Performance in JDBC

http://www.precisejava.com/javaperf/j2ee/JDBC.htm#JDBC110

I found this very useful link on net.
I wrote a program to grab 5million rows of data from DB and to store it on my harddrive.
It took almost 12 hours

I used the following function from ResultSet to improve the performance.
resultSet.setFetchSize(2000);

By default the FetchSize is 10 rows, By varying size you see the performance change.

Below are the statistics for pulling 100000 rows
setFetchSize      Minutes
10                      12
2000                  4.5
20000                2.6
100000              java.lang.OutOfMemoryError: requested array is larger than heap

CachedRowSet

 ResultSet resultSet = stmt.executeQuery(query);  
 CachedRowSet crs = new CachedRowSetImpl(); //com.sun.rowset.CachedRowSetImpl  
 crs.populate(resultSet);  

Access DB Connection from standalone application

 public static Connection getDatabaseConn() throws NamingException{  
      Context ctx=null;  
      Connection conn = null;       
      Properties env = new Properties();   
      env.put(Context.INITIAL_CONTEXT_FACTORY,"weblogic.jndi.WLInitialContextFactory");   
      env.put(Context.PROVIDER_URL,"t3://127.0.0.1:7001");   
      ctx = new InitialContext(env);   
      try {  
           dataSource = (DataSource) ctx.lookup("ExtDevDB");     //jndi datasource name  
      } catch (NamingException e) {  
           e.printStackTrace();  
      }  
      try{  
      conn = dataSource.getConnection();  
      }catch(Exception e){  
           e.printStackTrace();  
      }finally{  
      }  
      return conn;       
 }  

Use t3 protocol to connect Weblogic server.

Degrees Minutes Seconds to Decimal Degrees

 public class LongLat {  
      public static void main(String args[]){  
           double LongDouble=0;  
           double direction=0;  
           int checkDegree=0;  
           BufferedReader br = new BufferedReader(new InputStreamReader(System.in));  
           String input=null;  
           System.out.println("Enter Longitude or Latitude");  
           try{  
                input=br.readLine().toUpperCase();  
           }catch(Exception e){  
                System.out.println("IO error");  
                System.exit(1);  
           }            
           Pattern p=Pattern.compile("[NEWS]");  
           Matcher m=p.matcher(input);            
           if(input.contains("N") || input.contains("E"))  
                direction=1;  
           else if(input.contains("W") || input.contains("S"))  
                direction=-1;  
           if(input.contains("N") || input.contains("S"))  
                checkDegree=90;  
           else if(input.contains("W") || input.contains("E"))  
                checkDegree=180;  
           input=m.replaceFirst("");  
           input=input.trim();  
           String[] LongDMS=input.split(" ");  
           if(!(Integer.parseInt(LongDMS[0])<=checkDegree)){  
                System.out.println("Degree should be less than "+checkDegree);  
                System.exit(1);  
           }  
           if(!(Integer.parseInt(LongDMS[1])<=60)){  
                System.out.println("Minutes should be in between 0 and "+60);  
                System.exit(1);  
           }  
           if(!(Integer.parseInt(LongDMS[2])<=60)){  
                System.out.println("Second should be in between 0 and "+60);  
                System.exit(1);  
           }  
           if(LongDMS.length==3)  
                LongDouble=Double.valueOf(LongDMS[0])+((Double.valueOf(LongDMS[1])*60)+Double.valueOf(LongDMS[2]))/3600;  
           LongDouble=LongDouble*direction;  
           System.out.println(LongDouble);  
      }  
 }  

 Enter Longitude or Latitude  
 W87 43 41  
 -87.72805555555556  

Random number generator

 private static int RandomNumberGenerator(int aStart, int aEnd, Random aRandom){  
      if ( aStart > aEnd ) {  
       throw new IllegalArgumentException("Start cannot exceed End.");  
      }  
      long range = (long)aEnd - (long)aStart + 1;  
      long fraction = (long)(range * aRandom.nextDouble());  
      int randomNumber = (int)(fraction + aStart);    
      return randomNumber;  
 }  

