Restlet accepts JSON input from client and respond with POST - json

Question

I am writing a program which accepts a JSON input with the following format from client:
{
"campaignID": 1,
"clientID": 1,
"pmapID": 1,
"ward": "1-Bedded (Private)",
"age": 20,
"attr1": "EXA1(A)",
"attr2": "EO",
"attr3": "11/02/2012",
"attr4": "SIN",
"attr5": "N",
"attr6": "Y"
}
I'd like to read the JSON input, save all the attributes into local variables (String, int, ...) and finally respond with a POST("JSON") which will return a single float/double value (e.g. {"PMC": 30.12} ).
public class RestletApplication extends Application
{
#Override
public synchronized Restlet createInboundRoot()
{
Router router = new Router(getContext());
router.attach("/pmc/calculate", PMCResource.class);
return router;
}
}
I have written the function so far but am lost how to read the JSON input:
public class PMCResource extends ServerResource
{
#Post("JSON")
public Representation post(Representation entity) throws ResourceException {
try {
if (entity.getMediaType().isCompatible(MediaType.APPLICATION_JSON))
{
// Read JSON file and parse onto local variables
// Do processing & return a float value
}
} catch (Exception e) {
getResponse().setStatus(Status.SERVER_ERROR_INTERNAL);
}
}
}
5 May 2016 - Edited the resource class
// Imports
public class PMCResource extends ServerResource
{
static Logger LOGGER = LoggerFactory.getLogger(PMCResource.class);
#Override
#Post("JSON")
public Representation post(Representation entity) throws ResourceException
{
PMCMatrixDAO matrix = new PMCMatrixDAOImpl();
JsonObjectBuilder response = Json.createObjectBuilder();
try
{
if (entity.getMediaType().isCompatible(MediaType.APPLICATION_JSON))
{
InputStream is = new FileInputStream(getClass().getResource("/input.json").getFile());
try (JsonReader reader = Json.createReader(is)) {
JsonObject obj = reader.readObject();
double result = matrix.calculatePMC(obj);
response.add("PMC", result);
}
}
} catch (Exception e) {
getResponse().setStatus(Status.SERVER_ERROR_INTERNAL);
}
return new StringRepresentation(response.build().toString());
}
}
The Implementation class
public class PMCMatrixDAOImpl implements PMCMatrixDAO
{
public double calculatePMC(JsonObject obj)
{
int campaignID = obj.getInt("campaignID");
int clientID = obj.getInt("clientID");
int pmapID = obj.getInt("pmapID");
String ward = obj.getString("ward");
int age = obj.getInt("age");
String attr1 = obj.getString("attr1");
String attr2 = obj.getString("attr2");
String attr3 = obj.getString("attr3");
String attr4 = obj.getString("attr4");
String attr5 = obj.getString("attr5");
String attr6 = obj.getString("attr6");
// SQL processing
double dPMC = sqlQueryCall(...);
return dPMC;
}
}

