웹 서비스 인터뷰 질문 - SOAP, RESTful
자세한 답변이 포함된 웹 서비스 인터뷰 질문에 오신 것을 환영합니다. 최근에 저는 웹 서비스에 대해 많은 글을 썼습니다. Java에서 SOAP 및 RESTful 웹 서비스를 만드는 방법.
웹 서비스 인터뷰 질문
웹 서비스란 무엇입니까? 웹 서비스의 장점은 무엇입니까? 다른 유형의 웹 서비스는 무엇입니까?\n\n\n비누란 무엇입니까? SOAP 웹 서비스의 장점은 무엇입니까? SOAP 웹 서비스의 단점은 무엇입니까? WSDL이란 무엇입니까? WSDL의 다른 구성 요소는 무엇입니까? UDDI가 무엇인가요? SOAP 웹 서비스에서 하향식과 상향식 접근 방식의 차이점은 무엇입니까?\n\n\nREST 웹 서비스란 무엇입니까? REST 웹 서비스의 장점은 무엇입니까? REST 웹 서비스의 단점은 무엇입니까? 편안한 웹 서비스의 리소스는 무엇입니까?\n\n\nRestful Web Services에서 지원되는 다양한 HTTP 메서드는 무엇입니까?\n\n\nSOAP와 REST 웹 서비스를 비교하시겠습니까?\n\n\n웹 서비스를 테스트하는 다른 방법은 무엇입니까?\n\n\n웹 서비스에서 사용자 세션을 유지할 수 있습니까?\n\n\nSOA와 웹 서비스의 차이점은 무엇입니까? HTTP 요청에서 Accept 및 Content-Type 헤더의 용도는 무엇입니까?\n\n\nSOAP와 REST 웹 서비스 중에서 어떻게 선택하시겠습니까?\n\n\nJAX-WS API란 무엇입니까? SOAP 웹 서비스를 구현하기 위해 Java에서 일부 프레임워크의 이름을 지정하시겠습니까?\n\n\nJAX-WS API에서 사용되는 중요한 주석의 이름을 지정하시겠습니까?\n\n\njavax.xml.ws.Endpoint 클래스의 용도는 무엇입니까? RPC 스타일과 문서 스타일 SOAP 웹 서비스의 차이점은 무엇입니까? SOAP 웹 서비스의 WSDL 파일을 얻는 방법은 무엇입니까? sun-jaxws.xml 파일이란? JAX-RS API란 무엇입니까? JAX-RS API 구현의 이름을 지정하시겠습니까?\n\n\nwsimport 유틸리티란 무엇입니까? JAX-RS API에서 사용되는 중요한 주석의 이름을 지정하시겠습니까?\n\n\n@XmlRootElement 주석의 용도는 무엇입니까? HTTP 응답에서 다른 상태 코드를 설정하는 방법은 무엇입니까?\n\n\n웹 서비스란 무엇입니까? 웹 서비스는 클라이언트 응용 프로그램이 네트워크를 통해 웹 서비스에 액세스할 수 있는 클라이언트-서버 모델에서 작동합니다. 웹 서비스는 끝점 URL을 제공하고 Java, 셸 스크립트 또는 기타 다른 기술로 작성된 클라이언트 프로그램을 통해 네트워크를 통해 액세스할 수 있는 메서드를 노출합니다. 웹 서비스는 상태 비저장이며 웹 애플리케이션과 같은 사용자 세션을 유지하지 않습니다.\n\n\n웹 서비스의 장점은 무엇입니까? 웹 서비스의 장점 중 일부는 다음과 같습니다. 상호 운용성: 웹 서비스는 네트워크를 통해 액세스할 수 있고 HTTP/SOAP 프로토콜에서 실행되며 XML/JSON을 사용하여 데이터를 전송하므로 모든 프로그래밍 언어로 개발할 수 있습니다. 웹 서비스는 자바 프로그래밍으로 작성할 수 있고 클라이언트는 PHP로 작성할 수 있으며 그 반대도 가능합니다.\n재사용성: 하나의 웹 서비스를 여러 클라이언트 애플리케이션에서 동시에 사용할 수 있습니다.\n느슨한 결합: 웹 서비스 클라이언트 코드는 서버 코드와 완전히 독립적이므로 애플리케이션에서 느슨한 결합을 달성했습니다.\n웹 애플리케이션처럼 쉽게 배포하고 통합할 수 있습니다.\n여러 서비스 버전을 동시에 실행할 수 있습니다.\n\n\n\n다른 유형의 웹 서비스는 무엇입니까?\n웹 서비스에는 두 가지 유형이 있습니다.\n\nSOAP 웹 서비스: SOAP 프로토콜에서 실행되며 XML 기술을 사용하여 데이터를 전송합니다.\n편안한 웹 서비스: 아키텍처 스타일이며 거의 항상 HTTP/HTTPS 프로토콜에서 실행됩니다. REST는 웹 서비스가 리소스이고 해당 URI로 식별될 수 있는 상태 비저장 클라이언트-서버 아키텍처입니다. 클라이언트 애플리케이션은 HTTP GET/POST 메서드를 사용하여 Restful 웹 서비스를 호출할 수 있습니다.
