Java URL

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Java URL is a class in the Java programming language that represents a Uniform Resource Locator (URL) reference. It is used to create, read, and manipulate URLs, which are used to locate resources on the internet or within a local network. The URL class provides methods for accessing various components of a URL, such as the protocol, host, port, path, and query string. It can also be used to open a connection to a URL and retrieve data from it. Here is an example of how to create a URL object in Java:

import java.net.*;

public class URLExample {
   public static void main(String[] args) throws Exception {
      URL url = new URL("https://www.example.com");
      System.out.println("Protocol: " + url.getProtocol());
      System.out.println("Host: " + url.getHost());
      System.out.println("Port: " + url.getPort());
      System.out.println("Path: " + url.getPath());
      System.out.println("Query: " + url.getQuery());
   }
}

This code creates a URL object for the “https://www.example.com” URL and then prints out various components of the URL using the methods provided by the URL class.

Constructors of Java URL class:

The Java URL class provides several constructors that can be used to create a URL object. Here are the available constructors:

  1. URL(String spec) – Creates a URL object from the specified string representation of a URL. For example, URL url = new URL("https://www.example.com");
  2. URL(String protocol, String host, int port, String file) – Creates a URL object from the specified protocol, host, port, and file components. For example, URL url = new URL("https", "www.example.com", 443, "/index.html");
  3. URL(String protocol, String host, int port, String file, URLStreamHandler handler) – Same as the previous constructor, but allows a custom URLStreamHandler to be specified. This is rarely used.
  4. URL(URL context, String spec) – Creates a URL object from a base URL and a relative URL. The base URL is specified by the context parameter, and the relative URL is specified by the spec parameter. For example, URL url = new URL(new URL("https://www.example.com"), "/index.html");
  5. URL(URL context, String spec, URLStreamHandler handler) – Same as the previous constructor, but allows a custom URLStreamHandler to be specified. This is rarely used.

Note that the constructors can throw a MalformedURLException if the specified URL string is invalid.

Commonly used methods of Java URL class:

The Java URL class provides a variety of methods for accessing and manipulating the various components of a URL. Here are some commonly used methods:

  1. openStream() – Returns an input stream that can be used to read the contents of the resource specified by the URL.
  2. openConnection() – Returns a URLConnection object that can be used to further customize the connection to the resource specified by the URL.
  3. getProtocol() – Returns the protocol component of the URL as a string (e.g., “http”, “https”, “ftp”).
  4. getHost() – Returns the host component of the URL as a string (e.g., “www.example.com“).
  5. getPort() – Returns the port component of the URL as an int. If no port is specified in the URL, it returns the default port for the protocol (e.g., 80 for HTTP).
  6. getPath() – Returns the path component of the URL as a string (e.g., “/index.html”).
  7. getQuery() – Returns the query component of the URL as a string (e.g., “q=java+url”).
  8. getFile() – Returns the file component of the URL as a string, which includes the path and query components (e.g., “/index.html?q=java+url”).
  9. toString() – Returns the string representation of the URL.
  10. toURI() – Returns a URI object representing the same URL. This can be useful for performing additional URI-specific operations.

Note that the methods may throw various exceptions, such as IOException or URISyntaxException, depending on the operation being performed.

Example of Java URL class:

Sure! Here is an example of using the Java URL class to retrieve and display the contents of a webpage:

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

public class URLExample {
   public static void main(String[] args) throws Exception {
      URL url = new URL("https://www.example.com");
      BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream()));
      String line;
      while ((line = reader.readLine()) != null) {
         System.out.println(line);
      }
      reader.close();
   }
}

This code creates a URL object for the “https://www.example.com” URL, opens a connection to the URL, and reads the contents of the webpage using a BufferedReader. It then prints each line of the webpage to the console. Note that this code uses a try-with-resources block to automatically close the BufferedReader after it is used. Also note that the code may throw an IOException if there is an error reading from the stream.