Ws rest

Web Services and REST

Patrik Nordwall

Roadmap

Introduction to Web Services

Introduction to REST

Design Challenges

Introduction to Web Services

Patrik Nordwall

Outline

Concepts (SOAP, WSDL, ...)

XML Schema

Demo

What is a Web Service?

Application integration based on open
standards (HTTP, XML)

Published Interface

Application functionality packaged as a
single unit and exposed to the network

SOAP

• Simple Object Access Protocol
• Service Invocation
• Cross-platform remote calls
• Usually XML over HTTP (POST)

SOAP Example - request
<?xml version="1.0"?>
<soap:Envelope xmlns:soap="http://www.w3.org/2003/
<soap:Header>
</soap:Header>
<soap:Body>
<m:GetStockPrice xmlns:m="http://www.example.o
<m:StockName>IBM</m:StockName>
</m:GetStockPrice>
</soap:Body>
</soap:Envelope>

SOAP Example - response
<soap:Envelope
xmlns:soap="http://www.w3.org/2001/12/soap-envelop
soap:encodingStyle="http://www.w3.org/2001/12/soap

<soap:Body xmlns:m="http://www.example.org/stock">
<m:GetStockPriceResponse>
<m:Price>34.5</m:Price>
</m:GetStockPriceResponse>
</soap:Body>

</soap:Envelope>

WSDL
‘wiz-del’

• Web Service Description Language
• Machine-readable language
For tools - not humans

WSDL Structure

• portType - operations
• messages
• types
• binding - communication protocols

WSDL Example
<message name="getTermRequest">
<part name="term" type="xs:string"/>
</message>

<message name="getTermResponse">
<part name="value" type="xs:string"/>
</message>

<portType name="glossaryTerms">
<operation name="getTerm">
<input message="getTermRequest"/>
<output message="getTermResponse"/>
</operation>
</portType>

WSDL Binding

<binding type="glossaryTerms" name="b1">
   <soap:binding style="document"
   transport="http://schemas.xmlsoap.org/soap/http
   <operation>
     <soap:operation soapAction="http://example.co
     <input><soap:body use="literal"/></input>
     <output><soap:body use="literal"/></output>
</operation>
</binding>

UDDI
• Universal Discovery and Directory
Interface
• Kind of yellow pages
• You probably don’t need all UDDI
features

XML Schema
Data deﬁnition in XML format
Important for Service Contract

XML Example

<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>

XSD Example
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.w3schools.com"
xmlns="http://www.w3schools.com"
elementFormDefault="qualified">

<xs:element name="note">
<xs:complexType>
    <xs:sequence>
      <xs:element name="to" type="xs:string"/>
      <xs:element name="from" type="xs:string"/>
      <xs:element name="heading" type="xs:string"/>
      <xs:element name="body" type="xs:string"/>
    </xs:sequence>
</xs:complexType>
</xs:element>

</xs:schema>

XML Example

<note
xmlns="http://www.w3schools.com"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3schools.com note.xsd">

<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>

XSD Types
<xs:element name="lastname" type="xs:string"/>
<xs:element name="age" type="xs:integer"/>
<xs:element name="dateborn" type="xs:date"/>

XSD Types
<xs:element name="age" type="xs:integer"/>
<xs:element name="dateborn" type="xs:date"/>

• xs:string
• xs:decimal
• xs:integer
• xs:boolean
• xs:date
• xs:time

XSD Restriction

<xs:element name="age" type="Age"/>

<xs:simpleType name="Age">
<xs:restriction base="xs:integer">
<xs:minInclusive value="0"/>
<xs:maxInclusive value="120"/>
</xs:restriction>
</xs:simpleType>

XSD Optional/Required

<xs:attribute name="lang" type="xs:string" use="required"/>

<xs:element name="body" type="xs:string" minOccurs="0"/>

<xs:element name="body" type="xs:string" nillable="true"/>

XSD Default Values

<xs:attribute name="lang" type="xs:string" default="EN"/>

XSD Any Order

<xs:element name="person">
<xs:complexType>
<xs:all>
<xs:element name="firstname" type="xs:string"/>
</xs:all>
</xs:complexType>
</xs:element>

