Re: Regular expression search and replace

From:

Daniel Pitts <newsgroup.spamfilter@virtualinfinity.net>

Newsgroups:

comp.lang.java.programmer

Date:

Wed, 19 May 2010 15:28:56 -0700

Message-ID:

<ECZIn.27719$wV2.348@newsfe23.iad>

On 5/19/2010 3:20 PM, markspace wrote:

Daniel Pitts wrote:

On 5/19/2010 2:01 PM, Jimmy wrote:

Below are the example of possible input strings:

myparam1=myvalue1&param1=value2&param3=value3
&myparam1=myvalue1&param1=value2&param3=value3
?myparam1=myvalue1&param1=value2&param3=value3
"myparam1=myvalue1&param1=value2&param3=value3"
"&myparam1=myvalue1&param1=value2&param3=value3"
"?myparam1=myvalue1&param1=value2&param3=value3"

I like to replace value of "param1" with "somevalue". Can it be done
in 1 expression replacement? Cuz pattern [\"&?]* works for searching,
but reusing the same pattern will get rid of the first non-alpha
character.

Something along the lines of:
str = str.replaceAll("([?&]?)param1=([^&]*)", "$1param1=somevalue");
(untested)

Assuming "somevalue" is not really a constant, you might need to use
Matcher.quoteReplacement(String) to get this to work consistently. Also,
is that first ([?&]) bit really needed? It doesn't seem so to me, but
maybe I missed something.

Yes, it is needed so as not to match "myparam1" accidentally.

In reality, even though you can do this in one fell regex swoop, it is
often better to fully parse into a Map<String, List<String>>, and do
your manipulation much more precisely, and then recreate the string. At
least, if you are dealing with HTTP query parameters, that has been my
experience.

package test;

import java.util.regex.Matcher;

/**
*
* @author Brenden
*/
public class ReplaceTest {
public static void main( String[] args )
{
String test = "&myparam1=myvalue1&param1=value2&param3=value3";
String replace = "some$1value";
test = test.replaceAll( "(myparam1=)[^&]*",
"$1"+Matcher.quoteReplacement( replace ) );
System.out.println( test );
}
}

Output:
run:
&myparam1=some$1value&param1=value2&param3=value3
BUILD SUCCESSFUL (total time: 0 seconds)

--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>