Sending an Email

 java.util.Properties props = new java.util.Properties();  
 props.put("mail.smtp.host", "here you have to give the smtp host address");  
 props.put("mail.smtp.port", "smtp port number, it may or may not required");  
 Session session = Session.getDefaultInstance(props, null);  
 // Construct the message  
 try {  
      Message msg = new MimeMessage(session);  
      String emailfrom=request.getParameter("emailfrom");  
      String emailto=request.getParameter("emailto");  
      String comment="Hi there";  
      msg.setContent(comment,"text/html");  
      msg.setFrom(new InternetAddress(request.getParameter("emailfrom")));  
      msg.setRecipients(Message.RecipientType.TO,InternetAddress.parse(request.getParameter("emailto")));  
      msg.setSubject("Enter the subject here");  
      msg.setSentDate(new Date());  
      // Sends the message  
      Transport.send(msg);  
      response.getWriter().print("success");  
 } catch (AddressException e) {  
      // TODO Auto-generated catch block  
      response.getWriter().print("failed");  
      e.printStackTrace();  
 } catch (MessagingException e) {  
      // TODO Auto-generated catch block  
      response.getWriter().print("failed");  
      e.printStackTrace();  
 }  

How to use Proxy in java

 Proxy proxy =null;  
 URL url;  
 String decodedXml=null;  
 DataInputStream inStream=null;  
 proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress(ProxyAddress, ProxyPort));  
 // Above line creates proxy with given address and port
 url = new URL(getUrl);  // you need to give your url here
 URLConnection conn = url.openConnection(proxy);// it creates a connection using proxy
 String flag;  
 inStream = new DataInputStream(conn.getInputStream());  

Quarz scheduler

http://www.quartz-scheduler.org/docs/index.html

Calculating Time in milliseconds, in java

            long start = System.currentTimeMillis();
            float elapsedTimeMillis;
           

            Put the code here

            elapsedTimeMillis = (System.currentTimeMillis()-start);
            elapsedTimeMillis =elapsedTimeMillis/1000;
            System.out.println("getting xml rowset"+elapsedTimeMillis);

Use of getServletContext()

When i was doing a project there was a necessity to send an object from one servlet to another servlet. Actually, i was implementing MVC architecture so you can understand in between servlets there is a JSP. So, here is the problem. How to forward an object between servlets?

I came up with an idea of putting the object into session. But, my brother told session is not at all a good idea because it takes lot of server resource. Later, I came up with an idea of using request object and faced trouble sending the objects in request object.

I was thing to implement the logic in different way so that i do not need to send the object to other servlet and i did it with the help of javascript.

Even after the completion of the project, i have question in my mind Is there any other way to send an object between servlets? i found the answer, that is getServletContext()

In servlet1

Resident r=new Resident();

...

...

getServletContext().setAttribute("Obj",r);

In servlet2

Object o= getServletContext().getAttribute("Obj");

Resident r=(Resident)o;

Example:

 

Corrections:

The way i implemented above is wrong for forwarding an Object to another Servlet, the correct way is to put it in Session scope or request scope and then access it. ServletContext is more like static or global declaration for all Servlet's.

tricky question on switch-case

#include
int main()
{
int a=10;
switch(a)
{
case '1': // even if a=1 this case doest not work because it is checking for char '1';
printf("ONE\n");
break;
case '2':
printf("TWO\n");
break;
defa1ut:
printf("NONE\n");
}
return 0;
}

The above program compiles with out any error, but when you run it, it does not give any output

The reason is spelling of key word default is wrong.

Java basic program

Here i am demonstrating a simple program

public class test

{

public static void main(String args[])

{

System.out.println("Hello");

}

}

Save the above file as test.java

Compile the above program: javac test.java

run the program: java test

Output would be: Hello

In Java we write every thing in class. A class should contain a main method which is static and should return void. String args[] is used to take command line arguments.

so far we learned basic program we into some more depth

we will learn different ways of calling a method

public class test

{

public static void main(String args[])

{

int i;

test1 t=new test1(); // creating a instance of test1

i=t.normal(); // calling a method in class test1

System.out.println(i);

}

}

class test1 // this class should not be public

{

public int normal(){

try{

return 10;

}finally{

return 20;

}

}

}

Save the above file as test.java

Compile the above program: javac test.java

run the program: java test

Output would be: 20

Above program we wrote two classes, and accessing a method in one class from another class.

public class test

{

public static int normal(){ // this method should be static

try{

return 10;

}finally{

return 20;

}

}

public static void main(String args[])

{

int i;

test1 t=new test1(); // creating a instance of test1

i=t.normal(); // calling a method in class test1

System.out.println(i);

}

}

Save the above file as test.java

Compile the above program: javac test.java

run the program: java test

Output would be: 20

In the above above program we wrote two methods in one class and both method are static. We made normal method static because we want to access it from main method.

