Question

Why am I getting this error:

java.lang.IndexOutOfBoundsException: Index: 4 , Size: 4

I am not defining anything and have used the same logic on another servlet that is working fine. In my other servlet I am selecting all products, so I used two arraylists: one inside the other. I tried that here but still have the same error. I clearly understand the error but I have no idea how to resolve it in this syntax.

Thank you.

ConnectionPool pool = ConnectionPool.getInstance();
Connection connection = pool.getConnection();
PreparedStatement ps = null;
ResultSet rs = null;

int product_id =Integer.parseInt(req.substring(req.lastIndexOf("/")+1));  

ArrayList al = null;
String query = "select * from Product where product_id="+product_id;

try {
    ps = connection.prepareStatement(query);
    rs = ps.executeQuery(query);

    while (rs.next()) {
        al = new ArrayList();

        al.add(rs.getString("product_id"));
        al.add(rs.getString("product_name"));
        al.add(rs.getString("product_description"));
        al.add(rs.getDouble("product_price"));
    }

The next JSP page from this servlet is:

    <%! 
        String product_id=""; 
        String product_name=""; 
        String product_description=""; 
        double product_price = 0; 
    ArrayList  productList=null; 
    %> 

    <% 
    if(request.getAttribute("productList")!=null && request.getAttribute("productList")!="") { 
        productList = (ArrayList)request.getAttribute("productList"); 
        product_id = productList.get(1).toString(); 
        product_name = productList.get(2).toString(); 
        product_description = productList.get(3).toString(); 
        product_price = (Double) productList.get(4);
    } 
    %>

Answer 1

you possibly are getting that exception on this line

int product_id =Integer.parseInt(req.substring(req.lastIndexOf("/")+1));

from your code, this could be the only case. when you call subString() on req index is going out of bound. the best test would be to put a sysout the length of req

EDIT AFTER POSTING THE STACKTRACE

change your java code to this
al = new ArrayList();
while (rs.next()) {
al.add(rs.getString(“product_id”)); // stored in the al at index 0
al.add(rs.getString(“product_name”));// stored in the al at index 1
al.add(rs.getString(“product_description”));// stored in the al at index 2
al.add(rs.getDouble(“product_price”));// stored in the al at index 3
}

heres where its throwing the exception

 line1:  product_id = productList.get(1).toString(); 
 line2:               product_name = productList.get(2).toString(); 
 line3:               product_description = productList.get(3).toString(); 
 line4               product_price = (Double) productList.get(4); /// its going indexoutfbound    here

your list has only 4 elements and you are trying to get the 5th element with above code.
}

change them to

  product_id = productList.get(0).toString(); 
                product_name = productList.get(1).toString(); 
                product_description = productList.get(2).toString(); 
                product_price = (Double) productList.get(3);
}