Wednesday, January 20, 2010

Using Hibernate Transformers

There are times we have a class, we would like to fill with data according the data returned from a query. The class is a simple POJO and not an Hibernate entity, so Hibernate won’t recognize this class.
This can be done in Hibernate by using Transformers. Let’s have a look on a simple example, showing how Transformers can be used. First, let’s have a look at a simple POJO class named: “UserActivityStat”.
This class contains some statistical information. We would like to fill the statistical information of an instance, directly from running an Hibernate HQL.
public class UserActivityStat
{
private int totalPhotos;
private int totalViews;

public UserActivityStat() {
}

public int getTotalPhotos() {
return totalPhotos;
}

public void setTotalPhotos(int totalPhotos) {
this.totalPhotos = totalPhotos;
}

public int getTotalViews() {
return totalViews;
}

public void setTotalViews(int totalViews) {
this.totalViews = totalViews;
}
}
Now, let’s have a look at a simple method, that uses hibernate HQL and the Transformers class to fill “UserActivityStat” instance with data:
public UserActivityStat getUserActivityStat(User user)
{
return (UserActivityStat)hibernateSession.createQuery("select count(*) as totalPhotos, sum(p.views) as totalViews " +
"from Photo p where p.user = :user " +
"p.dateCreated  <= :now").
setParameter("user", user).
setTimestamp("now", new Date()).
setResultTransformer(Transformers.aliasToBean(UserActivityStat.class)).uniqueResult();
}
Note, that each of the 2 columns has an alias. This alias must be the name of the property on the “UserActivityStat” class. Also note for the use of the “setResultTransformer” along the “Transformers” class.

Tuesday, January 19, 2010

Calculate the distance between 2 Ips in Java using maxmind

Calculating the distance between 2 ips can be done easily by using the great geo service: Maxmind.

Maxmind is an affordable geo service with broad range of solutions like:

  • Country
  • City
  • Organization
  • ISP

and more…

Maxmind services comes in 2 flavors:

  • Paid service: This is very accurate data, in a reasonable low cost.
  • Free service: This is a little less accurate data, but a totally free service.

In order to calculate the distance between 2 IPs, we will use the free version of Maxmind. The free service is called: geoLite. we will use the service named: geoLite city. The geoLite city data contains location information. The location contains latitude and longitude information for ip ranges. Latitude and longitude information is a coordinate method used in may location services such GPS.

In order to use Maxmind we need 2 things:

Calculating the distance between 2 IPs is very easy, since Maxmind did all the hard work for us. We just have to get “Location” instance for the 2 IP and use the “distance” method of the “Location” instance. The returned result is the distance between the 2 IPs in kilometers.

Let’s have a look at a sample code that calculates the distance between Google and Apple:

package com.bashan.blog.maxmind;
import com.maxmind.geoip.Location;
import com.maxmind.geoip.LookupService;
import java.io.IOException;
/**
 * @author Bashan
 */
public class MaxmindTest {
  public static void main(String args[]) throws Exception {
    LookupService lookupService = new LookupService("C:\\GeoLiteCity.dat");
    Location locationGoogle = lookupService.getLocation("74.125.39.147");
    Location locationMicrosoft = lookupService.getLocation("17.251.200.70");
    System.out.println("Google is located on: " + locationGoogle.city);
    System.out.println("Apple is located on: " + locationMicrosoft.city);
    System.out.print("Distance: " + locationGoogle.distance(locationMicrosoft) + " kilometers");
  }
}

And the output:

Google is located on: Mountain View
Apple is located on: Cupertino
Distance: 13.218970226605398 kilometers
Not too far as you can see… ;-)

Saturday, January 16, 2010

Get real IP from request in Java

Simply getting the IP of the remote client in Java is an easy task. Assuming we have a request instance, we can simply invoke the “getRemoteAddr” method:

request.getRemoteAddr();

The problem, is that the IP we get is not always the correct IP. For example if our server is behind a load balancer, the method “request.getRemoteAddr” returns the IP of the load balancer and not the IP of the remote client. Another common example, is that the client is behind some proxy or even several proxies. The IP we will get will not be the correct IP.

Fortunately, In most of the cases when a request passes in a load balancer or a proxy, the IP of the remote client is passed in the header of the request. The header key most of the time is: x-forwarded-for. The header value can be one or more IP addresses. The first address, is the address of the remote client. The second or any other IP is the IP of the proxy on the way. The IP of the last proxy is the IP returned in: “request.getRemoteAddr”. For example, if we have 3 proxies, the request header will look like:

x-forwarded-for: client1, proxy1, proxy2

The IP of the client if the first IP. The IP of the third proxy will be returned when calling to: “request.getRemoteAddr”.

There is one none-common case that may happen. The first IP can be an IP of a private network (for example, an IP that starts with “192” or “10”). I such case we will want to take the second IP.

