如何从JSP文件中的对象提取每个字段？

Question

I have a class which contains three list string as mentioned below -

public class Response {

private List<String> hash = new LinkedList<String>();
private List<String> name = new LinkedList<String>();
private List<Integer> count = new LinkedList<Integer>();

// getters and setters
}

Now I have a servlet from which I putting values in my Response object as shown below -

Response rr = new Response();

rr.setName(Arrays.asList("Test1", "test2", "Test3"));
rr.setHash(Arrays.asList("Test4", "Test5", "Test6"));
rr.setCount(Arrays.asList(0, 1, 2));

Now from that same servlet only, I am passing the above object values to my JSP page as mentioned below -

req.setAttribute("data", rr);
final RequestDispatcher dispatcher = req.getRequestDispatcher("/admin/testing.jsp");
dispatcher.forward(req, resp);

And below is my JSP page in which I am getting the value of that same object successfully. In the below JSP page, I am trying to extract the value of each field and putting it in its respective columns in the table -

Meaning, I have three columns in the below table in my JSP, first is Hash , second is Name and third is Count . Now I need to extract all the value of hash from that object in Hash column, and similarly extract all the value of name from that object in Name column and etc.

<p>The data from servlet: ${data}</p>

<TABLE BORDER="1" CELLPADDING="3" CELLSPACING="1">
<TR>
<TH>Hash</TH>
<TH>Name</TH>
<TH>Count</TH>
</TR>
<% for (int i = 0; i < 3; i++) { %>
<TR>
<TD>
${data.getHash().get(<%=i%>)}
</TD>
<TD>
${data.getName().get(<%=i%>)}
</TD>
<TD>
${data.getCount().get(<%=i%>)}
</TD>
</TR>
<% } %>
</TABLE>

But everytime, it is giving me this exception -

interpolated runtime values are forbidden by
the JSP spec at '${data.getHash().get(<%=i%>)}'

Any idea what wrong I am doing? And how can I extract all the fields values from that object in my table?

Currently, all my three list in Response class will have only 3 elements.

Final output will look like -

In the table, Hash column will have three data inside it, Name column will have three data inside it, Count column will have three data inside it..

Answer 1

Use JSTL <c:forEach> in the presentation layer.
I'd suggest you to change your structure like this:

public class Response {

private String hash;
private String name;
private Integer count;

// getters and setters
}

In the servlet

List<Response> list = new ArrayList<Response>();
Response rr = new Response();
rr.setHash("hash1");
rr.setName("name1");
rr.setCount(1);
list.add(rr);
Response rr2 = new Response();
rr2.setHash("hash2");
rr2.setName("name2");
rr2.setCount(2);
list.add(rr2);
req.setAttribute("data", list);

In JSP

<TABLE BORDER="1" CELLPADDING="3" CELLSPACING="1">
<TR>
   <TH>Hash</TH>
   <TH>Name</TH>
   <TH>Count</TH>
</TR>
<c:forEach var="rr" items="${data}">
<TR>
   <TD>${rr.hash}</TD>
   <TD>${rr.name}</TD>
   <TD>${rr.count}</TD>
</TR>
</c:forEach>
</TABLE>

Answer 2

You are mixing the el and scriplets in your jsp .It is recommended that use JSTL and el not scriplets .

 <c:forEach var="i" begin="0" end="3">
    <TR>
     <TD>
        ${data.getHash().get(i)}
     </TD>
     <TD>
       ${data.getName().get(i)}
     </TD>
     <TD>
       ${data.getCount().get(i)}
     </TD>
   </TR>
</c:forEach>

There is a curious and confusing inconsistency in JSP syntax when non-String tag attributes are the results of JSP expressions. Let's suppose we want to pass an object of class examples.Values (a kind of list) to a tag extension. The syntax:

 <wrox:list values=”<%=values%>”

is problematic, because we know from the JSP specification that an expression “is evaluated and the result is coerced to a String which is subsequently emitted into the current out JspWriter object”. In the case of the custom tag above, however, the value of the expression is not coerced to a String, but passed to the tag handler as its original type.

Answer 3

Either iterate through scriptlet as,

<%for (int i = 0; i < 3; i++){ %>
<TR>
    <TD>
        <%=data.getHash().get(i) %>
    </TD>
    <TD>
        <%=data.getName().get(i) %>
    </TD>
    <TD>
        <%=data.getCount().get(i) %>
    </TD>
</TR>
<%} %>

or use JSTL as,

<c:forEach var="i" begin="0" end="3">
<TR>
 <TD>
    ${data.getHash().get(i)}
 </TD>
 <TD>
   ${data.getName().get(i)}
 </TD>
 <TD>
   ${data.getCount().get(i)}
 </TD>
</TR>
</c:forEach>

But don't intermix them.