java.util.BitSet是个非常方便的比特位数据存储和操作类，一个 bit 具有2个值：0和1，正好可以用来表示 false 和 true，适用于判断“数据是否存在”的场景。
但是，这个从JDK1.0版本就存在的类，Jackson,Fastjson这些主流的JSON工具却并没有对它提供序列化和反序列化支持。
所以如果要在自己的数据结构中用到BitSet,就要自己实现序列化和反序列化。
上篇博客《java:java.util.BitSet对象的Fastjson序列化和反序列化实现》介绍了Fastjson实现，本文说明Jackson如何支持BitSet类型的序列化和反序列化
以下是BitSet对象的Jackson序列化和反序列化实现,
主要思路就是在序列化过程中将BitSet的数据转为JSON数组(如[7707,8822]或单个数字(当设置SerializationFeature.WRITE_SINGLE_ELEM_ARRAYS_UNWRAPPED特性时).
在反序列化阶段，根据TOKEN类型不同，将数据序列化为long[]再调用BitSet.valueOf方法转为BitSet对象返回。

/*** {@link BitSet} 的JACKSON序列化和反序列化实现* @author guyadong* @since 3.30.1*/
public class BitsetJacksonCodec {public static final Deserializer DESERIALIZER = new Deserializer();public static final Serializer SERIALIZER = new Serializer();/*** {@link BitSet}反序列化实现*/public static class Deserializer extends JsonDeserializer<BitSet> {private final JsonDeserializer<?> longArrayDeserializer = PrimitiveArrayDeserializers.forType(long.class);@Overridepublic BitSet deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException {ObjectMapper mapper = (ObjectMapper) jp.getCodec();switch(jp.currentTokenId()) {case JsonTokenId.ID_NULL:jp.nextToken();return null;case JsonTokenId.ID_START_ARRAY:{long[] longs = (long[]) longArrayDeserializer.deserialize(jp, ctxt);return BitSet.valueOf(longs);}case JsonTokenId.ID_STRING:{/** 将文本递归解析 */String text = jp.getText();jp.nextToken();return mapper.readValue(text, BitSet.class);}default:{/** 数字类型:VALUE_NUMBER_INT */BitSet bitSet = BitSet.valueOf(new long[] {jp.getNumberValue().longValue()});jp.nextToken();return bitSet;}}}}/*** {@link BitSet}序列化实现*/public static class Serializer extends JsonSerializer<BitSet> {@SuppressWarnings({ "rawtypes" })private final JsonSerializer longArraySerializer = StdArraySerializers.findStandardImpl(long[].class);@SuppressWarnings("unchecked")@Overridepublic void serialize(BitSet value, JsonGenerator gen, SerializerProvider serializers)throws IOException, JsonProcessingException {if(null == value) {gen.writeNull();}else {longArraySerializer.serialize(value.toLongArray(), gen, serializers);}}}
}

测试及调用示例：

	@Testpublic void test5JacksonCodec() {try {BitSet bitSet = BitSet.valueOf(new byte[] {27,30});ObjectMapper mapper = new ObjectMapper();SimpleModule module = new SimpleModule().addDeserializer(BitSet.class, BitsetJacksonCodec.DESERIALIZER).addSerializer(BitSet.class, BitsetJacksonCodec.SERIALIZER);mapper.registerModule(module);{/** 序列化为数组 */ String json = mapper.writeValueAsString(bitSet);log("JSON:{}",json);assertTrue(json.equals("[7707]"));BitSet parsed = mapper.readValue(json, BitSet.class);assertTrue(bitSet.equals(parsed));}{mapper.enable(SerializationFeature.WRITE_SINGLE_ELEM_ARRAYS_UNWRAPPED);/** 序列化为数字 */ String json = mapper.writeValueAsString(bitSet);log("JSON:{}",json);assertTrue(json.equals("7707"));BitSet parsed = mapper.readValue(json, BitSet.class);assertTrue(bitSet.equals(parsed));}{mapper.disable(SerializationFeature.WRITE_SINGLE_ELEM_ARRAYS_UNWRAPPED);/** 序列化为数字 */ String json = mapper.writeValueAsString(new TestBean(bitSet, 32));log("JSON:{}",json);assertTrue(json.equals("{\"bitSet\":[7707],\"age\":32}"));TestBean parsed = mapper.readValue(json, TestBean.class);assertTrue(bitSet.equals(parsed.bitSet));}}catch (Throwable e) {e.printStackTrace();fail();}}public static class TestBean{BitSet bitSet;Integer age;public TestBean() {}public TestBean(BitSet bitSet, Integer age) {this.bitSet = bitSet;this.age = age;}public BitSet getBitSet() {return bitSet;}public void setBitSet(BitSet bitSet) {this.bitSet = bitSet;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}}

完整实现代码参见码云仓库：https://gitee.com/l0km/sql2java/blob/dev/sql2java-base/src/main/java/gu/sql2java/json/BitsetJacksonCodec.java
完整测试代码参见码云仓库：https://gitee.com/l0km/sql2java/blob/dev/sql2java-base/src/test/java/gu/sql2java/BitSetJsonCodecTest.java