1. Ejemplo 4
Modificar el servlet contador de modo de generar una respuesta que muestre la IP de todos los computadores que lo han contactado hasta ahora
Use un vector o un arreglo para ir guardándolas

2. (se reinicializa vacío cada vez que parte el servidor)
Usandor un arreglo
(se reinicializa vacío cada vez que parte el servidor)
import java.io.*; import javax.servlet.*;
import javax.servlet.http.*;
public class AddressesServlet extends HttpServlet {
int nIP = 0;
String[] IPs = new String[1000];
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws
IOException, ServletException {
String ip = request.getRemoteHost();
IPs[nIP++] = ip;
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<h1> Han visitado este sitio </h1><br>");
for (int i = 0; i < nIP; i++)
out.println("<br> "+ IPs[i]);
out.close(); }

3. Optener Ip del cliente y guardarla en el arreglo
import java.io.*; import javax.servlet.*;
import javax.servlet.http.*;
public class AddressesServlet extends HttpServlet {
int nIP = 0;
String[] IPs = new String[1000];
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws
IOException, ServletException {
String ip = request.getRemoteHost();
IPs[nIP++] = ip;
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<h1> Han visitado este sitio </h1><br>");
for (int i = 0; i < nIP; i++)
out.println("<br> "+ IPs[i]);
out.close(); }
Optener Ip del cliente y guardarla en el arreglo

4. Imprimir cada String separado por una línea horizontal
import java.io.*; import javax.servlet.*;
import javax.servlet.http.*;
public class AddressesServlet extends HttpServlet {
int nIP = 0;
String[] IPs = new String[1000];
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws
IOException, ServletException {
String ip = request.getRemoteHost();
IPs[nIP++] = ip;
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<h1> Han visitado este sitio </h1><br>");
for (int i = 0; i < nIP; i++)
out.println("<hr> "+ IPs[i]);
out.close(); }
Imprimir cada String separado por una línea horizontal

5. Solución con vector que contiene las IP
Import util package
import java.io.*; import javax.servlet.*;
import javax.servlet.http.*; import java.util.*;
public class AddressesServlet extends HttpServlet {
Vector IPs = new Vector();
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws
IOException, ServletException {
String ip = request.getRemoteHost();
IPs.add(ip);
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<h1> Han visitado este sitio </h1><br>");
for (int i = 0; i < IPs.size(); i++)
out.println("<hr> "+ IPs.elementAt(i));
out.close(); }
Create empty vector
Get IP and add it to the end
Print every string to the
browser separated with
a horizontal bar

6. Usando un Archivo import java.io.*; import javax.servlet.*;
import javax.servlet.http.*;
public class AddressesServlet extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws
IOException, ServletException {
String ip = request.getRemoteHost();
PrintWriter file = new PrintWriter(
new FileWriter(“ips.txt”,true));
file.println(ip); file.close();
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<h1> Han visitado este sitio </h1><br>");
BufferedReade infile = new BufferedReader(
new FileReader(“ips.txt”));
for (int i = 0; i < nIP; i++){
String linea = infile.readLine();
out.println("<br> "+ IPs[i]); }
out.close();

7. Otro ejemplo
Modificar el ejemplo anterior para que en vez de repetir la ip muestre cuantas veces ha visitado ese cliente al servlet
Solución 1: use un vector que contenga objetos de la clase Node, el cual contiene un String (para guardar el número IP) y un entero (para contar las visitas del cliente)
public class Node {
int count; String ip;
Node(String x, int y) {
ip = x; count = y; }

8. public class ShowCountsServlet extends HttpServlet {
Vector v = new Vector();
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String ip = request.getRemoteHost();
Node aux; int p =0;
while(p < v.size()) {
aux = (Node)v.elementAt(p);
if (ip.equals(aux.ip)) break;
p++; }
if (p == v.size()) {
aux = new Node(ip,0);
v.add(aux);
out.println("agregado");
aux.count++;
out.println("<h1> Following clients visited this site </h1><br>");
for (int i = 0; i < v.size(); i++) {
aux = (Node)v.elementAt(i);
out.print("<hr> "+ aux.ip+" has been "+aux.count+" times here");
out.close();

9. Vector containing the “nodes”
public class ShowCountsServlet extends HttpServlet {
Vector v = new Vector();
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String ip = request.getRemoteHost();
Node aux; int p =0;
while(p < v.size()) {
aux = (Node)v.elementAt(p);
if (ip.equals(aux.ip)) break;
p++; }
if (p == v.size()) {
aux = new Node(ip,0);
v.add(aux);
out.println("agregado");
aux.count++;
out.println("<h1> Following clients visited this site </h1><br>");
for (int i = 0; i < v.size(); i++) {
aux = (Node)v.elementAt(i);
out.print("<hr> "+ aux.ip+" has been "+aux.count+" times here");
out.close();
Vector containing the “nodes”

