---

## Key Components

### Core Classes

- **Crawler** (`Crawler.java`): Main orchestrator - `execute()`, `addUrl()`, `cleanup()`, `stop()`
- **CrawlerContext** (`CrawlerContext.java`): Execution context - `sessionId`, `status`, `accessCount`, `numOfThread`, `maxDepth`, `maxAccessCount`

                            throw new WebApiException(HttpServletResponse.SC_NOT_FOUND, "Not found: " + favoriteUrl);
                        }

                        if (!favoriteLogService.addUrl(userCode, (userInfo, favoriteLog) -> {
                            favoriteLog.setUserInfoId(userInfo.getId());
                            favoriteLog.setUrl(favoriteUrl);
                            favoriteLog.setDocId(docId);

    oneValueAccumulatorByAddAllEmptyStats.addAll(Stats.of());

    twoValuesAccumulator = new StatsAccumulator();
    twoValuesAccumulator.addAll(TWO_VALUES);

    twoValuesAccumulatorByAddAllStats = new StatsAccumulator();
    twoValuesAccumulatorByAddAllStats.addAll(Stats.of(ONE_VALUE));
    twoValuesAccumulatorByAddAllStats.addAll(Stats.of(OTHER_ONE_VALUE));

    oneValueAccumulatorByAddAllEmptyStats.addAll(Stats.of());

    twoValuesAccumulator = new StatsAccumulator();
    twoValuesAccumulator.addAll(TWO_VALUES);

    twoValuesAccumulatorByAddAllStats = new StatsAccumulator();
    twoValuesAccumulatorByAddAllStats.addAll(Stats.of(ONE_VALUE));
    twoValuesAccumulatorByAddAllStats.addAll(Stats.of(OTHER_ONE_VALUE));

    assertEquals(HashMultiset.create(asList("a", "b", "b", "b", "c")), multiset);
  }

  public void testBuilderAddAllIterator() {
    Iterator<String> iterator = asList("a", "b", "a", "c").iterator();
    ImmutableMultiset<String> multiset =
        new ImmutableMultiset.Builder<String>().addAll(iterator).build();
    assertEquals(HashMultiset.create(asList("a", "b", "a", "c")), multiset);
  }

  }

  public void testBuilderAddAll_iterable() {
    List<String> a = asList("a", "b");
    List<String> b = asList("c", "d");
    ImmutableList<String> list = new ImmutableList.Builder<String>().addAll(a).addAll(b).build();
    assertEquals(asList("a", "b", "c", "d"), list);
    b.set(0, "f");
    assertEquals(asList("a", "b", "c", "d"), list);
  }

  public void testBuilderAddAll_iterator() {

    emptyAccumulatorByAddAllEmptyPairedStats.addAll(emptyAccumulator.snapshot());

    oneValueAccumulator = new PairedStatsAccumulator();
    oneValueAccumulator.add(ONE_VALUE, OTHER_ONE_VALUE);

    oneValueAccumulatorByAddAllEmptyPairedStats = new PairedStatsAccumulator();
    oneValueAccumulatorByAddAllEmptyPairedStats.add(ONE_VALUE, OTHER_ONE_VALUE);
    oneValueAccumulatorByAddAllEmptyPairedStats.addAll(emptyAccumulator.snapshot());

    assertEquals(HashMultiset.create(asList("a", "b", "b", "b", "c")), multiset);
  }

  public void testBuilderAddAllIterator() {
    Iterator<String> iterator = asList("a", "b", "a", "c").iterator();
    ImmutableMultiset<String> multiset =
        new ImmutableMultiset.Builder<String>().addAll(iterator).build();
    assertEquals(HashMultiset.create(asList("a", "b", "a", "c")), multiset);
  }

  }

  public void testBuilderAddAll_iterable() {
    List<String> a = asList("a", "b");
    List<String> b = asList("c", "d");
    ImmutableList<String> list = new ImmutableList.Builder<String>().addAll(a).addAll(b).build();
    assertEquals(asList("a", "b", "c", "d"), list);
    b.set(0, "f");
    assertEquals(asList("a", "b", "c", "d"), list);
  }

  public void testBuilderAddAll_iterator() {

    private final Adder adder;

    FailsToForwardReturnValue(Adder adder) {
      this.adder = adder;
    }

    @Override
    public int add(int a, int b) {
      return adder.add(a, b) + 1;
    }

    @Override
    public String toString() {
      return adder.toString();
    }
  }

  private static final class FailsToPropagateException implements Adder {