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Java consuming restful api with httpclient. Having trouble with Jackson json MismatchedInputException

This is my first time using jackson/consuming apis/httpclient. I'm getting this error com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type java.util.ArrayList<WallHaven> from Object value (token JsonToken.START_OBJECT) . The api I'm trying to consume is https://wallhaven.cc/help/api
try {
HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
.GET()
.uri(URI.create("https://wallhaven.cc/api/v1/w/pkgkkp"))
.build();
HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
ObjectMapper mapper = new ObjectMapper();
List<WallHaven> posts = mapper.readValue(response.body(), new TypeReference<List<WallHaven>>() {
});
posts.forEach(System.out::println);
} catch (Exception e) {
e.printStackTrace();
}
The api json format is https://pastebin.com/tbSaVJ1T
Here's my WallHaven class
public class WallHaven {
public Data data;
public WallHaven(Data data) {
this.data = data;
}
public WallHaven() {
}
#Override
public String toString() {
return "WallHaven{" +
"data=" + data.getPath() +
'}';
}
}
Data contains all the other classes/variables

This is happening because you're trying to deserialize a Json Object into a List in java. The error message explains it by saying that the starting character (JsonToken.START_OBJECT) is the start of a json object not a json array, so you can't deserialize it directly into a List, but should deserialize it into an object.
Try changing:
List<WallHaven> posts = mapper.readValue(response.body(), new TypeReference<List<WallHaven>>())
into
WallHaven post = mapper.readValue(response.body(), new TypeReference<WallHaven>())

Retrieve value from returned JSON object in Java

I am a receiving a JSON object and I need to save the values to my DB. But I'm having an issue figuring out how to retrieve the particular values in the JSON object.
In this case, I want to retrieve the values of 'originationNumber' and 'messageBody'
The response object -
{"originationNumber":"***","destinationNumber":"***","messageKeyword":"KEYWORD_***","messageBody":"Answer ","previousPublishedMessageId":"1slamq6mdpucd8q4i7iabf1sikc629ga253tr6o0","inboundMessageId":"88bc02fc-aff3-4277-ac1d-f27b6d3b6abb"}
Method to receive message -
public String getReceivedMessages(Messaging receivedMessage) {
BasicAWSCredentials awsCredentials = new BasicAWSCredentials(awsAccessKey, awsSecretKey);
AmazonSQS sqsClient = AmazonSQSClientBuilder.standard()
.withCredentials(new AWSStaticCredentialsProvider(awsCredentials))
.withRegion(String.valueOf(awsRegion)).build();
StringBuilder sb = new StringBuilder();
String queueUrl = "https://sqs.us-east-1.amazonaws.com/1234567/GetReceivedMessages";
List<Message> messages = sqsClient.receiveMessage(new ReceiveMessageRequest(queueUrl)
.withMaxNumberOfMessages(1).withWaitTimeSeconds(20)).getMessages();
for (Message message : messages) {
sb.append(message.getBody());
sqsClient.deleteMessage(queueUrl, message.getReceiptHandle());
}
// Save messages to DB
String userId = connectionRequestRepository.getUserId();
Date date = new Date();
Timestamp now = new Timestamp(date.getTime());
receivedMessage.setUserId(userId);
receivedMessage.setOriginationNumber("");
receivedMessage.setDestinationNumber("***");
receivedMessage.setMessageBody("");
receivedMessage.setMessageType("RECEIVED");
receivedMessage.setCreatedAt(now);
messagingRepository.save(receivedMessage);
System.out.println(sb); <--- Prints response object to console
return sb.toString();
}

