MismatchedInpuException is base class for all JsonMappingExceptions. It occurred when input is not mapping with target definition or mismatch between as required for fulfilling the deserialization. This exception is used for some input problems, but in most cases, there should be more explicit subtypes to use.

Example of MismatchedInputException

When we deserialize JSON data with property DeserializationFeature.UNWRAP_ROOT_VALUE then it will check root name as className. Here in this case class name “StudentDetail” while passing JSON having a root name as “student” that’s what throwing MismatchedInputException because of mismatch of root name.

public class StudentDetail {
	private int rollNumber;
	private String firstName;
	private String lastName;
	//getter and setter of class
	}

import java.io.IOException;

import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;

public class TestJacksonExample2 {

	public static void main(String[] args) {
	    String json="{\"student\":{\"rollNumber\":21 , \"firstName\":\"Saurabh\" , \"lastName\":\"Gupta\"}}";

		try
		{
	    ObjectMapper mapper = new ObjectMapper();
	    //Before  deserialize this properties will unwrap the json.
	    mapper.enable(DeserializationFeature.UNWRAP_ROOT_VALUE);

	    StudentDetail student= mapper.readValue(json, StudentDetail.class);
	    System.out.println(student);
		}
		catch(IOException ex)
		{
			ex.printStackTrace();
		}
		catch(Exception ex)
		{
			ex.printStackTrace();
		}

	}

Stacktrace of MismatchedInputException

com.fasterxml.jackson.databind.exc.MismatchedInputException: Root name 'student' does not match expected ('StudentDetail') for type [simple type, class com.fiot.json.jackson.exceptions.StudentDetail]
 at [Source: (String)"{"Student":{"rollNumber":21 , "firstName":"Saurabh" , "lastName":"Gupta"}}"; line: 1, column: 2]
    at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:59)
    at com.fasterxml.jackson.databind.DeserializationContext.reportInputMismatch(DeserializationContext.java:1356)
    at com.fasterxml.jackson.databind.ObjectMapper._unwrapAndDeserialize(ObjectMapper.java:4087)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4011)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3004)
    at com.fiot.json.jackson.exceptions.TestJacksonExample2.main(TestJacksonExample2.java:19)

Solution

To resolve this issue use the annotation @JsonRootName as below so that overwrite root name as “student” on default root name (StudentDetail)

@JsonRootName(value = "student")
public class StudentDetail {
	private int rollNumber;
	private String firstName;
	private String lastName;
	//getter and setter of class
	}

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References

https://fasterxml.github.io/jackson-databind/javadoc/2.9/com/fasterxml/jackson/databind/exc/MismatchedInputException.html