Spring Boot + Apache Kafka Tutorial - #12 - Create REST API to Send JSON Object

Welcome to Spring Boot + Apache Kafka Tutorial series.
In this lecture, we will create a REST API to send a JSON message in request. The REST API intern converts JSON into a User object and sends it to Kafka Producer. Kafka Producer intern sends that user object to Kafka topic.
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[@user-oq2qz1st3f]

Спасибо огромное!!!! Ты очень хорошо все объясняешь.👍👍👍👍

[@wahyuusman6777]

many thanks about your tutorial, cuz your video i very help for learning about kafka

[@shailendraraj4951]

great explanation

[@johnbrooks8839]

Those who are getting the error trying to cast your User object to a String may need to update your producer properties to have a key serializer and value serializer instead of "deserializer".

[@krishnasarkar252]

I have added this but still got same error

[@Andrzej3935]

Greate lessons

[@tonydeveloperdndndn]

Nice presentation and explanation.

[@JavaGuides]

Glad you liked it!

[@meduriravindra4238]

Please explain how to consume old data from Kafka after the old data get updated. Is it a possible scenario atleast from interview point of view ?

[@pavanraju6485]

How to consume data by using browser or postman?

[@anshikamishra5938]

Some of the windows commands are not working for me giving "The syntax for the command is incorrect" specially when using --from-beginning

[@krishnamadhav7639]

At 2:07, you have added PostMapping("/publish") and in the previous video in MessageController class you have added GetMapping("/publish"). Can you please explain the reason behind it? Please clarify this.
As per my understanding at both the places it should be GetMapping annotation only.

[@arthurmukelyan404]

Hi, I am getting 405 request method not supported, but I can’t understand why, anyone can help me?

[@adityakendhe5630]

hello sir,
I am getting null pointer exception related to kafka template while using rest api to send json object on console.
And in postman it is showing internal server error.
please help.

[@JustFootBallThings623]

I am getting the same error too did u get solution?

[@adityakendhe5630]

@@JustFootBallThings623 my code is correct...so i guess its due to some of the libraries or dependencies missing on our IDE unlike used in lecture. In better way i skipped it and and continued with lecture.
in next lecture he made real time project. Thats important.

[@lky100047]

add
import org.apache.kafka.common.serialization.StringSerializer;
import org.springframework.kafka.support.serializer.JsonSerializer;
to every java class work for me

[@poojagamskar6872]

recheck the previous learning vedio u must have missed creating constructor for kafka template,so u r getting null pointer exception

[@elakkiyap5509]

hai sir. i tried to send Json Message to kafka topic but am getting internal server error in postman . As well as in intellij, ERROR [dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.apache.kafka.common.errors.SerializationException: Can't convert value of class in.inspired.services.model.User to class org.apache.kafka.common.serialization.StringSerializer specified in value.serializer] with root cause java.lang.ClassCastException: class in.inspired.services.model.User cannot be cast to class java.lang.String (in.inspired.services.model.User is in unnamed module of loader 'app'; java.lang.String is in module java.base of loader 'bootstrap')...how to overcome this error. kindly help in this

[@newtanagmukhopadhyay4716]

did you resolve it?

[@elakkiyap5509]

@@newtanagmukhopadhyay4716 yes sir. i resolved it. however thank you for your presence to help me.

[@newtanagmukhopadhyay4716]

@@elakkiyap5509 ah dont call me sir pls its embrassing for me. im just 22

[@elakkiyap5509]

@@newtanagmukhopadhyay4716oh. Am sorry.

[@divyanshukumar5460]

Even I am getting this error, can u please help me to resolve this

[@vinay2841]

Anyone please help me to resolve this error org.apache.kafka.common.errors.SerializationException: Can't convert value of class com.vinay.kafka.payload.User to class org.apache.kafka.common.serialization.StringSerializer

[@shanmugamsekar2070]

i also get this error

[@vinay2841]

@@shanmugamsekar2070 Have u got a solution?

[@sanyamkharche6646]

@@vinay2841
To ensure that the User class is properly serialized and deserialized as JSON, you need to add the necessary Jackson annotations.e.g. @JsonProperty annotation. Add this dependency in your pom.xml if using a spring boot project.

com.fasterxml.jackson.core
jackson-databind

[@MDAnashAnsari]

Replace your KafkaConsumer class code with the below code if you are getting :- org.apache.kafka.common.errors.SerializationException: Can't convert value of class com.vinay.kafka.payload.User to class org.apache.kafka.common.serialization.StringSerializer
public class KafkaConsumer {
@KafkaListener(topics = "nepdroid", groupId = "myGroup")
public void consume(User user) {
log.info(String.format("Message received -> %s", user.toString()));
}
}