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[BAEL-2547] jackson deserialization class-casting exception
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Lines changed: 305 additions & 0 deletions

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‎jackson-modules/jackson-conversions-2/src/main/java/com/baeldung/jackson/tocollection/Book.java‎

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package com.baeldung.jackson.tocollection;
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import java.util.Objects;
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public class Book {
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private Integer bookId;
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private String title;
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private String author;
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public Book() {}
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public Book(Integer bookId, String title, String author) {
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this.bookId = bookId;
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this.title = title;
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this.author = author;
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}
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@Override
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public boolean equals(Object o) {
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if (this == o) {
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return true;
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}
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if (!(o instanceof Book)) {
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return false;
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}
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Book book = (Book) o;
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if (!Objects.equals(bookId, book.bookId)) {
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return false;
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}
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if (!Objects.equals(title, book.title)) {
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return false;
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}
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return Objects.equals(author, book.author);
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}
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@Override
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public int hashCode() {
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int result = bookId != null ? bookId.hashCode() : 0;
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result = 31 * result + (title != null ? title.hashCode() : 0);
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result = 31 * result + (author != null ? author.hashCode() : 0);
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return result;
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}
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public Integer getBookId() {
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return bookId;
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}
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public void setBookId(Integer bookId) {
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this.bookId = bookId;
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}
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public String getTitle() {
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return title;
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}
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public void setTitle(String title) {
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this.title = title;
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}
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public String getAuthor() {
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return author;
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}
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public void setAuthor(String author) {
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this.author = author;
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}
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}

‎jackson-modules/jackson-conversions-2/src/main/java/com/baeldung/jackson/tocollection/JsonToCollectionUtil.java‎

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package com.baeldung.jackson.tocollection;
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import com.fasterxml.jackson.core.type.TypeReference;
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import com.fasterxml.jackson.databind.ObjectMapper;
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import com.fasterxml.jackson.databind.type.CollectionType;
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import java.io.IOException;
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import java.util.ArrayList;
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import java.util.List;
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public class JsonToCollectionUtil {
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private JsonToCollectionUtil(){}
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public static <T> List<T> jsonArrayToList(String json, Class<T> elementClass) throws IOException {
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ObjectMapper objectMapper = new ObjectMapper();
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CollectionType listType = objectMapper.getTypeFactory().constructCollectionType(ArrayList.class, elementClass);
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return objectMapper.readValue(json, listType);
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}
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public static <T> List<T> jsonArrayToList2(String json, Class<T> elementClass) throws IOException {
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return new ObjectMapper().readValue(json, new TypeReference<List<T>>() {});
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}
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}

‎jackson-modules/jackson-conversions-2/src/main/resources/to-java-collection/books.json‎

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[ {
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"bookId" : 1,
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"title" : "A Song of Ice and Fire",
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"author" : "George R. R. Martin"
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}, {
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"bookId" : 2,
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"title" : "The Hitchhiker's Guide to the Galaxy",
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"author" : "Douglas Adams"
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}, {
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"bookId" : 3,
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"title" : "Hackers And Painters",
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"author" : "Paul Graham"
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} ]

‎jackson-modules/jackson-conversions-2/src/main/resources/to-java-collection/books.xml‎

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<ArrayList>
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<item>
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<bookId>1</bookId>
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<title>A Song of Ice and Fire</title>
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<author>George R. R. Martin</author>
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</item>
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<item>
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<bookId>2</bookId>
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<title>The Hitchhiker's Guide to the Galaxy</title>
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<author>Douglas Adams</author>
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</item>
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<item>
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<bookId>3</bookId>
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<title>Hackers And Painters</title>
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<author>Paul Graham</author>
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</item>
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</ArrayList>

‎jackson-modules/jackson-conversions-2/src/test/java/com/baeldung/jackson/tocollection/DeserializeToJavaCollectionUnitTest.java‎

