CODEWITHSUNDEEP
javajsp
Ilan
Ilan

Reputation: 759

java.util.ArrayList cannot be cast to bean.Book

I want to use bean in a JSP page with an arrayList. Here is the servlet code : 

public class ResServlet extends HttpServlet{
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
    String isbn = request.getParameter("isbn");
    String title = request.getParameter("title");
    String author = request.getParameter("author");
    String publisher = request.getParameter("publisher");
    String year = request.getParameter("year");
    ArrayList<Book> book = JDBC.getBooks(Integer.valueOf(isbn), title, author, publisher, Integer.valueOf(year));
    request.setAttribute("book", book);
    System.out.println("Class ResServlet :\t ISBN : " + isbn + "| title : " + title + " | author : " + author + " | publisher " + publisher + " | year : " + year );

    RequestDispatcher dispatcher = request.getRequestDispatcher("book.jsp");
    dispatcher.forward(request, response);

    }
}

One I have initialized my arrayList, I make a redirection to a JSP page named "book.jsp". This JSP page contains this piece of code :

<jsp:useBean id="book" class="bean.Book" scope="request"/>
<c:forEach items="${book}" var="b">
        <tr>
            <td><c:out value="${b.title}"/></td>
        </tr>
</c:forEach>

When I run my application, I have got that stacktrace from book.jsp : 

java.lang.ClassCastException: java.util.ArrayList cannot be cast to bean.Book
    org.apache.jsp.book_jsp._jspService(book_jsp.java:139)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:444)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:386)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:330)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    servlet.ResServlet.doGet(ResServlet.java:29)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)

Thanks for your help!

Upvotes: 1

Views: 1151

Answers (1)

M. le Rutte
M. le Rutte

Reputation: 3563

<jsp:useBean id="book" class="bean.Book" scope="request"/> tells the JSP that in the request scope you are passing a bean.Book instance under the name of book. The servlet compiler will actually create Java code that will cast the resulting object to the declared class.

However you are passing a java.util.ArrayList, which is not assignable to a bean.Book.

Define your book (or should it be books) as <jsp:useBean id="book" class="java.util.Collection" scope="request"/> The most general form of an ArrayList is a Collection.

<jsp:useBean id="books" class="java.util.Collection" scope="request"/>
<c:forEach items="${books}" var="book">
    <tr>
        <td><c:out value="${book.title}"/></td>
    </tr>
</c:forEach>

Upvotes: 2

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