Mastering Regular Expressions in Java 2nd Edition.pdf

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Perl, .NET, Java, and More

Regular

Expressions

Jeffrey E.F. Friedl

Mastering

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Mastering Regular Expressions

Second Edition

Jeffrey E. F. Friedl

Beijing • Cambridge • Farnham • Köln • Paris • Sebastopol • Taipei • Tokyo

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Java

Java didn’t come with a regex package until Java 1.4, so early programmers had to

do without regular expressions. Over time, many programmers independently

developed Java regex packages of varying degrees of quality, functionality, and

complexity. With the early-2002 release of Java 1.4, Sun entered the fray with their

java.util.regex package. In preparing this chapter, I looked at Sun’s package,

and a few others (detailed starting on page 372). So which one is best? As you’ll

soon see, there can be many ways to judge that.

In This Chapter Before looking at what’s in this chapter, it’s important to mention

what’s not in this chapter. In short, this chapter doesn’t restate everything from

Chapters 1 through 6. I understand that some readers interested only in Java may

be inclined to start their reading with this chapter, and I want to encourage them

not to miss the beneﬁts of the preface and the earlier chapters: Chapters 1, 2,

and 3 introduce basic concepts, features, and techniques involved with regular

expressions, while Chapters 4, 5, and 6 offer important keys to regex understand-

ing that directly apply to every Java regex package that I know of.

As for this chapter, it has several distinct parts. The ﬁrst part, consisting of “Judging

a Regex Package” and “Object Models,” looks abstractly at some concepts that help

you to understand an unfamiliar package more quickly, and to help judge its suit-

ability for your needs. The second part, “Packages, Packages, Packages,” moves

away from the abstract to say a few words about the speciﬁc packages I looked at

while researching this book. Finally, we get to the real fun, as the third part talks

in speciﬁcs about two of the packages, Sun’s java.util.regex and Jakarta’s ORO

package.

365

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366

Chapter 8: Java

Judging a Regex Package

The ﬁrst thing most people look at when judging a regex package is the regex ﬂa-

vor itself, but there are other technical issues as well. On top of that, “political”

issues like source code availability and licensing can be important. The next sec-

tions give an overview of some points of comparison you might use when select-

ing a regex package.

143)

• Rich Flavor? How full-featured is the ﬂavor? How many of the items on

page 113 are supported? Are they supported well? Some things are more

important than others: lookaround and lazy quantiﬁers, for example, are more

important than possessive quantiﬁers and atomic grouping, because look-

around and lazy quantiﬁers can’t be mimicked with other constructs, whereas

possessive quantiﬁers and atomic grouping can be mimicked with lookahead

that allows capturing parentheses.

• Unicode Support? How well is Unicode supported? Java strings support Uni-

code intrinsically, but does !\w" know which Unicode characters are “word”

characters? What about !\d" and !\s" ? Does !\b" understand Unicode? (Does its

idea of a word character match !\w" ’s idea of a word character?) Are Unicode

properties supported? How about blocks? Scripts? (

119) Which version of

Unicode’s mappings do they support: Version 3.0? Version 3.1? Version 3.2?

Does case-insensitive matching work properly with the full breadth of Uni-

code characters? For example, does a case-insensitive ‘ ß ’ really match ‘ SS ’?

(Even in lookbehind?)

• How Flexible? How ﬂexible are the mechanics? Can the regex engine deal

only with String objects, or the whole breadth of CharSequence objects? Is it

easy to use in a multi-threaded environment?

• How Convenient? The raw engine may be powerful, but are there extra

“convenience functions” that make it easy to do the common things without a

lot of cumbersome overhead? Does it, borrowing a quote from Perl, “make the

easy things easy, and the hard things possible?”

• JRE Requirements? What version of the JRE does it require? Does it need the

latest version, which many may not be using yet, or can it run on even an old

(and perhaps more common) JRE ?

Technical Issues

Some of the technical issues to consider are:

• Engine Type? Is the underlying engine an NFA or DFA ?Ifan NFA ,isita POSIX

NFA or a Traditional NFA ? (See Chapter 4

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Judging a Regex Package

367

• Ef ﬁcient? How efﬁcient is it? The length of Chapter 6 tells you how much

there is to be said on this subject. How many of the optimizations described

there does it do? Is it efﬁcient with memory, or does it bloat over time? Do

you have any control over resource utilization? Does it employ lazy evaluation

to avoiding computing results that are never actually used?

• Does it Work? When it comes down to it, does the package work? Are there

a few major bugs that are “deal-breakers?” Are there many little bugs that

would drive you crazy as you uncover them? Or is it a bulletproof, rock-solid

package that you can rely on?

Of course, this list just the tip of the iceberg — each of these bullet points could be

expanded out to a full chapter on its own. We’ll touch on them when comparing

packages later in this chapter.

Social and Political Issues

Some of the non-technical issues to consider are:

• Documented? Does it use Javadoc? Is the documentation complete? Correct?

Approachable? Understandable?

• Maintained? Is the package still being maintained? What’s the turnaround

time for bugs to be ﬁxed? Do the maintainers really care about the package? Is

it being enhanced?

• Suppor t and Popular ity? Is there ofﬁcial support, or an active user community

you can turn to for reliable support (and that you can provide support to,

once you become skilled in its use)?

• Ubiquity? Can you assume that the package is available everywhere you go,

or do you have to include it whenever you distribute your programs?

• Licensing? May you redistribute it when you distribute your programs? Are

the terms of the license something you can live with? Is the source code avail-

able for inspection? May you redistribute modiﬁed versions of the source

code? Must you?

Well, there are certainly a lot of questions. Although this book can give you the

answers to some of them, it can’t answer the most important question: which is

right for you? I make some recommendations later in this chapter, but only you

can decide which is best for you. So, to give you more background upon which to

base your decision, let’s look at one of the most basic aspects of a regex package:

its object model.

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