confusion about getters in web application

Question

I was making a pretty basic web app with servlet and jsp and I had the following setup:

public class DataManager {
    //some method implementations omitted since they are not important
    public DataManager(){}

    public class Author{
        public int id;
        public String name;
        public String born;
        public String died;
    }

    public Author getAuthor(int authorId){} 
    public ArrayList<Author> getAuthors(){}
}

public class AuthorsServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        ServletContext context = getServletContext();
        DataManager dm = (DataManager) context.getAttribute("datamanager");
        ArrayList<DataManager.Author> authors = dm.getAuthors();

        request.setAttribute("authors", authors);
        request.getRequestDispatcher("/authors.jsp").forward(request, response);

    }
}

In my jsp file I had:

<c:forEach var="author" items="${authors}">
    <tr>
        <td>${author.id}</td>
        <td><a href="author.jsp">${author.name}</a></td>
        <td>${author.born}</td>
        <td>${author.died}</td>
    </tr>
</c:forEach>

However I kept getting an error that says Property 'id' not found on type db.DataManager$Author until I put in getters in the inner Author class of my DataManager class:

public class Author{
    public int id;
    public String name;
    public String born;
    public String died;
    public int getId(){ return id; }
    public String getName(){ return name;}
    public String getBorn(){return born; }
    public String getDied(){ return died;}
}

I have two (kind of basic) questions:

1. Why do I have to add getters to access a public inner class's variables?

2. Even after I put in the getters, I didn't directly called them (i.e. author.id instead of author.getId()) is there a naming convention where the compiler follows, so I have to define getFoo to get the value of a foo variable?

Answer 1

The runtime environment calls author.getId() automatically in order to evaluate${author.id}. This is why you need to define the getters (explicitly, because Java does not define them implicitly) even though the fields are public.

There is a naming convention: if the name of the filed is fooFieldExample, the name of the getter should be getFooFieldExample (notice the big F of foo)

Answer 2

Why do I have to add getters to access a public inner class's variables?

Because that is what jsp specification expects it to be, $author.id statement converts author.getId() where id should have a public accessor method getId();

Even after I put in the getters, I didn't directly called them (i.e. author.id instead of author.getId()) is there a naming convention where the compiler follows, so I have to define getFoo to get the value of a foo variable?

Yes, it is naming convention. Remember that JSPs are meant for design purpose and developed by page designers.JSps are not designed by java programmers. So $author.id is more convenient to non-programmers.

Expression $author.id is an Expression Language syntax which is used to access variables those are available in JSP pages. Expression Language $author.id is translated into author.getId();

Answer 3

Declaring a class fields as private and define Getters and setters for them are usual java best practices (almost imperative). They are so usual in Java that most frameworks and even standards rely on them, for example: JSP EL langauage transforms this author.id in author.getId().

You should declare your fields private and use getters and setters.