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      Course
      URL Processing

      Java Tutorial

      This Java tutorial is tailored for newcomers, offering a journey from basic principles to complex Java programming techniques. Completing this tutorial equips you with a solid understanding of Java, preparing you for advanced learning. You'll emerge ready to tackle the challenges of becoming a top-tier software engineer, with the skills to innovate and excel in the vast world of software development.

      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 HTTP, HTTPS, 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
      public equals(Object obj)
      This method compares this URL for equality with another object.
      2
      public String getAuthority()
      This method returns the authority of the URL.
      3
      public Object getContent()
      This method returns the contents of this URL.
      4
      public Object getContent(Class<?>[] classes)
      This method returns the contents of this URL.
      5
      public int getDefaultPort()
      This method returns the default port for the protocol of the URL.
      6
      public String getFile()
      This method returns the filename of the URL.
      7
      public String getHost()
      This method returns the host of the URL.
      8
      public String getPath()
      This method returns the path of the URL.
      9
      public int getPort()
      This method returns the port of the URL.
      10
      public String getProtocol()
      This method returns the protocol of the URL.
      11
      public String getQuery()
      This method returns the query part of the URL.
      12
      public String getRef()
      This method returns the reference part of the URL.
      13
      public String getUserInfo()
      This method returns the userInfo part of the URL.
      14
      public int hashCode()
      This method creates and return an integer suitable for hash table indexing.
      15
      public URLConnection openConnection()
      This method returns a URLConnection instance that represents a connection to the remote object referred to by the URL.
      16
      public URLConnection openConnection(Proxy proxy)
      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
      public InputStream openStream()
      This method opens a connection to this URL and returns an InputStream for reading from that connection.
      18
      public boolean sameFile(URL other)
      This method compares two URLs, excluding the fragment component.
      19
      public static void setURLStreamHandlerFactory(URLStreamHandlerFactory fac)
      This method sets an application's URLStreamHandlerFactory.
      20
      public String toExternalForm()
      This method constructs and return a string representation of this URL.
      21
      public String toString()
      This method constructs and return a string representation of this URL.
      22
      public String toURI()
      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
      void addRequestProperty(String key, String value)
      Adds a general request property specified by a key-value pair.
      2
      boolean getAllowUserInteraction()
      Returns the value of the allowUserInteraction field for this object.
      3
      int getConnectTimeout()
      Returns setting for connect timeout.
      4
      Object getContent()
      Retrieves the contents of this URL connection.
      5
      Object getContent(Class[] classes)
      Retrieves the contents of this URL connection.
      6
      String getContentEncoding()
      Returns the value of the content-encoding header field.
      7
      int getContentLength()
      Returns the value of the content-length header field.
      8
      long getContentLengthLong()
      Returns the value of the content-length header field as long.
      9
      String getContentType()
      Returns the value of the content-type header field.
      10
      long getDate()
      Returns the value of the date header field.
      11
      static boolean getDefaultAllowUserInteraction()
      Returns the default value of the allowUserInteraction field.
      12
      boolean getDefaultUseCaches()
      Returns the default value of a URLConnection's useCaches flag.
      13
      static boolean getDefaultUseCaches(String protocol)
      Returns the default value of the useCaches flag for the given protocol.
      14
      boolean getDoInput()
      Returns the value of this URLConnection's doInput flag.
      15
      boolean getDoOutput()
      Returns the value of this URLConnection's doOutput flag.
      16
      long getExpiration()
      Returns the value of the expires header field.
      17
      static FileNameMap getFileNameMap()
      Loads filename map (a mimetable) from a data file.
      18
      String getHeaderField(int n)
      Returns the value for the nth header field.
      19
      String getHeaderField(String name)
      Returns the value of the named header field.
      20
      long getHeaderFieldDate(String name, long Default)
      Returns the value of the named field parsed as date.
      21
      int getHeaderFieldInt(String name, int Default)
      Returns the value of the named field parsed as a number.
      22
      String getHeaderFieldKey(int n)
      Returns the key for the nth header field.
      23
      long getHeaderFieldLong(String name, long Default)
      Returns the value of the named field parsed as a number.
      24
      Map<String,List<String>> getHeaderFields()
      Returns an unmodifiable Map of the header fields.
      25
      long getIfModifiedSince()
      Returns the value of this object's ifModifiedSince field.
      26
      InputStream getInputStream()
      Returns an input stream that reads from this open connection.
      27
      int getLastModified()
      Returns the value of the last-modified header field.
      28
      OutputStream getOutputStream()
      Returns an output stream that writes to this connection.
      29
      Permission getPermission()
      Returns a permission object representing the permission necessary to make the connection represented by this object.
      30
      int getReadTimeout()
      Returns setting for read timeout. 0 return implies that the option is disabled (i.e., timeout of infinity).
      31
      Map<String,List<String>> getRequestProperties()
      Returns an unmodifiable Map of general request properties for this connection.
      32
      String getRequestProperty(String key)
      Returns the value of the named general request property for this connection.
      33
      URL getURL()
      Returns the value of this URLConnection's URL field.
      34
      boolean getUseCaches()
      Returns the value of this URLConnection's useCaches field.
      35
      static String guessContentTypeFromName(String fname)
      Tries to determine the content type of an object, based on the specified "file" component of a URL.
      36
      static String guessContentTypeFromStream(InputStream is)
      Tries to determine the type of an input stream based on the characters at the beginning of the input stream.
      37
      void setAllowUserInteraction(boolean allowuserinteraction)
      Set the value of the allowUserInteraction field of this URLConnection.
      38
      void setConnectTimeout(int timeout)
      Sets a specified timeout value, in milliseconds, to be used when opening a communications link to the resource referenced by this URLConnection.
      39
      static void setContentHandlerFactory(ContentHandlerFactory fac)
      Sets the ContentHandlerFactory of an application.
      40
      static void setDefaultAllowUserInteraction(boolean defaultallowuserinteraction)
      Sets the default value of the allowUserInteraction field for all future URLConnection objects to the specified value.
      41
      void setDefaultUseCaches(boolean defaultusecaches)
      Sets the default value of the useCaches field to the specified value.
      42
      static void setDefaultUseCaches(String protocol, boolean defaultVal)
      Sets the default value of the useCaches field for the named protocol to the given value.
      43
      void setDoInput(boolean doinput)
      Sets the value of the doInput field for this URLConnection to the specified value.
      44
      void setDoOutput(boolean dooutput)
      Sets the value of the doOutput field for this URLConnection to the specified value.
      45
      static void setFileNameMap(FileNameMap map)
      Sets the FileNameMap.
      46
      void setIfModifiedSince(long ifmodifiedsince)
      Sets the value of the ifModifiedSince field of this URLConnection to the specified value.
      47
      void setReadTimeout(int timeout)
      Sets the read timeout to a specified timeout, in milliseconds.
      48
      void setRequestProperty(String key, String value)
      Sets the general request property.
      49
      void setUseCaches(boolean usecaches)
      Sets the value of the useCaches field of this URLConnection to the specified value.
      50
      String toString()
      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.....