10. initialize response header get writer to browser get IP of client
public class ShowCountsServlet extends HttpServlet {
Vector v = new Vector();
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String ip = request.getRemoteHost();
Node aux; int p =0;
while(p < v.size()) {
aux = (Node)v.elementAt(p);
if (ip.equals(aux.ip)) break;
p++; }
if (p == v.size()) {
aux = new Node(ip,0);
v.add(aux);
out.println("agregado");
aux.count++;
out.println("<h1> Following clients visited this site </h1><br>");
for (int i = 0; i < v.size(); i++) {
aux = (Node)v.elementAt(i);
out.print("<hr> "+ aux.ip+" has been "+aux.count+" times here");
out.close();
initialize response header
get writer to browser
get IP of client

11. Search for a Node in the vector containing a string with the ip
public class ShowCountsServlet extends HttpServlet {
Vector v = new Vector();
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String ip = request.getRemoteHost();
Node aux; int p =0;
while(p < v.size()) {
aux = (Node)v.elementAt(p);
if (ip.equals(aux.ip)) break;
p++; }
if (p == v.size()) {
aux = new Node(ip,0);
v.add(aux);
out.println("agregado");
aux.count++;
out.println("<h1> Following clients visited this site </h1><br>");
for (int i = 0; i < v.size(); i++) {
aux = (Node)v.elementAt(i);
out.print("<hr> "+ aux.ip+" has been "+aux.count+" times here");
out.close();
Search for a Node in the vector
containing a string with the ip
of the client

12. If the ip was not there, create a new Node with that ip and a
public class ShowCountsServlet extends HttpServlet {
Vector v = new Vector();
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String ip = request.getRemoteHost();
Node aux; int p =0;
while(p < v.size()) {
aux = (Node)v.elementAt(p);
if (ip.equals(aux.ip)) break;
p++; }
if (p == v.size()) {
aux = new Node(ip,0);
v.add(aux);
out.println("agregado");
aux.count++;
out.println("<h1> Following clients visited this site </h1><br>");
for (int i = 0; i < v.size(); i++) {
aux = (Node)v.elementAt(i);
out.print("<hr> "+ aux.ip+" has been "+aux.count+" times here");
out.close();
If the ip was not there, create
a new Node with that ip and a
count = 0

13. In any case, the Node containing the ip
public class ShowCountsServlet extends HttpServlet {
Vector v = new Vector();
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String ip = request.getRemoteHost();
Node aux; int p =0;
while(p < v.size()) {
aux = (Node)v.elementAt(p);
if (ip.equals(aux.ip)) break;
p++; }
if (p == v.size()) {
aux = new Node(ip,0);
v.add(aux);
out.println("agregado");
aux.count++;
out.println("<h1> Following clients visited this site </h1><br>");
for (int i = 0; i < v.size(); i++) {
aux = (Node)v.elementAt(i);
out.print("<hr> "+ aux.ip+" has been "+aux.count+" times here");
out.close();
In any case, the Node containing the ip
of the client will be at position p.
We use it for retrieving the Node and
incrementing the count variable.

14. Fina Finally, retrieve each elemento of the
public class ShowCountsServlet extends HttpServlet {
Vector v = new Vector();
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String ip = request.getRemoteHost();
Node aux; int p =0;
while(p < v.size()) {
aux = (Node)v.elementAt(p);
if (ip.equals(aux.ip)) break;
p++; }
if (p == v.size()) {
aux = new Node(ip,0);
v.add(aux);
out.println("agregado");
aux.count++;
out.println("<h1> Following clients visited this site </h1><br>");
for (int i = 0; i < v.size(); i++) {
aux = (Node)v.elementAt(i);
out.print("<hr> "+ aux.ip+" has been "+aux.count+" times here");
out.close();
Finally, retrieve each elemento of the
Vector printing the ip and count variables
Fina

15. Exercise
Modificar el ShowCountsServlet para que muestre el que lo ha visitado más

16. Solución Casi todo el programa se mantiene igual Solo cambia el output
public class ShowCountsServlet extends HttpServlet {
Vector v = new Vector();
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException { ….
Node nmax = (Node)v.elementAt(0);
for (int i = 1; i < v.size(); i++) {
Node aux = (Node)v.elementAt(i);
if (aux.count > nmax.count)
nmax = aux; }
out.print(“ the client with highest number of visits is “+nmax.ip
out.println(“and has been "+nmax.count+" times here");
out.close();
Casi todo el programa se mantiene igual
Solo cambia el output
En vez de imprimir todos, buscamos el mayor
… y lo imprimimos

