Java String trim - how to minimize

Question

Java doc says String.trim() Returns a copy of the string.

I have below code in my method, it does trim as mentioned and results in creating new string thrice.

String foo = getFoo(storedProcedureResult);
if(foo !=null && !foo.trim().isEmpty()){ // --> creates new string
  if(foo.trim().substring(1).equals("bar")){ // --> creates new string
  } else if(foo.trim().substring(4,6).equals("bar")){ // --> creates new string
  }
}

I made an attempt to minimize this with below code:

 String foo = getFoo(storedProcedureResult);
    if(foo !=null && !(foo=foo.trim()).isEmpty()){ // --> creates new string only once
      if(foo.substring(1).equals("bar")){ 
      } else if(foo.substring(4,6).equals("bar")){ 
      }
    }

Now, Sonar reports Assignments should not be made from within sub-expressions. How do I efficiently minimize the usage of trim in my method? I am bothering because this method is being used in production and invoked 250+ times per second and should not create more String objects unnecessarily.

Answer 1

You can write:

String foo = getFoo(storedProcedureResult);
if(foo != null) foo = foo.trim();
if(foo !=null && !foo.isEmpty()){
  if(foo.substring(1).equals("bar")){ 
  } else if(foo.substring(4,6).equals("bar")){ 
  }
}

You can also create an utility method for this:

static String safeTrim(String s) {
    return s == null ? null : s.trim();
}

And use it:

String foo = safeTrim(getFoo(storedProcedureResult));

Actually such method exists in Apache Commons Lang.

More generic solution would be to convert null string to empty via the special method:

static String nullToEmpty(String s) {
    return s == null ? "" : s;
}

And use it like this:

String foo = nullToEmpty(getFoo(storedProcedureResult)).trim();
if(!foo.isEmpty()){
  if(foo.substring(1).equals("bar")){ 
  } else if(foo.substring(4,6).equals("bar")){ 
  }
}

Actually such method is available in Google Guava.

Finally you may use Java-8 Optional if you don't want to create/use non-standard methods:

String foo = Optional.ofNullable(getFoo(storedProcedureResult))
                     .map(String::trim).orElse("");
if(!foo.isEmpty()){
  if(foo.substring(1).equals("bar")){ 
  } else if(foo.substring(4,6).equals("bar")){ 
  }
}