OpenNLP Custom POS Tagger : How to make Dictionary override input tags - dictionary

Question

I am using OpenNLP for creating my own POS Tagger as follows
public Trainer(String trainingData, String modelSavePath, String dictionary){
try {
dataIn = new MarkableFileInputStreamFactory(
new File(classLoader.getResource(trainingData).getFile()));
lineStream = new PlainTextByLineStream(dataIn, "UTF-8");
ObjectStream<POSSample> sampleStream = new WordTagSampleStream(lineStream);
POSTaggerFactory fac=new POSTaggerFactory();
if(dictionary!=null && dictionary.length()>0)
{
fac.setDictionary(new Dictionary(new FileInputStream(classLoader.getResource(dictionary).getFile())));
}
model = POSTaggerME.train("en", sampleStream, TrainingParameters.defaultParams(), fac);
} catch (IOException e) {
// Failed to read or parse training data, training failed
e.printStackTrace();
} finally {
if (lineStream != null) {
try {
lineStream.close();
} catch (IOException e) {
// Not an issue, training already finished.
// The exception should be logged and investigated
// if part of a production system.
e.printStackTrace();
}
}
}
OutputStream modelOut = null;
try {
modelOut = new BufferedOutputStream(new FileOutputStream(modelSavePath));
//modelOut = new BufferedOutputStream(new FileOutputStream(new File(getClass().getResource(modelSavePath).toURI())));
model.serialize(modelOut);
} catch (IOException e) {
// Failed to save model
e.printStackTrace();
} finally {
if (modelOut != null) {
try {
modelOut.close();
} catch (IOException e) {
// Failed to correctly save model.
// Written model might be invalid.
e.printStackTrace();
}
}
}
}
which works well and saves the newly created model as a bin file. I want the dictionary terms to overwrite the words in my input and i do not see this behavior.
So consider the input
Mary_NNP had_VBD a_DT little_JJ lamb_NN
Now i want the tag to be
lamb_LAMB
so put this in the dictionary
<?xml version="1.0" encoding="UTF-8"?>
<dictionary>
<entry tags="LAMB">
<token>lamb</token>
</entry>
</dictionary>
But when i try out the newly trained tagger, i still see the tag as NN for lamb
However, if my training data is
Mary_NNP had_VBD a_DT little_JJ lamb_LAMB
then it works as expected. Also, if i do not have the word lamb in my training data at all, then the custom generated tagger uses the dictionary tag.
How can i make sure that the dictionary tag always overrides the training data tag? Do i have to modify the training in any way?