Improving performance of Java String methods

Regular expression matching always comes with the cost of pattern matching. In case the pattern is not precompiled then the the expression parsing happens every time the code is invoked.

Some of Java String methods use regular expressions e.g. matches(...), replaceFirst(...), replaceAll(...) and split(...). These methods actually use Pattern matching library methods internally however these patterns are parsed every time these methods are invoked. The performance impact is significant if these methods are called too frequently or in high traffic zone.

Java library provides Pattern package which could be used to precompile the regular expressions.

Here are equivalent code which uses the precompiled pattern.

1) String.split(regex)

[java]

private static final String regex = "\\.";

String[] keys = str.split(regex);

[/java]

 

[java]
import java.util.regex.Pattern;
private static final Pattern myPattern = Pattern.compile(regex);
String[] keys = myPattern.split(str);

[/java]

2) String.replace*(regex...)

2.1) replaceFirst() - http://docs.oracle.com/javase/6/docs/api/java/lang/String.html#replaceFirst(java.lang.String, java.lang.String)

[java]

str.replaceFirst(regex, repl) yields exactly the same result as the expression
"Pattern.compile(regex).matcher(str).replaceFirst(repl)""

[/java]

 

[java]

private static final String regex = "\\.";
private static final Pattern myPattern = Pattern.compile(regex);
myPattern.matcher(str).replaceFirst(repl);

[/java]

 

2.2) replaceAll() - http://docs.oracle.com/javase/6/docs/api/java/lang/String.html#replaceAll(java.lang.String, java.lang.String)

[java]

str.replaceAll(regex, repl) yields exactly the same result as the expression
"Pattern.compile(regex).matcher(str).replaceAll(repl)""

[/java]

 

[java]

private static final String regex = "\\.";
private static final Pattern myPattern = Pattern.compile(regex);
myPattern.matcher(str).replaceAll(repl);

[/java]

3) matches(regex) - http://docs.oracle.com/javase/6/docs/api/java/lang/String.html#matches(java.lang.String)

[java]

str.matches(regex) yields exactly the same result as the expression
"Pattern.matches(regex, str)"

[/java]

 

[java]
private static final String regex = "\\.";
private static final Pattern myPattern = Pattern.compile(regex);
myPattern.matches(regex, str);

[/java]

The Zen of Python, by Tim Peters (python -m this)

$ python -m this
The Zen of Python, by Tim Peters

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!