XSD Choice

<xs:element name="person">
<xs:complexType>
<xs:choice>
<xs:element name="employee" type="employee"/>
<xs:element name="member" type="member"/>
</xs:choice>
</xs:complexType>
</xs:element>

XSD Extension
<xs:element name="employee" type="fullpersoninfo"/>

<xs:complexType name="personinfo">
<xs:sequence>
<xs:element name="firstname" type="xs:string"/>
</xs:sequence>
</xs:complexType>

<xs:complexType name="fullpersoninfo">
<xs:complexContent>
<xs:extension base="personinfo">
<xs:sequence>
<xs:element name="address" type="xs:string"/>
<xs:element name="city" type="xs:string"/>
<xs:element name="country" type="xs:string"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>

WS Tools

• Apache CXF
• Axis 2
• Spring Web Services
• Metro (GlassFish)
• WebLogic (wsdlc)
• JBossWS
• ...

Introduction to REST

Patrik Nordwall

Outline

What is REST?

JSON

Demo

REST is NOT

Architecture
Protocol
Technology

REST is an architectural style

REST

• Representational State Transfer
• 'RESTful' == Conforming to the REST
constraints

Principles
• Give every “thing” an ID
• Link things together
• Use standard methods
• Communicate stateless
• Resources with multiple representations

URIs

http://example.com/customers/1234
http://example.com/orders/2007/10/776654
http://example.com/products/4554
http://example.com/processes/salary-increase-234
http://example.com/products?color=green

Link Things Together

<order self='http://example.com/customers/1234' >
<amount>23</amount>
<product ref='http://example.com/products/4554' />
<customer ref='http://example.com/customers/1234' />
</order>

Standard Methods
GET PUT POST DELETE
Collection URI List the URIs Replace the Create a new Delete the
http://ex.com/ and perhaps entire collection entry entire collection
customer other details

Element URI Retrieve a Update or if it Element as Delete the
http://ex.com/ representation doesn't exist, collection, entire element
customer/123 create it. create a new
entry in it, or
partial update

GET = Safe, only retrieval, caching
PUT, DELETE = Idempotent

Stateless

Stateless communication

State can live in resource state

State can live in client

Resources
• Can be anything - things, not actions
• Resources live on server
• Representations are transfered to clients
• Multiple representations of resources for
different needs

Content Type
• Multiple representations of resources for
different needs
• Mime-types (Accept header)
– text/xml
– application/json
– application/vnd.mycompany.customer+xml
– text/x-vcard

JSON

Objects {}
&
Lists []

JSON

{
"name" : "Patrik",
"age" : 37,
"parent" : true
}

JSON
[
{
"title": "Perpendicular",
"artist": "Deep Purple"
},
{
"title": "Dover Calais",
"artist" : "Style"
}
]

JSON
{
"name" : "Patrik",
"children" : [
"Ebba",
"Klara"
]
}

REST Tools

Jersey
Apache CXF
Restlet
RestEasy
Spring 3.0
Restfulie

Design Challenges
of Web Services and
RESTful Web Services

Patrik Nordwall

Outline

Hypermedia

Evolving interfaces

Scaling out

Other Challenges

Hypermedia

Link things together
One entry point
Links declare transitions to next step
Don’t need a static contract description

HATEOAS

Hypermedia As The
Engine Of Application State

API Types

Infrastructure

Domain CRUD

Application

URI Templates

http://example.com/products/{productNumber}

Restbucks

GET a Cup Of Coffee
Make selection
Pay
Wait for a while
Collect drink

Restbucks - Normal Flow

Customer POST http://restbucks.com/order Restbucks

201 + order



201 + order

PUT http://restbucks.com/payment/1234
201 + receipt



201 + order

201 + receipt

GET http://restbucks.com/order/1234
200 + order



201 + order

201 + receipt

GET http://restbucks.com/order/1234
200 + order

DELETE http://restbucks.com/receipt/1234
200 + completed order

Restbucks - Cancel


201 + order

DELETE http://restbucks.com/order/1234
200 + order

Restbucks - Update


201 + order

POST http://restbucks.com/order/1234
200 + order

POST Order

<order xmlns=″http://schemas.restbucks.com″ >
<item>
<milk>semi</milk>
<size>large</size>
<drink>cappuccino</drink>
</item>
<location>takeAway</location>
</order>

