Replace word starting with '@' in a string

I have a string in which I have placeholders such as @parent and @email. I want to replace those placeholders with some value.
For e.g:

Dear @parent, your email is @email

will be transformed as

Dear parent_name, your email is email_address

I am using the following code to replace @parent with a string. But it is not replacing the pattern.

String messageBody = "Dear @parent,how are you"; 
messageBody = messageBody.replaceAll("\\b@parent\\b", massCommunicationMessageWrapper.getParentName());

If I use the following code it replaces the pattern

String messageBody = "Dear @parent,how are you"; 
messageBody = messageBody.replaceAll("\\bparent\\b", massCommunicationMessageWrapper.getParentName());

What regex should be written to replace the word "@parent"?

>Solution :

The definition fo \b states:

There are three different positions that qualify as word boundaries:

  • Before the first character in the string, if the first character is a word character.
  • After the last character in the string, if the last character is a word character.
  • Between two characters in the string, where one is a word character and the other is not a word character.

Our "word" ("@parent") does not start with a word character. Therefore, the leading \b does not match since there is a non-word character (a blank) on the left and a non-word character (an @) on the right.

I would suggest to remove the leading \b:

String messageBody = "Dear @parent,how are you"; 
messageBody = messageBody.replaceAll("@parent\\b", massCommunicationMessageWrapper.getParentName()); demo

Noteworthy behaviour

Notice that the current implementation does allow for "chaining" multiple placeholders right next to each other, i.e.


would process with the current regular expression schema if @first, @second and @thirs are separate variables.

Furthermore, the current solution does replace something like "Dear@parent, how are you?" (note the missing blank between "Dear" and "@parent").

Finally, the input "Dear @parentign" would not be processed when we want to replace "@parent".

Closing comment

For more complex scenarios, I recommend using a solution backed by a template engine, e.g. freemarker.

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