Answer 1

In order to parse your JSON file, and since you're using Maven I'll assume you have it on your classpath, you can do it using a FileInputStream or a FileReader. So, assuming your JSON file is called input.json and it is on the root of your src/main/resources folder, you can load it the following way:
using a FileInputStream:
InputStream is = new FileInputStream(getClass().getResource("/input.json").getFile());
try (JsonReader reader = Json.createReader(is)) {
// file processing is done here
}
using a FileReader:
FileReader fr = new FileReader(getClass().getResource("/input.json").getFile());
try (JsonReader reader = Json.createReader(fr)) {
// file processing is done here
}
Ok, so now that we have our JsonReader created, lets retrieve the contents of our JSON file:
InputStream is = new FileInputStream(getClass().getResource("/input.json").getFile());
try (JsonReader reader = Json.createReader(is)) {
JsonObject obj = reader.readObject();
// retrieve JSON contents
int campaingID = obj.getInt("campaignID");
int clientID = obj.getInt("clientID");
int pmapID = obj.getInt("pmapID");
String ward = obj.getString("ward");
int age = obj.getInt("age");
String attr1 = obj.getString("attr1");
String attr2 = obj.getString("attr2");
String attr3 = obj.getString("attr3");
String attr4 = obj.getString("attr4");
String attr5 = obj.getString("attr5");
String attr6 = obj.getString("attr6");
}
As an alternative of having several variables across your method, you could create a simple POJO, having those variable as attributes, and then populate it using Jackson:
public class MyPojo {
private int campaingID;
private int clientID;
private int pmapID;
private String ward;
private int age;
private String attr1;
private String attr2;
private String attr3;
private String attr4;
private String attr5;
private String attr6;
// getters & setters
}
Finally, in order to send the response back to your client, you could do this:
JsonObject response = Json.createObjectBuilder().add("PMC", 30.12).build();
return new StringRepresentation(response.toString());
So, the entire solution could look like this:
#Override
#Post("JSON")
public Representation post(Representation entity) throws ResourceException {
JsonObjectBuilder response = Json.createObjectBuilder();
try {
if (entity.getMediaType().isCompatible(MediaType.APPLICATION_JSON)) {
InputStream is = new FileInputStream(getClass().getResource("/input.json").getFile());
try (JsonReader reader = Json.createReader(is)) {
JsonObject obj = reader.readObject();
// retrieve JSON contents
int campaingID = obj.getInt("campaignID");
int clientID = obj.getInt("clientID");
int pmapID = obj.getInt("pmapID");
String ward = obj.getString("ward");
int age = obj.getInt("age");
String attr1 = obj.getString("attr1");
String attr2 = obj.getString("attr2");
String attr3 = obj.getString("attr3");
String attr4 = obj.getString("attr4");
String attr5 = obj.getString("attr5");
String attr6 = obj.getString("attr6");
}
// Do processing & execute your SQL query call here
double result = sqlQueryCall(...);
response.add("PMC", result);
}
} catch (Exception e) {
getResponse().setStatus(Status.SERVER_ERROR_INTERNAL);
}
return new StringRepresentation(response.build().toString());
}
As a side note, the JsonReader class belongs to the Java EE API which, for compiling purposes it's okay. Although, for running purposes, one requires the declaration of a JSON-API implementation dependency in one's Maven project. For instance:
<dependency>
<groupId>org.glassfish</groupId>
<artifactId>javax.json</artifactId>
<version>1.0.4</version>
</dependency>
Below is the way one can communicate to the REST web service through a client:
Create a simple POJO object that will contain the information to send, as mentioned above (MyPojo).
Your REST service would look something like this:
public class PMCResource extends ServerResource {
static Logger LOGGER = Logger.getLogger(RestletMain.class.getName());
#Post("JSON")
public Representation post(MyPojo entity) throws ResourceException {
PMCMatrixDAO matrix = new PMCMatrixDAOImpl();
JsonObjectBuilder response = Json.createObjectBuilder();
try {
double result = matrix.calculatePMC(entity);
response.add("PMC", result);
} catch (Exception e) {
getResponse().setStatus(Status.SERVER_ERROR_INTERNAL);
}
return new StringRepresentation(response.build().toString());
}
}
Modify your PMCMatrixDAOImpl in order to process your POJO:
public double calculatePMC(MyPojo pojo) {
(...)
}
Create a client that allows you to test your REST service:
public class PMCResourceMain {
public static void main(String[] args) {
// take into account the context-root, if exists, and path to your REST service
ClientResource resource = new ClientResource("http://<host>:<port>");
MyPojo myPojo = new MyPojo();
myPojo.setCampaingID(1);
myPojo.setClientID(1);
myPojo.setPmapID(1);
myPojo.setWard("1-Bedded (Private)");
myPojo.setAge(20);
myPojo.setAttr1("EXA1(A)");
myPojo.setAttr2("EO");
myPojo.setAttr3("11/02/2012");
myPojo.setAttr4("SIN");
myPojo.setAttr5("N");
myPojo.setAttr6("Y");
try {
resource.post(myPojo, MediaType.APPLICATION_JSON).write(System.out);
} catch (ResourceException | IOException e) {
e.printStackTrace();
}
}
}
Full Restlet documentation can be found here.

Answer 2

For the benefit of those who landed in the same situation as me, here's my solution:
Resource class
#Override
#Post("JSON")
public Representation post(Representation entity) throws ResourceException
{
PMCMatrixDAO matrix = new PMCMatrixDAOImpl();
JsonObjectBuilder response = Json.createObjectBuilder();
try {
String json = entity.getText(); // Get JSON input from client
Map<String, Object> map = JsonUtils.toMap(json); // Convert input into Map
double result = matrix.calculatePMC(map);
response.add("PMC", result);
} catch (IOException e) {
LOGGER.error(this.getClass() + " - IOException - " + e);
getResponse().setStatus(Status.SERVER_ERROR_INTERNAL);
}
return new StringRepresentation(response.build().toString());
}
JSON conversion utility class
public class JsonUtils {
private static final Logger LOG = LoggerFactory.getLogger(JsonUtils.class);
private JsonUtils() {
}
public static String toJson(Object object) {
String jsonString = null;
ObjectMapper mapper = new ObjectMapper();
try {
jsonString = mapper.writeValueAsString(object);
} catch (JsonProcessingException e) {
LOG.error(e.getMessage(), e);
}
return jsonString;
}
public static Map<String, Object> toMap(String jsonString) {
Map<String, Object> map = new ConcurrentHashMap<>();
ObjectMapper mapper = new ObjectMapper();
try {
map = mapper.readValue(jsonString, new TypeReference<Map<String, Object>>() {
});
} catch (IOException e) {
LOG.error(e.getMessage(), e);
}
return map;
}
}
And the implementation class which handles all the processing
public class PMCMatrixDAOImpl implements PMCMatrixDAO
{
public double calculatePMC(Map<String, Object> map)
{
int campaignID = (int) map.get("campaignID");
int clientID = (int) map.get("clientID");
int pmapID = (int) map.get("pmapID");
String ward = (String) map.get("ward");
int age = (int) map.get("age");
String attr1 = (String) map.get("attr1");
String attr2 = (String) map.get("attr2");
String attr3 = (String) map.get("attr3");
String attr4 = (String) map.get("attr4");
String attr5 = (String) map.get("attr5");
String attr6 = (String) map.get("attr6");
// SQL processing
double dPMC = sqlQueryCall(...);
return dPMC;
}
}