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REST
(REpresentational State Transfer)
2012. 10
Youn-Hee Han
LINK@KOREATECH
http://link.koreatech.ac.kr
REST의 개념 이해
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What is REST?
 REST (Representational State Transfer)
– 대규모 네트워크 시스템을 위한 설계패턴 또는 아키텍처
– 웹을 기반으로 하는 대규모 네트워크 시스템 설계 및 구현을 위한 일종
의 원칙들의 모음
– 2000년 Roy Fielding의 박사 학위 논문에서 처음 제안.
• Architectural Styles and the Design of Network-based Software
Architectures (DOCTOR OF PHILOSOPHY)
 http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm
– 최근 추가된 뜻
• XML과 HTTP를 사용하는 단순한 웹 기반 인터페이스를 지칭
(즉, REST의 원칙을 따르는 Web Services)
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What is REST?
 왜 Representational State Transfer 이라고 명칭을 붙였나?
All Resources on WEB are represented as XML by URL (Representation)
URL
CLICK
표현
(다른 URL 포함)
Representational State Transfer은 잘 디자인된 웹 어플리케이션이 어떻
게 동작하는 지에 대한 이미지를 떠올리게 하기 위한 용어이다.
즉 웹을 거대한 Virtual State Machine이라고 생각하면
우리는 그 웹의 상태를 XML등으로 표현된 것으로 확인할 수 있고
그 전에 알고 있던 또는 XML에 포함된 링크를 선택/호출함으로써
Machine내에 존재하는 State가 전이되고 새로운 표현 (New State
Representation)이 보여지게 된다
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What is REST?
 좀 더 현실적인 REST의 설명
Web Service를 구현하는 기존 방식인 SOAP, XML-RPC보다 매우 간단
최근 Open API 구현에 많이 사용
많은 웹2.0 회사들이 Open API의 구현 방법으로 많이 사용.
구글, 플리커, 아마존 등의 Open API가 REST 방식으로 구현되어 공개
서비스의 서버 플랫폼 구축에 있어 필수적인 아키텍쳐로 인식됨
REST는 실제 표준은 아니지만 HTTP/URL/MIME Type같은 웹 표준만을
사용
– 구글이 오랫동안 제공해온 SOAP 기반 검색 API 서비스가 2006년 12월
5일 부로 중단
–
–
–
–
–
–
• 대신 구글은 REST 기반의 Ajax Search API를 대안으로 제시
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What is REST?
 REST is not a standard
– You will not see the W3C REST specification.
– You will not see IBM or Microsoft or Sun selling a REST
developer's toolkit.
 REST is just a design pattern
– You can only understand it and design your Web services
according to its rules.
 REST does prescribe the use of standards:
–
–
–
–
HTTP
URL
XML/HTML/JSON/GIF/JPEG/etc. (Resource Representations)
text/xml, text/html, image/gif, image/jpeg, etc. (Resource
Types, MIME Types)
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What is REST?
 REST의 성공 요인
– 상태를 유지하지 않는 (Stateless) 클라이언트/서버 구조를 가진다.
– 작고 어디에서나 적용되는 인터페이스를 가진다.
– GET, POST, PUT, DELETE
• PUT과 DELETE 메소드는 HTTP스펙에는 존재하지만 지원하는 브라우저는 거
의 없다.
– 모든 자원은 URL를 이용하여 유일하게 지칭될 수 있다.
– 자원들의 표현(Representation)들이 URL을 통해 서로 연결되어 있다.
– REST의 원칙에는 쿠키나 세션을 사용하지 않는다.
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CRUD Operations in REST
 URL을 통해 필요한 자원을 계속해서 추적하여…
– 얻어(GET) 가거나
– 생성(POST) 하거나
– 삽입(PUT)
– 삭제(DELETE)
할 수 있게 분류 설계한다.
 CRUD/HTTP 사이의 대응
– 전체 시스템은 단지 다음 4개의 명령을 사용해서만 동작한다.