비누란 무엇입니까?
SOAP는 Simple Object Access Protocol의 약자입니다. SOAP는 웹 서비스 설계 및 개발을 위한 XML 기반 산업 표준 프로토콜입니다. XML 기반이기 때문에 플랫폼과 언어에 독립적입니다. 따라서 우리 서버는 JAVA를 기반으로 하고 클라이언트는 .NET, PHP 등을 기반으로 할 수 있으며 그 반대도 가능합니다.
SOAP 웹 서비스의 장점은 무엇입니까?
SOAP web services have all the advantages that web services has, some of the additional advantages are:
- WSDL document provides contract and technical details of the web services for client applications without exposing the underlying implementation technologies.
- SOAP uses XML data for payload as well as contract, so it can be easily read by any technology.
- SOAP protocol is universally accepted, so it's an industry standard approach with many easily available open source implementations.
SOAP 웹 서비스의 단점은 무엇입니까?
Some of the disadvantages of SOAP protocol are:
- Only XML can be used, JSON and other lightweight formats are not supported.
- SOAP is based on the contract, so there is a tight coupling between client and server applications.
- SOAP is slow because payload is large for a simple string message, since it uses XML format.
- Anytime there is change in the server side contract, client stub classes need to be generated again.
- Can't be tested easily in browser
WSDL이란 무엇입니까?
WSDL stands for Web Service Description Language. WSDL is an XML based document that provides technical details about the web service. Some of the useful information in WSDL document are: method name, port types, service end point, binding, method parameters etc.
WSDL의 다른 구성 요소는 무엇입니까?
Some of the different tags in WSDL xml are:
- xsd:import namespace and schemaLocation: provides WSDL URL and unique namespace for web service.
- message: for method arguments
- part: for method argument name and type
- portType: service name, there can be multiple services in a wsdl document.
- operation: contains method name
- soap:address for endpoint URL.
UDDI가 무엇인가요?
UDDI is acronym for Universal Description, Discovery and Integration. UDDI is a directory of web services where client applications can lookup for web services. Web Services can register to the UDDI server and make them available to client applications.
SOAP 웹 서비스에서 하향식과 상향식 접근 방식의 차이점은 무엇입니까?
In Top Down approach first WSDL document is created to establish the contract between web service and client and then code is written, it's also termed as contract first approach. This is hard to implement because classes need to be written to confirm the contract established in WSDL. Benefit of this approach is that both client and server code can be written in parallel. In Bottom Up approach, first web service code is written and then WSDL is generated. It's also termed as contract last approach. This approach is easy to implement because WSDL is generated based on code. In this approach client code have to wait for WSDL from server side to start their work.
REST 웹 서비스란 무엇입니까?
