`@JsonDeserialize.contentConverter` does not work for non-builtin collections

[mwisnicki]

I'm trying to use content converter with Guava collections like so:

@JsonDeserialize(contentConverter = DoublingConverter.class)
public ImmutableList<Integer> ints;

However this does not seem to do anything despite Jackson having deserializers for Guava.
Changing collection to one of built-in types makes the program work.

I would expect that if Jackson can deserialize given collection type, it will also be able to apply converters to it.
Posting here rather than to datatypes project since this is not related to specific collection implementation but rather a generic problem.

TestImmutableListContentConverter .java

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.util.StdConverter;
import com.fasterxml.jackson.datatype.guava.GuavaModule;
import com.google.common.collect.ImmutableList;

public class TestImmutableListContentConverter {

    static class Holder {
        @JsonDeserialize(contentConverter = DoublingConverter.class)
        public ImmutableList<Integer> ints;
    }

    static class DoublingConverter extends StdConverter<Integer, Integer> {
        @Override
        public Integer convert(Integer value) {
            return value != null ? value * 2 : null;
        }
    }

    public static void main(String[] args) throws Exception {
        var json = """
                { "ints": [1,2,3] }
                """;
        var om = new ObjectMapper();
        om.registerModule(new GuavaModule());
        var value = om.readValue(json, Holder.class);
        System.out.println(value.ints);
    }

}

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>test-jackson-guava</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>16</maven.compiler.source>
        <maven.compiler.target>16</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>com.fasterxml.jackson.datatype</groupId>
            <artifactId>jackson-datatype-guava</artifactId>
            <version>2.13.0-rc1</version>
        </dependency>
    </dependencies>

</project>

[cowtowncoder]

Belongs under Guava datatype library since this requires support by deserializers provided there; will transfer.

[cowtowncoder]

Would be great to have a test case, if anyone wants something easy to do. Implementation should not be difficult either, need to have a look at default CollectionDeserializer, lift necessary handling.

[mwisnicki]

But isn't this a bug in common code?

[mwisnicki]

Would be great to have a test case, if anyone wants something easy to do. Implementation should not be difficult either, need to have a look at default CollectionDeserializer, lift necessary handling.

Should I submit my testcase in a form of PR adding unit test?

[cowtowncoder]

@mwisnicki Unlikely based on your mentioning that it works for built-in collections? Guava datatype provides its own Immutable-type deserializers which need to handle a few aspects wrt customizations and configuration.

If it turns out the problem happens to be in jackson-databind we can transfer it back of course.

[cowtowncoder]

Yes, PR for the unit test would be a great start! It does not have to be separate if you (or anyone else) can figure out the fix too but it can be.