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BAEL-8487: Fix the JsonMappingException: Can not deserialize instance of java.util.HashMap out of START_ARRAY token #17853

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Merged
merged 1 commit into from
Nov 29, 2024
Merged

BAEL-8487: Fix the JsonMappingException: Can not deserialize instance of java.util.HashMap out of START_ARRAY token #17853

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33 changes: 33 additions & 0 deletions jackson-modules/jackson-exceptions/src/main/java/com/baeldung/mappingexception/Person.java
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Original file line number Diff line number Diff line change
@@ -0,0 +1,33 @@
package com.baeldung.mappingexception;

public class Person {

private String firstName;
private String lastName;

public Person() {

}

public Person(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}

public String getFirstName() {
return firstName;
}

public void setFirstName(String firstName) {
this.firstName = firstName;
}

public String getLastName() {
return lastName;
}

public void setLastName(String lastName) {
this.lastName = lastName;
}

}
49 changes: 44 additions & 5 deletions ...ceptions/src/test/java/com/baeldung/mappingexception/JacksonMappingExceptionUnitTest.java
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Original file line number Diff line number Diff line change
@@ -1,23 +1,28 @@
package com.baeldung.mappingexception;

import static org.assertj.core.api.Assertions.assertThat;
import static org.hamcrest.Matchers.containsString;
import static org.hamcrest.Matchers.notNullValue;
import static org.junit.Assert.*;
import static org.junit.Assert.assertThat;
import static org.junit.Assert.assertThrows;
import static org.junit.Assert.assertTrue;
import static org.junit.jupiter.api.Assertions.assertEquals;

import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.baeldung.exceptions.EmptyObject;
import com.baeldung.exceptions.Person;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.SerializationFeature;
import org.junit.Test;

import com.baeldung.exceptions.EmptyObject;
import com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility;
import com.fasterxml.jackson.annotation.PropertyAccessor;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

public class JacksonMappingExceptionUnitTest {

Expand Down Expand Up @@ -89,4 +94,38 @@ public void givenEmptyBean_whenSerializing_thenCorrect() throws JsonProcessingEx
assertEquals("{}", json);
}

@Test
public void givenJsonArray_whenDeserializingToMap_thenThrowException() {
final String json = "[{\"firstName\":\"Abderrahim\",\"lastName\":\"Azhrioun\"}, {\"firstName\":\"Nicole\",\"lastName\":\"Smith\"}]";
final ObjectMapper mapper = new ObjectMapper();

Exception exception = assertThrows(JsonMappingException.class, () -> mapper.readValue(json, HashMap.class));

assertTrue(exception.getMessage()
.contains("Cannot deserialize value of type `java.util.HashMap<java.lang.Object,java.lang.Object>` from Array value (token `JsonToken.START_ARRAY`)"));
}

@Test
public void givenJsonArray_whenDeserializingToListOfMap_thenConvert() throws JsonProcessingException {
final List<Map<String, String>> expectedListOfMaps = Arrays.asList(Map.of("firstName", "Abderrahim", "lastName", "Azhrioun"), Map.of("firstName", "Nicole", "lastName", "Smith"));
final String json = "[{\"firstName\":\"Abderrahim\",\"lastName\":\"Azhrioun\"}, {\"firstName\":\"Nicole\",\"lastName\":\"Smith\"}]";
final ObjectMapper mapper = new ObjectMapper();

List<Map<String, String>> personList = mapper.readValue(json, new TypeReference<>() {});

assertThat(expectedListOfMaps).isEqualTo(personList);
}

@Test
public void givenJsonArray_whenDeserializingToListOfCustomObjects_thenConvert() throws JsonProcessingException {
final List<Person> expectedPersonList = Arrays.asList(new Person("Abderrahim", "Azhrioun"), new Person("Nicole", "Smith"));
final String json = "[{\"firstName\":\"Abderrahim\",\"lastName\":\"Azhrioun\"}, {\"firstName\":\"Nicole\",\"lastName\":\"Smith\"}]";
final ObjectMapper mapper = new ObjectMapper();

List<Person> personList = mapper.readValue(json, new TypeReference<>() {});

assertThat(expectedPersonList).usingRecursiveComparison()
.isEqualTo(personList);
}

}