You can use jackson library for that.
Solution 1: You can use ObjectMapper as below:
Message Class to map JSON to Java Object:
public class Message {
private String originationNumber;
private String messageBody;
// public getter and setters methods
}
Create Object From JSON String:
Message message = null;
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
try {
message = objectMapper.readValue(payload, Message.class);
} catch (JsonProcessingException e) {
// Log Or do some action as per need
}
Here message will have those values. DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES is used here to skip exception as there are other fields also in JSON and not present in Java Class (as we don't need them).
Solution 2: Alternatively you can use JsonNode from same Jackson library and read nodes one by one as below:
ObjectMapper mapper = new ObjectMapper();
JsonNode actualObj = mapper.readTree("{\"originationNumber\":\"***\",\"destinationNumber\":\"***\",\"messageKeyword\":\"KEYWORD_***\",\"messageBody\":\"Answer \",\"previousPublishedMessageId\":\"1slamq6mdpucd8q4i7iabf1sikc629ga253tr6o0\",\"inboundMessageId\":\"88bc02fc-aff3-4277-ac1d-f27b6d3b6abb\"}");
String originationNumber = actualObj.get("originationNumber");
String messageBody = actualObj.get("messageBody");
In this approach you won't need to create Message class.

You can convert the json string into a json object
https://www.javatpoint.com/how-to-convert-string-to-json-object-in-java
String string = "{\"originationNumber\":\"***\",\"destinationNumber\":\"***\",\"messageKeyword\":\"KEYWORD_***\",\"messageBody\":\"Answer \",\"previousPublishedMessageId\":\"1slamq6mdpucd8q4i7iabf1sikc629ga253tr6o0\",\"inboundMessageId\":\"88bc02fc-aff3-4277-ac1d-f27b6d3b6abb\"}";
JSONObject json = new JSONObject(string);
System.out.println(json.toString());
String destinationNumber = json.getString("destinationNumber");
System.out.println(destinationNumber);

where ur json like
{"originationNumber":"***",
"destinationNumber":"***",
"messageKeyword":"KEYWORD_***",
"messageBody":"Answer","previousPublishedMessageId":"1slamq6mdpucd8q4i7iabf1sikc629ga253tr6o0",
"inboundMessageId":"88bc02fc-aff3-4277-ac1d-f27b6d3b6abb"
}
it like
"key":Value
i think ur code will be like
receivedMessage.setUserId(userId);
receivedMessage.setOriginationNumber("originationNumber");
receivedMessage.setDestinationNumber("destinationNumber");
receivedMessage.setMessageBody("messageBody");
receivedMessage.setMessageType("RECEIVED");
receivedMessage.setCreatedAt(now);
messagingRepository.save(receivedMessage);

