URL Encoding and Decoding using Java

It is common requirement to implement URL encoding and decoding in Java while creating crawlers or downloaders. This post focus on creating modules for encoding and decoding of the passed url using Java.

Language Used:
Java

Git Location:
https://github.com/csanuragjain/extra/tree/master/EncodeDecodeURL

Program:
main method:

 public static void main(String[] args) {  
           // TODO Auto-generated method stub  
           String url="https%3A%2F%2Fr1---sn-ci5gup-cags.googlevideo.com%2Fvideoplayback%3Fpcm2cms%3Dyes%26mime%3Dvideo%252Fmp4%26pl%3D21%26itag%3D22%26\u0026itag=43\u0026type=video%2Fwebm%3B+codecs%3D%22vp8.0%2C+vorbis%22\u0026quality=medium";  
           String url2="https://r1---sn-ci5gup-cags.googlevideo.com/videoplayback?pcm2cms=yes&mime=video/mp4&pl=21&itag=22&&itag=43&type=video/webm; codecs=\"vp8.0, vorbis\"&quality=medium";  
           String decodeURL = decode(url);  
           System.out.println("Decoded URL: "+decodeURL);  
           String encodeURL = encode(url2);  
           System.out.println("Encoded URL2: "+encodeURL);  
      }  

How it works:
1) url is the variable having encoded url which we want to decode
2) url2 is the variable having an url which we want to encode
3) We call the decode method which decodes the url and then print the same.
4) We call the encode method which encodes the url2 and then print the same.

encode method:

      public static String encode(String url)  
      {  
                try {  
                     String encodeURL=URLEncoder.encode( url, "UTF-8" );  
                     return encodeURL;  
                } catch (UnsupportedEncodingException e) {  
                     return "Issue while encoding" +e.getMessage();  
                }  
      }  

How it works:
1) We use the encode method of a predefined java class named URLEncoder
2) encode method of URLEncoder takes 2 arguments
3) 1st argument defines the url to be encoded
4) 2nd argument defines the encoding scheme to be used
5) After encoding the resulting encoded url is returned

decode method:

      public static String decode(String url)  
      {  
                try {  
                     String prevURL="";  
                     String decodeURL=url;  
                     while(!prevURL.equals(decodeURL))  
                     {  
                          prevURL=decodeURL;  
                          decodeURL=URLDecoder.decode( decodeURL, "UTF-8" );  
                     }  
                     return decodeURL;  
                } catch (UnsupportedEncodingException e) {  
                     return "Issue while decoding" +e.getMessage();  
                }  
      }  

How it works:
1) Since same url can be encoded multiple times so we need to decode until url cannnot be decoded further.
2) For eg: "video%252Fmp4" is result of 2 encoding. On decoding it once we get "video%2Fmp4". Now url need to be further decoded so when we apply decoding again we get "video/mp4", which is the result.
3) We use the decode method of a predefined java class named URLDecoder
4) decode method of URLDecoder takes 2 arguments
5) 1st argument defines the url to be decoded
6) 2nd argument defines the decoding scheme to be used
7) After decoding the resulting decoded url is returned
8) We create 2 variables prevURL which is empty and decodeURL which contain the url to be decoded.

 Variable State:  
 prevURL = ""  
 decodeURL ="somethingvideo%252Fmp4"  

9) We create an iteration which runs until prevURL!=decodeURL
10) Now we update prevURL to decodeURL and update decodeURL with the decoded value of the url passed.

 Variable State:  
 prevURL = "somethingvideo%252Fmp4"  
 decodeURL ="somethingvideo%2Fmp4"  

11) Since prevURL!=decodeURL so Step 10 runs again

 Variable State:  
 prevURL = "somethingvideo%2Fmp4"  
 decodeURL ="somethingvideo/mp4"  

12) Since prevURL!=decodeURL so Step 10 runs again

 Variable State:  
 prevURL = "somethingvideo/mp4"  
 decodeURL ="somethingvideo/mp4"  

13) Since prevURL=decodeURL so the decoded url is returned.

Output:

 Decoded URL: https://r1---sn-ci5gup-cags.googlevideo.com/videoplayback?pcm2cms=yes&mime=video/mp4&pl=21&itag=22&&itag=43&type=video/webm; codecs="vp8.0, vorbis"&quality=medium  
 Encoded URL2: https%3A%2F%2Fr1---sn-ci5gup-cags.googlevideo.com%2Fvideoplayback%3Fpcm2cms%3Dyes%26mime%3Dvideo%2Fmp4%26pl%3D21%26itag%3D22%26%26itag%3D43%26type%3Dvideo%2Fwebm%3B+codecs%3D%22vp8.0%2C+vorbis%22%26quality%3Dmedium  

Full Program:

 package com.cooltrickshome;  
 import java.io.UnsupportedEncodingException;  
 import java.net.URLDecoder;  
 import java.net.URLEncoder;  
 public class URLEncodeDecode {  
      public static void main(String[] args) {  
           // TODO Auto-generated method stub  
           String url="https%3A%2F%2Fr1---sn-ci5gup-cags.googlevideo.com%2Fvideoplayback%3Fpcm2cms%3Dyes%26mime%3Dvideo%252Fmp4%26pl%3D21%26itag%3D22%26\u0026itag=43\u0026type=video%2Fwebm%3B+codecs%3D%22vp8.0%2C+vorbis%22\u0026quality=medium";  
           String url2="https://r1---sn-ci5gup-cags.googlevideo.com/videoplayback?pcm2cms=yes&mime=video/mp4&pl=21&itag=22&&itag=43&type=video/webm; codecs=\"vp8.0, vorbis\"&quality=medium";  
           String decodeURL = decode(url);  
           System.out.println("Decoded URL: "+decodeURL);  
           String encodeURL = encode(url2);  
           System.out.println("Encoded URL2: "+encodeURL);  
      }  
      public static String decode(String url)  
      {  
                try {  
                     String prevURL="";  
                     String decodeURL=url;  
                     while(!prevURL.equals(decodeURL))  
                     {  
                          prevURL=decodeURL;  
                          decodeURL=URLDecoder.decode( decodeURL, "UTF-8" );  
                     }  
                     return decodeURL;  
                } catch (UnsupportedEncodingException e) {  
                     return "Issue while decoding" +e.getMessage();  
                }  
      }  
      public static String encode(String url)  
      {  
                try {  
                     String encodeURL=URLEncoder.encode( url, "UTF-8" );  
                     return encodeURL;  
                } catch (UnsupportedEncodingException e) {  
                     return "Issue while encoding" +e.getMessage();  
                }  
      }  
 }  

Hope it helps :)