What is the difference between REST and HTTP protocols?

Question

什么是REST协议，它与HTTP协议有什么不同？

Answer 1

REST is a design style for protocols, it was developed by Roy Fielding in his PhD dissertation and formalised the approach behind HTTP/1.0, finding what worked well with it, and then using this more structured understanding of it to influence the design of HTTP/1.1. So, while it was after-the-fact in a lot of ways, REST is the design style behind HTTP.

Fielding's dissertation can be found at http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm and is very much worth reading, and also very readable. PhD dissertations can be pretty hard-going, but this one is wonderfully well-described and very readable to those of us without a comparable level of Computer Science. It helps that REST itself is pretty simple; it's one of those things that are obvious after someone else has come up with it. (It also for that matter encapsulates a lot of things that older web developers learnt themselves the hard way in one simple style, which made reading it a major "a ha!" moment for many).

Other application-level protocols as well as HTTP can also use REST, but HTTP is the classic example.

Because HTTP uses REST, all uses of HTTP are using a REST system. The description of a web application or service as RESTful or non-RESTful relates to whether it takes advantage of REST or works against it.

The classic example of a RESTful system is a "plain" website without cookies (cookies aren't always counter to REST, but they can be): Client state is changed by the user clicking a link which loads another page, or doing GET form queries which brings results. POST form queries can change both server and client state (the server does something on the basis of the POST, and then sends a hypertext document that describes the new state). URIs describe resources, but the entity (document) describing it may differ according to content-type or language preferred by the user. Finally, it's always been possible for browsers to update the page itself through PUT and DELETE though this has never been very common and if anything is less so now.

The classic example of a non-RESTful system using HTTP is something which treats HTTP as if it was a transport protocol, and with every request sends a POST of data to the same URI which is then acted upon in an RPC-like manner, possibly with the connection itself having shared state.

A RESTful computer-readable (ie not a website in a browser, but something used programmatically) system would obtain information about the resources concerned by GETting URI which would then return a document (eg in XML, but not necessarily) which would describe the state of the resource, including URIs to related resources (hypermedia therefore), change their state through PUTting entities describing the new state or DELETEing them, and have other actions performed by POSTing.

Key advantages are:

Scalability: The lack of shared state makes for a much more scalable system (demonstrated to me massively when I removed all use of session state from a heavily hit website, while I was expecting it to give a bit of extra performance, even a long-time anti-session advocate like myself was blown-away by the massive gain from removing what had been pretty slim use of sessions, it wasn't even why I had been removing them!)

Simplicity: There are a few different ways in which REST is simpler than more RPC-like models, in particular there are only a few "verbs" that are ever possible, and each type of resource can be reasoned about in reasonable isolation to the others.

Lightweight Entities: More RPC-like models tend to end up with a lot of data in the entities sent both ways just to reflect the RPC-like model. This isn't needed. Indeed, sometimes a simple plain-text document is all that is really needed in a given case, in which case with REST, that's all we would need to send (though this would be an "end-result" case only, since plain-text doesn't link to related resources). Another classic example is a request to obtain an image file, RPC-like models generally have to wrap it in another format, and perhaps encode it in some way to let it sit within the parent format (eg if the RPC-like model uses XML, the image will need to be base-64'd or similar to fit into valid XML). A RESTful model would just transmit the file the same as it does to a browser.

Human Readable Results: Not necessarily so, but it is often easy to build a RESTful webservice where the results are relatively easy to read, which aids debugging and development no end. I've even built one where an XSLT meant that the entire thing could be used by humans as a (relatively crude) website, though it wasn't primarily for human-use (essentially, the XSLT served as a client to present it to users, it wasn't even in the spec, just done to make my own development easier!).

Looser binding between server and client: Leads to easier later development or moves in how the system is hosted. Indeed, if you keep to the hypertext model, you can change the entire structure, including moving from single-host to multiple hosts for different services, without changing client code at all.

Caching: For the GET operations where the client obtains information about the state of a resource, standard HTTP caching mechanisms allow both for statements that the resource won't meaningfully change until a certain date at the earliest (no need to query at all until then) or that it hasn't changed since the last query (send a couple hundred bytes of headers saying this rather than several kilobytes of data). The improvement in performance can be immense (big enough to move the performance of something from the point where it is impractical to use to the point where performance is no longer a concern, in some cases).

Availability of toolkits: Because it works at a relatively simple level, if you have a webserver you can build a RESTful system's server and if you have any sort of HTTP client API (XHR in browser javascript, HttpWebRequest in .NET, etc) you can build a RESTful system's client.

