I simply have a Map. But it can return a Map, which may also return a Map. It's possible up to 3 to 4 nested Maps. So when I want to access a nested value, I need to do this:
((Map)((Map)((Map)CacheMap.get("id")).get("id")).get("id")).get("id")
Is there a cleaner way to do this?
The reason I'm using a Map instead of mapping it to an object is for maintainability (e.g. when there are new fields).
Note:
Map<String, Object>
It has to be Object because it won't always return a Hashmap. It may return a String or a Long.
Further clarification:
What I'm doing is I'm calling an api which returns a json response which I save as a Map.
Here's some helper methods that may help things seem cleaner and more readable:
#SuppressWarnings("unchecked")
public static Map<String, Object> getMap(Map<String, Object> map, String key) {
return (Map<String, Object>)map.get(key);
}
#SuppressWarnings("unchecked")
public static String getString(Map<String, Object> map, String key) {
return (String)map.get(key);
}
#SuppressWarnings("unchecked")
public static Integer geInteger(Map<String, Object> map, String key) {
return (Integer)map.get(key);
}
// you can add more methods for Date, Long, and any other types you know you'll get
But you would have to nest the calls:
String attrValue = getString(getMap(getMap(map, id1), id2), attrName);
Or, if you want something more funky, add the above methods as instance methods to a map impl:
public class FunkyMap extends HashMap<String, Object> {
#SuppressWarnings("unchecked")
public FunkyMap getNode(String key) {
return (FunkyMap)get(key);
}
#SuppressWarnings("unchecked")
public String getString(String key) {
return (String)get(key);
}
#SuppressWarnings("unchecked")
public Integer geInteger(String key) {
return (Integer)get(key);
}
// you can add more methods for Date, Long, and any other types you know you'll get
}
Deserialize into this class with your json library (you'll probably have to provide it with a factory method for the map class impl), then you can chain the calls more naturally:
String attrValue = map.getNode(id1).getNode(id2).getString(attrName);
The funky option is what I did for a company, and it worked a treat :)
If you don't know the depth of the JSON tree and if you worry about maintainability if new fields are added, I would recommend not to deserialize the full tree in a Map but instead use a low-level parser.
For example, if your JSON looks like the following:
{
"id": {
"id": {
"id": {
"id": 22.0
}
}
}
}
You could write something like that to get the id using Jackson:
public Object getId(String json) throws JsonParseException, IOException
{
ObjectMapper mapper = new ObjectMapper();
JsonNode root = mapper.readTree(json);
JsonNode id = root.get("id");
while (id != null && id.isObject())
{
id = id.get("id");
}
//Cannot find a JsonNode for the id
if (id == null)
{
return null;
}
//Convert id to either String or Long
if (id.isTextual())
return id.asText();
if (id.isNumber())
return id.asLong();
return null;
}
Related
I have this class whose attributes should be serialized to JSon using Jackson:
public class MicroClinicalInfo {
#JsonProperty
private Map<String, String> clinicalInfo;
#JsonCreator
public MicroClinicalInfo() {}
public MicroClinicalInfo(DtoMicroSampleInfo dto) {
this.clinicalInfo = new HashMap<String, String>();
for(/* each clinical info entity received from EJB in dto */) {
this.clinicalInfo.put(clinicalInfoKey, clinicalInfoDescr);
}
}
}
Now, if clinical info do not exist, produced JSon is {"clinicalInfo":{}} but in this case frontend developer wants me to return an empty array and not an empty object. So, I should return {"clinicalInfo":[]}. How can I do that?
I was trying with:
#JsonGetter
public Map<String, String> getClinicalInfo() {
if (this.clinicalInfo != null && !this.clinicalInfo.isEmpty()) {
return this.clinicalInfo;
}
else {
}
}
but I don't know how to give a uniform vision. Because serialization of a not empty HashMap is correct, but I don't know how to render it as an empty array.
Thank you all
When reading a JSON file, i would like to map my class as follows:
public class Effect {
private final String type;
private final Map<String, String> parameters;
public Effect(String type, Map<String, String> parameters) {
this.type = type;
this.parameters = parameters;
}
public String getType() {
return this.type;
}
public Map<String, String> getParameters() {
return this.parameters;
}
}
{
"type": {
"key1": "value1",
"key2": "value2",
}
}
So, the mapped JSON object consists of type as the only key and parameters as its value.
