Java – URL Processing

URL stands for Uniform Resource Locator and represents a resource on the World Wide Web, such as a Web page or FTP directory.

This section shows you how to write Java programs that communicate with a URL. A URL can be broken down into parts, as follows −

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

Examples of protocols include , , FTP, and File. The path is also referred to as the filename, and the host is also called the authority.

The following is a URL to a web page whose protocol is HTTP −

https://www.amrood.com/index.htm?language=en#j2se

Notice that this URL does not specify a port, in which case the default port for the protocol is used. With HTTP, the default port is 80.

Constructors

The java.net.URL class represents a URL and has a complete set of methods to manipulate URL in Java.

The URL class has several constructors for creating URLs, including the following −

Sr.No.	Constructors & Description
1	public URL(String protocol, String host, int port, String file) throws MalformedURLException Creates a URL by putting together the given parts.
2	public URL(String protocol, String host, String file) throws MalformedURLException Identical to the previous constructor, except that the default port for the given protocol is used.
3	public URL(String url) throws MalformedURLException Creates a URL from the given String.
4	public URL(URL context, String url) throws MalformedURLException Creates a URL by parsing together the URL and String arguments.

The URL class contains many methods for accessing the various parts of the URL being represented. Some of the methods in the URL class include the following −

Sr.No.	Method & Description
1	This method compares this URL for equality with another object.
2	This method returns the authority of the URL.
3	This method returns the contents of this URL.
4	This method returns the contents of this URL.
5	This method returns the default port for the protocol of the URL.
6	This method returns the filename of the URL.
7	This method returns the host of the URL.
8	This method returns the path of the URL.
9	This method returns the port of the URL.
10	This method returns the protocol of the URL.
11	This method returns the query part of the URL.
12	This method returns the reference part of the URL.
13	This method returns the userInfo part of the URL.
14	This method creates and return an integer suitable for hash table indexing.
15	This method returns a URLConnection instance that represents a connection to the remote object referred to by the URL.
16	This method acts as openConnection(), except that the connection will be made through the specified proxy; Protocol handlers that do not support proxing will ignore the proxy parameter and make a normal connection.
17	This method opens a connection to this URL and returns an InputStream for reading from that connection.
18	This method compares two URLs, excluding the fragment component.
19	This method sets an application”s URLStreamHandlerFactory.
20	This method constructs and return a string representation of this URL.
21	This method constructs and return a string representation of this URL.
22	This method returns a URI equivalent to this URL.

Example

The following URLDemo program demonstrates the various parts of a URL. A URL is entered on the command line, and the URLDemo program outputs each part of the given URL.

// File Name : URLDemo.java
import java.io.IOException;
import java.net.URL;

public class URLDemo {

   public static void main(String [] args) {
      try {
         URL url = new URL("https://www.tutorialspoint.com/index.htm?language=en#j2se");
         
         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();
      }
   }
}

A sample run of the this program will produce the following result −

Output

URL is https://www.tutorialspoint.com/index.htm?language=en#j2se
protocol is https
authority is www.tutorialspoint.com
file name is /index.htm?language=en
host is www.tutorialspoint.com
path is /index.htm
port is -1
default port is 443
query is language=en
ref is j2se

URLConnections Class Methods

The openConnection() method returns a java.net.URLConnection, an abstract class whose subclasses represent the various types of URL connections.

For example −

If you connect to a URL whose protocol is HTTP, the openConnection() method returns an HttpURLConnection object.
If you connect to a URL that represents a JAR file, the openConnection() method returns a JarURLConnection object, etc.

The URLConnection class has many methods for setting or determining information about the connection, including the following −

Sr.No.	Method & Description
1	Adds a general request property specified by a key-value pair.
2	Returns the value of the allowUserInteraction field for this object.
3	Returns setting for connect timeout.
4	Retrieves the contents of this URL connection.
5	Retrieves the contents of this URL connection.
6	Returns the value of the content-encoding header field.
7	Returns the value of the content-length header field.
8	Returns the value of the content-length header field as long.
9	Returns the value of the content-type header field.
10	Returns the value of the date header field.
11	Returns the default value of the allowUserInteraction field.
12	Returns the default value of a URLConnection”s useCaches flag.
13	Returns the default value of the useCaches flag for the given protocol.
14	Returns the value of this URLConnection”s doInput flag.
15	Returns the value of this URLConnection”s doOutput flag.
16	Returns the value of the expires header field.
17	Loads filename map (a mimetable) from a data file.
18	Returns the value for the nth header field.
19	Returns the value of the named header field.
20	Returns the value of the named field parsed as date.
21	Returns the value of the named field parsed as a number.
22	Returns the key for the nth header field.
23	Returns the value of the named field parsed as a number.
24	Returns an unmodifiable Map of the header fields.
25	Returns the value of this object”s ifModifiedSince field.
26	Returns an input stream that reads from this open connection.
27	Returns the value of the last-modified header field.
28	OutputStream getOutputStream() Returns an output stream that writes to this connection.
29	Returns a permission object representing the permission necessary to make the connection represented by this object.
30	Returns setting for read timeout. 0 return implies that the option is disabled (i.e., timeout of infinity).
31	Returns an unmodifiable Map of general request properties for this connection.
32	Returns the value of the named general request property for this connection.
33	Returns the value of this URLConnection”s URL field.
34	Returns the value of this URLConnection”s useCaches field.
35	Tries to determine the content type of an object, based on the specified “file” component of a URL.
36	Tries to determine the type of an input stream based on the characters at the beginning of the input stream.
37	Set the value of the allowUserInteraction field of this URLConnection.
38	Sets a specified timeout value, in milliseconds, to be used when opening a communications link to the resource referenced by this URLConnection.
39	Sets the ContentHandlerFactory of an application.
40	Sets the default value of the allowUserInteraction field for all future URLConnection objects to the specified value.
41	Sets the default value of the useCaches field to the specified value.
42	Sets the default value of the useCaches field for the named protocol to the given value.
43	Sets the value of the doInput field for this URLConnection to the specified value.
44	Sets the value of the doOutput field for this URLConnection to the specified value.
45	static void setFileNameMap(FileNameMap map) Sets the FileNameMap.
46	Sets the value of the ifModifiedSince field of this URLConnection to the specified value.
47	Sets the read timeout to a specified timeout, in milliseconds.
48	Sets the general request property.
49	Sets the value of the useCaches field of this URLConnection to the specified value.
50	Returns a String representation of this URL connection.

Example

The following URLConnectionDemo program connects to a URL entered from the command line.

If the URL represents an HTTP resource, the connection is cast to HttpURLConnection, and the data in the resource is read one line at a time.

package com.tutorialspoint;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;

public class URLConnDemo {
   public static void main(String [] args) {
      try {
         URL url = new URL("https://www.tutorialspoint.com");
         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();
      }
   }
}

A sample run of this program will produce the following result −

Output

$ java URLConnDemo

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

java_networking.htm

Learn Java – URL Processing work project make money

Java – URL Processing

Constructors

Example

Output

URLConnections Class Methods

Example

Output

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