Regex using result for replace String

Question

I want select all the text between <h3> and /h3> <. After selection I like to replace the value of my String with the result. In the following example the result should be Basic Information

String test="&lt;h3&gt;Basic Information&lt;/h3&gt; &lt;div&gt;";
test = test.replaceAll("&lt;h3&gt;(.*?)&lt;/h3&gt;", "$1");

But at the moment the result is

Basic Information <div>

I don't see why you'd expect to get only "Basic Information" as a result with this code. Are you sure that replaceAll is really what you want? Perhaps you rather need to extract the match instead of replacing it. — Lucas Trzesniewski
– Lucas Trzesniewski, Commented May 15, 2016 at 10:22

anubhava · Accepted Answer · 2016-05-15 10:39:04Z

4

With regex you can do:

String test="&lt;h3&gt;Basic Information&lt;/h3&gt; &lt;div&gt;";
String repl = test.replaceFirst(".*&lt;h3&gt;([^&]+).*/h3&gt; &lt;.*", "$1");
//=> Basic Information

Though you can avoid regex altogether and use String APIs to extract same text as well.

Alternatively you can use this regex for matching:

&lt;h3&gt;([^&]+).*/h3&gt; &lt;

and grab captured group #1 using Pattern and Matches APIs.

edited May 15, 2016 at 10:39

answered May 15, 2016 at 10:24

anubhava

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1 Comment

João Esperancinha Over a year ago

yes, one example would be to use String splits just for performance sake. Unless the use if for something bigger. These are actually xml snippets so if they become big enough maybe a SAX parser could do the job better.

João Esperancinha · Accepted Answer · 2016-05-15 13:23:33Z

1

Try this:

Pattern pattern = Pattern.compile("&lt;h3&gt;(.*)&lt;\\/h3&gt;");
Matcher matcher = pattern.matcher("&lt;h3&gt;Basic Information&lt;/h3&gt; &lt;div&gt;");
matcher.find();
StringBuffer sb = new StringBuffer();
matcher.appendReplacement(sb,"$1");
String result = sb.toString();

The reason why you cannot do that with just replaceFirst it's because the appendTail method is called at the end of the replaceFirst method. The matcher will replace the groups you did not specified with empty,the groups you did specified with their value and of course the non-matching bits which well, since no match was created for them, they do not get replaced at all.

In the case of your query:

group 0: <h3>

group 1: Basic Information

group 0: </h3>

non-match: <div>

This is just a generic example of what you can do with the matchers. Of course if you just want the group in specific... Well just use:

matcher.group(1)

edited May 15, 2016 at 13:23

answered May 15, 2016 at 10:55

João Esperancinha

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6 Comments

RealSkeptic Over a year ago

Why use the StringBuffer instead of just calling group(1)? And sb.toString; is not valid java.

João Esperancinha Over a year ago

This is just an example. Of course you can use group for it. I mean if you just want to replace groups without having the unmatched Strings about then StringBuffer is still better. If you just want one specific group... well just get the group. I just edited it.

João Esperancinha Over a year ago

@RealSkeptic btw, care to explain what do you mean by sb.toString() is not Java? AFAIK, StringBuffer contents are converted to string by the toString() method.

João Esperancinha Over a year ago

@RealSkeptic Another thing that you can do is to look at the API to see if sb.toString() is java or not:

@Override public synchronized String toString() { if (toStringCache == null) { toStringCache = Arrays.copyOfRange(value, 0, count);} return new String(toStringCache, true);}

... when I look at the API it looks prety valid java hey :)

RealSkeptic Over a year ago

It's not valid Java without parentheses. You wrote sb.toString instead of sb.toString(), and you weren't returning the value anywhere (which is legal but meaningless).

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