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package com.baeldung.jackson.tocollection;
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import com.fasterxml.jackson.core.JsonProcessingException;
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import com.fasterxml.jackson.core.type.TypeReference;
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import com.fasterxml.jackson.databind.JsonNode;
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import com.fasterxml.jackson.databind.ObjectMapper;
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import com.fasterxml.jackson.databind.type.CollectionType;
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import com.fasterxml.jackson.dataformat.xml.XmlMapper;
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import org.assertj.core.util.Lists;
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import org.junit.jupiter.api.BeforeEach;
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import org.junit.jupiter.api.Test;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.Scanner;
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import static org.assertj.core.api.Assertions.assertThat;
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import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
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public class DeserializeToJavaCollectionUnitTest {
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private ObjectMapper objectMapper;
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private XmlMapper xmlMapper;
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private List<Book> expectedBookList;
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@BeforeEach
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void setup() {
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objectMapper = new ObjectMapper();
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xmlMapper = new XmlMapper();
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expectedBookList = Lists.newArrayList(
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new Book(1, "A Song of Ice and Fire", "George R. R. Martin"),
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new Book(2, "The Hitchhiker's Guide to the Galaxy", "Douglas Adams"),
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new Book(3, "Hackers And Painters", "Paul Graham"));
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}
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private String readFile(String path) {
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try (Scanner scanner = new Scanner(getClass().getResourceAsStream(path), "UTF-8")) {
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return scanner.useDelimiter("\\A").next();
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}
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}
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/*====================
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* JSON tests
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*====================
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*/
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@Test
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void givenJsonString_whenDeserializingToList_thenThrowingClassCastException() throws JsonProcessingException {
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String jsonString = readFile("/to-java-collection/books.json");
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List<Book> bookList = objectMapper.readValue(jsonString, ArrayList.class);
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assertThat(bookList).size().isEqualTo(3);
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assertThatExceptionOfType(ClassCastException.class)
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.isThrownBy(() -> bookList.get(0).getBookId())
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.withMessageMatching(".*java.util.LinkedHashMap cannot be cast to .*com.baeldung.jackson.tocollection.Book.*");
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}
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@Test
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void givenJsonString_whenDeserializingWithTypeReference_thenGetExpectedList() throws JsonProcessingException {
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String jsonString = readFile("/to-java-collection/books.json");
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List<Book> bookList = objectMapper.readValue(jsonString, new TypeReference<List<Book>>() {});
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assertThat(bookList.get(0)).isInstanceOf(Book.class);
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assertThat(bookList).isEqualTo(expectedBookList);
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}
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@Test
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void givenJsonString_whenDeserializingWithJavaType_thenGetExpectedList() throws JsonProcessingException {
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String jsonString = readFile("/to-java-collection/books.json");
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CollectionType listType = objectMapper.getTypeFactory().constructCollectionType(ArrayList.class, Book.class);
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List<Book> bookList = objectMapper.readValue(jsonString, listType);
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assertThat(bookList.get(0)).isInstanceOf(Book.class);
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assertThat(bookList).isEqualTo(expectedBookList);
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}
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@Test
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void givenJsonString_whenDeserializingWithConvertValueAndTypeReference_thenGetExpectedList() throws JsonProcessingException {
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String jsonString = readFile("/to-java-collection/books.json");
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JsonNode jsonNode = objectMapper.readTree(jsonString);
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List<Book> bookList = objectMapper.convertValue(jsonNode, new TypeReference<List<Book>>() {});
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assertThat(bookList.get(0)).isInstanceOf(Book.class);
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assertThat(bookList).isEqualTo(expectedBookList);
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}
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@Test
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void givenJsonString_whenDeserializingWithConvertValueAndJavaType_thenGetExpectedList() throws JsonProcessingException {
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String jsonString = readFile("/to-java-collection/books.json");
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JsonNode jsonNode = objectMapper.readTree(jsonString);
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List<Book> bookList = objectMapper.convertValue(jsonNode, objectMapper.getTypeFactory().constructCollectionType(ArrayList.class, Book.class));
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assertThat(bookList.get(0)).isInstanceOf(Book.class);
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assertThat(bookList).isEqualTo(expectedBookList);
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}
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/*====================
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* XML tests
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*====================
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*/
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@Test
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void givenXml_whenDeserializingToList_thenThrowingClassCastException() throws JsonProcessingException {
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String xml = readFile("/to-java-collection/books.xml");
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List<Book> bookList = xmlMapper.readValue(xml, ArrayList.class);
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assertThat(bookList).size().isEqualTo(3);
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assertThatExceptionOfType(ClassCastException.class)
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.isThrownBy(() -> bookList.get(0).getBookId())
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.withMessageMatching(".*java.util.LinkedHashMap cannot be cast to .*com.baeldung.jackson.tocollection.Book.*");
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}
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@Test
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void givenXml_whenDeserializingWithTypeReference_thenGetExpectedList() throws JsonProcessingException {
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String xml = readFile("/to-java-collection/books.xml");
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List<Book> bookList = xmlMapper.readValue(xml, new TypeReference<List<Book>>() {});
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assertThat(bookList.get(0)).isInstanceOf(Book.class);
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assertThat(bookList).isEqualTo(expectedBookList);
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}
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@Test
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void givenXml_whenDeserializingWithConvertValueAndTypeReference_thenGetExpectedList() throws JsonProcessingException {
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String xml = readFile("/to-java-collection/books.xml");
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List node = xmlMapper.readValue(xml, List.class);
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List<Book> bookList = xmlMapper.convertValue(node, new TypeReference<List<Book>>() {});
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assertThat(bookList.get(0)).isInstanceOf(Book.class);
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assertThat(bookList).isEqualTo(expectedBookList);
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}
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@Test
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void givenXml_whenDeserializingWithConvertValueAndJavaType_thenGetExpectedList() throws JsonProcessingException {
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String xml = readFile("/to-java-collection/books.xml");
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List node = xmlMapper.readValue(xml, List.class);
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List<Book> bookList = xmlMapper.convertValue(node, objectMapper.getTypeFactory().constructCollectionType(ArrayList.class, Book.class));
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assertThat(bookList.get(0)).isInstanceOf(Book.class);
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assertThat(bookList).isEqualTo(expectedBookList);
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}
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}

