How to use Arrays.asList() method to return a list of objects?

Question

I'm setting up a RestController using Spring-boot. This project requires me to return a list of object (in this case objects of class Book). How do I do that?

I've tried Arrays.asList() method by passing a object of class Book shown below:

java

@RestController
public class BookController {

    @GetMapping("/books")
    public List<Book> getAllBooks() {

        return Arrays.asList(new Book(1l, "Book name", "Book author"));

    }
}

java

public class Book {

    Long id;
    String name;
    String author;

    public Book(Long id, String name, String author) {
        super();
        this.id = id;
        this.name = name;
        this.author = author;
    }

    public Long getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getAuthor() {
        return author;
    }

    @Override
    public String toString() {
        return "Book [id=" + id + ", name=" + name + ", author=" + author + "]";
    }
}

I've got this error "Type mismatch: cannot convert from List<Object> to List<Book>". How can I fix this?

What problem with your code? did you get any error or any unexpected result? — Youcef LAIDANI
– Youcef LAIDANI, Commented Jun 9, 2019 at 11:18
I've got this error "Type mismatch: cannot convert from List<Object> to List<Book>" from the return statement of getAllBooks() method — Azhar Uddin Azad
– Azhar Uddin Azad, Commented Jun 9, 2019 at 11:21
Adding import java.util.*; and commenting out the jpa annotation makes it compile fine with javac -Xlint:all *.java. (Also, use List.of since Java SE 9.) — Tom Hawtin - tackline
– Tom Hawtin - tackline, Commented Jun 9, 2019 at 12:46

Vuk Djapic · Accepted Answer · 2019-12-17 11:54:01Z

17

It happened to me several times, and the reason was always that IDE somehow auto imported other Arrays class, from junit package, not the one from java.util. So check your imports part and put import java.util.Arrays; if another Arrays class is imported instead. @Tom Hawtin - tackline suggested similar, but nothing else is needed except correct import.

answered Dec 17, 2019 at 11:54

Vuk Djapic

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