Java Jackson-如何替换序列化映射
我需要将一个包含列表和映射的图形序列化为JSON。每个映射实例都包含一个UUID字段。该图可以包含多个具有相同UUID的映射实例。具有相同UUID的映射被认为是相同的 在序列化过程中，我希望替换以前仅由其UUID序列化的映射实例 与杰克逊一起实现这一目标的最佳方式是什么Java Jackson-如何替换序列化映射,java,jackson,Java,Jackson,我需要将一个包含列表和映射的图形序列化为JSON。每个映射实例都包含一个UUID字段。该图可以包含多个具有相同UUID的映射实例。具有相同UUID的映射被认为是相同的 在序列化过程中，我希望替换以前仅由其UUID序列化的映射实例 与杰克逊一起实现这一目标的最佳方式是什么 谢谢您可以为图形类实现自定义序列化程序 public class IdentifiableSerializerTest { public static void main(String[] args) throws J
谢谢您可以为图形类实现自定义序列化程序
public class IdentifiableSerializerTest {
public static void main(String[] args) throws JsonProcessingException {
ObjectMapper mapper = createObjectMapper();
test(mapper);
}
interface Identifiable {
Long getId();
}
public static ObjectMapper createObjectMapper() {
ObjectMapper mapper = new ObjectMapper();
// disable quoting - for testing purpose
mapper.configure(JsonGenerator.Feature.QUOTE_FIELD_NAMES, false);
mapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);
// register serializer for Identifiable type
SimpleModule module = new SimpleModule();
module.addSerializer(Identifiable.class, new IdentifiableSerializer(mapper.writer()));
mapper.registerModule(module);
// lifecycle hook to re-init IdentifiableSerializer on root-level serialize calls
mapper.setSerializerProvider(new IdentifiableSerializerProvider());
return mapper;
}
/**
* This class serves to intercept root-level serialize calls in order to
* clean the map of visited objects, see {@link IdentifiableSerializer#visited}.
*
* TODO: this seems lot of code just to get a hook on root-level serialize calls...
*/
public static class IdentifiableSerializerProvider extends DefaultSerializerProvider {
public IdentifiableSerializerProvider() { super(); }
protected IdentifiableSerializerProvider(SerializerProvider src, SerializationConfig config, SerializerFactory f) {
super(src, config, f);
}
@Override
public DefaultSerializerProvider createInstance(SerializationConfig config, SerializerFactory f) {
return new IdentifiableSerializerProvider(this, config, f);
}
@Override
public void serializeValue(JsonGenerator gen, Object value) throws IOException {
IdentifiableSerializer.reset();
super.serializeValue(gen, value);
}
}
public static class IdentifiableSerializer extends JsonSerializer<Identifiable> {
private static ThreadLocal<Set> visited = new ThreadLocal<Set>() {
@Override
protected Set initialValue() {
return new HashSet();
}
};
public static void reset() {
visited.get().clear();
}
private final ObjectWriter delegate;
public IdentifiableSerializer(ObjectWriter delegate) {
this.delegate = delegate;
}
@Override
public void serialize(Identifiable value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
Long id = value.getId();
Set seen = visited.get();
if (seen.contains(id)) {
jgen.writeStartObject();
jgen.writeNumberField("@REF", id);
jgen.writeEndObject();
}
else {
seen.add(id);
delegate.writeValue(jgen, value);
}
}
}
static class IdentifiableMap extends HashMap implements Identifiable {
static long counter = 0;
Long id = counter++;
{
put("@ID", id);
}
@Override
public Long getId() {
return id;
}
}
public static void test(ObjectMapper mapper) throws JsonProcessingException {
Map myMap = new IdentifiableMap() {{
put("key1", 1);
put("key2", 2);
put("key3", 3);
}};
List<Map> myList = Arrays.asList(myMap, myMap);
String expected = "[{key1:1,key2:2,key3:3,@ID:0},{@REF:0}]";
String actual = mapper.writeValueAsString(myList);
Assert.assertEquals(expected, actual);
System.out.println("SUCCESS");
}
}
@Override
public void serialize(T value, JsonGenerator jgen, SerializerProvider provider)
throws IOException, JsonProcessingException
当你这么做的时候，你需要让jackson知道你的连载程序。您可以通过使用
@JsonSerialize（using=CustomSerializer.class）public class IdentifiableSerializerTest {
public static void main(String[] args) throws JsonProcessingException {
ObjectMapper mapper = createObjectMapper();
test(mapper);
}
interface Identifiable {
Long getId();
}
public static ObjectMapper createObjectMapper() {
ObjectMapper mapper = new ObjectMapper();
// disable quoting - for testing purpose
mapper.configure(JsonGenerator.Feature.QUOTE_FIELD_NAMES, false);
mapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);
// register serializer for Identifiable type
SimpleModule module = new SimpleModule();
module.addSerializer(Identifiable.class, new IdentifiableSerializer(mapper.writer()));
mapper.registerModule(module);
// lifecycle hook to re-init IdentifiableSerializer on root-level serialize calls
mapper.setSerializerProvider(new IdentifiableSerializerProvider());
return mapper;
}
/**
* This class serves to intercept root-level serialize calls in order to
* clean the map of visited objects, see {@link IdentifiableSerializer#visited}.
*
* TODO: this seems lot of code just to get a hook on root-level serialize calls...