애플리케이션 작업
HTTP 명령
Create
POST (non idempotent)
Read
GET (safe, idempotent)
Update
PUT (idempotent)
Delete
DELETE (idempotent)
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REST vs. RPC (Remote Procedure Call)-style
 REST vs RPC-style (Java RMI, CORBA, DCOM, SOAP…)
 REST URL
– 서버 주소/서비스 이름/자원
– Examples
• 잘 된 구성 - http://wisefree.com/employee/603045 (O)
• 잘못 된 구성 - http://wisefree.com/employee/getEmployee?id=603045 (X)
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Web Design, Axiom 0
(Tim Berners-Lee, director of W3C)
 Axiom 0: all resources on the Web must be uniquely identified
with a URI.
URL1
resource1
URL2
resource2
URL3
resource3
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Example1: Airline Reservation Service
 The airline wants to ensure that its premier members get
immediate service, its frequent flyer members get expedited
service and all others get regular service
 There are two main approaches to implementing the reservation
service…
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Approach 1
 "Press 1 for Premier, Press 2 for…“
– The airline provides a single telephone number.
– Upon entry into the system a customer encounters an automated
message, "Press 1 if you are a premier member, press 2 if you are a
frequent flyer, press 3 for all others."
Premier
Customer
Representative
Premier Members
Airline Reservations
Answering
Machine
F.F.
Customer
Representative
Frequent Flyer Members
Regular
Customer
Representative
Regular Members
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Approach 2
 " Telephone Numbers are Cheap! Use Them!”
– The airline provides several telephone numbers - one number for
premier members, a different number for frequent flyers, and still
another for regular customers.
1-800-Premier
Premier
Customer
Representative
Premier Members
1-800-Frequent
F.F.
Customer
Representative
Frequent Flyer Members
1-800-Reservation
Regular
Customer
Representative
Regular Members
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Approach 2:
URLs are Cheap! Use Them!
The airline provides several URLs - one URL for
premier members, a different URL for frequent flyers,
and still another for regular customers.
http://www.kings-air/reservations/premier
client
Premier Members
http://www.kings-air/reservations/frequent-flyer
client
Frequent Flyer Members
http://www.kings-air/reservations/regular
client
Regular Members
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Premier
Member
Reservation
Service
Frequent
Flyer
Reservation
Service
Regular
Member
Reservation
Service
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Approach 2 Advantages
 The different URLs are discoverable by search engines
and UDDI registries.
 It's easy to understand what each service does simply
by examining the URL.
 There is no need to introduce rules.
– Priorities are elevated to the level of a URL.
– "What you see is what you get."
 It's easy to implement high priority
– simply assign a fast machine at the premier member URL.
 There is no bottleneck.
– There is no central point of failure.
 Consistent with Axiom 0.
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Three Fundamental Aspects
of the REST Design Pattern
 Resources
– Every distinguishable entity is a resource.
• A resource may be a Web site, an HTML page, an XML
document, or a Web service, etc.
 URL can identify Resources
– Every resource is uniquely identified by a URL.
– This is Tim Berners-Lee Web Design, Axiom 0.
 CRUD operations
Resources
URLs
Simple Operations (CRUD)
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REST 방식의 웹서비스 구현 및 실습
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REST 구현 방법
 방법 1] Restlet 라이브러리 사용
– 자바를 위한 경량화 REST framework
– 오픈소스 프로젝트
– 서블릿의 프로그래밍 모델을 기반
• JSR (Java Specification Requests) 311
 Java API for RESTful Web Services (이하 JSR 311)
– Restlet 홈페이지
• http://www.restlet.org
 방법 2] Java EE에서 지원하는 REST 라이브러리 사용
– JAX-WS (Java API for XML Web Services) 라이브러리
• XML과 웹 서비스 관련 API
– JAX-WS의 핵심은 SOAP-WSDL이여서 그다지 쓰이지 않았음.
