Jackson does not support deserializing new Java 9 unmodifiable collections #2900
Description
Describe the bug
Java 9 introduced new unmodifiable collection APIs. For instance, List.of.
Today, Jackson has a special deserializer for Collections.unmodifiableList but not for these new classes:
Version information
2.11.2
To Reproduce
@Test
public void testUnmodifiableList() throws JsonMappingException, JsonProcessingException {
final ObjectMapper mapper = new ObjectMapper();
mapper.activateDefaultTypingAsProperty(
new NoCheckSubTypeValidator(),
ObjectMapper.DefaultTyping.NON_FINAL,
"@class"
);
final List<String> list = Collections.unmodifiableList(Collections.singletonList("a"));
final String actualJson = mapper.writeValueAsString(list);
System.out.println(actualJson);
final List output = mapper.readValue(actualJson, List.class);
System.out.println(output);
}
@Test
public void testJava9UmodifiableList() throws JsonMappingException, JsonProcessingException {
final ObjectMapper mapper = new ObjectMapper();
mapper.activateDefaultTypingAsProperty(
new NoCheckSubTypeValidator(),
ObjectMapper.DefaultTyping.NON_FINAL,
"@class"
);
final List<String> list = List.of("a");
final String actualJson = mapper.writeValueAsString(list);
System.out.println(actualJson);
final List output = mapper.readValue(actualJson, List.class);
System.out.println(output);
}
@Test
public void testJava9ListWrapped() throws JsonMappingException, JsonProcessingException {
final ObjectMapper mapper = new ObjectMapper();
mapper.activateDefaultTypingAsProperty(
new NoCheckSubTypeValidator(),
ObjectMapper.DefaultTyping.NON_FINAL,
"@class"
);
final List<String> list = Collections.unmodifiableList(List.of("a"));
final String actualJson = mapper.writeValueAsString(list);
System.out.println(actualJson);
final List output = mapper.readValue(actualJson, List.class);
System.out.println(output);
}testJava9UmodifiableList fails. The other 2 pass.
Expected behavior
I would think the new classes are added as additional aliases as candidates for special deserialization.
Unfortunately, I think this is tricky for two reasons:
- These are Java 9 classes and Jackson supports a lower minimum Java version. I'm not sure if there's a way to add them without breaking backwards compatibility or introducing a new Java 9 add-on library, like there exists for Java 8.
- There are multiple classes. For List.of, there seem to be 3 different ones depending on the number of arguments:
- Empty list if 0 arguments.
- List12 if 1 or 2 arguments.
- ListN if more than 2 arguments.
Source: https://hg.openjdk.java.net/jdk/jdk11/file/1ddf9a99e4ad/src/java.base/share/classes/java/util/List.java#l1031