Spring Beans: Can you add elements into an injected list? [duplicate]-CodePudding

I am quite new at Spring Beans and I'm trying to build a rest controller that implements the CRUD operations.

I have a config file that has a @Bean that returns a list of Book type:

@Configuration
public class BookConfig {

    @Bean
    public static List<Book> books() {
        return Arrays.asList(
            new Book(1, "ABC", "Author ABC"),
            new Book(2, "DEF", "Author DEF"),
            new Book(3, "GHI", "Author GHI"));
    }
}

And the rest controller in which I constructor-injected the above Bean:

@RestController
@RequestMapping("/api/v1/books")
public class BookRestController {

    private List<Book> books;

    @Autowired
    public BookRestController(List<Book> books) {
        this.books = books;
    }

    @PostMapping("")
    public void registerBook(@RequestBody Book book) {
        books.add(book); // this throws **UnsupportedOperationException**
    }
}

At the POST method I try to add my book that comes from the request the my list of books, but I get an UnsupportedOperationException.

Is it just not possible to alter an injected collection or how should it be done?

CodePudding user response：

We can achieve this with small steps again if this is for tutorial purposes.

You can create a class that hosts the list.
we can provide getter and setter methods in that class.
Inject this class afterward.

Class would become

//BadNamedCLass
DataManager {
 private final List<Book> books = ArrayList<Book>();
 {
 // init block to add item to books if you want during initialization
 }
// getters
//setters
}

Config becomes:

@Configuration
public class BookConfig {

    @Bean
    public DataManager dataManager() {
        return new DataManager();
    }
}

Controller code becomes

...
    @Autowired
    public BookRestController(DataManager dataManager) {
        this.dataManager= dataManager;
    }
...

For the exception please follow this link