Resiliance: In particular, the lack of shared state means that a client can die and come back into use without the server knowing, and even the server can die and come back into use without the client knowing. Obviously communications during that period will fail, but once the server is back online things can just continue as they were. This also really simplifies the use of web-farms for redundancy and performance - each server acts like it's the only server there is, and it doesn't matter that its actually only dealing with a fraction of the requests from a given client.

Answer 2

REST is an approach that leverages the HTTP protocol, and is not an alternative to it.

• http://en.wikipedia.org/wiki/Representational_State_Transfer

Data is uniquely referenced by URL and can be acted upon using HTTP operations (GET, PUT, POST, DELETE, etc). A wide variety of mime types are supported for the message/response but XML and JSON are the most common.

For example to read data about a customer you could use an HTTP get operation with the URL http://www.example.com/customers/1 . If you want to delete that customer, simply use the HTTP delete operation with the same URL.

The Java code below demonstrates how to make a REST call over the HTTP protocol:

String uri =
    "http://www.example.com/customers/1";
URL url = new URL(uri);
HttpURLConnection connection =
    (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.setRequestProperty("Accept", "application/xml");

JAXBContext jc = JAXBContext.newInstance(Customer.class);
InputStream xml = connection.getInputStream();
Customer customer =
    (Customer) jc.createUnmarshaller().unmarshal(xml);

connection.disconnect();

For a Java (JAX-RS) example see:

• http://bdoughan.blogspot.com/2010/08/creating-restful-web-service-part-45.html

Answer 3

REST is not a protocol, it is a generalized architecture for describing a stateless, caching client-server distributed-media platform. A REST architecture can be implemented using a number of different communication protocols, though HTTP is by far the most common.

Answer 4

REST is not a protocol, it is a way of exposing your application, mostly done over HTTP.

for example, you want to expose an api of your application that does getClientById
instead of creating a URL

yourapi.com/getClientById?id=4
you can do
yourapi.com/clients/id/4

since you are using a GET method it means that you want to GET data

You take advantage over the HTTP methods: GET/DELETE/PUT
yourapi.com/clients/id/4 can also deal with delete, if you send a delete method and not GET, meaning that you want to dekete the record

Answer 5

All the answers are good.

I hereby add a detailed description of REST and how it uses HTTP .

REST = Representational State Transfer

REST is a set of rules, that when followed, enable you to build a distributed application that has a specific set of desirable constraints.

It is stateless, which means that ideally no connection should be maintained between the client and server.

It is the responsibility of the client to pass its context to the server and then the server can store this context to process the client's further request. For example, session maintained by server is identified by session identifier passed by the client.

Advantages of Statelessness:

1. Web Services can treat each method calls separately.
2. Web Services need not maintain the client's previous interaction.
3. This in turn simplifies application design.
4. HTTP is itself a stateless protocol unlike TCP and thus RESTful Web Services work seamlessly with the HTTP protocols.

Disadvantages of Statelessness:

1. One extra layer in the form of heading needs to be added to every request to preserve the client's state.
2. For security we may need to add a header info to every request.

HTTP Methods supported by REST:

GET: /string/someotherstring :
It is idempotent(means multiple calls should return the same results every time) and should ideally return the same results every time a call is made

PUT:
Same like GET. Idempotent and is used to update resources.

POST: should contain a url and body
Used for creating resources. Multiple calls should ideally return different results and should create multiple products.

DELETE:
Used to delete resources on the server.

HEAD:

The HEAD method is identical to GET except that the server MUST NOT return a message-body in the response. The meta information contained in the HTTP headers in response to a HEAD request SHOULD be identical to the information sent in response to a GET request.

OPTIONS:

This method allows the client to determine the options and/or requirements associated with a resource, or the capabilities of a server, without implying a resource action or initiating a resource retrieval.

HTTP Responses

Go here for all the responses .

Here are a few important ones:
200 - OK
3XX - Additional information needed from the client and url redirection
400 - Bad request
401 - Unauthorized to access
403 - Forbidden
The request was valid, but the server is refusing action. The user might not have the necessary permissions for a resource, or may need an account of some sort.

404 - Not Found
The requested resource could not be found but may be available in the future. Subsequent requests by the client are permissible.

405 - Method Not Allowed A request method is not supported for the requested resource; for example, a GET request on a form that requires data to be presented via POST, or a PUT request on a read-only resource.

404 - Request not found
500 - Internal Server Failure
502 - Bad Gateway Error