Singleton

Singleton design patters are used where there is only one instance of an object is required.

Here is an example of singleton class.

public class singleton
{
private static singleton instance=null;
static public singleton getInstance()
{
if(instance==null)
instance=new singleton();
return instance;
}
private singleton()
{}
.
.
.
.
}

Remote Method Invocation (RMI)

Following file are needed to put on Client

Conversion.java

ConversionClient.java

Data.java

On server:

Conversion.java

ConversionImpl.java

ConversionServer.java

Data.java

Conversion.java

public interface Conversion extends java.rmi.Remote

{

public Data conversion1(Data km) throws java.rmi.RemoteException;

public Data conversion2(Data km) throws java.rmi.RemoteException;

}

Data.java

import java.io.*;

public class Data implements Serializable {

    private static final long serialVersionUID = 1L;

    private float km;

    private int miles;

    private long foot;

    public Data() {

    }

    public float getKm() {

        return km;

    }

    public void setKm(float km) {

        this.km = km;

    }

    public int getMiles() {

        return miles;

    }

    public void setMiles(int miles) {

        this.miles =miles ;

    }

    public long getFoot() {

        return foot;

    }

    public void setFoot(long foot) {

        this.foot = foot;

    }

}

ConversionClient.java

import java.rmi.Naming; 

import java.rmi.RemoteException; 

import java.net.MalformedURLException; 

import java.rmi.NotBoundException; 

import java.io.*; 

import java.util.*;

import java.net.*;

public class ConversionClient

{

public static void main(String[] args) throws Exception

{

// Converting the hostname to ip address

InetAddress ia=InetAddress.getByName(args[0]);

// Looking up for the remote object in remote server

Conversion c=(Conversion) Naming.lookup("rmi://"+ia.getHostAddress()+":3000/ConversionServer");

// Enter kilometers

System.out.println("Enter Kilometers\n");

Scanner ob=new Scanner(System.in);

float km=ob.nextFloat();

System.out.println("val is "+km);

Data d=new Data();

d.setKm(km);

//passing values to two methods

int s=c.conversion1(d).getMiles();

long t=c.conversion2(d).getFoot();

// printing out the values 

System.out.println(km+"Kilometers ="+s+"Miles ");

System.out.println(km+"Kilometers ="+t+"Foot ");

}

}

ConversionImpl.java

import java.rmi.Naming; 

import java.rmi.RemoteException; 

import java.net.MalformedURLException; 

import java.rmi.NotBoundException; 

public class ConversionImpl extends java.rmi.server.UnicastRemoteObject implements Conversion

{

private static final long serialVersionUID = 1L;

public ConversionImpl() throws java.rmi.RemoteException

{

super();

}

// converts from Km to Miles

public synchronized Data conversion1(Data value) throws java.rmi.RemoteException

{

int r=(int)Math.round(value.getKm() * 0.62137119);

//System.out.println("r="+r);

value.setMiles(r);

return value;

}

// converts from Km to Foot

public synchronized Data conversion2(Data value) throws java.rmi.RemoteException

{

long r=(long)Math.round(value.getKm() * 3280.8399);

//System.out.println("r="+r);

value.setFoot(r);

return value;

}

}

ConversionServer.java

// This program is used to put the object referrence in rmiregistry

import java.rmi.*;

import java.net.*;

public class ConversionServer

{

public static void main(String args[])throws Exception

{

Conversion c=new ConversionImpl();

InetAddress ia=InetAddress.getLocalHost();

String h=ia.getHostName();

Naming.rebind("rmi://"+ia.getHostAddress()+":3000/ConversionServer",c); // putting the object referrence in rmi registry

}

}

To Compile:

1.a. Copy the folder "client" to the machine where you want to run client.

  b. Go to the folder "client" and run the command

     % javac *.java

2.a. Copy the folder "server" to the machine where you want to run the server.

  b. Go to the folder "server" and run the command

     % javac *.java

To Run the program:

1.On server machine

  a. Open a window to start rmiregistry

     % rmiregistry 3000

  b. Go to the folder "server" 

  c. Start the Server on another window

java ConversionServer 

2.a  Go to the folder "client" in client machine

  b. Start the client using the command

        java ConversionClient

I/O in Java

To read Float from command line:

import java.util.Scanner;

Scanner s=new Scanner(System.in);

float f=s.nextFloat();

Scanner: To scan the text

System.in: To receive data from standard input stream

for more information: http://java.sun.com/j2se/1.5.0/docs/api/java/util/Scanner.html