src/test/java/com/fasterxml/jackson/databind/deser/jdk/JDKCollectionsDeserTest.java

package com.fasterxml.jackson.databind.deser.jdk;

import java.util.*;

import com.fasterxml.jackson.annotation.JsonTypeInfo;

import com.fasterxml.jackson.core.type.TypeReference;

import com.fasterxml.jackson.databind.*;

/**
 * Tests for special collection/map types via `java.util.Collections`
 */
public class JDKCollectionsDeserTest extends BaseMapTest
{
    static class XBean {
        public int x;

        public XBean() { }
        public XBean(int x) { this.x = x; }
    }

    /*
    /**********************************************************************
    /* Test methods
    /**********************************************************************
     */

    private final static ObjectMapper MAPPER = new ObjectMapper();
    
    // And then a round-trip test for singleton collections
    public void testSingletonCollections() throws Exception
    {
        final TypeReference<?> xbeanListType = new TypeReference<List<XBean>>() { };

        String json = MAPPER.writeValueAsString(Collections.singleton(new XBean(3)));
        Collection<XBean> result = MAPPER.readValue(json, xbeanListType);
        assertNotNull(result);
        assertEquals(1, result.size());
        assertEquals(3, result.iterator().next().x);

        json = MAPPER.writeValueAsString(Collections.singletonList(new XBean(28)));
        result = MAPPER.readValue(json, xbeanListType);
        assertNotNull(result);
        assertEquals(1, result.size());
        assertEquals(28, result.iterator().next().x);
    }

    // [databind#1868]: Verify class name serialized as is
    public void testUnmodifiableSet() throws Exception
    {
        ObjectMapper mapper = new ObjectMapper();
        mapper.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL, JsonTypeInfo.As.PROPERTY);

        Set<String> theSet = Collections.unmodifiableSet(Collections.singleton("a"));
        String json = mapper.writeValueAsString(theSet);

        assertEquals("[\"java.util.Collections$UnmodifiableSet\",[\"a\"]]", json);

        // 04-Jan-2018, tatu: Alas, no way to make this actually work well, at this point.
         //   In theory could jiggle things back on deser, using one of two ways:
         //
         //   1) Do mapping to regular Set/List types (abstract type mapping): would work, but get rid of immutability
         //   2) Have actually separate deserializer OR ValueInstantiator
        /*
        Set<String> result = mapper.readValue(json, Set.class);
        assertNotNull(result);
        assertEquals(1, result.size());
        */
    }
}