Writing a Java code that will get the IP from the request is quite easy. We will use assistance from code of these older posts: Convert IP String to numeric representation and numeric representation to IP String in Java, Test if IPv4 belongs to a private network address. The general logic of the code is:

  • Look for “x-forwarded-for” header.
  • If header exists, get the first IP.
  • Check that:
    • IP is valid.
    • IP is not a private IP.
  • If IP passes these 2 tests. Return this IP. If not move to the next IP and do the same test and so on.
  • If header doesn’t exist. Return the IP from calling “request.getRemoteAddr”.

Let’s see how it looks in Java:

package com.bashan.blog.ip;
import org.apache.commons.lang.text.StrTokenizer;
import javax.servlet.http.HttpServletRequest;
import java.util.regex.Pattern;
/**
 * @author Bashan
 */
public class IpUtils {
  public static final String _255 = "(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)";
  public static final Pattern pattern = Pattern.compile("^(?:" + _255 + "\\.){3}" + _255 + "$");
  public static String longToIpV4(long longIp) {
    int octet3 = (int) ((longIp >> 24) % 256);
    int octet2 = (int) ((longIp >> 16) % 256);
    int octet1 = (int) ((longIp >> 8) % 256);
    int octet0 = (int) ((longIp) % 256);
    return octet3 + "." + octet2 + "." + octet1 + "." + octet0;
  }
  public static long ipV4ToLong(String ip) {
    String[] octets = ip.split("\\.");
    return (Long.parseLong(octets[0]) << 24) + (Integer.parseInt(octets[1]) << 16) +
        (Integer.parseInt(octets[2]) << 8) + Integer.parseInt(octets[3]);
  }
  public static boolean isIPv4Private(String ip) {
    long longIp = ipV4ToLong(ip);
    return (longIp >= ipV4ToLong("10.0.0.0") && longIp <= ipV4ToLong("10.255.255.255")) ||
        (longIp >= ipV4ToLong("172.16.0.0") && longIp <= ipV4ToLong("172.31.255.255")) ||
        longIp >= ipV4ToLong("192.168.0.0") && longIp <= ipV4ToLong("192.168.255.255");
  }
  public static boolean isIPv4Valid(String ip) {
    return pattern.matcher(ip).matches();
  }
  public static String getIpFromRequest(HttpServletRequest request) {
    String ip;
    boolean found = false;
    if ((ip = request.getHeader("x-forwarded-for")) != null) {
      StrTokenizer tokenizer = new StrTokenizer(ip, ",");
      while (tokenizer.hasNext()) {
        ip = tokenizer.nextToken().trim();
        if (isIPv4Valid(ip) && !isIPv4Private(ip)) {
          found = true;
          break;
        }
      }
    }
    if (!found) {
      ip = request.getRemoteAddr();
    }
    return ip;
  }
}

Note that the class “StrTokenizer” used to iterate the IPs of the header, is the Apache version from Apache commons lang.

You can download the class here.

Friday, January 15, 2010

Test if IPv4 belongs to a private network address

Sometime we need to check if a given IP belongs to a private network. IP of a private network belong to a special range of IPs. It is most likely, that if you have a small local network at your home or work, the IP in that network is starting with “192” or “10”. For example: “192.168.0.1” or “10.0.0.1”.

The ranges of private network IPs is:



STARTEND
10.0.0.010.255.255.255
172.16.0.0 172.31.255.255
192.168.0.0 192.168.255.255

Since we are dealing here with range of IPs, it will be much easier to convert the IPs to long representation. We will use the code from this blog: Convert IP String to numeric representation and numeric representation to IP String in Java, to easily do the job.

Let’s have a look at the function “isIPv4Private”:

package com.bashan.blog.ip;
/**
 * @author Bashan
 */
public class IpUtils {
  public static String longToIpV4(long longIp) {
    int octet3 = (int) ((longIp >> 24) % 256);
    int octet2 = (int) ((longIp >> 16) % 256);
    int octet1 = (int) ((longIp >> 8) % 256);
    int octet0 = (int) ((longIp) % 256);
    return octet3 + "." + octet2 + "." + octet1 + "." + octet0;
  }
  public static long ipV4ToLong(String ip) {
    String[] octets = ip.split("\\.");
    return (Long.parseLong(octets[0]) << 24) + (Integer.parseInt(octets[1]) << 16) +
        (Integer.parseInt(octets[2]) << 8) + Integer.parseInt(octets[3]);
  }
  public static boolean isIPv4Private(String ip)
  {
    long longIp = ipV4ToLong(ip);
    return (longIp >= ipV4ToLong("10.0.0.0") && longIp <= ipV4ToLong("10.255.255.255")) ||
        (longIp >= ipV4ToLong("172.16.0.0") && longIp <= ipV4ToLong("172.31.255.255")) ||
        longIp >= ipV4ToLong("192.168.0.0") && longIp <= ipV4ToLong("192.168.255.255");
  }
  public static void main(String[] args) {
    System.out.println(isIPv4Private("210.5.80.10"));
    System.out.println(isIPv4Private("192.168.0.1"));
  }
}
You can download the class here.