REST is the acronym for REpresentational State Transfer. REST is an architectural style for developing applications that can be accessed over the network. REST architectural style was brought in light by Roy Fielding in his doctoral thesis in 2000. REST is a stateless client-server architecture where web services are resources and can be identified by their URIs. Client applications can use HTTP GET/POST methods to invoke Restful web services. REST doesn’t specify any specific protocol to use, but in almost all cases it’s used over HTTP/HTTPS. When compared to SOAP web services, these are lightweight and doesn’t follow any standard. We can use XML, JSON, text or any other type of data for request and response.
REST 웹 서비스의 장점은 무엇입니까?
Some of the advantages of REST web services are:
- Learning curve is easy since it works on HTTP protocol
- Supports multiple technologies for data transfer such as text, xml, json, image etc.
- No contract defined between server and client, so loosely coupled implementation.
- REST is a lightweight protocol
- REST methods can be tested easily over browser.
REST 웹 서비스의 단점은 무엇입니까?
Some of the disadvantages of REST are:
- Since there is no contract defined between service and client, it has to be communicated through other means such as documentation or emails.
- Since it works on HTTP, there can't be asynchronous calls.
- Sessions can't be maintained.
편안한 웹 서비스의 리소스는 무엇입니까?
Resource is the fundamental concept of Restful architecture. A resource is an object with a type, relationship with other resources and methods that operate on it. Resources are identified with their URI, HTTP methods they support and request/response data type and format of data.
Restful Web Services에서 지원되는 다양한 HTTP 메서드는 무엇입니까?
Restful web services supported HTTP methods are - GET, POST, PUT, DELETE and HEAD.
SOAP와 REST 웹 서비스를 비교하시겠습니까?
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-->
| SOAP | REST
|
| --- | --- |
| SOAP is a standard protocol for creating web services.
| REST is an architectural style to create web services.
|
| SOAP is acronym for Simple Object Access Protocol. | REST is acronym for REpresentational State Transfer. |
| SOAP uses WSDL to expose supported methods and technical details.
| REST exposes methods through URIs, there are no technical details.
|
| SOAP web services and client programs are bind with WSDL contract
| REST doesn't have any contract defined between server and client
|
| SOAP web services and client are tightly coupled with contract.
| REST web services are loosely coupled.
|
| SOAP learning curve is hard, requires us to learn about WSDL generation, client stubs creation etc.
| REST learning curve is simple, POJO classes can be generated easily and works on simple HTTP methods.
|
| SOAP supports XML data format only
| REST supports any data type such as XML, JSON, image etc.
|
| SOAP web services are hard to maintain, any change in WSDL contract requires us to create client stubs again and then make changes to client code.
| REST web services are easy to maintain when compared to SOAP, a new method can be added without any change at client side for existing resources.
|
| SOAP web services can be tested through programs or software such as Soap UI.
| REST can be easily tested through CURL command, Browsers and extensions such as Chrome Postman.
|
웹 서비스를 테스트하는 다른 방법은 무엇입니까?
SOAP web services can be tested programmatically by generating client stubs from WSDL or through software such as Soap UI. REST web services can be tested easily with program, curl commands and through browser extensions. Resources supporting GET method can be tested with browser itself, without any program.
웹 서비스에서 사용자 세션을 유지할 수 있습니까?
Web services are stateless so we can't maintain user sessions in web services.
SOA와 웹 서비스의 차이점은 무엇입니까?
Service Oriented Architecture (SOA) is an architectural pattern where applications are designed in terms of services that can be accessed through communication protocol over network. SOA is a design pattern and doesn't go into implementation. Web Services can be thought of as Services in SOAP architecture and providing means to implement SOA pattern.
HTTP 요청에서 Accept 및 Content-Type 헤더의 용도는 무엇입니까?
These are important headers in Restful web services. Accept headers tells web service what kind of response client is accepting, so if a web service is capable of sending response in XML and JSON format and client sends Accept header as "application/xml" then XML response will be sent. For Accept header "application/json", server will send the JSON response. Content-Type header is used to tell server what is the format of data being sent in the request. If Content-Type header is "application/xml" then server will try to parse it as XML data. This header is useful in HTTP Post and Put requests.
SOAP와 REST 웹 서비스 중에서 어떻게 선택하시겠습니까?
