Chapter 147. HL7 DataFormat

HL7 is often used with the HL7 MLLP protocol, which is a text based TCP socket based protocol. This component ships with a Mina and Netty4 Codec that conforms to the MLLP protocol so you can easily expose an HL7 listener accepting HL7 requests over the TCP transport layer. To expose a HL7 listener service, the camel-mina2 or camel-netty4 component is used with the HL7MLLPCodec (mina2) or HL7MLLPNettyDecoder/HL7MLLPNettyEncoder (Netty4).

HL7 MLLP codec can be configured as follows:

<endpoint id="hl7MinaListener" uri="mina2:tcp://localhost:8888?sync=true&amp;codec=#hl7codec"/>

<bean id="hl7codec" class="org.apache.camel.component.hl7.HL7MLLPCodec">
    <property name="charset" value="iso-8859-1"/>
</bean>

from("hl7MinaListener")
  .bean("patientLookupService");

<bean id="patientLookupService" class="com.mycompany.healthcare.service.PatientLookupService"/>

import ca.uhn.hl7v2.HL7Exception;
import ca.uhn.hl7v2.model.Message;
import ca.uhn.hl7v2.model.v24.segment.QRD;

public class PatientLookupService {
    public Message lookupPatient(Message input) throws HL7Exception {
        QRD qrd = (QRD)input.get("QRD");
        String patientId = qrd.getWhoSubjectFilter(0).getIDNumber().getValue();

        // find patient data based on the patient id and create a HL7 model object with the response
        Message response = ... create and set response data
        return response
    }

<endpoint id="hl7NettyListener" uri="netty4:tcp://localhost:8888?sync=true&amp;encoder=#hl7encoder&amp;decoder=#hl7decoder"/>

<bean id="hl7decoder" class="org.apache.camel.component.hl7.HL7MLLPNettyDecoderFactory"/>
<bean id="hl7encoder" class="org.apache.camel.component.hl7.HL7MLLPNettyEncoderFactory"/>

from("hl7NettyListener")
  .bean("patientLookupService");

The HL7 MLLP codec uses plain String as its data format. Camel uses its Type Converter to convert to/from strings to the HAPI HL7 model objects, but you can use the plain String objects if you prefer, for instance if you wish to parse the data yourself.

As of Camel 2.14.1 you can also let both the Mina and Netty codecs use a plain byte[] as its data format by setting the produceString property to false. The Type Converter is also capable of converting the byte[] to/from HAPI HL7 model objects.

The HL7v2 model uses Java objects from the HAPI library. Using this library, you can encode and decode from the EDI format (ER7) that is mostly used with HL7v2.

The sample below is a request to lookup a patient with the patient ID 0101701234.

MSH|^~\\&|MYSENDER|MYRECEIVER|MYAPPLICATION||200612211200||QRY^A19|1234|P|2.4
QRD|200612211200|R|I|GetPatient|||1^RD|0101701234|DEM||

Using the HL7 model you can work with a ca.uhn.hl7v2.model.Message object, e.g. to retrieve a patient ID:

Message msg = exchange.getIn().getBody(Message.class);
QRD qrd = (QRD)msg.get("QRD");
String patientId = qrd.getWhoSubjectFilter(0).getIDNumber().getValue();  // 0101701234

This is powerful when combined with the HL7 listener, because you don’t have to work with byte[], String or any other simple object formats. You can just use the HAPI HL7v2 model objects. If you know the message type in advance, you can be more type-safe:

QRY_A19 msg = exchange.getIn().getBody(QRY_A19.class);
String patientId = msg.getQRD().getWhoSubjectFilter(0).getIDNumber().getValue();

The HL7 component ships with a HL7 data format that can be used to marshal or unmarshal HL7 model objects.

The HL7 dataformat supports 2 options which are listed below.

To use the data format, simply instantiate an instance and invoke the marshal or unmarshal operation in the route builder:

  DataFormat hl7 = new HL7DataFormat();

  from("direct:hl7in")
    .marshal(hl7)
    .to("jms:queue:hl7out");

In the sample above, the HL7 is marshalled from a HAPI Message object to a byte stream and put on a JMS queue.
The next example is the opposite:

  DataFormat hl7 = new HL7DataFormat();

  from("jms:queue:hl7out")
    .unmarshal(hl7)
    .to("patientLookupService");

Here we unmarshal the byte stream into a HAPI Message object that is passed to our patient lookup service.

  from("direct:hl7in")
    .marshal().hl7()
    .to("jms:queue:hl7out");

  from("jms:queue:hl7out")
    .unmarshal().hl7()
    .to("patientLookupService");

The unmarshal operation adds these fields from the MSH segment as headers on the Camel message:

All headers except CamelHL7Context `are `String types. If a header value is missing, its value is null.

The HL7 Data Format supports the following options:

To use HL7 in your Camel routes you’ll need to add a dependency on camel-hl7 listed above, which implements this data format.