*/
public static class IdentifiableSerializerProvider extends DefaultSerializerProvider {
public IdentifiableSerializerProvider() { super(); }
protected IdentifiableSerializerProvider(SerializerProvider src, SerializationConfig config, SerializerFactory f) {
super(src, config, f);
}
@Override
public DefaultSerializerProvider createInstance(SerializationConfig config, SerializerFactory f) {
return new IdentifiableSerializerProvider(this, config, f);
}
@Override
public void serializeValue(JsonGenerator gen, Object value) throws IOException {
IdentifiableSerializer.reset();
super.serializeValue(gen, value);
}
}
public static class IdentifiableSerializer extends JsonSerializer<Identifiable> {
private static ThreadLocal<Set> visited = new ThreadLocal<Set>() {
@Override
protected Set initialValue() {
return new HashSet();
}
};
public static void reset() {
visited.get().clear();
}
private final ObjectWriter delegate;
public IdentifiableSerializer(ObjectWriter delegate) {
this.delegate = delegate;
}
@Override
public void serialize(Identifiable value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
Long id = value.getId();
Set seen = visited.get();
if (seen.contains(id)) {
jgen.writeStartObject();
jgen.writeNumberField("@REF", id);
jgen.writeEndObject();
}
else {
seen.add(id);
delegate.writeValue(jgen, value);
}
}
}
static class IdentifiableMap extends HashMap implements Identifiable {
static long counter = 0;
Long id = counter++;
{
put("@ID", id);
}
@Override
public Long getId() {
return id;
}
}
public static void test(ObjectMapper mapper) throws JsonProcessingException {
Map myMap = new IdentifiableMap() {{
put("key1", 1);
put("key2", 2);
put("key3", 3);
}};
List<Map> myList = Arrays.asList(myMap, myMap);
String expected = "[{key1:1,key2:2,key3:3,@ID:0},{@REF:0}]";
String actual = mapper.writeValueAsString(myList);
Assert.assertEquals(expected, actual);
System.out.println("SUCCESS");
}
}
公共类IdentifiableSerializerTest{
公共静态void main（字符串[]args）引发JsonProcessingException{
ObjectMapper映射器=createObjectMapper（）；
测试（制图员）；
}
接口可识别{
长getId（）；
}
公共静态对象映射器createObjectMapper（）{
ObjectMapper mapper=新的ObjectMapper（）；
//禁用报价-用于测试目的
配置（JsonGenerator.Feature.QUOTE\u字段名称，false）；
configure（JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES，true）；
//可识别类型的注册序列化程序
SimpleModule=新的SimpleModule（）；
module.addSerializer（identificatable.class，新的identificatableSerializer（mapper.writer（））；
映射器注册表模块（模块）；
//在根级别序列化调用上重新初始化IdentifiableSerializer的生命周期挂钩
setSerializerProvider（新的可识别SerializerProvider（））；
返回映射器；
}
/**
*此类用于拦截根级别的序列化调用，以便
*清理访问对象的映射，请参阅{@link-identiableserializer#visted}。
*
*TODO:这似乎有很多代码只是为了在根级别序列化调用上获得一个钩子。。。
*/
公共静态类IdentifiableSerializerProvider扩展了DefaultSerializerProvider{
公共可标识SerializerProvider（）{super（）；}
受保护的可标识SerializerProvider（SerializerProvider src、SerializationConfig配置、SerializerFactory f）{
超级（src，config，f）；
}
@凌驾
公共DefaultSerializerProvider createInstance（SerializationConfig配置，SerializerFactory f）{
返回新的IdentifiableSerializerProvider（this，config，f）；
}
@凌驾
公共void序列化值（JsonGenerator gen，对象值）引发IOException{
IdentifiableSerializer.reset（）；
super.value（gen，value）；
}
}
公共静态类IdentifiableSerializer扩展了JsonSerializer{
访问的私有静态ThreadLocal=新建ThreadLocal（）{
@凌驾
受保护的集合初始值（）{
返回新的HashSet（）；
}
};
公共静态无效重置（）{
已访问。获取（）。清除（）；
}
私人代表；
公共可标识序列化程序（ObjectWriter委托）{
this.delegate=委托；
}
@凌驾
public void serialize（可识别值、JsonGenerator jgen、SerializerProvider提供程序）引发IOException{
Long id=value.getId（）；
Set seen=visted.get（）；
如果（见。包含（id））{
jgen.writeStartObject（）；
jgen.writeNumberField（“@REF”，id）；
jgen.writeEndObject（）；
}
否则{
见。添加（id）；
delegate.writeValue（jgen，value）；
}
}
}
静态类IdentifiableMap扩展HashMap实现可识别{
静态长计数器=0；
长id=计数器++；
{
put（“@ID”，ID）；
}
@凌驾
公共长getId（）{
返回id；
}
}
公共静态无效测试（ObjectMapper映射器）抛出JsonProcessingException{
Map myMap=新的可识别地图（）{{
放置（“键1”，1）；
放置（“键2”，2）；
放置（“键3”，3）；
}};
List myList=Arrays.asList（myMap，myMap）；
字符串应为=“[{key1:1，key2:2，key3:3，@ID:0}，{@REF:0}]”；
String actual=mapper.writeValueAsString（myList）；
Assert.assertEquals（预期、实际）；
System.out.println（“成功”）；
}
}