Order Response
<item>
<milk>semi</milk>
<size>large</size>
</item>
<cost>2. 0</cost>
<status>unpaid</status>
<link uri=″http://restbucks.com/order/1234″ rel=″cancel″/>
<link uri=″http://restbucks.com/payment/1234″ rel=″payment″/>
<link uri=″http://restbucks.com/order/1234″ rel=″update″/>
<link uri=″http://restbucks.com/order/1234″ rel=″self″/>
</order>

PUT Payment
<payment xmlns=″http://schemas.restbucks.com″>
<amount>2. 0</amount>
<cardholderName>Michael Faraday</cardholderName>
<cardNumber>11223344</cardNumber>
<expiryMonth>12</expiryMonth>
<expiryYear>12</expiryYear>
</payment>

Payment Response
<payment xmlns=″http://schemas.restbucks.com″>
<amount>2. 0</amount>
<cardholderName>Michael Faraday</cardholderName>
<cardNumber>11223344</cardNumber>
<expiryMonth>12</expiryMonth>
<expiryYear>12</expiryYear>
<link uri=″http://restbucks.com/order/1234″ rel=″order″/>
<link uri=″http: //restbucks.com/receipt/1234″ rel=″receipt″/>
</payment>

GET Order Response
<item>
<milk>semi</milk>
<size>large</size>
</item>
<cost>2. 0</cost>
<status>preparing</status>
</order>

...GET Order Response
<item>
<milk>semi</milk>
<size>large</size>
</item>
<cost>2. 0</cost>
<status>ready</status>
<link uri=″http://restbucks.com/receipt/1234″ rel=″receipt″/>
</order>

DELETE Receipt Response
<item>
<milk>semi</milk>
<size>large</size>
</item>
<cost>2. 0</cost>
<status>taken</status>
</order>

Restbucks - Conﬂict


201 + order

201 + receipt

POST http://restbucks.com/order/1234
409 Conflict

Links
<item>
<milk>semi</milk>
<size>large</size>
</item>
<cost>2. 0</cost>
<status>unpaid</status>
<link uri=″http://restbucks.com/order/1234″ rel=″cancel″/>
<link uri=″http://restbucks.com/order/1234″ rel=″update″/>
</order>

rel attribute
• Sematics of the referred resource
• Client must know meaning of rel, not uri
• Part of media type speciﬁcation


rel attribute
• Sematics of the referred resource
• Client must know meaning of rel, not uri
• Part of media type speciﬁcation
payment:
The linked resource allows the consumer to begin paying
for the order. Initiating payment involves PUTting an
appropriate resource representation to the specified
URI, as defined in the Restbucks media type.


Better Links
<order xmlns=″http://schemas.restbucks.com″
xmlns:dap=″http://schemas.restbucks.com/dap″>

<dap:link mediaType=″application/vnd.restbucks+xml″
uri=″http://restbucks.com/order/1234″
rel=″http://relations.restbucks.com/cancel″/>

<dap:link mediaType=″application/vnd.restbucks+xml″
uri=″http://restbucks.com/payment/1234″
rel=″http://relations.restbucks.com/payment″/>

More Beneﬁts

Toggle availability of features

Possibilities to change URLs

More ﬂexible clients

Live Documentation
• Provide text/html representation as
documentation
• Forms and links to interact with Service
• Great for exploring the API

What about WADL?
• Static contracts
• Nothing about ordering of interaction
• Intention is tooling
• Might be useful for CRUD Services

Evolving Interfaces
Why?
• Impossible to predict the future
• All cannot jump simultaneously

Evolving Interfaces
Why?
• Impossible to predict the future
• All cannot jump simultaneously

