Dealing with a Vector<object> in JSP

[John Goodwin]

I'm fairly new to JSP and I'm trying to send a Vector of Product objects to my forEach tag so I can create a table of each product. Each row will contain the Product members.

I use the forEach extensively and with great success on ArrayLists of strings and even vectors of strings and there seems to be no end of examples of using forEach with a single dimension string array but I need to do it on an vector of objects containing members that I'll be accessing via EL.

Servlet code

		SQLData SQL = new SQLData();
		Vector<Product> products = new Vector<Product>();
		products = SQL.getProductList();
		request.setAttribute("products", products);
		String address = "PaymentConfig.jsp";

The JSP Code

    <%@ page import="com.Layer.Types.Product" %>
    <%@ page import="java.util.Vector" %>
   .
   . 
   .
   .
	<taglib:forEach items="${products}" var="prods">
         	<option>${prods.name}</option>
      	</taglib:forEach>   

I keep getting the following error;
"Cannot convert [com.Layer.Types.Product@5e876450] of type class java.util.Vector to class [Ljava.lang.Object;"

I could really use some ideas about what I'm doing wrong.

Thanks!

John

[Bear Bibeault]

Welcome to the Ranch!

John Goodwin wrote:I'm fairly new to JSP and I'm trying to send a Vector of Product objects to my forEach tag

Use a List implementation rather than a Vector. Firstly, Vector is an old collection from the the Jurassic period of Java and shouldn't be used except in special circumstances, of which this is not one. ALso, Vector isn't supported by JSTL; List is.

The JSP Code

    <%@ page import="com.Layer.Types.Product" %>
    <%@ page import="java.util.Vector" %>
   .
   . 
   .
   .
	<taglib:forEach items="${products}" var="prods">
         	<option>${prods.name}</option>
      	</taglib:forEach>   

A few things about your code:

Ditch the imports. They're superfluous.

For the JSTL core library use the convential "c" prefix, not "taglib". Not following conventions is a faux pas.

[John Goodwin]

Hey Bear,
First, thanks for your kind response.

The references to Taglib are refering to my custom tag library. I just like the custom tags. It works for all string lists pretty flawlessly and since I didn't want the tag to access the members, I figured it would be fine as Object[].

public class ForEachTag extends SimpleTagSupport {
  private Object[] items;
  private String attributeName;

  public void setItems(Object[] items) {
    this.items = items;
  }

  public void setVar(String attributeName) {
    this.attributeName = attributeName;
  }

  @Override
  public void doTag() throws JspException, IOException {
    for(Object item: items) {
      getJspContext().setAttribute(attributeName, item);
      getJspBody().invoke(null);
    }
  }
}

I'll try changing it over from a Vector to an ArrayList.

Thanks,
John

[Bill Gorder]

Umm. Why create a custom tag library offering only a subset of the functionality of that already provided with JSTL?

http://docs.oracle.com/javaee/5/jstl/1.1/docs/tlddocs/c/forEach.html

[Bear Bibeault]

I agree with Bill. Save custom tags for things that the JSTL doesn't provide and use the JSTL for what it does.

[John Goodwin]

Honestly, I used the custom tags because it's just what I spent more time focusing on and what comes to mind first.
But you make a good point so I'll spend more time reaquainting myself with JSTL again.

Thanks

John

[Bear Bibeault]

[Luke Zechariah]

John, Bear, Bill,

How do you write the jsp if I have to write using custom tags only for the code in Tag Handler class below:

public class ForEachTag extends SimpleTagSupport {   
  private Object[] items;   
  private String attributeName;   
  
  public void setItems(Object[] items) {   
    this.items = items;   
  }   
  
  public void setVar(String attributeName) {   
    this.attributeName = attributeName;   
  }   
  

  public void doTag() throws JspException, IOException {   
    for(Object item: items) {   
      getJspContext().setAttribute(attributeName, item);   
      getJspBody().invoke(null);   
    }   
  }   
}  

Thanks,
Luke.

[Paul Clapham]

Well, that tag library declaration says that after

items=

the JSP compiler is expecting something which can be cast to an array of Objects. A Vector can't be cast to an array of objects.

You could change the signature of the method to something like

public void setItems(Vector<?> items)

but then you're locked into using Vector and only Vector -- an extremely reactionary step.

However if you're dead set upon rewriting the JSTL tag, and you want to support all manner of Lists and arrays, then the signature you want is

public void setItems(Object items)

along with various code which tests whether that Object is indeed a List or an array along with casts to the appropriate type before working with the object. But frankly I wouldn't bother when JSTL already does all of that for me.