Leif ÅstrandProduct Manager

Comparing GWT Transport Mechanisms

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Transport

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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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Good

• It just works

Bad

• Low level

RequestBuilder

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Real world usage

8 %lördag 24 januari 15

What to send?

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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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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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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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{ name: "John Doe", yearOfBirth: 1900, address: { street: "Happy Street 1", city: "Turku" }, emailAddresses: ["john@doe.com", "johndoe@gmail.com"]}

JSON

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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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Good

• It’s standard• Human readable

format• Compact format

Bad

• Not completely typesafe

• Boilerplate• Client only

JSONValue

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What about the server?

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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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ReflectionCode generation

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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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Good

• Minimal boiler plate• Can share code

between server and client

Bad

• Only creating and reading strings

Jackson

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Where to send?

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public interface ContactService { public void saveContact(Contact contact); public List<Contact> getContacts();}

Remote Procedure Call

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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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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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Most popular!

51 %lördag 24 januari 15

Where to send JSON?

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GET /contacts

DELETE /contacts/5

PUT /contacts { name: "John Doe", ... }

REST

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@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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@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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Good

• Any server• Any client

Bad

• Some boilerplate

resty-gwt

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Real world usage

6 %lördag 24 januari 15

Wild ideas

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Send interfaces instead of objects

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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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New possibilities

Send partial updates

Manage entity identity

Use instance methods for RPC

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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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Define messageGenerate code

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message Contact { required string name = 1; required int32 yearOfBirth = 2; repeated string emailAddresses = 3; optional Address address = 4; }

Contact message

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Good

• Any language• Google's data

interchange format• Backwards

compatible

Bad

• Binary format• Not very widely

used

Protocol Buffers

lördag 24 januari 15

What if we put the server in control?

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public class ContactState extends SharedState { public String name;

@DelegateToWidget public int yearOfBirth;}

@OnStateChange("name")private void updateName() { doSomethingWithTheName(getState().name);}

@Overrideprotected ContactState getState() { return (ContactState) super.getState();}

State synchronization

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public interface ContactRpc extends ServerRpc { public void deleteContact(int id);}

// Register RPC handler on the serverregisterRpc(new ContactRpc() { @Override public void deleteContact(int id) { ContactDAO.deleteById(id); }});

// Send RPC from the clientpublic void sendDelete(int contactId) { getRpcProxy(ContactRpc.class).deleteContact(contactId);}

RPC

lördag 24 januari 15

Good

• Stateful server• Server push

Bad

• Stateful server• Tied to the

framework

Vaadin Connectors

lördag 24 januari 15

What if we completely hide the transport?

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// Fire event@InjectEvent<Contact> contactEvent;

public void updateContact(Contact contact) { contactEvent.fire(contact);}

// Listen to eventpublic void contactUpdateObserver(@Observes Contact contact) { ContactDAO.updateContact(contact);}

CDI events

lördag 24 januari 15

Good

• Transparent communication

• Server push

Bad

• Transparent communication

• Tied to the framework

Errai Bus

lördag 24 januari 15

Questions?

Answers?

Please rate the talk at gwtcreate.com/agenda? leif@vaadin.com

lördag 24 januari 15