Decoding "%5c"

[saat reddy]

Hi,

I am using URLDecoder.decode(String, "UTF-8") for decoding url encoded strings. I used encodeURIComponent() for encoding the strings in javascript. the decode method is not decoding "\" correctly. "\" is getting encoded as %5c", but when I pass the string to decode, it is getting decoded as "\\". I am seeing that for each "\" I enter it is decoding as double characters "\\", so if I enter "\\", which is "%5c%5c"
I am seeing it is decoded as "\\\\". How can I decode "\" correctly.

Thanks

[Campbell Ritchie]

Welcome to the Ranch.

I saw your posting earlier and thought somebody else would answer better than I can, but I shall try.

You know that \ is a sort of meta-character in Java strings; it "escapes" the character following. If I remember correctly there are about 8 escape combinations:

\b Backspace

\t Tab (horizontal)

\n newline (or more precisely the line-feed character 0x0a)

\r return (the carriage return character 0x0d)

\f form feed

\' Single quote (not smart quotes)

\" Double quote (not smart quotes)

\\ Backslash

You can also insert a Unicode or octal character with an escape sequence like \u1234 or\123. So it is not at all surprising that Java will translate a backslash to \\. That is the normal Java way of writing backslash.

[Peter Chase]

Originally posted by Campbell Ritchie:
You know that \ is a sort of meta-character in Java strings; it "escapes" the character following.

Backslash is a special character in Java string literals (and char literals, too). That is, when you want to type a fixed string into your source code, you have to use backslash escape codes for some special characters (including backslash).

Once the characters are stored in a Java String object on the heap, the special meaning of backslash is gone. A backslash in a Java String object is just a backslash, nothing more.
[ October 16, 2007: Message edited by: Peter Chase ]

[Campbell Ritchie]

You have put it rather better than I did, Mr Chase.

[Jesper de Jong]

Saat,

Are you sure that URLDecoder.decode(...) decodes "%5c" to \\ instead of \? I wrote a small program to check it, and it prints a single backslash, not two backslashes.

How are you displaying the decoded string?

This prints just a single backslash:

import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
 
public class Test {
    public static void main(String[] args) throws UnsupportedEncodingException {
        System.out.println(URLDecoder.decode("%5c", "UTF-8"));
    }
}