In Java RESTful web services, it is common to send and receive data in different formats. One of the challenges is to transform and map the response data from the server to the desired format on the client side. This is where response transformation and mapping techniques come into play. In this blog post, we will learn how to implement response transformation and mapping in Java RESTful web services.

Table of Contents

• Response Transformation vs. Response Mapping
• Using JSON Serialization/Deserialization
• Using XML Serialization/Deserialization
• Custom Response Transformation and Mapping
• Conclusion

Response Transformation vs. Response Mapping

Before we dive into implementation details, let’s clarify the difference between response transformation and response mapping.

Response transformation involves converting the server-side data into a specific format for the client to consume. For example, transforming Java objects into JSON or XML format.

Response mapping, on the other hand, focuses on mapping the server-side data to a client-side data model. It involves converting the server-side objects into client-side objects with the desired structure. This can be useful when the server returns a complex data structure that needs to be mapped into a simpler model on the client side.

Using JSON Serialization/Deserialization

JSON (JavaScript Object Notation) is a widely used format for data exchange. In Java, there are libraries like Jackson or Gson that provide JSON serialization and deserialization capabilities.

To use JSON serialization, you need to annotate your server-side classes with appropriate annotations, such as @JsonIgnore to exclude certain fields or @JsonProperty to specify custom field names. On the client-side, you can use the same library to deserialize the JSON response into Java objects.

Example code:

// Server-side
class Person {
  @JsonProperty("full_name")
  String fullName;
  int age;
  // ...
}

// Client-side
String jsonResponse = // JSON response from server
ObjectMapper objectMapper = new ObjectMapper();
Person person = objectMapper.readValue(jsonResponse, Person.class);

Using XML Serialization/Deserialization

XML (eXtensible Markup Language) is another widely used format for data exchange. In Java, you can use libraries like JAXB (Java Architecture for XML Binding) or XStream for XML serialization and deserialization.

To use XML serialization, you need to annotate your server-side classes with appropriate JAXB annotations. On the client-side, you can use the same library to deserialize the XML response into Java objects.

Example code:

// Server-side
@XmlRootElement
class Person {
  @XmlElement(name = "full_name")
  String fullName;
  int age;
  // ...
}

// Client-side
String xmlResponse = // XML response from server
JAXBContext jaxbContext = JAXBContext.newInstance(Person.class);
Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
StringReader reader = new StringReader(xmlResponse);
Person person = (Person) unmarshaller.unmarshal(reader);

Custom Response Transformation and Mapping

In some cases, the default serialization/deserialization provided by libraries might not be sufficient. In such situations, you can implement custom transformation and mapping logic.

For example, you can define custom converters or transformers that convert the server-side objects into client-side objects. This gives you full control over the transformation process.

Example code:

// Server-side
class Person {
  String fullName;
  int age;
  // ...
}

// Client-side
class ClientPerson {
  String name;
  int age;
  // ...
  
  public static ClientPerson fromPerson(Person person) {
    ClientPerson clientPerson = new ClientPerson();
    clientPerson.name = Formatter.formatFullName(person.fullName);
    clientPerson.age = person.age;
    return clientPerson;
  }
}

Person person = // Server-side person object
ClientPerson clientPerson = ClientPerson.fromPerson(person);

Conclusion

In this blog post, we have seen how to implement response transformation and mapping in Java RESTful web services. We explored the usage of JSON and XML serialization/deserialization libraries, as well as implementing custom transformation and mapping logic. By applying these techniques, you can ensure that the data sent and received by your RESTful web services is in the format and structure that best suits your client applications.

#java #restful