17. Create a new empty hastable
public class HashExampleServlet extends HttpServlet {
Hashtable h = new Hashtable();
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws
IOException, ServletException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String ip = request.getRemoteHost();
Integer i = (Integer)h.get(ip);
if (i == null) {
i = new Integer(0);
h.put(ip,i); }
int ival = i.intValue();
h.put(ip,new Integer(ival+1)); //replaces the older pair
out.println("<h1> Han visitado este sitio </h1><br>");
Enumeration e = h.keys();
while (e.hasMoreElements()) {
ip = (String)e.nextElement();
i = (Integer)h.get(ip);
ival = i.intValue();
out.print("<hr> "+ ip+" has been "+ival+" times here");
out.close();
Create a new empty hastable

18. Get client’s IP and use it to retrieve the associated
public class HashExampleServlet extends HttpServlet {
Hashtable h = new Hashtable();
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws
IOException, ServletException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String ip = request.getRemoteHost();
Integer i = (Integer)h.get(ip);
if (i == null) {
i = new Integer(0);
h.put(ip,i); }
int ival = i.intValue();
h.put(ip,new Integer(ival+1)); //replaces the older pair
out.println("<h1> Han visitado este sitio </h1><br>");
Enumeration e = h.keys();
while (e.hasMoreElements()) {
ip = (String)e.nextElement();
i = (Integer)h.get(ip);
ival = i.intValue();
out.print("<hr> "+ ip+" has been "+ival+" times here");
out.close();
Get client’s IP and use it
to retrieve the associated
information (count)

19. If there was no pair (ip, count) having this
public class HashExampleServlet extends HttpServlet {
Hashtable h = new Hashtable();
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws
IOException, ServletException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String ip = request.getRemoteHost();
Integer i = (Integer)h.get(ip);
if (i == null) {
i = new Integer(0);
h.put(ip,i); }
int ival = i.intValue();
h.put(ip,new Integer(ival+1)); //replaces the older pair
out.println("<h1> Han visitado este sitio </h1><br>");
Enumeration e = h.keys();
while (e.hasMoreElements()) {
ip = (String)e.nextElement();
i = (Integer)h.get(ip);
ival = i.intValue();
out.print("<hr> "+ ip+" has been "+ival+" times here");
out.close();
If there was no pair (ip, count) having this
IP has key then we put a new one

20. At this point, i will contain the
public class HashExampleServlet extends HttpServlet {
Hashtable h = new Hashtable();
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws
IOException, ServletException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String ip = request.getRemoteHost();
Integer i = (Integer)h.get(ip);
if (i == null) {
i = new Integer(0);
h.put(ip,i); }
int ival = i.intValue();
h.put(ip,new Integer(ival+1)); //replaces the older pair
out.println("<h1> Han visitado este sitio </h1><br>");
Enumeration e = h.keys();
while (e.hasMoreElements()) {
ip = (String)e.nextElement();
i = (Integer)h.get(ip);
ival = i.intValue();
out.print("<hr> "+ ip+" has been "+ival+" times here");
out.close();
At this point, i will contain the
Integer containing the count associated
to this ip. We get the int value
We use it for incrementing the count
value and replacing the older pair
whith this new one

21. Get Enumeration object containing keys
public class HashExampleServlet extends HttpServlet {
Hashtable h = new Hashtable();
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws
IOException, ServletException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String ip = request.getRemoteHost();
Integer i = (Integer)h.get(ip);
if (i == null) {
i = new Integer(0);
h.put(ip,i); }
int ival = i.intValue();
h.put(ip,new Integer(ival+1)); //replaces the older pair
out.println("<h1> Han visitado este sitio </h1><br>");
Enumeration e = h.keys();
while (e.hasMoreElements()) {
ip = (String)e.nextElement();
i = (Integer)h.get(ip);
ival = i.intValue();
out.print("<hr> "+ ip+" has been "+ival+" times here");
out.close();
Get Enumeration object containing keys
As long as there are elements
Get the next key element (IP)
Get the associates info
Get int value in order to print it

22. Get Enumeration object containing keys
public class HashExampleServlet extends HttpServlet {
Hashtable h = new Hashtable();
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws
IOException, ServletException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String ip = request.getRemoteHost();
Integer i = (Integer)h.get(ip);
if (i == null) {
i = new Integer(0);
h.put(ip,i); }
int ival = i.intValue();
h.put(ip,new Integer(ival+1)); //replaces the older pair
out.println("<h1> Han visitado este sitio </h1><br>");
Enumeration e = h.keys();
while (e.hasMoreElements()) {
ip = (String)e.nextElement();
i = (Integer)h.get(ip);
ival = i.intValue();
out.print("<hr> "+ ip+" has been "+ival+" times here");
out.close();
Get Enumeration object containing keys
As long as there are elements
Get the next key element (IP)
Get the associates info
Get int value in order to print it