Web Services work on client-server model and when it comes to choose between SOAP and REST, it all depends on project requirements. Let's look at some of the conditions affecting our choice:
- Do you know your web service clients beforehand? If Yes, then you can define a contract before implementation and SOAP seems better choice. But if you don't then REST seems better choice because you can provide sample request/response and test cases easily for client applications to use later on.
- How much time you have? For quick implementation REST is the best choice. You can create web service easily, test it through browser/curl and get ready for your clients.
- What kind of data format are supported? If only XML then you can go with SOAP but if you think about supporting JSON also in future then go with REST.
JAX-WS API란 무엇입니까?
JAX-WS stands for Java API for XML Web Services. JAX-WS is XML based Java API to build web services server and client application. It’s part of standard Java API, so we don’t need to include anything else which working with it. Refer to [JAX-WS Tutorial](/community/tutorials/jax-ws-tutorial) for a complete example.
SOAP 웹 서비스를 구현하기 위해 Java에서 일부 프레임워크의 이름을 지정하시겠습니까?
We can create SOAP web services using JAX-WS API, however some of the other frameworks that can be used are Apache Axis and Apache CXF. Note that they are not implementations of JAX-WS API, they are totally different framework that work on Servlet model to expose your business logic classes as SOAP web services. Read more at [Java SOAP Web Service Eclipse](/community/tutorials/soap-webservices-in-java-example-eclipse) example.
JAX-WS API에서 사용되는 중요한 주석의 이름을 지정하시겠습니까?
Some of the important annotations used in JAX-WS API are:
- @WebService
- @SOAPBinding
- @WebMethod
javax.xml.ws.Endpoint 클래스의 용도는 무엇입니까?
Endpoint class provides useful methods to create endpoint and publish existing implementation as web service. This comes handy in testing web services before making further changes to deploy it on actual server.
RPC 스타일과 문서 스타일 SOAP 웹 서비스의 차이점은 무엇입니까?
RPC style generate WSDL document based on the method name and it's parameters. No type definitions are present in WSDL document. Document style contains type and can be validated against predefined schema. Let's look at these with a simple program. Below is a simple test program where I am using Endpoint to publish my simple SOAP web service. `TestService.java`
```
package com.journaldev.jaxws.service;
import javax.jws.WebMethod;
import javax.jws.WebService;
import javax.jws.soap.SOAPBinding;
import javax.xml.ws.Endpoint;
@WebService
@SOAPBinding(style = SOAPBinding.Style.RPC)
public class TestService {
@WebMethod
public String sayHello(String msg){
return "Hello "+msg;
}
public static void main(String[] args){
Endpoint.publish("https://localhost:8888/testWS", new TestService());
}
}
```
When I run above program and then access the WSDL, it gives me below XML. `rpc.xml`
```
<?xml version='1.0' encoding='UTF-8'?>
<!-- Published by JAX-WS RI (https://jax-ws.java.net). RI's version is JAX-WS RI 2.2.10 svn-revision#919b322c92f13ad085a933e8dd6dd35d4947364b. --><!-- Generated by JAX-WS RI (https://jax-ws.java.net). RI's version is JAX-WS RI 2.2.10 svn-revision#919b322c92f13ad085a933e8dd6dd35d4947364b. -->
<definitions xmlns:wsu="https://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" xmlns:wsp="https://www.w3.org/ns/ws-policy" xmlns:wsp1_2="https://schemas.xmlsoap.org/ws/2004/09/policy" xmlns:wsam="https://www.w3.org/2007/05/addressing/metadata" xmlns:soap="https://schemas.xmlsoap.org/wsdl/soap/" xmlns:tns="https://service.jaxws.journaldev.com/" xmlns:xsd="https://www.w3.org/2001/XMLSchema" xmlns="https://schemas.xmlsoap.org/wsdl/" targetNamespace="https://service.jaxws.journaldev.com/" name="TestServiceService">
<types/>
<message name="sayHello">
<part name="arg0" type="xsd:string"/>
</message>
<message name="sayHelloResponse">
<part name="return" type="xsd:string"/>
</message>
<portType name="TestService">
<operation name="sayHello">