– JAX-WS2에서 HTTP바인딩과 함께 REST 지원
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REST 구현 방법
 RESTlet 라이브러리 설치
– http://www.restlet.org/downloads/stable (version 2.0.15)
– Edition for Java SE
– D 드라이브의 특정 폴더에 압축 해제
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REST 구현 방법
 RESTlet 소스를 저장할 폴더로 이동
 RESTlet 주요 라이브러리를 Java의 CLASSPATH에 추가
– 소스 저장 폴더에 다음과 같은 두 개의 bat 파일 구성
• jc.bat
javac -classpath "%CLASSPATH%;D:\0.MY_KUT_DATA\restlet-jse2.0.15\lib\org.restlet.jar" %1
• j.bat
java -classpath "%CLASSPATH%;D:\0.MY_KUT_DATA\restlet-jse2.0.15\lib\org.restlet.jar;." %1
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Restlet Example-1
 HelloWorld 예제 – Server
import
import
import
import
RESTletHelloWorld.java
org.restlet.Server;
org.restlet.data.Protocol;
org.restlet.resource.Get;
org.restlet.resource.ServerResource;
public class RESTletHelloWorld extends ServerResource {
public static void main(String[] args) throws Exception {
// Create the HTTP server and listen on port 8182
new Server(Protocol.HTTP, 8182, RESTletHelloWorld.class).start();
}
@Get
public String toString() {
return “Hello, RESTlet World!";
}
}
컴파일: jc RESTletHelloWorld.java
실행: j RESTletHelloWorld
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Restlet Example-1
 HelloWorld 예제 – Client
– 방법 1: 브라우저에서 http://localhost:8182/ 접속
– 방법 2
RESTletHelloWorldClient.java
import org.restlet.resource.ClientResource;
public class RESTletHelloWorldClient extends ClientResource {
public static void main(String[] args) throws Exception {
// Create the client resource
ClientResource resource = new ClientResource("http://localhost:8182/");
// Write the response entity on the console
resource.get().write(System.out);
컴파일: jc RESTletHelloWorldClient.java
}
}
실행: j RESTletHelloWorldClient
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Restlet Example-2
 TextMessage 예제 – Server (1/2)
RESTInfoService.java
import
import
import
import
import
import
import
org.restlet.Application;
org.restlet.Request;
org.restlet.Response;
org.restlet.Restlet;
org.restlet.Server;
org.restlet.data.MediaType;
org.restlet.data.Protocol;
public class RESTInfoService extends Application {
public static void main(String[] args) throws Exception {
// Create the HTTP server and listen on port 8182
Server server = new Server(Protocol.HTTP, 8182);
server.setNext(new RESTInfoService());
server.start();
}
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Restlet Example-2
 TextMessage 예제 – Server (2/2)
RESTInfoService.java
public Restlet restlet = new Restlet() {
@Override
public void handle(Request request, Response response) {
String message = "Method : " + request.getMethod()
+ '\n' + "Resource URI : " + request.getResourceRef()
+ '\n' + "IP address : " + request.getClientInfo().getAddress()
+ '\n' + "Agent name : " + request.getClientInfo().getAgentName()
+ '\n' + "Agent version : " + request.getClientInfo().getAgentVersion();
};
}
}
response.setEntity(message, MediaType.TEXT_PLAIN);
@Override
public Restlet createInboundRoot() {
return restlet;
}
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Restlet Example-3
 Route 예제 – Server (1/3)
RESTRouteService.java
import
import
import
import
import
import
import
import
org.restlet.Application;
org.restlet.Request;
org.restlet.Response;
org.restlet.Restlet;
org.restlet.Server;
org.restlet.data.MediaType;
org.restlet.data.Protocol;
org.restlet.routing.Router;
public class RESTRouteService extends Application {
public static void main(String[] args) throws Exception {
// Create the HTTP server and listen on port 8182
Server server = new Server(Protocol.HTTP, 8182);
server.setNext(new RESTRouteService());
server.start();
}
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Restlet Example-3
