java - Guava Joiner 对 null 元素抛出 NPE

Question

这里Joiner的初始化是否不正确？我有以下类，当我尝试使用 joiner 连接示例 paths 数组时，我收到一个 NullPointerException。

public class CPath {
  private static final Joiner joiner = Joiner.on("/");

  private String[] elements;

  @Override
  public String toString() {
    return joiner.join(elements);
  }
}

// main method
final String[] paths = {"a/b/c", "d", "", null, "e/f/g", "h/i", null, ""};
final CPath c3 = new CPath(paths);
c3.toString(); //<<<< NPE

Answer 1

您必须使用 skipNulls() 或 useForNull(defaultValue)，它位于其文档的顶部；

If neither skipNulls() nor useForNull(String) is specified, the joining methods will throw NullPointerException if any given element is null.

所以你必须像这样初始化joiner；

Joiner joiner = Joiner.on("/").skipNulls();

或

Joiner joiner = Joiner.on("/").useForNull("");

Documentation of Joiner from Guava