com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type

Error

Exception in thread "main" com.fasterxml.Hymanson.databind.exc.MismatchedInputException: Cannot deserialize value of type `java.util.ArrayList<hello.Employee>` from Object value (token `JsonToken.START_OBJECT`)
 at [Source: (String)"{"employees":[{"id":111,"name":"Alan"}, {"id":112,"name":"James"}]}"; line: 1, column: 1]
	at com.fasterxml.Hymanson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:59)
	at com.fasterxml.Hymanson.databind.DeserializationContext.reportInputMismatch(DeserializationContext.java:1746)
	at com.fasterxml.Hymanson.databind.DeserializationContext.handleUnexpectedToken(DeserializationContext.java:1520)
	at com.fasterxml.Hymanson.databind.DeserializationContext.handleUnexpectedToken(DeserializationContext.java:1467)
	at com.fasterxml.Hymanson.databind.deser.std.CollectionDeserializer.handleNonArray(CollectionDeserializer.java:396)
	at com.fasterxml.Hymanson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:252)
	at com.fasterxml.Hymanson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:28)
	at com.fasterxml.Hymanson.databind.deser.DefaultDeserializationContext.readRootValue(DefaultDeserializationContext.java:323)
	at com.fasterxml.Hymanson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4730)
	at com.fasterxml.Hymanson.databind.ObjectMapper.readValue(ObjectMapper.java:3677)

Java Code

/**
 * @author lautturi.com 
 * Java example: parse json string to list of class objects in java
 */

class Employee {

	String name;
	int id;

	public Employee() {

	}
  // getter and setter
  ...
}

public class Lautturi {

	public static void main(String[] args) throws JsonMappingException, JsonProcessingException {

		String jsonString = "{\"employees\":[{\"id\":111,\"name\":\"Alan\"}, {\"id\":112,\"name\":\"James\"}]}";
		ObjectMapper mapper = new ObjectMapper();

		List<Employee> list = mapper.readValue(jsonString,
				TypeFactory.defaultInstance().constructCollectionType(List.class, Employee.class));
		System.out.println(list);
		
		// print the list 
		for (Employee emp : list) {
			System.out.println(emp.getId());
			System.out.println(emp.getName());
		}
	}
}

Cause

jsonString is not a list of Employees. (many data) But it's a data of employees.

Solution - Method 1 modify json string

change json string:

String jsonString = "{\"employees\":[{\"id\":111,\"name\":\"Alan\"}, {\"id\":112,\"name\":\"James\"}]}";

to

String jsonString = "[{\"id\":111,\"name\":\"Alan\"}, {\"id\":112,\"name\":\"James\"}]";

Solution - Method 2 rebuild object data struct to correspond to the json string

create a new class EmployeeList to match the employees in structure of json.

/**
 * @author lautturi.com 
 * Java example: java parse json string to list of objects
 */

import java.util.*;
import com.fasterxml.Hymanson.core.JsonProcessingException;
import com.fasterxml.Hymanson.databind.JsonMappingException;
import com.fasterxml.Hymanson.databind.ObjectMapper;
import com.fasterxml.Hymanson.databind.type.TypeFactory;

class Employee {

	String name;
	int id;

	public Employee() {

	}

	public Employee(String string, int i) {
		name = string;
		id = i;
	}

	public void setId(int i) {
		id = i;
	}

	public int getId() {
		return id;
	}

	public void setName(String str) {
		name = str;
	}

	public String getName() {
		return name;
	}
}

class EmployeeList {
	private List<Employee> employees;

	public void EmployeeList() {

	}

	public List<Employee> getEmployeeList() {
		return employees;
	}

	public void setEmployeeList(List<Employee> list) {
		employees = list;
	}

}

public class Lautturi {

	public static void main(String[] args) throws JsonMappingException, JsonProcessingException {

		String jsonString = "{\"employees\":[{\"id\":111,\"name\":\"Lautturi\"}, {\"id\":112,\"name\":\"James\"}]}";
		
		ObjectMapper mapper = new ObjectMapper();
		EmployeeList employeList = mapper.readValue(jsonString,EmployeeList.class);
		
		// print the list 
		for (Employee emp : employeList.getEmployees()) {
			System.out.println(emp.getId());
			System.out.println(emp.getName());
		}
	}
}

output:

111
Lautturi
112
James