Advice:
• You need a versioning strategy
• Know your consumers
• Be pragmatic

Types of Changes
• 2.1.3
• major.minor.point
• major = not compatible (new xml ns)
• minor = compatible
• point = no change to contract

Compatibility scenarios
• No compatibility
• Backwards Compatible
– old v1.0 consumer can use new v1.1 provider
• Forwards Compatible
– new v1.1 consumer can use old v1.0 provider

Not Backwards Compatible
Removing an operation

Renaming an operation

Changing the parameters of an operation

Changing the structure of a data type

Backwards Compatibility

Ignore
missing

Ignore unknown

Forwards Compatibility

Ignore unknown

Ignore missing

Optional Elements
v1
v1

v1
v1:
<xs:complexType name="address" >
<xs:sequence>
<xs:element name="street" type="xs:string"
minOccurs="1" maxOccurs="1"/>
<xs:element name="country" type="xs:string"
</xs:sequence>
</xs:complexType>

Optional Elements
v1
v2

v2
v2:
<xs:complexType name="address" >
<xs:sequence>
<xs:element name="street" type="xs:string"
<xs:element name="country" type="xs:string"
<xs:element name="careOf" type="xs:string"
</xs:sequence>
</xs:complexType>

##any v1
v1

v1
v1:
<xs:complexType name="customer" >
<xs:sequence>
<xs:element name="name" type="xs:string" />
<xs:element name="address" type="address"
minOccurs="0" maxOccurs="unbounded"/>
<xs:element name="eov1"/>
<xs:any namespace="##any" processContents="lax"
minOccurs="0" maxOccurs="unbounded" />
</xs:sequence>
<xs:attribute name="id" type="xs:string" use="required"/>
</xs:complexType>

##any v1
v2

v2
v2:
<xs:complexType name="customer" >
<xs:sequence>
<xs:element name="name" type="xs:string" />
<xs:element name="address" type="address"
minOccurs="0" maxOccurs="unbounded"/>
<xs:element name="vip" type="xs:boolean" />
<xs:any namespace="##any" processContents="lax"
minOccurs="0" maxOccurs="unbounded" />
</xs:sequence>
<xs:attribute name="id" type="xs:string" use="required"/>
</xs:complexType>

xs:extension
<xs:complexType name="instrument" abstract="true">

<xs:complexType name="stock" >
<xs:complexContent>
<xs:extension base="instrument">

v1
v2

v1

xs:extension
<xs:complexType name="instrument" abstract="true">

<xs:complexType name="stock" >
<xs:complexContent>

<xs:complexType name="bond" >
<xs:complexContent>

v1
v2

v2

Versioned Namespace

<types>
<schema targetNamespace=
"http://example.com/2003/10/15/stockquote.xsd"
xmlns="http://www.w3.org/2000/10/XMLSchema">
<element name="TradePriceRequest">
<complexType>
<all>
<element name="tickerSymbol" type="string"/>
</all>
</complexType>
</element>
<element name="TradePriceResponse">
<complexType>

Transformation

v1
T

v2

v2

Versioning of RESTful
Services

Versioning Example
V 1.0

<account>
<name>Inigo Montoya</name>
</account>

Versioning Example
V 1.1

<account>
<email-address>mailto:prepare-to-die@youkilledmyfather.
</account>

V 1.0 consumers can ignore email-address

Versioning Example
V 2.0

<account>
<email-addresses>
<email-address priority='1'>mailto:prepare-to-die@youkil
<email-address priority='2'>mailto:vengeance@youkilledm
<email-address>
</account>

Will break v1.1 consumers

Use Different URLs

V 1.1 client use
http://foo.example/api/v1/accounts/3

V 2.0 client use

http://foo.example/api/accounts/3?v=2

Use Different URLs

. ..
V 1.1 client use ut
, b
le
V 2.0 client use ss
ib
P o

http://foo.example/api/accounts/3?v=2

Clients must support both versions if they store URLs

Vendor MIME type

• application/vnd.mycompany.myapp+xml
• Accept header of request
• Content-Type header of response

