "unknown"; |
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String repo = parts.length > 1 ? parts[1] : "repo"; |
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return new Article("[GitHub] " + owner + "/" + repo, url, |
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"(GitHub stub)", owner, LocalDate.now()); |
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} |
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@Override public String getName() { return "GithubParseStrategy"; } |
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@Override public int getPriority(){ return 10; } |
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} |
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// ─────────────────────────────────────────────
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// 策略实现2：通用默认兜底（priority=999）
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// ─────────────────────────────────────────────
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class DefaultParseStrategy implements ParseStrategy { |
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private static final Pattern URL_PATTERN = |
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Pattern.compile("^https?://[^\\s/$.?#].[^\\s]*$"); |
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@Override |
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public boolean supports(String url) { |
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return url != null && URL_PATTERN.matcher(url).matches(); |
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} |
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@Override |
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public Article parse(String url) { |
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String domain = url.replaceFirst("https?://", "").replaceAll("/.*", ""); |
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return new Article("文章来自 " + domain, url, |
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"(default stub)", "unknown", LocalDate.now()); |
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} |
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@Override public String getName() { return "DefaultParseStrategy"; } |
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@Override public int getPriority(){ return 999; } |
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} |
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// ─────────────────────────────────────────────
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// 策略选择器
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// ─────────────────────────────────────────────
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class StrategySelector { |
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private final List<ParseStrategy> strategies = new ArrayList<>(); |
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public StrategySelector() { |
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strategies.add(new GithubParseStrategy()); |
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strategies.add(new DefaultParseStrategy()); |
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strategies.sort(Comparator.comparingInt(ParseStrategy::getPriority)); |
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} |
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public ParseStrategy select(String url) { |
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return strategies.stream() |
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.filter(s -> s.supports(url)) |
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.findFirst().orElse(null); |
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} |
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public List<ParseStrategy> getAll() { return List.copyOf(strategies); } |
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} |
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import java.util.concurrent.atomic.AtomicInteger; |
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import java.util.function.Supplier; |
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import java.util.logging.Logger; |
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// ─────────────────────────────────────────────
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// 必做1：UrlFormatException（Unchecked / Runtime）
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// 选择 RuntimeException 理由：
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// URL 格式错误属于调用方编程错误（非法参数），
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// 不应强迫上层 catch，符合 Unchecked 语义。
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// ─────────────────────────────────────────────
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class UrlFormatException extends RuntimeException { |
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private final String invalidUrl; |
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public UrlFormatException(String url) { |
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// 保留根因信息，避免"异常包装丢失根因"问题
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super("URL 格式不合法，必须以 http:// 或 https:// 开头：" + url); |
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this.invalidUrl = url; |
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} |
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/** 构造器2：包装底层异常，保留完整调用链 */ |
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public UrlFormatException(String url, Throwable cause) { |
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super("URL 格式不合法：" + url, cause); |
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this.invalidUrl = url; |
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} |
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public String getInvalidUrl() { return invalidUrl; } |
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} |
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// ─────────────────────────────────────────────
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// 必做2：RetryUtils —— 指数退避重试
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// wait = base * 2^attempt (base = 500ms)
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// ─────────────────────────────────────────────
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class RetryUtils { |
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private static final Logger log = Logger.getLogger(RetryUtils.class.getName()); |
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private static final long BASE_MS = 500; // 500ms 基准
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private static final int MAX_RETRY = 4; // 最多重试次数
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/** |
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* 执行带指数退避重试的操作 |
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* @param task 要执行的任务，返回 true 表示成功 |
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* @param maxRetry 最大重试次数 |
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* @return true = 最终成功，false = 全部失败 |
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*/ |
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public static boolean retry(Supplier<Boolean> task, int maxRetry) { |
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for (int attempt = 0; attempt <= maxRetry; attempt++) { |
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if (attempt > 0) { |
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long waitMs = BASE_MS * (1L << attempt); // base * 2^attempt
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log.info(String.format("第 %d 次重试，等待 %d ms ...", attempt, waitMs)); |
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try { |
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Thread.sleep(waitMs); |
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} catch (InterruptedException e) { |
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Thread.currentThread().interrupt(); |
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log.warning("重试等待被中断"); |
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return false; |
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} |
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} |
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try { |
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if (task.get()) { |
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if (attempt > 0) log.info("第 " + attempt + " 次重试成功"); |
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return true; |
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} |
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log.warning("第 " + attempt + " 次尝试失败（任务返回 false）"); |
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} catch (Exception e) { |
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log.warning("第 " + attempt + " 次尝试抛出异常：" + e.getMessage()); |
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} |
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} |
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log.severe("已达最大重试次数 " + maxRetry + "，放弃。"); |
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return false; |
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} |
