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JFlex is a lexical analyzer generator (also known as scanner generator) for Java.

JFlex takes as input a specification with a set of regular expressions and corresponding actions.It generates Java source of a lexer that reads input, matches the input against the regularexpressions in the spec file, and runs the corresponding action if a regular expressionmatched. Lexers usually are the first front-end step in compilers, matching keywords, comments,operators, etc, and generating an input token stream for parsers.

JFlex lexers are based on deterministic finite automata (DFAs).They are fast, without expensive backtracking.

For documentation and more information see theJFlex documentationand thewiki.

You needMaven 3.5.2 or later, and JDK 8 or later.

1. Place grammar files insrc/main/flex/ directory.

2. Extend the projectPOM build section with themaven-jflex-plugin

     <build>    <plugins>      <plugin>        <groupId>de.jflex</groupId>        <artifactId>jflex-maven-plugin</artifactId>        <version>1.9.0</version>        <executions>          <execution>            <goals>              <goal>generate</goal>            </goals>          </execution>        </executions>      </plugin>    </plugins>  </build>

3. Voilà: Java code is produced intarget/generated-sources/ during thegenerate-sources phase(which happens before thecompile phase) and included in the compilation scope.

You need ant, the binary JFlex jar and JDK 8 or later.

1. Define ant task

   <taskdefclassname="jflex.anttask.JFlexTask"name="jflex"classpath="path-to-jflex.jar"/>

2. Use it

   <jflexfile="src/grammar/parser.flex"destdir="build/generated/"/><javacsrcdir="build/generated/"destdir="build/classes/"/>

We provide ajflex rule

load("@jflex_rules//jflex:jflex.bzl","jflex")jflex(name="",# Choose a rule namesrcs= [],# Add input lex specificationsoutputs= [],# List expected generated files)

See the samplesimple BUILDfile.

You need the binary jflex jar and JDK 8 or later.

You can also use JFlex directly from the command line:

jflex/bin/jflex src/grammar/parser.flex

Or:

java -jar jflex-full-1.9.0.jar -d output src/grammar/parser.flex

SeeBuild tool plugins.

Have a look at the sample project:simple and otherexamples.

JFlex is free software, contributions are welcome.See theContributing page for instructions.

The top level directory of the JFLex git repository contains:

• cup A copy of the CUP runtime
• cup-maven-plugin A simple Maven plugin to generate a parser with CUP.
• docs the Markdown sources for the user manual
• java Java sources [WIP, Bazel]
• javatests Java sources of test [WIP, Bazel]
• jflex JFlex, the scanner/lexer generator for Java
• jflex-maven-plugin the JFlex maven plugin, that helps to integrate JFlex in your project
• jflex-unicode-plugin the JFlex unicode maven plugin, used for compiling JFlex
• testsuite the regression test suite for JFlex,
• third_party third-party libraries used by examples of theBazel build system

JFlex can be built with Bazel.Migration to Bazel is still work in progress, concerning the test suite, for instance.

You needBazel.

bazel build //jflex:jflex_bin

This buildsbazel-bin/jflex/jflex_bin, that you can use

bazel-bin/jflex/jflex_bin --info

Or:

bazel run //jflex:jflex_bin -- --info

Build uberjar (aka fatjar aka deploy jar)

bazel build jflex/jflex_bin_deploy.jar

You need JDK 8 or later.

./mvnw install

This generatesjflex/target/jflex-full-1.9.1-SNAPSHOT.jar that you can use, e.g.

java -jar jflex-full-1.9.1-SNAPSHOT.jar --info