‎jackson-modules/jackson-conversions-2/src/test/java/com/baeldung/jackson/tocollection/JsonToCollectionUtilUnitTest.java‎

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package com.baeldung.jackson.tocollection;
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import org.assertj.core.util.Lists;
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import org.junit.jupiter.api.BeforeEach;
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import org.junit.jupiter.api.Test;
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import java.io.IOException;
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import java.util.List;
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import java.util.Scanner;
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import static org.assertj.core.api.Assertions.assertThat;
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import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
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class JsonToCollectionUtilUnitTest {
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private List<Book> expectedBookList;
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@BeforeEach
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void setup() {
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expectedBookList = Lists.newArrayList(
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new Book(1, "A Song of Ice and Fire", "George R. R. Martin"),
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new Book(2, "The Hitchhiker's Guide to the Galaxy", "Douglas Adams"),
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new Book(3, "Hackers And Painters", "Paul Graham"));
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}
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private String readFile(String path) {
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try (Scanner scanner = new Scanner(getClass().getResourceAsStream(path), "UTF-8")) {
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return scanner.useDelimiter("\\A").next();
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}
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}
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@Test
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void givenJsonString_whenCalljsonArrayToList_thenGetExpectedList() throws IOException {
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String jsonString = readFile("/to-java-collection/books.json");
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List<Book> bookList = JsonToCollectionUtil.jsonArrayToList(jsonString, Book.class);
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assertThat(bookList.get(0)).isInstanceOf(Book.class);
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assertThat(bookList).isEqualTo(expectedBookList);
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}
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@Test
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void givenJsonString_whenCalljsonArrayToList2_thenGetException() throws IOException {
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String jsonString = readFile("/to-java-collection/books.json");
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List<Book> bookList = JsonToCollectionUtil.jsonArrayToList2(jsonString, Book.class);
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assertThat(bookList).size().isEqualTo(3);
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assertThatExceptionOfType(ClassCastException.class)
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.isThrownBy(() -> bookList.get(0).getBookId())
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.withMessageMatching(".*java.util.LinkedHashMap cannot be cast to .*com.baeldung.jackson.tocollection.Book.*");
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}
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}

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