InetAddress and URLs for Java network programming

A dedicated network development package is available in Java---Java.net,java network programming provides two communication protocols: TCP (Transmission Control Protocol) and UDP (Datagram protocol).

I. IP (Internet Protocol) and InetAddress class

1.IP Introduction

Each computer on the Internet has a unique identity, the IP address, that represents itself.

IP address = Network address + host address

2.InetAddress

This class mainly represents the IP address, there are two sub-classes: inet4address, Inet6address, the former represents IPV4, the latter represents IPV6.

Common methods of the InetAddress class are:

	method	description
static inetaddress	getbyname (String host)
static inetaddress	getlocalhost ()	returns to the local host.
String	GetHostName ()	Gets the host name of this IP address.
boolean	isreachable (int timeout)	test if the address can be reached.

To test the InetAddress class:

Package org.demo.net;import java.net.inetaddress;/** * Test inetaddress class * @author Oushine */public class Inetaddressdemo { C1/>public static void Main (string[] args) {        try {            //declare and get local InetAddress object            inetaddress iaddress1= Inetaddress.getlocalhost ();            Declares and obtains the remote InetAddress object            inetaddress iaddress2=inetaddress.getbyname ("www.baidu.com");            Obtain the local IP address            System.out.println ("Native IP address is:" +iaddress1.gethostaddress ());            Obtain the remote IP address            System.out.println ("Baidu's IP Address is:" +iaddress2.gethostaddress ());            SYSTEM.OUT.PRINTLN ("This machine can reach:" +iaddress1.isreachable);        } catch (Exception e) {            e.printstacktrace ();}}    }

Results:

Two. URLs and URLConnection

1.URL

The URL (Uniform Resource Locator) is a Uniform resource locator that can be used directly to find resources on the Internet (such as a Web page).

Common methods for URL classes:

Type	Method	Describe
Construction method	URL(String spec)	Creates an object based on the String representation URL .
Construction method	URL(String protocol, String host, int port, String file)	protocolThe object is created according to the designation, host port number, and file URL .
URLConnection	openConnection()	Returns an URLConnection object that represents the connection to the URL referenced remote object.
inputstream	openstream ()	open to this   URL   Connection and returns a   that is used to read from the connection; InputStream .

To read content using a URL:

Package Org.demo.net;import Java.io.inputstream;import Java.net.malformedurlexception;import java.net.URL;import Java.util.scanner;public class Urldemo {public    static void Main (string[] args) {        URL url;        try {            //Specify the URL URL of the action            = new URL ("http", "www.baidu.com", "/index.html");            Open input stream, read URL content            inputstream inputstream=url.openstream ();            Scanner scan=new Scanner (inputstream);            Sets the read delimiter            scan.usedelimiter ("\ n");            while (Scan.hasnext ()) {                //output content                System.out.println (Scan.next ());            }        } catch (Exception e) {            E.printstacktrace ();}}}    

Results:

The HTML code is displayed.

2.URLConnection

URLConnection is a class that encapsulates a general method of accessing remote network resources through which you can establish a connection to a remote server and examine some of the properties of a remote resource.

Common methods:

	method	description
int	getcontentlength ()	return   content-length   Header field values.
String	getcontenttype ()	return to   Content-type The value of the   header field.
inputstream	getInputStream ()

The URLConnection object can be obtained through the OpenConnection () method of the URL class.

get basic information about the URL:

Package Org.demo.net;import Java.net.url;import Java.net.urlconnection;public class Urlconnectiondemo {public    static void Main (string[] args) {        try {            url url=new url ("http://www.baidu.com");            Establish a connection            urlconnection urlconn=url.openconnection ();            SYSTEM.OUT.PRINTLN ("Content size:" +urlconn.getcontentlength ());            System.out.println ("Content type:" +urlconn.getcontenttype ());        } catch (Exception e) {            e.printstacktrace ();}}    }

Operation Result:

Three. Urlencoder and Urldecoder

In Java, if you need to complete the encoding and decoding operations, you will use Urlencoder and Urldecoder two classes.

Methods of the Urlencoder class:

Type	Method	Describe
static String	encode(String s, String enc)	Converts a string to a format using the specified encoding mechanism application/x-www-form-urlencoded .

Methods of the Urldecoder class:

Type	Method	Describe
static String	decode(String s, String enc)	Decodes a string using the specified encoding mechanism application/x-www-form-urlencoded .

encoding and decoding operations:

Package Org.demo.net;import Java.net.urldecoder;import Java.net.urlencoder;public class Codedemo {public    static void Main (string[] args) {        String keyword= "Oushine yang";        try {            String encode=urlencoder.encode (KeyWord, "UTF-8");            SYSTEM.OUT.PRINTLN ("After encoding:" +encode);            String Decode=urldecoder.decode (EnCode, "UTF-8");            System.out.println ("After decoding:" +decode);        } catch (Exception e) {            e.printstacktrace ();}}            }

Operation Result:

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InetAddress and URLs for Java network programming