java - 不平凡的(看似)StringIndexOutOfBoundsException

Question

我们的崩溃日志系统显示崩溃，我不明白它是如何发生的。用户输入未知。我已添加日志记录，但结果只有在下一个版本(约 2 周)后才能看到。

下面的代码如何抛出下一个异常:

Crashes with java.lang.StringIndexOutOfBoundsException length=0; index=1

不是因为并发问题？换句话说，它可能在什么情况下崩溃以及如何避免它(不将其包装到 try-catch 中)？如果是并发问题，可能会出现什么情况(我没有看到并发问题，但也许我错了)？

private String contactName; // has getter and setter

public String getFirstSymbol() {
  String firstSymbol = "";
  String trimmed = contactName.trim();
  if (!TextUtils.isEmpty(trimmed)) { // TextUtils.isEmpty is Android method: return str == null || str.length() == 0;
    String[] parts = trimmed.toUpperCase().split("\\s+");
    firstSymbol = parts[0].substring(0, 1); // crashes here:
  }
  return firstSymbol;
 }

上周 7 台设备上发生了约 100 次崩溃。

这是堆栈跟踪

  Fatal Exception: java.lang.StringIndexOutOfBoundsException: length=0; index=1
  at java.lang.String.substring(String.java:1971)
  at my.app.model.Contact.getFirstSymbol(Contact.java:256)
  at my.app.ui.AvatarView.bind(AvatarView.java:73)
  at my.app.viewholder.CallLogViewHolder.bind(CallLogViewHolder.java:50)
  at my.app.viewholder.CallLogViewHolder.bind(CallLogViewHolder.java:23)
  at my.app.ContactListAdapter.onBindViewHolder(ContactListAdapter.java:68)
  at my.app.ContactListAdapter.onBindViewHolder(ContactListAdapter.java:25)
  at androidx.recyclerview.widget.RecyclerView$Adapter.onCreateViewHolder(RecyclerView.java:6781)
  at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:6781)
  at androidx.recyclerview.widget.RecyclerView$Adapter.getItemCount(RecyclerView.java:6781)
  at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:6823)
  at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:5752)
  at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6019)
  at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5858)
  at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5854)
  at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2230)
  at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1557)
  at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1517)
  at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:612)
  at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3924)
  at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3641)
  at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4194)
  at android.view.View.layout(View.java:20964)
  at android.view.ViewGroup.layout(ViewGroup.java:6440)
  at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
  at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
  at android.view.View.layout(View.java:20964)
  at android.view.ViewGroup.layout(ViewGroup.java:6440)
  at androidx.viewpager.widget.ViewPager.onLayout(ViewPager.java:1775)
  at android.view.View.layout(View.java:20964)
  at android.view.ViewGroup.layout(ViewGroup.java:6440)
  at com.google.android.material.appbar.HeaderScrollingViewBehavior.layoutChild(HeaderScrollingViewBehavior.java:142)
  at com.google.android.material.appbar.HeaderScrollingViewBehavior.findFirstDependency(HeaderScrollingViewBehavior.java:142)
  at com.google.android.material.appbar.ViewOffsetBehavior.onLayoutChild(ViewOffsetBehavior.java:41)
  at com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior.onMeasureChild(AppBarLayout.java:1556)
  at androidx.coordinatorlayout.widget.CoordinatorLayout.onLayout(CoordinatorLayout.java:888)
  at android.view.View.layout(View.java:20964)
  at android.view.ViewGroup.layout(ViewGroup.java:6440)
  at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
  at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
  at android.view.View.layout(View.java:20964)
  at android.view.ViewGroup.layout(ViewGroup.java:6440)
  at com.google.android.material.appbar.HeaderScrollingViewBehavior.layoutChild(HeaderScrollingViewBehavior.java:142)
  at com.google.android.material.appbar.HeaderScrollingViewBehavior.findFirstDependency(HeaderScrollingViewBehavior.java:142)
  at com.google.android.material.appbar.ViewOffsetBehavior.onLayoutChild(ViewOffsetBehavior.java:41)
  at com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior.onMeasureChild(AppBarLayout.java:1556)
  at androidx.coordinatorlayout.widget.CoordinatorLayout.onLayout(CoordinatorLayout.java:888)
  at android.view.View.layout(View.java:20964)
  at android.view.ViewGroup.layout(ViewGroup.java:6440)
  at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
  at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
  at android.view.View.layout(View.java:20964)
  at android.view.ViewGroup.layout(ViewGroup.java:6440)
  at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1791)
  at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1635)
  at android.widget.LinearLayout.onLayout(LinearLayout.java:1544)
  at android.view.View.layout(View.java:20964)
  at android.view.ViewGroup.layout(ViewGroup.java:6440)
  at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
  at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
  at android.view.View.layout(View.java:20964)
  at android.view.ViewGroup.layout(ViewGroup.java:6440)
  at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1791)
  at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1635)
  at android.widget.LinearLayout.onLayout(LinearLayout.java:1544)
  at android.view.View.layout(View.java:20964)
  at android.view.ViewGroup.layout(ViewGroup.java:6440)
  at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
  at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
  at com.android.internal.policy.DecorView.onLayout(DecorView.java:955)
  at android.view.View.layout(View.java:20964)
  at android.view.ViewGroup.layout(ViewGroup.java:6440)
  at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3092)
  at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2779)
  at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1863)
  at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8072)
  at android.view.Choreographer$CallbackRecord.run(Choreographer.java:911)
  at android.view.Choreographer.doCallbacks(Choreographer.java:723)
  at android.view.Choreographer.doFrame(Choreographer.java:658)
  at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:897)
  at android.os.Handler.handleCallback(Handler.java:790)
  at android.os.Handler.dispatchMessage(Handler.java:99)
  at android.os.Looper.loop(Looper.java:164)
  at android.app.ActivityThread.main(ActivityThread.java:7000)
  at java.lang.reflect.Method.invoke(Method.java)
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:441)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1408)

Answer 1

这里不存在线程安全/并发问题。此方法可能与其他线程共享的唯一值是contactName 的值。这是一个String 引用。 String 是不可变的。此方法从(可能)共享的不可变 String 派生的其他值都是线程限制的。

除此之外，我也很困惑。 trim 应删除 \s+ 匹配的任何前导或尾随字符。 !isEmpty 保护消除了空字符串的可能性。因此 parts 数组应该至少有 1 个元素，并且第一个元素应该至少有一个字符。

但异常(exception)情况似乎有所不同。

因此，这留下了人们通常会认为荒谬的“替代”解释:

• 也许这是在 JIT 编译器损坏的平台上发生的。
• 可能发生这种情况的平台在 String 或 Pattern 中存在错误。
• 可能是硬件问题。
• 也许您的应用的某个版本的编译代码与您正在查看的源代码不匹配。

这些“替代”解释都无法为您提供任何前进的方向。因此，如果您找不到更好的解释，我建议您用 try { ... } catch 包围此违规代码，并尝试记录 contactName 的长度和内容 触发问题的字符串。将此包含在下一个版本中，如果/当您开始出现故障时，请准备好发布具有真正修复功能的次要版本。或者，只需将其视为用户输入了空联系人姓名......或类似的内容。