<dependency>

    <groupId>javax.servlet</groupId>

    <artifactId>javax.servlet-api</artifactId>

    <version>4.0.0-b01</version>

    <scope>provided</scope>

</dependency>

<plugin>

    <groupId>org.eclipse.jetty</groupId>

    <artifactId>jetty-maven-plugin</artifactId>

    <version>9.4.0.M1</version>

    <configuration>

        <webApp>

            <contextPath>/front-controller</contextPath>

        </webApp>

    </configuration>

</plugin>

public class Book {

    private String author;

    private String title;

    private Double price;

​

    // standard constructors, getters and setters

}

public interface Bookshelf {

    default void init() {

        add(new Book("Wilson, Robert Anton & Shea, Robert", 

          "Illuminati", 9.99));

        add(new Book("Fowler, Martin", 

          "Patterns of Enterprise Application Architecture", 27.88));

    }

​

    Bookshelf getInstance();

​

    <E extends Book> boolean add(E book);

​

    Book findByTitle(String title);

}

public interface Bookshelf {

    default void init() {

        add(new Book("Wilson, Robert Anton & Shea, Robert", 

          "Illuminati", 9.99));

        add(new Book("Fowler, Martin", 

          "Patterns of Enterprise Application Architecture", 27.88));

    }

​

    Bookshelf getInstance();

​

    <E extends Book> boolean add(E book);

​

    Book findByTitle(String title);

}

public class FrontControllerServlet extends HttpServlet {

    @Override

    protected void doGet(HttpServletRequest request, 

      HttpServletResponse response) {

        FrontCommand command = getCommand(request);

        command.init(getServletContext(), request, response);

        command.process();

    }

​

    private FrontCommand getCommand(HttpServletRequest request) {

        try {

            Class type = Class.forName(String.format(

              "com.baeldung.enterprise.patterns.front." 

              + "controller.commands.%sCommand",

              request.getParameter("command")));

            return (FrontCommand) type

              .asSubclass(FrontCommand.class)

              .newInstance();

        } catch (Exception e) {

            return new UnknownCommand();

        }

    }

}

public abstract class FrontCommand {

    protected ServletContext context;

    protected HttpServletRequest request;

    protected HttpServletResponse response;

​

    public void init(

      ServletContext servletContext,

      HttpServletRequest servletRequest,

      HttpServletResponse servletResponse) {

        this.context = servletContext;

        this.request = servletRequest;

        this.response = servletResponse;

    }

​

    public abstract void process() throws ServletException, IOException;

​

    protected void forward(String target) throws ServletException, IOException {

        target = String.format("/WEB-INF/jsp/%s.jsp", target);

        RequestDispatcher dispatcher = context.getRequestDispatcher(target);

        dispatcher.forward(request, response);

    }

}

public class SearchCommand extends FrontCommand {

    @Override

    public void process() throws ServletException, IOException {

        Book book = new BookshelfImpl().getInstance()

          .findByTitle(request.getParameter("title"));

        if (book != null) {

            request.setAttribute("book", book);

            forward("book-found");

        } else {

            forward("book-notfound");

        }

    }

}

public class SearchCommand extends FrontCommand {

    @Override

    public void process() throws ServletException, IOException {

        Book book = new BookshelfImpl().getInstance()

          .findByTitle(request.getParameter("title"));

        if (book != null) {

            request.setAttribute("book", book);

            forward("book-found");

        } else {

            forward("book-notfound");

        }

    }

}

public class UnknownCommand extends FrontCommand {

    @Override

    public void process() throws ServletException, IOException {

        forward("unknown");

    }

}