How to do URL decoding in Java?

问题

In Java, I want to convert this:

https%3A%2F%2Fmywebsite%2Fdocs%2Fenglish%2Fsite%2Fmybook.do%3Frequest_type

To this:

https://mywebsite/docs/english/site/mybook.do&request_type

This is what I have so far:

class StringUTF 
{
    public static void main(String[] args) 
    {
        try{
            String url = 
               \"https%3A%2F%2Fmywebsite%2Fdocs%2Fenglish%2Fsite%2Fmybook.do\" +
               \"%3Frequest_type%3D%26type%3Dprivate\";

            System.out.println(url+\"Hello World!------->\" +
                new String(url.getBytes(\"UTF-8\"),\"ASCII\"));
        }
        catch(Exception E){
        }
    }
}

But it doesn\'t work right. What are these %3A and %2F formats called and how do I convert them?

回答1:

This does not have anything to do with character encodings such as UTF-8 or ASCII. The string you have there is URL encoded. This kind of encoding is something entirely different than character encoding.

Try something like this:

try {
    String result = java.net.URLDecoder.decode(url, StandardCharsets.UTF_8.name());
} catch (UnsupportedEncodingException e) {
    // not going to happen - value came from JDK's own StandardCharsets
}

Java 10 added direct support for Charset to the API, meaning there's no need to catch UnsupportedEncodingException:

String result = java.net.URLDecoder.decode(url, StandardCharsets.UTF_8);

Note that a character encoding (such as UTF-8 or ASCII) is what determines the mapping of characters to raw bytes. For a good intro to character encodings, see this article.

回答2:

The string you've got is in application/x-www-form-urlencoded encoding.

Use URLDecoder to convert it to Java String.

URLDecoder.decode( url, "UTF-8" );

回答3:

This has been answered before (although this question was first!):

"You should use java.net.URI to do this, as the URLDecoder class does x-www-form-urlencoded decoding which is wrong (despite the name, it's for form data)."

Basically:

String url = "https%3A%2F%2Fmywebsite%2Fdocs%2Fenglish%2Fsite%2Fmybook.do%3Frequest_type";
System.out.println(new java.net.URI(url).getPath());

will give you:

https://mywebsite/docs/english/site/mybook.do?request_type

回答4:

%3A and %2F are URL encoded characters. Use this java code to convert them back into : and /

String decoded = java.net.URLDecoder.decode(url, "UTF-8");

回答5:

 try {
        String result = URLDecoder.decode(urlString, "UTF-8");
    } catch (UnsupportedEncodingException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

回答6:

public String decodeString(String URL)
    {

    String urlString="";
    try {
        urlString = URLDecoder.decode(URL,"UTF-8");
        } catch (UnsupportedEncodingException e) {
            // TODO Auto-generated catch block

        }

        return urlString;

    }

回答7:

I use apache commons

String decodedUrl = new URLCodec().decode(url);

The default charset is UTF-8

回答8:

import java.io.UnsupportedEncodingException;
import java.net.URISyntaxException;

public class URLDecoding { 

    String decoded = "";

    public String decodeMethod(String url) throws UnsupportedEncodingException
    {
        decoded = java.net.URLDecoder.decode(url, "UTF-8"); 
        return  decoded;
//"You should use java.net.URI to do this, as the URLDecoder class does x-www-form-urlencoded decoding which is wrong (despite the name, it's for form data)."
    }

    public String getPathMethod(String url) throws URISyntaxException 
    {
        decoded = new java.net.URI(url).getPath();  
        return  decoded; 
    }

    public static void main(String[] args) throws UnsupportedEncodingException, URISyntaxException 
    {
        System.out.println(" Here is your Decoded url with decode method : "+ new URLDecoding().decodeMethod("https%3A%2F%2Fmywebsite%2Fdocs%2Fenglish%2Fsite%2Fmybook.do%3Frequest_type")); 
        System.out.println("Here is your Decoded url with getPath method : "+ new URLDecoding().getPathMethod("https%3A%2F%2Fmywebsite%2Fdocs%2Fenglish%2Fsite%2Fmybook.do%3Frequest")); 

    } 

}

You can select your method wisely :)

来源：https://stackoverflow.com/questions/6138127/how-to-do-url-decoding-in-java