<input wsam:Action="https://service.jaxws.journaldev.com/TestService/sayHelloRequest" message="tns:sayHello"/>
<output wsam:Action="https://service.jaxws.journaldev.com/TestService/sayHelloResponse" message="tns:sayHelloResponse"/>
</operation>
</portType>
<binding name="TestServicePortBinding" type="tns:TestService">
<soap:binding transport="https://schemas.xmlsoap.org/soap/http" style="rpc"/>
<operation name="sayHello">
<soap:operation soapAction=""/>
<input>
<soap:body use="literal" namespace="https://service.jaxws.journaldev.com/"/>
</input>
<output>
<soap:body use="literal" namespace="https://service.jaxws.journaldev.com/"/>
</output>
</operation>
</binding>
<service name="TestServiceService">
<port name="TestServicePort" binding="tns:TestServicePortBinding">
<soap:address location="https://localhost:8888/testWS"/>
</port>
</service>
</definitions>
```
Notice that **types** element is empty and we can't validate it against any schema. Now just change the `SOAPBinding.Style.RPC` to `SOAPBinding.Style.DOCUMENT` and you will get below WSDL. `document.xml`
```
<?xml version='1.0' encoding='UTF-8'?>
<!-- Published by JAX-WS RI (https://jax-ws.java.net). RI's version is JAX-WS RI 2.2.10 svn-revision#919b322c92f13ad085a933e8dd6dd35d4947364b. --><!-- Generated by JAX-WS RI (https://jax-ws.java.net). RI's version is JAX-WS RI 2.2.10 svn-revision#919b322c92f13ad085a933e8dd6dd35d4947364b. -->
<definitions xmlns:wsu="https://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" xmlns:wsp="https://www.w3.org/ns/ws-policy" xmlns:wsp1_2="https://schemas.xmlsoap.org/ws/2004/09/policy" xmlns:wsam="https://www.w3.org/2007/05/addressing/metadata" xmlns:soap="https://schemas.xmlsoap.org/wsdl/soap/" xmlns:tns="https://service.jaxws.journaldev.com/" xmlns:xsd="https://www.w3.org/2001/XMLSchema" xmlns="https://schemas.xmlsoap.org/wsdl/" targetNamespace="https://service.jaxws.journaldev.com/" name="TestServiceService">
<types>
<xsd:schema>
<xsd:import namespace="https://service.jaxws.journaldev.com/" schemaLocation="https://localhost:8888/testWS?xsd=1"/>
</xsd:schema>
</types>
<message name="sayHello">
<part name="parameters" element="tns:sayHello"/>
</message>
<message name="sayHelloResponse">
<part name="parameters" element="tns:sayHelloResponse"/>
</message>
<portType name="TestService">
<operation name="sayHello">
<input wsam:Action="https://service.jaxws.journaldev.com/TestService/sayHelloRequest" message="tns:sayHello"/>
<output wsam:Action="https://service.jaxws.journaldev.com/TestService/sayHelloResponse" message="tns:sayHelloResponse"/>
</operation>
</portType>
<binding name="TestServicePortBinding" type="tns:TestService">
<soap:binding transport="https://schemas.xmlsoap.org/soap/http" style="document"/>
<operation name="sayHello">
<soap:operation soapAction=""/>
<input>
<soap:body use="literal"/>
</input>
<output>
<soap:body use="literal"/>
</output>
</operation>
</binding>
<service name="TestServiceService">
<port name="TestServicePort" binding="tns:TestServicePortBinding">
<soap:address location="https://localhost:8888/testWS"/>
</port>
</service>
</definitions>
```
Open schemaLocation URL in browser and you will get below XML. `schemaLocation.xml`
```
<?xml version='1.0' encoding='UTF-8'?>
<!-- Published by JAX-WS RI (https://jax-ws.java.net). RI's version is JAX-WS RI 2.2.10 svn-revision#919b322c92f13ad085a933e8dd6dd35d4947364b. -->
<xs:schema xmlns:tns="https://service.jaxws.journaldev.com/" xmlns:xs="https://www.w3.org/2001/XMLSchema" version="1.0" targetNamespace="https://service.jaxws.journaldev.com/">
<xs:element name="sayHello" type="tns:sayHello"/>
<xs:element name="sayHelloResponse" type="tns:sayHelloResponse"/>
<xs:complexType name="sayHello">
<xs:sequence>
<xs:element name="arg0" type="xs:string" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="sayHelloResponse">
<xs:sequence>
<xs:element name="return" type="xs:string" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
</xs:schema>
```
So here WSDL document can be validated against the schema definintion.
