Having trouble with regex in Java 11

Question

Trying to strip server name from: //some.server.name/path/to/a/dir (finishing with /path/to/a/dir)

I have tried 3 different regexes (hardcoded works), but the other two look like they should work but are not. Can anyone point me to why ?

cat test.java

import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class test
{
public static void main(String[] args) throws Exception
{

        String rootPath="//server.myco.com/some/path/to/a/doc/root";
        rootPath = rootPath.replace("//[\\w.]*","");
        System.out.println("rootPath - "+rootPath);
        rootPath = rootPath.replace("//[^/]*","");
        System.out.println("rootPath - "+rootPath);
        rootPath = rootPath.replace("//server.myco.com","");
        System.out.println("rootPath - "+rootPath);

}
}

Output:

rootPath - //server.myco.com/some/path/to/a/doc/root
rootPath - //server.myco.com/some/path/to/a/doc/root
rootPath - /some/path/to/a/doc/root

Java 11.0.6:

$ java --version
openjdk 11.0.6 2020-01-14
OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.6+10)
OpenJDK 64-Bit Server VM AdoptOpenJDK (build 11.0.6+10, mixed mode)

Were you looking for .replaceAll or .replaceFirst instead of .replace ? — The fourth bird
– The fourth bird, Commented Nov 14, 2023 at 18:25
Thanks, replaceAll did it. Why did I need replaceAll ? There is a single instance in the string. — Andy Knipp
– Andy Knipp, Commented Nov 14, 2023 at 18:28
Using .replace does not take a regex. If you want to replace a single occurrence, then use .replaceFirst — The fourth bird
– The fourth bird, Commented Nov 14, 2023 at 18:34

Mr. Polywhirl · Accepted Answer · 2023-11-14 18:34:23Z

3

Please refrain from using a regular expression to parse a URI. Most languages these days include libraries to parse a URI/URL into a various parts.

Here is a proper example:

import java.net.URI;
import java.net.URISyntaxException;

public class ExtractPath {
    public static void main(String[] args) {
        String rootPath = "//server.myco.com/some/path/to/a/doc/root";
        String path = extractPath(rootPath);
        System.out.println(path.equals("/some/path/to/a/doc/root")); // true
    }

    public static String extractPath(String location) {
        try {
            return new URI(location).getPath();
        } catch (URISyntaxException e) {
            throw new RuntimeException(e);
        }
    }
}

edited Nov 14, 2023 at 18:34

answered Nov 14, 2023 at 18:27

Mr. Polywhirl

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4 Comments

Usagi Miyamoto Over a year ago

Do not use URL for checking/parsing, use URI instead: "As mentioned, URL and URLConnection rely on protocol handlers which must be present, otherwise an Exception is thrown."

Andy Knipp Over a year ago

Its not a URL per se, but I see your point. Thanks.

Mr. Polywhirl Over a year ago

@UsagiMiyamoto I addressed this. Thanks.

Holger Over a year ago

When you’re going to wrap the URISyntaxException in an unchecked exception anyway, you can use return URI.create(location).getPath(); in the first place. Then, you’ll get an IllegalArgumentException wrapping the URISyntaxException if one occurred, without the need to do it yourself.

Reilas · Accepted Answer · 2023-11-14 20:11:05Z

1

You can utilize the URI class for this.

URI u = new URI("//server.myco.com/some/path/to/a/doc/root");
String p = u.getPath();

Output

/some/path/to/a/doc/root

answered Nov 14, 2023 at 20:11

Reilas

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Comments

Mukit09 · Accepted Answer · 2023-11-14 18:48:18Z

0

You should use this from the String class:

public String replaceAll(String regex, String replacement)

instead of this:

public String replace(CharSequence target, CharSequence replacement)

When you are calling replace("//[\\w.]*","") or replace("//[^/]*",""), it's searching "//[\\w.]*" or "//[^/]*" respectively, and trying to replace with the empty string. As there is no such string in the given string, no change is there.

But replaceAll("//[\\w.]*","") takes regex as the first argument. Hence it will work.

Oracle Java 11 reference for String replace() and replaceAll()

edited Nov 14, 2023 at 18:48

answered Nov 14, 2023 at 18:41

Mukit09

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