在Jackson中，如何将非Map Iterable序列化为数组？

Question

Basically, what is the easiest way to make this test pass without changing the asymptotic runtime (ie, please don't tell me to copy set1 and set2 into a list because the whole point of Iterables.concat() is to avoid the copy):

@Test
public void jacksonObjectMapperSerializesIterableAsList() throws IOException {
  SortedSet<String> set1 = new TreeSet<>();
  set1.add("a");
  set1.add("b");
  set1.add("c");
  SortedSet<String> set2 = new TreeSet<>();
  set2.add("d");
  set2.add("e");
  set2.add("f");

  ObjectMapper mapper = new ObjectMapper();

  // This part passes.
  StringWriter set1Writer = new StringWriter();
  mapper.writeValue(set1Writer, set1);
  assertEquals("[\"a\",\"b\",\"c\"]", set1Writer.toString());

  // This part fails.
  // The actual value is: {"empty":false}
  StringWriter setsWriter = new StringWriter();
  mapper.writeValue(setsWriter, com.google.common.collect.Iterables.concat(set1, set2));
  assertEquals("[\"a\",\"b\",\"c\",\"d\",\"e\",\"f\"]", setsWriter.toString());
}

Answer 1

Apparently the solution is to configure the ObjectMapper with the GuavaModule :

ObjectMapper mapper = new ObjectMapper().registerModule(new GuavaModule());

I think this was the relevant issue/fix: https://github.com/FasterXML/jackson-datatype-guava/issues/46