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hamcrest-text-patterns

A library for writing readable, composable regular expression matchers that integrates cleanly with Hamcrest.

Features

  • Easier to read (although more long-winded) than regular expressions.
  • Named capture groups: captured text is identified by name, not by the index of the group.
  • Composable: patterns can be easily combined into more complex patterns without worrying about breaking regex syntax or changing group identifiers.
  • Refactoring friendly: patterns can be refactored with your favourite IDE.

Parsing

Here's a simple example of using Hamcrest Text Patterns to parse date ranges, such as "12 Apr 1994 - 16 Mar 2005".

We can define components of the final text pattern using the factory methods defined in the Patterns class:

PatternComponent month = either(
  "jan", "feb", "mar", "apr", "may", "jun", 
  "jul", "aug", "sep", "oct", "nov", "dec");

PatternComponent digit = anyCharacterInCategory("Digit");

PatternComponent date = separatedBy(whitespace(),
  capture("day", exactly(2, digit)), 
  capture("month", caseInsensitive(month)), 
  capture("year", exactly(4, digit)));

We can combine these into a PatternMatcher for matching date ranges:

PatternMatcher dateRange = new PatternMatcher(separatedBy(whitespace(),
  capture("from", date), "-", capture("to", date)));

We can now parse date ranges from input text and extract the dates using the names of the capture groups we defined in the dateRange pattern: "from" and "to".

String input = "31 Dec 2003 - 16 aug 2008";

Parse parse = dateRange.parse(input);

assertThat(parse.get("from"), equalTo("31 Dec 2003"));
assertThat(parse.get("to"), equalTo("16 aug 2008"));

And, because we defined capture groups in our date pattern, we can extract the parts of the "from" and "to" dates:

assertThat(parse.get("from.day"), equalTo("31"));
assertThat(parse.get("from.month"), equalTo("Dec"));
assertThat(parse.get("from.year"), equalTo("2003"));

assertThat(parse.get("to.day"), equalTo("16"));
assertThat(parse.get("to.month"), equalTo("aug"));
assertThat(parse.get("to.year"), equalTo("2008"));

Matching

A PatternMatcher is a Hamcrest matcher, and so text patterns can be used with libraries that build upon Hamcrest, such as JUnit or jMock. For example:

String input = "31 Dec 2003 - 16 aug 2008";
assertThat(input, dateRange);

String badInput = "31 12 2003 - 16 08 2008";
assertThat(badInput, not(dateRange));

Writing New Pattern Components

The library does not cover all the Java regex functionality yet, so you may need to extend the library to add a feature you need.

For example, lets write a pattern component that matches ASCII control characters.

We must define a class that implements the PatternComponent interface.

public class AsciiControlCharacter implements PatternComponent {
  ...
}

Then, we must implement the buildRegex method to append the regex syntax for the pattern component to the StringBuilder.

public class AsciiControlCharacter implements PatternComponent {
  public void buildRegex(StringBuilder builder, GroupNamespace groups) {
    builder.append("\\p{Cntrl}");
  }
}

(We can ignore the groups parameter. That's used by the capture(...) and valueOf(...) pattern components to identify capture groups by name.)

Finally, we should write a static function to make patterns that use this component easy to read. For example, we could put factory functions for all the pattern components we need for our project in a single class and statically import them into the classes that use them.

public class ProjectSpecificPatterns {
  public static PatternComponent asciiControlCharacter() {
    return new AsciiControlCharacter();
  }
}

Maven

To use hamcrest-text-patterns with Maven 2/3, you must add the following repository to your project's pom.xml file:

<repository>
  <id>hamcrest-text-patterns-repo</id>
  <name>hamcrest-text-patterns repository on GitHub</name>
  <url>http://wcmatthysen.github.com/hamcrest-text-patterns/repository/</url>
</repository>

Then, you can add the following dependency:

<dependency>
  <groupId>org.hamcrest</groupId>
  <artifactId>hamcrest-text-patterns</artifactId>
  <version>0.0.1</version>
</dependency>

License

BSD License

Copyright (c) 2000-2008, www.hamcrest.org All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

Neither the name of Hamcrest nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.