Java URL Processing

URL (Uniform Resource Locator) Chinese called a Uniform Resource Locator, it is sometimes known as a Web page address. He expressed as a resource on the Internet, such as Web or FTP address.

This chapter we will introduce Java is treated as a URL. URL can be divided into the following sections.

protocol://host:port/path?query#ref

protocols (protocol) can be HTTP, HTTPS, FTP, and File. port is the port number. path for the file path and file name.

URL Examples HTTP protocol as follows:

http://www.w3cschool.cc/index.html?language=cn#j2se

Examples of the above URL does not specify a port, because the HTTP protocol default port number is 80.

URL class methods

In the java.net package defines the URL class that used to deal with content related to the URL. To create and use the URL class, the following were introduced.

java.net.URL provides a way to build wealth URL, and can access resources through java.net.URL.

URL class contains many methods for accessing the various parts of the URL, the specific methods and described as follows:

Examples

The above examples demonstrate the use of java.net URL class to get the various parts of the URL parameters:

// 文件名 : URLDemo.java

import java.net.*;
import java.io.*;

public class URLDemo
{
   public static void main(String [] args)
   {
      try
      {
         URL url = new URL("../../www.w3cschool.cc/index.html-language=cn#j2se.html");
         System.out.println("URL is " + url.toString());
         System.out.println("protocol is "
                                    + url.getProtocol());
         System.out.println("authority is "
                                    + url.getAuthority());
         System.out.println("file name is " + url.getFile());
         System.out.println("host is " + url.getHost());
         System.out.println("path is " + url.getPath());
         System.out.println("port is " + url.getPort());
         System.out.println("default port is "
                                   + url.getDefaultPort());
         System.out.println("query is " + url.getQuery());
         System.out.println("ref is " + url.getRef());
      }catch(IOException e)
      {
         e.printStackTrace();
      }
   }
}

The above examples compiled results are as follows:

URL is http://www.w3cschool.cc/index.html?language=cn#j2se
protocol is http
authority is www.w3cschool.cc
file name is /index.htm?language=cn
host is www.amrood.com
path is /index.html
port is -1
default port is 80
query is language=cn
ref is j2se

URLConnections class methods

openConnection () returns a java.net.URLConnection.

E.g:

• URL If you connect the HTTP protocol, openConnection () method returns HttpURLConnection object.

• If the URL you connect to a JAR file, openConnection () method returns JarURLConnection object.

• and many more...

URLConnection methods listed below:

Examples

The following example uses the HTTP protocol URL. openConnection return HttpURLConnection object.

// 文件名 : URLConnDemo.java

import java.net.*;
import java.io.*;
public class URLConnDemo
{
   public static void main(String [] args)
   {
      try
      {
         URL url = new URL("../../www.w3cschool.cc/index.html");
         URLConnection urlConnection = url.openConnection();
         HttpURLConnection connection = null;
         if(urlConnection instanceof HttpURLConnection)
         {
            connection = (HttpURLConnection) urlConnection;
         }
         else
         {
            System.out.println("Please enter an HTTP URL.");
            return;
         }
         BufferedReader in = new BufferedReader(
         new InputStreamReader(connection.getInputStream()));
         String urlString = "";
         String current;
         while((current = in.readLine()) != null)
         {
            urlString += current;
         }
         System.out.println(urlString);
      }catch(IOException e)
      {
         e.printStackTrace();
      }
   }
}

The above examples compiled results are as follows:

$ java URLConnDemo

.....a complete HTML content of home page of amrood.com.....