Untitled

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

@WebServlet(name = "ChangeServlet", urlPatterns = {"/ChangeServlet"})
public class ChangeServlet extends HttpServlet
{
    static String filename;

    public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
    {
        HttpSession httpSession = req.getSession(true);
        resp.setContentType("text/html;charset=utf-8");
        filename = (String) httpSession.getAttribute("filename");
        /*req.getRequestDispatcher("/change.jsp").forward(req, resp);*/
        req.getRequestDispatcher("Change").forward(req, resp);
    }
}

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Изменения страницы</title>
</head>


<body>
    <h3>
        Страница: <%= session.getAttribute("filename") %>
    </h3>

        <iframe height="500" width="800" src = <%= session.getAttribute("filenamefile") %> >
        Здесь будет вывод файла
        <!--<c:forEach var="filename" items="$//{files}">
            <c:out value = "$//{file}"/>
        </c:forEach>-->
    </iframe>

</body>
</html>

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.nio.charset.StandardCharsets;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

@WebServlet(name = "Change", urlPatterns = {"/Change"})
public class Change extends HttpServlet
{
static String filenamefile;

public void doGet(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
{
    HttpSession httpSession = req.getSession(true);
    filenamefile = (String) httpSession.getAttribute("filenamefile");
    resp.setContentType("text/html;charset=utf-8");
    PrintWriter pw = resp.getWriter();
    pw.println("" +
            "<%@page contentType="text/html" pageEncoding="UTF-8"%>n" +
            "<!DOCTYPE html>n" +
            "<html>n" +
            "    <head>n" +
            "        <meta charset="UTF-8">n" +
            "        <title>Изменения страницы</title>n" +
            "    </head>n" +
            "    n" +
            "    n" +
            "    <body>n" +
            "        <h3>n" +
            "            Страница: <%= session.getAttribute("filename") %>n" +
            "        </h3>n" +
            "        n" +
            "            <iframe height="500" width="800" src = <%= session.getAttribute("filenamefile") %> >n" +
            "            Здесь будет вывод файлаn");
            try (BufferedReader reader = new BufferedReader(
                new InputStreamReader(
                        new FileInputStream(filenamefile), StandardCharsets.UTF_8)))
            {
                String line;
                while ((line = reader.readLine()) != null)
                {
                    pw.println(line);
                }
            }
            pw.println("        </iframe>n" +
            "        n" +
            "    </body>n" +
            "</html>");
}
}