Content type negotiation

V 1.1 client ask for
Accept: application/vnd.mycompany.myapp+xml

V 2.0 client ask for
Accept: application/vnd.mycompany.myapp-v2+xml

Several Providers
Provider v1

Consumer
Provider v2

Accept: application/vnd.myapp-v2+xml, application/
vnd.myapp-v1+xml;q=0.8

Provider v1 answers with
Content-Type: application/vnd.myapp-v1+xml

GET to Update

GET /updateuser?name=Robert&newname=Bob

D !
BA
D !
BA
D !
B A

HTTP Caching
GET /foo HTTP/1.1
Host: www.foo.com
User‐Agent: FooBrowser/1.0
If‐Modified‐Since: Mon, 01 Jan 1979 ...
If‐None‐Match: abcdef0123456789
Accept: *

HTTP/1.1 200 OK
Content‐Type: text/html
Content‐Length: 24
Cache‐Control: public, max‐age=300 
Last‐Modified: Tue, 02 Jan 1979 ...
ETag: abcdef0123456789
Vary: Accept

Alice Gateway Cache Backend


GET /foo
Host: foo.com


GET /foo GET /foo
Host: foo.com Host: foo.com



200 OK
Cache‐Control: public, max‐age=60
ETag: abcdef012345

Hello World



200 OK 200 OK
Cache‐Control: public, max‐age=60 Cache‐Control: public, max‐age=60
ETag: abcdef012345 ETag: abcdef012345

Hello World Hello World

Bob (30 seconds later) Gateway Cache Backend


GET /foo
Host: foo.com


GET /foo
Host: foo.com

200 OK
Age: 30

Hello World

Carol (60 seconds later) Gateway Cache Backend


GET /foo
Host: foo.com


GET /foo
GET /foo Host: foo.com
Host: foo.com If‐None‐Match: abcdef012345


GET /foo

304 Not Modified


GET /foo

200 OK 304 Not Modified
Cache‐Control: public, max‐age=60 Cache‐Control: public, max‐age=60

Hello World

HTTPS Scalability Drawbacks

Cryptography costs

Prevents caching

Contract ﬁrst vs last

More up-front work
Need to learn all XML stuff

Decoupling
Better control

Validation and Errors

• Schema validation
• SOAP Fault
• Validation errors part of response
structure

HTTP Status Codes
200 - OK
201 - Created
301 - Moved
304 - Not modiﬁed
400 - Bad request
401 - Unauthorized
404 - Not found
405 - Method not allowed
409 - Conﬂict
500 - Internal Error
503 - Service Unavailable

Concurrency

HTTP/1.1 201 Created
...
ETag: "44bd59eeb984c"

PUT /orders/123 HTTP/1.1
...
If‐Match: "44bd59eeb984c"

412 Precondition Failed

Data Mapping
Do I need mapping framework?

Domain Objects != DTO

Tools
JAXB
Castor
XMLBeans
JiBX
XStream

Level of Detail

• Different consumers might need different
level of detail
• Different services?
• Include spec in request

Associations

• In REST you include links to associated
resources
• In practice you might need to embed
related data

Service Composition

• General vs speciﬁc services?
• Canonical Data Model?

Transactions

• WS-Transaction
• Stay out of distributed transactions

Interoperability

• WS-Interoperability
• WS-I test tools

Security

• HTTPS - transport level
• WS-Security
• Identify and authenticate the client
• Integrity of the message
• Safe from eavesdropping

Event-Driven Architecture

• Don’t use request-response for
everything
• Asynchronous messaging is often a
better alternative

Real World

• StreamFlow
• Amazon S3
http://docs.amazonwebservices.com/AmazonS3/latest/API/

• eBay
http://developer.ebay.com/support/docs/
http://developer.ebay.com/webservices/latest/eBaySvc.wsdl

{
"commands":[],
"contexts":
["services","users","cases
","organizations","surface
"],
"index":null,
"queries":[]
}

Questions?

Patrik Nordwall

Thanks for listening!

Patrik Nordwall

Ws rest

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