I would like to use #JsonCreator on the constructor, but can't figure out, how to map the fields. Do i need to write a custom deserializer or is there an easier way to map the class like i want?
I wrote a custom deserializer, which does what i want, but there might be an easier way, maybe with annotations alone, which i would like to know:
public class EffectDeserializer extends StdDeserializer<Effect> {
private static final long serialVersionUID = 1L;
public EffectDeserializer() {
super(Effect.class);
}
#Override
public Effect deserialize(JsonParser parser, DeserializationContext context) throws IOException, JsonProcessingException {
JsonNode node = parser.getCodec().readTree(parser);
Iterator<String> fieldNames = node.fieldNames();
if(fieldNames.hasNext()) {
String type = fieldNames.next();
Map<String, String> parameters = new HashMap<>();
for(Iterator<Entry<String, JsonNode>> fields = node.get(type).fields(); fields.hasNext(); ) {
Entry<String, JsonNode> field = fields.next();
parameters.put(field.getKey(), field.getValue().textValue());
}
return new Effect(type, parameters);
}
return null;
}
}
Another way i found would be adding a JsonCreator (constructor in this case), that takes a Map.Entry<String, Map<String, String> and uses that to initialize the values, like this:
#JsonCreator
public Effect(Map.Entry<String, Map<String, String>> entry) {
this.type = entry.getKey();
this.parameters = entry.getValue();
}
If there's no way to get it done with a "normal" constructor, i will probably end up using this, as it uses Jackson's default mapping for Map.Entry, reducing possible error margin.
Add a static factory method that accepts a Map with a dynamic key:
#JsonCreator
public static Effect create(Map<String, Map<String, String>> map) {
String type = map.keySet().iterator().next();
return new Effect(type, map.get(type));
}
EDIT: Just noticed this is basically an uglier version of your own solution using Map.Entry. I would go with that instead.
I have a little "Object":
Map<Integer, Map<WeekDay, Map<String, Data>>> obj
and I want to Map it to:
Map<Integer, Map<WeekDay, Map<String, DataDto>>> returnObj
how can I achive this?
The way I wanted to use was this one:
map(schedule, Map<Integer.class, Map<WeekDay.class, Map<String.class, DataDto.class>>>);
but at the "Map" I am stuck, becuase I can't add a .class behind them and in this state it doesn't work...
I would suggest to simplify your Map if possible:
class A {
WeekDay weekDay;
String str;
Data obj;
}
Map<Integer, A> map = ...;
Iterables.transform(map.values(), new Function<Data, DataDto>() {
#Override
public Object apply(String input) {
return ...;
}
});
or you can put it inside your class:
class Dictionary {
Map<Integer, Map<WeekDay, Map<String, Data>>> obj;
getDataDto(Integer key, Weekday weekDay, String str) {
final Data data = obj.get(key).get(weekDay).get(str);
return (new Function<Data, DataDto>() {
...
}).apply(data);
}
}
Think about operations you are going to use over your data structure and come up with the proper class. Your nested map doesn't look okay.
I would like to know if it is possible to customize the deserialization of json depending the field name, for example
{
id: "abc123",
field1: {...}
other: {
field1: {....}
}
}
I the previous json, I would like to have a custom deserializer for the fields named "field1", in any level in the json.
The reason: We have our data persisted as JSON, and we have a REST service that returns such data, but before return it, the service must inject extra information in the "field1" attribute.
The types are very dynamic, so we cannot define a Java class to map the json to use annotations.
An first approach was to deserialize to Map.class and then use JsonPath to search the $..field1 pattern, but this process is expensive for bigger objects.
I appreciate any help.
Thanks,
Edwin Miguel
You should consider registering a custom deserializer with the ObjectMapper for this purpose.
Then you should be able to simply map your JSON stream to a Map<String, Object> knowing that your field1 objects will be handled by your custom code.
