A Java JNI wrapper for CRF++ which is an open source C++ implementation of Conditional Random Fields (CRF) a machine learning algorithm for segmenting/labeling sequential data.

crfpp-java is a Java library that can be used across operating systems because it contains pre-compiled native libraries of CRF++ for Windows/Mac/Linux (For both 32-bit and 64-bit). At runtime, It will auto-detects your machine environment and loads the native library accordingly.

To build crfpp-java, you need to install JDK (1.6 or higher) and Maven.

For example, in Ubuntu 16.04, you might need to install JDK and Maven like this:

sudo apt-get install openjdk-8-jdk
sudo apt-get install maven

Then run the following command:

mvn package

The file target/crfpp-java-$(version).jar will be created. It is a non-executable JAR file that you can add into your classpath when compiling your Java code.

Alternatively, if you use Maven to manage dependencies, you can build and install crfpp-java into your Maven's local repository with the following command:

mvn install

• crfpp-java is not available in Maven's central repository, but you can run mvn install to build and install it into your Maven's local repository.

Add the following dependency to your pom.xml and specify the version number.

<dependency>
  <groupId>org.chasen.crfpp</groupId>
  <artifactId>crfpp-java<artifactId>
  <version>0.57</version>
</dependency>

First, import org.chasen.crfpp.Tagger in your code:

import org.chasen.crfpp.Tagger;

Then create a new Tagger and use Tagger#add(String) and Tagger#parse() to add and parse context respectively.

Tagger tagger = new Tagger("-m modelfile");
tagger.add("Confidence NN");
tagger.add("in IN");
tagger.add("the DT");
...
tagger.parse();

Finally, you can get tagging result by using Tagger#size(), Tagger.xsize(), Tagger#yname(int), Tagger#prob(int, int), etc.

System.out.println("conditional prob=" + tagger.prob() + " log(Z)=" + tagger.Z());
for (int i = 0; i < tagger.size(); ++i) {
  for (int j = 0; j < tagger.xsize(); ++j) {
    System.out.print(tagger.x(i, j) + "\t");
  }
  System.out.print(tagger.y2(i) + "\t");
  System.out.print("\n");

  System.out.print("Details");
  for (int j = 0; j < tagger.ysize(); ++j) {
    System.out.print("\t" + tagger.yname(j) + "/prob=" + tagger.prob(i,j)
     + "/alpha=" + tagger.alpha(i, j) + "/beta=" + tagger.beta(i, j));
  }
  System.out.print("\n");
}

// when -n20 is specified, you can access nbest outputs
System.out.println("nbest outputs:");
for (int n = 0; n < 10; ++n) {
  if (! tagger.next())
    break;
  System.out.println("nbest n=" + n + "\tconditional prob=" + tagger.prob());
  // you can access any information using tagger.y()...
}
System.out.println("Done");

The crfpp-java searches for native libraries (e.g CRFPP.dll on Windows, libCRFPP.so on Linux, etc.) according to the user platform (os.name and os.arch).

Even though, the natively compiled libraries are bundled into crfpp-java, you can still use your own compiled library file.

crfpp-java searches for native libraries in the following order:

1. If the system property org.chasen.crfpp.use.systemlib is set to true, it will lookup folders specified by java.lib.path system property (This is the default path that JVM searches for native libraries).

2. (System property: org.chasen.crfpp.lib.path)/(System property: org.chasen.crfpp.lib.name).

3. One of the bundled libraries in the JAR file extracted into the folder specified by java.io.tmpdir. If the system property org.chasen.crfpp.tempdir is set, use this folder instead of java.io.tmpdir.