Presentation about transport mechanisms in GWT, held at GWT.create 2015 in San Francisco and Munich.

1. Leif Åstrand
Product Manager
Comparing GWT
Transport Mechanisms
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2. Transport
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3. RequestBuilder builder = new RequestBuilder(RequestBuilder.GET, url);
try {
builder.sendRequest(requestDataString, new RequestCallback() {
@Override
public void onResponseReceived(Request request, Response response) {
int statusCode = response.getStatusCode();
String text = response.getText();
}
@Override
public void onError(Request request, Throwable exception) {
// TODO Handle asynchronous problems
}
});
} catch (RequestException e) {
// TODO Handle synchronous problems
}
RequestBuilder
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4. Good
• It just works
Bad
• Low level
RequestBuilder
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5. Real world usage
8 %
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6. What to send?
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7. public class Contact {
private String name;
private int yearOfBirth;
private List<String> emailAddresses;
private Address address;
public static class Address {
private String street;
private String city;
}
// + Getters and setters
}
Contact
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8. String data = contact.getName();
data += "," + contact.getYearOfBirth();
String[] parts = data.split(",");
contact.setName(parts[0]);
contact.setYearOfBirth(Integer.parseInt(parts[1]));
String conversion
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9. String data = contact.getName();
data += "," + contact.getYearOfBirth();
String[] parts = data.split(",");
contact.setName(parts[0]);
contact.setYearOfBirth(Integer.parseInt(parts[1]));
String conversion
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10. {
name: "John Doe",
yearOfBirth: 1900,
address: {
street: "Happy Street 1",
city: "Turku"
},
emailAddresses: ["john@doe.com", "johndoe@gmail.com"]
}
JSON
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11. JSONObject json = JSONParser.parseStrict(string).isObject();
contact.setName(json.get("name").isString().stringValue());
contact.setYearOfBirth(
(int) json.get("yearOfBirth").isNumber().doubleValue());
contact.setAddress(
parseAddress(json.get("address").isObject()));
JSONArray emailAddresses =
json.get("emailAddresses").isArray();
for (int i = 0; i < emailAddresses.size(); i++) {
contact.getEmailAddresses().add(
emailAddresses.get(i).isString().stringValue());
}
}
JSONValue parsing
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12. Good
• It’s standard
• Human readable
format
• Compact format
Bad
• Not completely
typesafe
• Boilerplate
• Client only
JSONValue
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13. What about the
server?
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14. ObjectMapper mapper = new ObjectMapper();
try {
Contact contact = mapper.readValue(string, Contact.class);
} catch (VariousExceptions e) {
// Do something sensible
}
Jackson on the server
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15. Reflection
Code generation
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16. public static interface ContactMapper extends
ObjectMapper<Contact> {}
public Contact parseContact(String string) {
ContactMapper mapper = GWT.create(ContactMapper.class);
Contact contact = mapper.read(jsonString);
return contact;
}
gwt-jackson
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17. Good
• Minimal boiler plate
• Can share code
between server and
client
Bad
• Only creating and
reading strings
Jackson
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18. Where to send?
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19. public interface ContactService {
public void saveContact(Contact contact);
public List<Contact> getContacts();
}
Remote Procedure Call
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20. public interface ContactService {
public AsyncResult<Void> saveContact(Contact contact);
public AsyncResult<List<Contact>> getContacts();
}
Asynchronous
public interface ContactServiceAsync {
public void saveContact(Contact contact,
AsyncCallback<Void> callback);
public void getContacts(AsyncCallback<List<Contact>>
callback);
}
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21. Good
• Simple but powerful
concept
• The default solution
• Optimized format
Bad
• Sending the entire
object graph
• Polymorphism can
cause huge files
• Optimized format
GWT-RPC
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22. Most popular!
51 %
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23. Where to send
JSON?
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24. GET /contacts
DELETE /contacts/5
PUT /contacts { name: "John Doe", ... }
REST
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25. @Path("/contacts")
public interface ContactsService {
@GET
public List<Contact> listContacts();
@Path("/{id}")
@DELETE
public void deleteContact(@PathParam("id") int id);
@PUT
public void createContact(Contact contact);
}
JAX-RS
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26. @Path("/contacts")
public interface ContactsService extends DirectRestService {
// Same content
}
ContactsService contactsService =
GWT.create(ContactsService.class);
REST.withCallback(myContactListCallback).
call(contactsService).listContacts();
resty-gwt
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27. Good
• Any server
• Any client
Bad
• Some boilerplate
resty-gwt
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28. Real world usage
6 %
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29. Wild ideas
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30. Send interfaces
instead of objects
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31. public interface Contact {
public void setName(String name);
public String getName();
public void setYearOfBirth(int yearOfBirth);
public int getYearOfBirth();
public void setAddress(Address address);
public Address getAddress();
public void setEmailAddresses(List<String> addresses);
public List<String> getEmailAddresses();
}
Contact interface
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32. New possibilities
Send partial updates
Manage entity identity
Use instance methods for RPC
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33. Good
• Entities do not need
to be GWT
compatible
• Combines RPC and
entity management
• Automatic request
handling
Bad
• Complex setup
• Heavy coupling with
the server
RequestFactory
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34. Define message
Generate code
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35. message Contact {
required string name = 1;
required int32 yearOfBirth = 2;
repeated string emailAddresses = 3;
optional Address address = 4;
}
Contact message
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36. Good
• Any language
• Google's data
interchange format
• Backwards
compatible
Bad
• Binary format
• Not very widely
used
Protocol Buffers
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37. What if we put
the server in
control?
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38. lördag 24 januari 15

39. public class ContactState extends SharedState {
public String name;
@DelegateToWidget
public int yearOfBirth;
}
@OnStateChange("name")
private void updateName() {
doSomethingWithTheName(getState().name);
}
@Override
protected ContactState getState() {
return (ContactState) super.getState();
}
State synchronization
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40. public interface ContactRpc extends ServerRpc {
public void deleteContact(int id);
}
// Register RPC handler on the server
registerRpc(new ContactRpc() {
@Override
public void deleteContact(int id) {
ContactDAO.deleteById(id);
}
});
// Send RPC from the client
public void sendDelete(int contactId) {
getRpcProxy(ContactRpc.class).deleteContact(contactId);
}
RPC
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41. Good
• Stateful server
• Server push
Bad
• Stateful server
• Tied to the
framework
Vaadin Connectors
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42. What if we
completely hide
the transport?
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43. // Fire event
@Inject
Event<Contact> contactEvent;
public void updateContact(Contact contact) {
contactEvent.fire(contact);
}
// Listen to event
public void contactUpdateObserver(@Observes Contact contact) {
ContactDAO.updateContact(contact);
}
CDI events
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44. Good
• Transparent
communication
• Server push
Bad
• Transparent
communication
• Tied to the
framework
Errai Bus
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45. Questions?
Answers?
Please rate the talk at
gwtcreate.com/agenda
? leif@vaadin.com
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