 Route 예제 – Server (2/3)
RESTRouteService.java
public Restlet restlet1 = new Restlet() {
public void handle(Request request, Response response) {
String message = "This is a information for students";
response.setEntity(message, MediaType.TEXT_PLAIN);
}
};
public Restlet restlet2 = new Restlet() {
public void handle(Request request, Response response) {
String message = "<?xml version='1.0' encoding='UTF-8'?><students>
<student><id>1</id><url>/students/1</url></student>
<student><id>2</id><url>/students/2</url></student></students>";
response.setEntity(message, MediaType.TEXT_XML);
}
};
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Restlet Example-3
 Route 예제 – Server (3/3)
RESTRouteService.java
public Restlet restlet3 = new Restlet() {
public void handle(Request request, Response response) {
String message = "<?xml version='1.0' encoding='UTF-8'?><student>
<id>1</id><name>Jun-Ha Jung</name><address>Seoul</address>
</student>";
response.setEntity(message, MediaType.TEXT_XML);
}
};
}
@Override
public Restlet createInboundRoot() {
Router router = new Router();
router.attach("http://localhost:8182/info", restlet1);
router.attach("http://localhost:8182/students", restlet2);
router.attach("http://localhost:8182/students/1", restlet3);
return router;
}
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Restlet Example-4
 QueryString 예제 – Server (1/2)
RestletQueryString.java
import
import
import
import
import
import
import
import
import
org.restlet.Application;
org.restlet.Request;
org.restlet.Response;
org.restlet.Restlet;
org.restlet.Server;
org.restlet.data.MediaType;
org.restlet.data.Form;
org.restlet.data.Protocol;
org.restlet.routing.Router;
public class RestletQueryString extends Application {
public static void main(String[] args) throws Exception {
// Create the HTTP server and listen on port 8182
Server server = new Server(Protocol.HTTP, 8182);
server.setNext(new RestletQueryString());
server.start();
}
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Restlet Example-4
 QueryString 예제 – Server (2/2)
RestletQueryString.java
public Restlet restlet1 = new Restlet() {
public void handle(Request request, Response response) {
Form queryString = request.getResourceRef().getQueryAsForm();
String num = queryString.getValues("num");
String message = "<?xml version='1.0' encoding='UTF-8'?><num>"
+ num + "</num>";
response.setEntity(message, MediaType.TEXT_XML);
}
};
}
@Override
public Restlet createInboundRoot() {
Router router = new Router();
router.attach("http://localhost:8182/query", restlet1);
return router;
}
– 테스트 – 웹 브라우저로 접속
• http://localhost:8182/query?num=10
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[실습]
 REST 기반 계산기 프로그램 (1/3)
– 클라이언트에서 호출할 URL 및 이에 대한 XML 응답
• http://localhost:8182/plus?num1=10&num2=9
<?xml version='1.0' encoding='UTF-8'?>
<plus>
<num1>10</num1>
<num2>9</num2>
<solution>18</solution>
</plus>
• http://localhost:8182/substraction?num1=10&num2=9
<?xml version='1.0' encoding='UTF-8'?>
<substraction>
<num1>10</num1>
<num2>9</num2>
<solution>1</solution>
</substraction>
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[실습]
 REST 기반 계산기 프로그램 (2/3)
– 클라이언트에서 호출할 URL 및 이에 대한 XML 응답
• http://localhost:8182/product?num1=10&num2=9
<?xml version='1.0' encoding='UTF-8'?>
<product>
<num1>10</num1>
<num2>9</num2>
<solution>90</solution>
</product>
• http://localhost:8182/divide?num1=10&num2=9
• http://localhost:8182/divide?num1=10&num2=0
<?xml version='1.0' encoding='UTF-8'?>
<divide>
<num1>10</num1>
<num2>9</num2>
<solution>1.111</solution>
</divide>
<?xml version='1.0' encoding='UTF-8'?>
<divide>
<num1>10</num1>
<num2>0</num2>
<solution>Error!</solution>
</divide>
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