The HAPI library is split into a base library and several structure libraries, one for each HL7v2 message version:

By default camel-hl7 only references the HAPI base library. Applications are responsible for including structure libraries themselves. For example, if an application works with HL7v2 message versions 2.4 and 2.5 then the following dependencies must be added:

<dependency>
    <groupId>ca.uhn.hapi</groupId>
    <artifactId>hapi-structures-v24</artifactId>
    <version>2.2</version>
    <!-- use the same version as your hapi-base version -->
</dependency>
<dependency>
    <groupId>ca.uhn.hapi</groupId>
    <artifactId>hapi-structures-v25</artifactId>
    <version>2.2</version>
    <!-- use the same version as your hapi-base version -->
</dependency>

Alternatively, an OSGi bundle containing the base library, all structures libraries and required dependencies (on the bundle classpath) can be downloaded from the central Maven repository.

<dependency>
    <groupId>ca.uhn.hapi</groupId>
    <artifactId>hapi-osgi-base</artifactId>
    <version>2.2</version>
</dependency>

HAPI provides a Terser class that provides access to fields using a commonly used terse location specification syntax. The Terser language allows to use this syntax to extract values from messages and to use them as expressions and predicates for filtering, content-based routing etc.

Sample:

import static org.apache.camel.component.hl7.HL7.terser;

   // extract patient ID from field QRD-8 in the QRY_A19 message above and put into message header
   from("direct:test1")
      .setHeader("PATIENT_ID",terser("QRD-8(0)-1"))
      .to("mock:test1");

   // continue processing if extracted field equals a message header
   from("direct:test2")
      .filter(terser("QRD-8(0)-1").isEqualTo(header("PATIENT_ID"))
      .to("mock:test2");

Often it is preferable to first parse a HL7v2 message and in a separate step validate it against a HAPI ValidationContext.

Sample:

import static org.apache.camel.component.hl7.HL7.messageConformsTo;
import ca.uhn.hl7v2.validation.impl.DefaultValidation;

   // Use standard or define your own validation rules
   ValidationContext defaultContext = new DefaultValidation();

   // Throws PredicateValidationException if message does not validate
   from("direct:test1")
      .validate(messageConformsTo(defaultContext))
      .to("mock:test1");

The HAPI Context is always configured with a ValidationContext (or a ValidationRuleBuilder), so you can access the validation rules indirectly. Furthermore, when unmarshalling the HL7DataFormat forwards the configured HAPI context in the CamelHL7Context header, and the validation rules of this context can be easily reused:

import static org.apache.camel.component.hl7.HL7.messageConformsTo;
import static org.apache.camel.component.hl7.HL7.messageConforms

  HapiContext hapiContext = new DefaultHapiContext();
  hapiContext.getParserConfiguration().setValidating(false); // don't validate during parsing

  // customize HapiContext some more ... e.g. enforce that PID-8 in ADT_A01 messages of version 2.4 is not empty
  ValidationRuleBuilder builder = new ValidationRuleBuilder() {
      @Override
      protected void configure() {
         forVersion(Version.V24)
              .message("ADT", "A01")
              .terser("PID-8", not(empty()));
         }
      };
  hapiContext.setValidationRuleBuilder(builder);

  HL7DataFormat hl7 = new HL7DataFormat();
  hl7.setHapiContext(hapiContext);

  from("direct:test1")
     .unmarshal(hl7)                // uses the GenericParser returned from the HapiContext
     .validate(messageConforms())   // uses the validation rules returned from the HapiContext
                                    // equivalent with .validate(messageConformsTo(hapiContext))
     // route continues from here

A common task in HL7v2 processing is to generate an acknowledgement message as response to an incoming HL7v2 message, e.g. based on a validation result. The ack expression lets us accomplish this very elegantly:

import static org.apache.camel.component.hl7.HL7.messageConformsTo;
import static org.apache.camel.component.hl7.HL7.ack;
import ca.uhn.hl7v2.validation.impl.DefaultValidation;

  // Use standard or define your own validation rules
   ValidationContext defaultContext = new DefaultValidation();

   from("direct:test1")
      .onException(Exception.class)
         .handled(true)
         .transform(ack()) // auto-generates negative ack because of exception in Exchange
         .end()
      .validate(messageConformsTo(defaultContext))
      // do something meaningful here

      // acknowledgement
      .transform(ack())

In the following example, a plain String HL7 request is sent to an HL7 listener that sends back a response:

In the next sample, HL7 requests from the HL7 listener are routed to the business logic, which is implemented as plain POJO registered in the registry as hl7service.

Then the Camel routes using the RouteBuilder may look as follows:

Note that by using the HL7 DataFormat the Camel message headers are populated with the fields from the MSH segment. The headers are particularly useful for filtering or content-based routing as shown in the example above.