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/** 使用默认最大重试次数 */ |
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public static boolean retry(Supplier<Boolean> task) { |
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return retry(task, MAX_RETRY); |
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} |
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/** |
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* 选做思考题优化： |
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* 如果某次失败是"永久失败"（如 404），则不应继续重试。 |
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* 通过 NonRetryableException 标记不可重试异常， |
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* 捕获到后立即终止重试循环。 |
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*/ |
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public static boolean retryWithFastFail(Supplier<Boolean> task, int maxRetry) { |
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for (int attempt = 0; attempt <= maxRetry; attempt++) { |
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if (attempt > 0) { |
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long waitMs = BASE_MS * (1L << attempt); |
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try { Thread.sleep(waitMs); } |
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catch (InterruptedException e) { |
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Thread.currentThread().interrupt(); |
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return false; |
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} |
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} |
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try { |
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if (task.get()) return true; |
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} catch (NonRetryableException e) { |
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// 选做思考题：404 / 永久失败 → 立即放弃，不再等待
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log.severe("不可重试异常，立即终止：" + e.getMessage()); |
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return false; |
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} catch (Exception e) { |
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log.warning("attempt " + attempt + " failed: " + e.getMessage()); |
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} |
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} |
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return false; |
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} |
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} |
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// ─────────────────────────────────────────────
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// 选做思考题辅助：不可重试异常（如 HTTP 404）
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// ─────────────────────────────────────────────
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class NonRetryableException extends RuntimeException { |
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private final int httpStatus; |
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public NonRetryableException(int httpStatus, String url) { |
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super("HTTP " + httpStatus + " 永久失败，不应重试：" + url); |
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this.httpStatus = httpStatus; |
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} |
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public int getHttpStatus() { return httpStatus; } |
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} |
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// ─────────────────────────────────────────────
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// 选做：CircuitBreaker（断路器）
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// 状态机：CLOSED → OPEN（连续失败 N 次）→ HALF_OPEN（冷却后）→ CLOSED
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// ─────────────────────────────────────────────
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class CircuitBreaker { |
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private static final Logger log = Logger.getLogger(CircuitBreaker.class.getName()); |
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public enum State { CLOSED, OPEN, HALF_OPEN } |
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private final int failureThreshold; // 连续失败多少次触发熔断
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private final long cooldownMs; // 熔断后冷却时间
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private volatile State state = State.CLOSED; |
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private final AtomicInteger failureCount = new AtomicInteger(0); |
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private volatile long openedAt = 0; |
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public CircuitBreaker(int failureThreshold, long cooldownMs) { |
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this.failureThreshold = failureThreshold; |
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this.cooldownMs = cooldownMs; |
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} |
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/** |
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* 执行一次操作，断路器保护： |
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* - OPEN 状态直接拒绝（不发请求） |
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* - 成功则重置计数器；失败则累加，超阈值触发熔断 |
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*/ |
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public boolean call(Supplier<Boolean> task) { |
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switch (getEffectiveState()) { |
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case OPEN: |
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log.warning("断路器 OPEN，请求被拒绝（冷却剩余 " |
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+ (cooldownMs - (System.currentTimeMillis() - openedAt)) + "ms）"); |
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return false; |
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case HALF_OPEN: |
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// 半开状态：放一个试探请求
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log.info("断路器 HALF_OPEN，尝试探测..."); |
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if (execute(task)) { |
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reset(); // 探测成功，恢复 CLOSED
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return true; |
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} |
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trip(); // 探测失败，重新熔断
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return false; |
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default: // CLOSED
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if (execute(task)) { |
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failureCount.set(0); |
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return true; |
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} |
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if (failureCount.incrementAndGet() >= failureThreshold) { |
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trip(); |
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} |
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return false; |
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} |
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} |
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private boolean execute(Supplier<Boolean> task) { |
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try { return Boolean.TRUE.equals(task.get()); } |
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catch (Exception e) { return false; } |
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} |
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private State getEffectiveState() { |
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if (state == State.OPEN |
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&& System.currentTimeMillis() - openedAt >= cooldownMs) { |
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state = State.HALF_OPEN; |
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} |
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return state; |
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} |
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private void trip() { |
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state = State.OPEN; |
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openedAt = System.currentTimeMillis(); |
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log.severe("断路器已熔断！连续失败 " + failureCount.get() + " 次。"); |
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} |
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private void reset() { |
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state = State.CLOSED; |
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failureCount.set(0); |
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log.info("断路器已恢复 CLOSED。"); |
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} |
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public State getState() { return getEffectiveState(); } |
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} |
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