I am writing a small Java program to keep and update a list of books in my personal library. A prompt asks the user for the book’s data and the new book is saved (appended) to an XML file. The method below from the Book class is responsible for this:

public void updateBookList(String title, String author, String publisher, int year, int numPages){
        XStream xstream = new XStream(new StaxDriver());
        xstream.alias("book", Book.class);

        Book book = new Book(title, author, publisher, year, numPages);
        String dataXml = xstream.toXML(book);

        try(FileWriter fw = new FileWriter("booklist.xml", true);
            BufferedWriter bw = new BufferedWriter(fw);
            PrintWriter out = new PrintWriter(bw))
        {
            out.println(dataXml);
        
        } catch (IOException e) {
            // fix later
        }
    }

The idea is that the file serves as a simple persistent storage of sorts, with all my books listed neatly in XML format.

However, after inserting two test books, this is what the XML looks like:

<?xml version="1.0" ?><book><title>Test1</title><author>Test1</author><publisher>Test1</publisher><year>1999</year><numPages>202</numPages><dateCreated>2024-07-17</dateCreated><dateModified>2024-07-17</dateModified></book>
<?xml version="1.0" ?><book><title>Test2</title><author>Test2</author><publisher>Test2</publisher><year>1999</year><numPages>234</numPages><dateCreated>2024-07-17</dateCreated><dateModified>2024-07-17</dateModified></book>

How can I append the data so the XML file looks something like this:

<?xml version="1.0" ?>

<book>
    <title>Test1</title>
    <author>Test1</author>
    <publisher>Test1</publisher>
    <year>1999</year>
    <numPages>202</numPages>
    <dateCreated>2024-07-17</dateCreated>
    <dateModified>2024-07-17</dateModified>
</book>

<book>
    <title>Test2</title>
    <author>Test2</author>
    <publisher>Test2</publisher>
    <year>1999</year>
    <numPages>234</numPages>
    <dateCreated>2024-07-17</dateCreated>
    <dateModified>2024-07-17</dateModified>
</book>