SOAP 웹 서비스의 WSDL 파일을 얻는 방법은 무엇입니까?
WSDL document can be accessed by appending ?wsdl to the SOAP endoint URL. In above example, we can access it at `https://localhost:8888/testWS?wsdl` location.
sun-jaxws.xml 파일이란?
This file is used to provide endpoints details when JAX-WS web services are deployed in servlet container such as Tomcat. This file is present in WEB-INF directory and contains endpoint name, implementation class and URL pattern. For example; `sun-jaxws.xml`
```
<?xml version="1.0" encoding="UTF-8"?>
<endpoints xmlns="https://java.sun.com/xml/ns/jax-ws/ri/runtime" version="2.0">
<endpoint
name="PersonServiceImpl"
implementation="com.journaldev.jaxws.service.PersonServiceImpl"
url-pattern="/personWS"/>
</endpoints>
```
JAX-RS API란 무엇입니까?
Java API for RESTful Web Services (JAX-RS) is the Java API for creating REST web services. JAX-RS uses annotations to simplify the development and deployment of web services. JAX-RS is part of JDK, so you don’t need to include anything to use it’s annotations.
JAX-RS API 구현의 이름을 지정하시겠습니까?
There are two major implementations of JAX-RS API.
1. Jersey: Jersey is the reference implementation provided by Sun. For using Jersey as our JAX-RS implementation, all we need to configure its servlet in web.xml and add required dependencies. Note that JAX-RS API is part of JDK not Jersey, so we have to add its dependency jars in our application.
2. RESTEasy: RESTEasy is the JBoss project that provides JAX-RS implementation.
wsimport 유틸리티란 무엇입니까?
We can use wsimport utility to generate the client stubs. This utility comes with standard installation of JDK. Below image shows an example execution of this utility for one of JAX-WS project. [](https://journaldev.nyc3.digitaloceanspaces.com/2015/10/wsimport-utility-parse-wsdl.png)
JAX-RS API에서 사용되는 중요한 주석의 이름을 지정하시겠습니까?
Some of the important JAX-RS annotations are:
- `@Path`: used to specify the relative path of class and methods. We can get the URI of a webservice by scanning the Path annotation value.
- `@GET`, `@PUT`, `@POST`, `@DELETE` and `@HEAD`: used to specify the HTTP request type for a method.
- `@Produces`, `@Consumes`: used to specify the request and response types.
- `@PathParam`: used to bind the method parameter to path value by parsing it.
@XmlRootElement 주석의 용도는 무엇입니까?
XmlRootElement annotation is used by JAXB to transform java object to XML and vice versa. So we have to annotate model classes with this annotation.
HTTP 응답에서 다른 상태 코드를 설정하는 방법은 무엇입니까?
For setting HTTP status code other than 200, we have to use `javax.ws.rs.core.Response` class for response. Below are some of the sample return statements showing it's usage.
```
return Response.status(422).entity(exception).build();
return Response.ok(response).build(); //200
```
For a complete example, please read [RESTEasy Tutorial](/community/tutorials/resteasy-tutorial-eclipse-tomcat).
웹 서비스 면접 질문은 여기까지입니다. 의견을 통해 어떻게 생각하는지 알려주세요. 내가 몇 가지 중요한 질문을 빠뜨렸다고 생각하는 경우 댓글을 통해 알려주시면 기꺼이 답변하고 목록에 추가하겠습니다.