JSON Response Has Escaped Quotations Using Jackson and JAX-RS Exception Mapper

I have a simple requirement where, if application encounters an exception, my JAX-RS Rest endpoint should return a custom JSON response with 500 HTTP header status.
Data needed to construct the response comes from an object with several properties (see below). The problem is, I am only interested in one or two values from each property (out of several dozens). And I cannot modify any of these models/classes (some have a Jackson annotation for JSON processing, e.g. null properties should be discarded during serialization).
public class MainObject {
private FirstProperty firstProperty;
private SecondProperty secondProperty;
private ThirdProperty thirdProperty;
// other codes
public String toString() {
ObjectMapper mapper = new ObjectMapper();
try { return mapper.writeValueAsString(this); }
catch (Exception e) { return null; }
}
}
public class FirstProperty {
private boolean bol = true;
private double dob = 5.0;
private List<String> subProperty;
// other properties
public String toString() {
ObjectMapper mapper = new ObjectMapper();
try { return mapper.writeValueAsString(this); }
catch (Exception e) { return null; }
}
}
#JsonSerialize(include=JsonSerialize.Inclusion.NON_NULL)
public class SecondProperty {
private String str;
private List<String> subProperty;
// other properties
public String toString() {
ObjectMapper mapper = new ObjectMapper();
try { return mapper.writeValueAsString(this); }
catch (Exception e) { return null; }
}
}
#JsonSerialize(include=JsonSerialize.Inclusion.NON_NULL)
public class ThirdProperty {
private int intProp = true;
private List<String> subProperty;
// other properties
public String toString() {
ObjectMapper mapper = new ObjectMapper();
try { return mapper.writeValueAsString(this); }
catch (Exception e) { return null; }
}
}
The expected JSON that I should be seeing coming back is on the client side (say, a browser -- testing in Edge):
{
"firstProperty" : { "subProperty" : [ "val1" ] },
"secondProperty" : { "str" : "val2", "subproperty" : [ "val3", "val6" ] },
"thirdProperty" : { "subProperty" : [ "val4" ] }
}
Instead, all my field names and their values have their quotations escaped, and extra double quotes around the entire value, e.g.:
{
"firstProperty" : "{ \"subProperty\" : [ \"val1\" ] }",
"secondProperty" : "{ \"str\" : \"val2\", \"subproperty\" : [ \"val3\", \"val6\" ] }",
"thirdProperty" : "{ \"subProperty\" : [ \"val4\" ] }"
}
Please note the extra " before and after the curly brackets. My environment is:
Java 1.8.45
FasterXML Jackson 2.9.8
Spring Boot 2.0.1
RestEasy (JBoss) JAX-RS
JBoss 6.4
I eliminated the majority of "noise" in the code to see at what point this happens. This is the controller:
#Path("/")
public class MainController {
#GET
#Produces(MediaType.APPLICATION_JSON)
#Path("/rest/path")
public MainObject getMainObject throws MyCustomException {
// A service call that throws MyCustomException
}
}
And JAX-RS ExceptionMapper where I send the response back:
#Provider
public class MyCustomExceptionMapper extends ExceptionMapper<MyCustomException> {
#Override
public Response toResponse(MyCustomException ex) {
HashMap<String, Object> responseBody = new HashMap<>();
String strEx = ex.getStrEx(); // Comes from SecondProperty.str stored in MyCustomException, not that it matters
// Instantiate an empty object that contains
MainObject obj = new MainObject();
obj.getFirstProperty().setSubProperty(ex.getStrs());
obj.getSecondProperty().setStr(strEx);
obj.getSecondProperty().setSubProperty(ex.getStrs());
obj.getThirdProperty().setSubProperty(ex.getStrs());
responseBody.put("firstProperty", serializeFirstProperty(obj.getFirstProperty()));
responseBody.put("secondProperty", serializeSecondProperty(obj.getSecondProperty()));
responseBody.put("thirdProperty", serializeThirdProperty(obj.getThirdProperty()));
Response response = Response.status(/* 500 status */).entity(responseBody).build();
return response;
}
}
Since I only need to send back a very small subset of overall properties from each of my types, I created a custom StdSerializer that would only populate a needed property. For brevity, I only do serializeFirstProperty() but they are all more or less identical:
private StdSerializer<FirstProperty> getFPSerializer(FirstProperty firstProperty) {
return new StdSerializer<FirstProperty>(FirstProperty.class) {
#Override
public void serialize(FirstProperty value, JsonGenerator gen, SerializerProvider provider) throws IOException {
gen.writeStartObject();
if (/* there are items in FirstProperty.subProperty */) {
gen.writeArrayFieldStart("subProperty");
for (String str : value.getSubProperty()) {
gen.writeString(str);
}
gen.writeEndArray();
}
gen.writeEndObject();
}
}
private <T> ObjectMapper getCustomOM(StdSerializer<?> serializer) {
ObjectMapper mapper = new ObjectMapper();
SimpleModule sm = new SimpleModule();
sm.addSerializer(serializer);
mapper.registerModule(module);
return mapper;
}
Then use these helper methods like:
private String serializeFirstProperty(FirstProperty firstProperty) {
ObjectMapper mapper = getCustomOM(getFPSerializer(firstProperty));
String ser = null;
try { ser = mapper.writeValueAsString(firstProperty); }
catch (JsonProcessingException e) { return null; }
return ser;
}
I have tried countless of configurations with ObjectMapper, e.g. disable(JsonParser.Feature.ALLOW_BACKLASH_ESCAPING_ANY_CHARACTER) (couldn't find any relevant flag for JsonGenerator which I really want to disable in a similar fashion).
Or explicitly returning Object from serializeFirstProperty(), or replacing all the \" with " in serializeFirstProperty() when ser is returned.
Or set custom StdSerializer's JsonGenerator.setCharacterEscapes(new CharacterEscapes() { //... } or play around with JAX-RS Response at no avail. I always seem to get a "string" value with quotations, e.g.:
"firstProperty" : "{ \"subProperty\" : [ \"val1\" ] }"
If I simply just do
responseBody.put("firstProperty", mapper.writeValueAsString(obj.getFirstProperty()));
somehow this produces the right JSON output, however, it includes a lot of unnecessary properties which I don't want in this exception handling case.
Funny thing is, when I peer into response (or responseBody map), everything looks right (I don't see values having double quotations).
Please also note that not only I can't modify the models, but some of their properties are instantiated during creation with default values, so not-null inclusion doesn't work, and they will appear in the final JSON if I don't use a custom serialization.
Does anyone know what's causing this escaped and extra quotations?

