HttpServlet and JSP integration

Question

I'm wondering is possible to integrate custom servlet logic with .jsp template view. For example I have the following servlet:

public class MyServlet extends HttpServlet {

  protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
      String name = "Mark";        
  }
}

and I want to place name variable inside jsp file(new.jsp) like:

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>New</title>
    </head>
    <body>
         <%= name %>

    </body>
</html>

My web.xml:

<servlet>
    <servlet-name>MyServlet</servlet-name>
    <jsp-file>/new.jsp</jsp-file>
</servlet>
<servlet-mapping>
    <servlet-name>MyServlet</servlet-name>
    <url-pattern>/new</url-pattern>
</servlet-mapping>

I don't want to put name in request.

Any help?

UPDATE

Great thanks, but I'm still having a trouble. Firstly, I updated my servlet:

public class MyServlet extends HttpServlet {

  protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
      String name = "Mark";
      request.setAttribute("name", name);
      request.getRequestDispatcher("/WEB-INF/new.jsp").forward(request, response);       
  }

  protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
      String name = "Mark";
      request.setAttribute("name", name);
      request.getRequestDispatcher("/WEB-INF/new.jsp").forward(request, response);       
  }
}

I also changed my view:

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>New</title>
    </head>
    <body>
         ${name}

    </body>
</html>

But when I use ${name} there's nothing displayed. I thought that I should import any jstl, but unfortunately if I use <%= request.getAttribute("name") %> I'm getting null.

UPDATE 2 Finally solved! It was my fault, I forgot set

<servlet>
   <servlet-name>MyServlet</servlet-name>
   <servlet-class>com.example.MyServlet</servlet-class>
</servlet>

Why can't you simply use `<% %>` tags for the code within the JSP? — Mauricio, Jun 28 '11 at 21:57
@Kyte: that's discouraged as per JSP 2.0 coding conventions. http://www.oracle.com/technetwork/articles/javase/code-convention-138726.html — BalusC, Jun 28 '11 at 22:05
Interesting. Good to know. (I admit I learned JSP/servlets caveman-style) — Mauricio, Jun 28 '11 at 22:09

score 5 · Accepted Answer · edited May 23 '17 at 12:19

You need to implement the doGet() method instead. A normal HTTP request (clicking a link, a bookmark or entering the URL straight in browser address bar) defaults to GET method.

In order to make objects available in JSP in a preprocessing servlet, you need to set it as an attribute in request, session or application scope. Finally you need to forward the request/response to the JSP so that it can be displayed.

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    String name = "Mark";
    request.setAttribute("name", name);
    request.getRequestDispatcher("/WEB-INF/new.jsp").forward(request, response);
}

If you fix the servlet mapping as follows

<servlet>
    <servlet-name>MyServlet</servlet-name>
    <servlet-class>com.example.MyServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>MyServlet</servlet-name>
    <url-pattern>/new</url-pattern>
</servlet-mapping>

then you can just invoke the servlet by http://localhost:8080/contextname/new. In the forwarded JSP you can access the name just by EL

${name}

Note that the JSP is placed in /WEB-INF folder in order to avoid direct access without the preprocessing servlet being called by entering the JSP URL in browser address bar instead.

@ryan: if there's nothing in the page scope with the same attribute name, you can just omit the explicit scope declaration. The `JspContext#findAttribute()` scans in page, request, session and appliation scopes. See also our EL wiki page which is linked in bottom of the answer. — BalusC, Jun 28 '11 at 22:06

score 1 · Answer 2 · answered Jun 28 '11 at 22:00

1

You can set name as a request attribute and get it in the JSP.

For example, in your servlet, you can do:

request.setAttribute("name", name);

and get it using:

<%= request.getAttribute("name") %>

or better yet, use EL:

${requestScope.name}

answered Jun 28 '11 at 22:00

ryanprayogo

11,587
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score 0 · Answer 3 · edited Jun 20 '20 at 09:12

If you don't want to put "name" in the request, then the only way is to use scriptlet within the JSP code. This is not a clean or standards based solution though.

REPEAT ## THIS IS NOT A CLEAN SOLUTION ## USE request to store the name as others have pointed out.

So for example

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>New</title>
    </head>
    <body>
    <% String name = "Mark" %> <%-- PUT THE name IN HERE --%>
         <%= name %>

    </body>
</html>

But what is the reason why you don't want to put name in the request? That was why servlets are there for.

HttpServlet and JSP integration

3 Answers3

See also:

Linked