Assignment On Java

Topics:1. Inet address2. Factory method3. URL connection4. File handling

Submitted to: submitted by:

Mr. Prakash Ankit Kumar

089

MCA(4th sem)

1. InetAddress The InetAddress class has no visible constructors. To create an InetAddress object, you have to use one of the available factory methods. Factory methods are merely a convention whereby static methods in a class return an instance of that class. This is done in lieu of overloading a constructor with various parameter lists when having unique method names makes the results much clearer. In the case of InetAddress, the three methods getLocalHost(), getByName(), and getAllByName() can be used to create instances of InetAddress. These methods are shown here:

static InetAddress getLocalHost( )

throws UnknownHostException

static InetAddress getByName(String hostName)

throws UnknownHostException

static InetAddress[ ] getAllByName(String hostName)

throws UnknownHostException

The getLocalHost( ) method simply returns the InetAddress object that represents the local host. The getByName( ) method returns an InetAddress for a host name passed to it. If these methods are unable to resolve the host name, they throw an UnknownHostException.On the Internet, it is common for a single name to be used to represent several machines. In the world of web servers, this is one way to provide some degree of scaling. The getAllByName( ) factory method returns an array of InetAddresses that represent all of the addresses that a particular name resolves to. It will also throw an UnknownHostException if it can't resolve the name to at least one address.

The following example prints the addresses and names of the local machine and two well-known Internet web sites:

// Demonstrate InetAddress.

import java.net.*;

class InetAddressTest

{

public static void main(String args[]) throws

UnknownHostException {

InetAddress Address = InetAddress.getLocalHost();

System.out.println(Address);

Address = InetAddress.getByName("starwave.com");

System.out.println(Address);

InetAddress SW[] = InetAddress.getAllByName("www.nba.com");

for (int i=0; i<SW.length; i++)

System.out.println(SW[i]);

}

}

Here is the output produced by this program. (Of course, the output you see will be slightly different.)

default/206.148.209.138

starwave.com/204.202.129.90

Uses of Class

java.net.InetAddressPackages that use InetAddress

java.lang Provides classes that are fundamental to the design of the Java

programming language.

java.net Provides the classes for implementing networking applications.

Uses of InetAddress in java.lang

Methods in java.lang with parameters of type InetAddress

void SecurityManager.checkMulticast(InetAddress maddr)

void SecurityManager.checkMulticast(InetAddress maddr, byte ttl)

Deprecated. Use #checkPermission(java.security.Permission) instead

Uses of InetAddress in java.net

Subclasses of InetAddress in java.net

Class Inet4Address .This class represents an Internet Protocol version 4 (IPv4) address. Class Inet6Address .This class represents an Internet Protocol version 6 (IPv6) address.

2 Factory method

Provides an abstraction or an interface and lets subclass or implementing classe decide which class or method should be instantiated or called, based on the conditions or parameters given.

Benefits:

Connect parallel class hierarchies. A class wants its subclasses to specify the object. A class cannot anticipate its subclasses, which must be created. A family of objects needs to be separated by using shared interface. The code needs to deal with interface, not implemented classes. Hide concrete classes from the client. Factory methods can be parameterized.

Related patterns include

Abstract Factory , which is a layer higher than a factory method.

Template method , which defines a skeleton of an algorithm to defer some Steps to subclasses or avoid subclasses

Prototype, which creates a new object by copying an instance, it reduces subclasses.

Singleton, which makes a returned factory method unique.

Examples

To illustrate such concept, let's use a simple example. To paint a picture, you may need several steps. A shape is an interface. Several implementing classes may be designed in the following way.

interface Shape {public void draw();}class Line implements Shape {Point x, y;Line(Point a, Point b) {x = a;y = b;}public void draw() {//draw a line;}}class Square implements Shape {Point start;int width, height;Square(Point s, int w, int h) {start = s;width = w;height = h;}public void draw() {//draw a square;}}class Circle implements Shape {....

}

class Painting {Point x, y;int width, height, radius;Painting(Point a, Point b, int w, int h, int r) {x = a;y = b;width = w;height = h;radius = r;}Shape drawLine() {return new Line(x,y);}Shape drawSquare() {return new Square(x, width, height);}Shape drawCircle() {return new Circle(x, radius);}....}

...Shape pic;Painting pt;//initializing pt....if (line)

pic = pt.drawLine();if (square)pic = pt.drawSquare();if (circle)pic = pt.drawCircle();

3. Uniform Resource Locator (URL)

A Uniform Resource Locator (URL) specifies the location of a resource on the Web. The HTMLReaderBean class shows how to connect to a URL from within an enterprise bean.

