jackson-dataformat-xml: Unable to serialize top-level Java8 Stream

A Stream nested in another object is serialized using a value wrapper just as a collection or array, serializing a Stream directly fails when more than one element is available as it tries to write a second root. If the Stream emits only a single element serialization works but without wrapping:

public class StreamTest {
    private static final ObjectMapper OBJECT_MAPPER = new XmlMapper()
            .registerModule(new Jdk8Module());
    
    private static class StreamContainer {
        @JsonProperty
        private Stream<String> stream;
        public StreamContainer(Stream<String> stream) { this.stream = stream; }
    }

    @Test
    public void testTopLevelOneElement() throws JsonProcessingException {
        assertNotEquals("<Head>a</Head>",
                OBJECT_MAPPER.writeValueAsString(Stream.of("a")));
    }
    
    @Test
    public void testTopLevelTwoElements() throws JsonProcessingException {
        try {
            assertEquals("<Head><item>a</item><item>b</item></Head>",
                    OBJECT_MAPPER.writeValueAsString(Stream.of("a", "b")));
        } catch (JsonMappingException e) {
            fail("Trying to output second root?", e);
        }
    }
    
    @Test
    public void testNestedOneElement() throws JsonProcessingException {
        assertEquals("<StreamContainer><stream>a</stream></StreamContainer>",
                OBJECT_MAPPER.writeValueAsString(new StreamContainer(Stream.of("a"))));
    }
    
    
    @Test
    public void testNestedTwoElements() throws JsonProcessingException {
        assertEquals("<StreamContainer><stream>a</stream><stream>b</stream></StreamContainer>",
                OBJECT_MAPPER.writeValueAsString(new StreamContainer(Stream.of("a", "b"))));
    }
}

The root element name is Head for Stream serialization as it’s determined from the actual class name ReferencePipeline$Head.

The cause lies in TypeUtil.isIndexedType(Class<?>) which just checks for Arrays and Collections and only if this returns true, a field name is written (and _nextName set).

It works for the nested Stream as _nextName is set due to the Stream being written as a field (multiple times).

About this issue

Original URL
State: open
Created 6 years ago
Comments: 17 (17 by maintainers)

Commits related to this issue

Update release notes wrt fixes from #597 (for #148, #302, #329) — committed to FasterXML/jackson-dataformat-xml by cowtowncoder a year ago

Most upvoted comments

jackson needs Jdk8Module to support Streams - see https://github.com/FasterXML/jackson-modules-java8

pjfanning on May 11, 2023

@JooHyukKim I would expect that Streams should be treated similarly to an Iterable - like a Collection but ideally without pulling the full Iterable or Stream into memory at one time.

pjfanning on May 11, 2023