add sample download file and article code (#4370)

javax-servlets/src/main/java/com/baeldung/servlets/DownloadServlet.java

@@ -0,0 +1,35 @@
+package com.baeldung.servlets;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+import javax.servlet.ServletException;
+import javax.servlet.annotation.WebServlet;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+@WebServlet("/download")
+public class DownloadServlet extends HttpServlet {
+    private final int ARBITARY_SIZE = 1048;
+
+    @Override
+    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+        resp.setContentType("text/plain");
+        resp.setHeader("Content-disposition", "attachment; filename=sample.txt");
+        
+        OutputStream out = resp.getOutputStream();
+        InputStream in = req.getServletContext().getResourceAsStream("/WEB-INF/sample.txt");
+
+        byte[] buffer = new byte[ARBITARY_SIZE];
+        
+        int numBytesRead;
+        while ((numBytesRead = in.read(buffer)) > 0) {
+            out.write(buffer, 0, numBytesRead);
+        }
+        
+        in.close();
+        out.flush();
+    }
+}

javax-servlets/src/main/webapp/sample.txt

@@ -0,0 +1 @@
+nice simple text file