The source code for this example is in the j2eetutorial/examples/src/ejb/htmlreader directory. To compile the code, go to the j2eetutorial/examples directory and type ant htmlreader. A sample HTMLReaderApp.ear file is in the j2eetutorial/examples/ears directory.

java.net.URLConnection

1. A URLConnection object represents a connection to a remote machine.2. You use it to read a resource from and write to a remote machine.3. To obtain an instance of URLConnection, call the openConnection method on a

URL object.4. To use a URLConnection object to write: set the value of doOutput to true using setDoOutput methods:

URL url = new URL ("http://www.google.com/");

InputStream inputStream = url.openStream ();

has the same effect as

URL url = new URL ("http://www.google.com/");

URLConnection urlConnection = url.openConnection ();

InputStream inputStream = urlConnection.getInputStream ();

The getContents method of the HTMLReaderBean class returns a String that contains the contents of an HTML file. This method looks up the java.net.URL object associated with a coded name (url/MyURL), opens a connection to it, and then reads its contents from an InputStream. Before deploying the application, you must map the coded name

(url/MyURL) to a JNDI name (a URL string). Here is the source code for the getContents method.

public StringBuffer getContents() throws HTTPResponseException

{

Context context;URL url;StringBuffer buffer;String line;int responseCode;HttpURLConnection connection;InputStream input;BufferedReader dataInput;

try {context = new InitialContext();url = (URL)context.lookup("java:comp/env/url/MyURL");connection = (HttpURLConnection)url.openConnection();responseCode = connection.getResponseCode();} catch (Exception ex) {throw new EJBException(ex.getMessage());}

if (responseCode != HttpURLConnection.HTTP_OK) {throw new HTTPResponseException("HTTP response code: " +String.valueOf(responseCode));}

try {buffer = new StringBuffer();input = connection.getInputStream();dataInput =

new BufferedReader(new InputStreamReader(input));while ((line = dataInput.readLine()) != null) {buffer.append(line);buffer.append('\n');}} catch (Exception ex) {throw new EJBException(ex.getMessage());}return buffer;}

4. File handling:

File handling is an integral part of nearly all programming projects. Files provide the means by which a program stores data, accesses stored data, or shares data. As a result, there are very few applications that don’t interact with a file in one form or another. Although no aspect of file handling is particularly difficult, a great many classes, interfaces, and methods are involved. Being able to effectively apply them to your projects is the mark of a professional.

Step 1 - Java file handling basics

One of the most frequently used task in programming is writing to and reading

from a file. To do this in Java there are more possibilities. At this time only the

most frequently used text file handling solutions will be presented.

Filename handling

To write anything to a file first of all we need a file name we want to use. The file name is a simple string like like this:

String fileName = "test.txt";

If you want to write in a file which is located elsewhere you need to define thecomplete file name and path in your fileName variable:

String fileName = "c:\\filedemo\\test.txt";

However if you define a path in your file name then you have to take care the path separator. On windows system the '\' is used and you need to backslash it so you need to write '\\', in Unix,Linux systems the separator is a simple slash '/'. To make your code OS independent you can get the separator character as follows:

String separator = File.separator ;

Open a file

To open a file for writing use the FileWriter class and create an instance from it.

The file name is passed in the constructor like this:

FileWriter writer = new FileWriter(fileName);

This code opens the file in overwrite mode. If you want to append to the file then

you need to use an other constructor like this:

FileWriter writer = new FileWriter(fileName,true);

Besides this the constructor can throw an IOException so we put all of the code inside

a try-catch block.

Write to file

At this point we have a writer object and we can send real content to the file. You can do this using the write() method, which has more variant but the most commonly used requires a string as input parameter.

Calling the write() method doesn't mean that it immediately writes the data into the file. The output is maybe cached so if you want to send your data immediately to the file you need to call the flush() method.

As last step you should close the file with the close() method and you are done.

The basic write method looks like this:

Code:

1. public void writeFile() {2. string fileName = "c:\\test.txt";3. try {4. FileWriter writer = new FileWriter(fileName,true);5. writer.write("Test text.");6. writer.close();7. }

8. catch (IOException e) {

9. e.printStackTrace();

10. }

11. }