I create a custom deserializer and added it to a SimpleModule for the ObjectMapper
public class CustomDeserializer extends StdDeserializer<Map> {
public CustomDeserializer() {
super(Map.class);
}
#Override
public Map deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException {
Map<String, Object> result = new HashMap<String, Object>();
jp.nextToken();
while (!JsonToken.END_OBJECT.equals(jp.getCurrentToken())) {
String key = jp.getText();
jp.nextToken();
if ("field1".equals(key)) {
MyObject fiedlObj= jp.readValueAs(MyObject.class);
//inject extra info
//...
result.put(key, fieldObj);
} else {
if (JsonToken.START_OBJECT.equals(jp.getCurrentToken())) {
result.put(key, deserialize(jp, ctxt));
} else if (JsonToken.START_ARRAY.equals(jp.getCurrentToken())) {
jp.nextToken();
List<Object> linkedList = new LinkedList<Object>();
while (!JsonToken.END_ARRAY.equals(jp.getCurrentToken())) {
linkedList.add(deserialize(jp, ctxt));
jp.nextToken();
}
result.put(key, linkedList);
} else {
result.put(key, jp.readValueAs(Object.class));
}
}
jp.nextToken();
}
return result;
}
}
The problem is that I had to implement the parsing for the remaining attributes.
For now, it is my solution...
to sum it up before the wall of text below :-)
I need help with how to deserialize a Dictionary using Jackson and a custom deserializer.
Right now I have an Android app communication with a .NET (C#) server. They use JSON to communicate.
On the JAVA-side, I am using Jackson to handle the JSON and on the .NET-side I am using the built in DataContractSerializer (I know, ppl will start commenting I should use something else, but Im not so... ;-) )
The problem is that I am sending Dictionaries from C# and I want that to be deserialized to HashMaps om the JAVA-side, but I havent found a good resource for how to do that.
One example of a Dictionary I am sending from C#:
// Here, the object Equipment is the key, and the int following indicates the amount
[DataMember]
public Dictionary<Equipment, int> EquipmentList { get; set; }
And just for reference, the Equipment object in C#:
[DataContract]
public class Equipment
{
[DataMember]
public uint Id { get; set; }
[DataMember]
public string Name { get; set; }
public override bool Equals(object obj)
{
if (obj.GetType() != this.GetType())
return false;
Equipment e = (Equipment)obj;
return e.Id == this.Id;
}
}
Its serialized correctly into decent JSON on the C#-side, the Dictionary looks like this:
//....
"EquipmentList":[
{
"Key":{
"EquipmentId":123,
"Name":"MyName"
},
"Value":1
}
//....
I have added a custom serializer (CustomMapSerializer), like this:
public static ObjectMapper mapper = new ObjectMapper();
private static SimpleDeserializers simpleDeserializers = new SimpleDeserializers();
private static StdDeserializerProvider sp = new StdDeserializerProvider();
public static void InitSerialization()
{
simpleDeserializers.addDeserializer(String.class, new CustomStringDeserializer());
simpleDeserializers.addDeserializer(Map.class, new CustomMapDeserializer());
sp.withAdditionalDeserializers(simpleDeserializers);
mapper.setDeserializerProvider(sp);
}
And decorated the field like this:
#JsonDeserialize(using=CustomMapDeserializer.class)
public Map<Equipment, Integer> EquipmentList;
And finally, when I run it I do get a break in the custom deserializer class, but I am not sure how to proceed from here:
public class CustomMapDeserializer extends JsonDeserializer<Map> {
#Override
public Map deserialize(JsonParser arg0, DeserializationContext arg1) throws IOException, JsonProcessingException
{
return new HashMap<Object, Object>(); // <-- I can break here
}
}
So, what I would like is some input on how to create a HashMap with the correct values in it, ie a deserialized Equipment as Key and an Int as value.
Anyone out there who can assist? =)
Ok, after a while testing and researching, this is what I came up with.
The custom deserializer looks like this:
public class CustomMapCoTravellerDeserializer extends JsonDeserializer<Map> {
#Override
public Map deserialize(JsonParser jp, DeserializationContext arg1) throws IOException, JsonProcessingException
{
HashMap<CoTravellers, Integer> myMap = new HashMap<CoTravellers, Integer>();
CoTravellers ct = new CoTravellers();
jp.nextToken(); // {
jp.nextToken(); // Key
jp.nextToken(); // {
jp.nextToken(); // "CoTravellerId"
jp.nextToken(); // CoTravellerId Id
int coTravellerValue = jp.getIntValue();
jp.nextToken(); // Name
jp.nextToken(); // Name Value
String coTravellerName = jp.getText();
jp.nextToken(); // }
jp.nextToken(); // "Value"
jp.nextToken(); // The value
int nbr = jp.getIntValue();
ct.CoTravellerId = coTravellerValue;
ct.Name = coTravellerName;
myMap.put(ct, nbr);
return myMap;
}
}
I think this will work, if I can only figure out the JsonMappingException I am getting... but I will post on that separately =)