Nifi Extract Email Body Text Processor

ExtractEmailBodyText.java

package foo;

import javax.mail.BodyPart;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMultipart;
import java.nio.charset.StandardCharsets;
import org.apache.nifi.annotation.behavior.InputRequirement;
import org.apache.nifi.annotation.documentation.CapabilityDescription;
import org.apache.nifi.annotation.documentation.Tags;
import org.apache.nifi.components.PropertyDescriptor;
import org.apache.nifi.flowfile.FlowFile;
import org.apache.nifi.logging.ComponentLog;
import org.apache.nifi.processor.AbstractProcessor;
import org.apache.nifi.processor.ProcessContext;
import org.apache.nifi.processor.ProcessSession;
import org.apache.nifi.processor.Relationship;
import org.apache.nifi.processor.exception.ProcessException;

import java.io.IOException;
import java.util.*;

@InputRequirement(InputRequirement.Requirement.INPUT_REQUIRED)
@Tags({"split", "email"})
@CapabilityDescription("Extracts the plain/text body from a multipart email")
public class ExtractEmailBodyText extends AbstractProcessor {
    public static final Relationship REL_SUCCESS = new Relationship.Builder()
            .name("success")
            .description("All successfully extracted FlowFiles are routed to this relationship")
            .build();
    public static final Relationship REL_FAILURE = new Relationship.Builder()
            .name("failure")
            .description("FlowFiles are transferred to this relationship when an error occurs")
            .build();

    public static final Set<Relationship> relationships = Collections.unmodifiableSet(
            new HashSet<>(Arrays.asList(new Relationship[]{REL_SUCCESS, REL_FAILURE})));

    public static final List<PropertyDescriptor> properties = Collections.unmodifiableList(
            Arrays.asList());

    @Override
    public Set<Relationship> getRelationships() {
        return relationships;
    }

    @Override
    public final List<PropertyDescriptor> getSupportedPropertyDescriptors() {
        return properties;
    }

    private String getTextFromMessage(Message message) throws MessagingException, IOException {
        if (message.isMimeType("text/plain")){
            return message.getContent().toString();
        }else if (message.isMimeType("multipart/*")) {
            String result = "";
            MimeMultipart mimeMultipart = (MimeMultipart)message.getContent();
            int count = mimeMultipart.getCount();
            for (int i = 0; i < count; i ++){
                BodyPart bodyPart = mimeMultipart.getBodyPart(i);
                if (bodyPart.isMimeType("text/plain")){
                    result = result + "\n" + bodyPart.getContent();
                    break;  //without break same text appears twice in my tests
                }
            }
            return result;
        }
        return "";
    }

    @Override
    public void onTrigger(ProcessContext context, ProcessSession session) throws ProcessException {
        final FlowFile flowFile = session.get();
        if (flowFile == null) {
            return;
        }

        final ComponentLog logger = getLogger();
        
        try {
            final FlowFile newFlowFile = session.write(flowFile, (inputStream, outputStream) -> {
                try {
                MimeMessage mime = new MimeMessage(null, inputStream);
                
                outputStream.write(getTextFromMessage(mime).getBytes(StandardCharsets.UTF_8));
                } catch( MessagingException e) {
                    throw new ProcessException("Not an Email", e);
                }
            });
            session.putAttribute(newFlowFile, "mime.type", "text/plain");
            session.transfer(newFlowFile, REL_SUCCESS);
        }
        catch (ProcessException e) {
            logger.error("Error: " + e.getLocalizedMessage());
            session.transfer(flowFile, REL_FAILURE);
        }

        session.commit();
    }
}