I think I misunderstood the question in the first attempt of answering it.
The problem is that you serialize a property as string (using mapper.writeValueAsString(this) and then add it to the responseBody which you think of being string to json object map but it is a string to Java object map. In your case at runtime it is a string mapping to another string (the serialized json object is represented as Java string) and a Java string is a Java object as well.
What you want to do instead is to construct a Java object responseBody instead of a map. It should act as a DTO having all the specific properties etc and then serializing it in in one action using the mapper. Because if you first serialize a property to a json string than it it is just a string from the Java point of view and the mapper has no chance to interpret it as a json object.

Adding a new element to an array in the json object java

I am writing automation script to validate json responses of REST APIs and i am using faster xml to serialize and convert java object to json format.
I have a user case where I have to get the json response and add a new array element to an existing array and post it back.
The json response after GET looks like this :
{
"name":"test",
"id":"1234",
"nodes":[
{
"nodeId":"node1"
},
{
"nodeId":"node2"
}
]
}
To this json response, I need to add a third entry for nodes array
{ "nodeId": "node3" } and then post this.
Can someone please help me understand how to add a new array element to an existing array?

You can try:
//Your JSON response will be in this format
String response = "{ \"name\":\"test\", \"id\":\"1234\", \"nodes\":[ { \"nodeId\":\"node1\" }, { \"nodeId\":\"node2\" } ] }";
try {
JSONObject jsonResponse = new JSONObject(response);
JSONArray nodesArray = jsonResponse.getJSONArray("nodes");
JSONObject newEntry = new JSONObject();
newEntry.put("nodeId","node3");
nodesArray.put(newEntry);
jsonResponse.put("nodes",nodesArray);
} catch (JSONException e) {
e.printStackTrace();
}
Now you can post your jsonResponse.toString() as required.

I would rather go for cleaner approach, create Object with below structure -
public class Response{
private String name;
private int id;
private List<Node> nodes;
<Getter & Setter>
}
public class Node{
private String nodeId;
}
Serialize the json -
Response response = objectMapper.readValue(responseJson,
Response.class);
Add the new incoming node object to response -
response.getNodes().add(New Node("{new node Value}"));
Deserialize before post -
objectMapper.writeValueAsString(response);

Deserializing json and delimiting newlines NDJ

I have a simple JSON file I'd like to parse (units.json) using gson and Java:
{"user_name": "happyman", "status": {"hp": 20, "karma": 7, "mp": 10}, "gold": 5.25,}
{"user_name": "sadman", "status": {"hp": 10, "karma": 2, "mp": 6}, "gold": 0.5,}
...
The problem I have is, how do I parse this file as it is not in an array format?
Currently I have a Filereader to the path being called by the JsonReader
FileReader fileReader = new FileReader(jsonFilePath);
JsonReader jsonReader = new JsonReader(fileReader);
jsonReader.beginObject();
while (jsonReader.hasNext()) {
String name = jsonReader.nextName();
if (name.equals("user_name")) {
System.out.println("user_id: "+jsonReader.nextString());
}
//...checks for other equals
However, with this code, I'm only able to get the first line.
I have a feeling it has something to do with the "hasNext()" not being the right method call in the while loop.
I appreciate the help! Thanks.

You can use this code with GSON library:
ObjectMapper mapr = new ObjectMapper();
Map<String,Object> map = mapr.readValue(jsonString, Map.class);
or
public class Units {
#JsonProperty("user_name")
public String user_name;
#JsonProperty("status")
public List<Attr> attrs;
..
}
public class Attr {
#JsonProperty("hp")
public String hp;
#JsonProperty("karma")
public String karma;
#JsonProperty("mp")
public String mp;
}
ObjectMapper mapr = new ObjectMapper();
Units unit = mapr.readValue(jsonString, Units.class);
for both you can use jsonString to define each json unit in your file.