In this session you will learn: Roy fielding has authored REST specification. REST webservices For more information, visit: https://www.mindsmapped.com/courses/software-development/java-developer-training-for-beginners/

1. Java/J2ee Programming Training
Java Rest

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Agenda
• Roy fielding has authored REST specification.
• REST webservices

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• concepts of rest are very closely related to HTTP
• Http is used by many of the web pages to send a request and receive an response.

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HTTPExchange
CLIENT SERVERHTTP
Request
CLIENT SERVER
HTTP
Response

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HTTP
• Hyper text transfer protocol
• way to exchange information
• the text we exchange is called hyper text
• its structured form of text
• hypertext contains links to other text i.e hyperlinks
• hypertext is written using a markup language called
• HYPER TEXT MARKUP LANGUAGE.

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Resource Locations
• REST API have URI and address
CLIENT SERVERDATA

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HTML RESPoNSE
• Html response to display the weather information has css, styles….to display weather information to
user.

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Weather Web Service
• RestAPI for weather service has data represented in JSON or XML format.
• API are address.
• developers should decide what those addresses be
• resource based addresses
• weatherapp.com/weatherLookup.do?zip =12345;

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Resource based URI
• weatherapp.com/zipcode/12345
• weatherapp.com/zipcode/56789
• weatherapp.com/country/usa

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HTTP Methods
• GET
• PUT
• POST
• DELETE

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Metadata
• HTTP status code
• successful-200OK
• error – 500 ->server error
standard status code is sent by the REST services to the client to interpret the message accordingly.

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Message Headers
• Client and server can exchange information in any format.
• content information is recorded in HTTP headers
• xml- text /xml
• JSON - > application/json
• A web service may return more than one format based on client request.

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Summary
• Resource based URI
• HTTP methods
• HTTP response codes
• Message Headers
• Content Negotiation

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Designing RESTFUL URI
• Messenger
• Post message
• like message
• profile information

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Diagram

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Restful Resource based URI
• Web Application URI…

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Restful Resource based URI
• best practices

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Static Websites
• uri that uniquely identifies each web page on the server
• static profile pages.
TOM.HT
ML
MIKE.HT
ML
TEST.HT
ML

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profiles/tom.html
profiles
tom.html
jack.html
fay.html
profiles/tom
profiles/{profileName}

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resources based uri
• messages/{messageID}
• messages/1
• messages/10
• Restful URI names should be nouns.
it should not have verb/action
its plural
messages/1
profiles/jack
They are not dependent on framework.

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RESOURCE URI for RELATIONS

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Resource Relations
• messages/{messageID}
• profiles/{profileName}
• messages/{messageID}/comments/{commentId}
• messages/{messageID}/shares/{shareID}
• messages/{messageID}/likes/{likeID}
first level
second level

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Collection URI
• Instance based uri
• A single instance of message is accessible by instance based uri
• have unique id to retrieve the instance
• collection based uri
• /messages
to access all the messages
• to access all the comments for messageid =2
• messages/2/comments
• /messages
• /messages/{messageID}/comments
• messages/{messageID}/shares
• messages/{messageID}/likes

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Filters Result
• paginationusing query parameters
• messages?offset=10%limit=10;
• offset( startingpoint)= starts at message#30
• limit( pagination ) fetches 10 messages starting from 30

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Filter parameters
• retrieve message based on date
• messages?year=2014&offset=10&limit=10

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Summary
• Instance based uri
• collection based uri
• Query parameter to achieve pagination and filtering

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HTTP Methods
• Action based URI
• getMessages.do?id=10
• Resource based URI
• /messages/10
/ get Messages .do?id = 10
/ messages /10

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HTTP Methods
Method
/getMessage.do?id=1
0
/messages/10 GET
/postMessage.do?id=
10
/messages/10 POST
/deleteMessage.do?id
=10
/messages/10 DELETE
/updateMessage.do?i
d=10
/messages/10 PUT

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Creating a New Message
• to create a new Message , request is made to collection URI
• /messages
• because we don’t have message id
• to create a profile
/profiles
• To create a new resource
• use POST
• response is messageID

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Collection URI Scenarios
METHOD RESOURCE URI COMMENTS
GET /messages get All Messages
DELETE /messages/10/comments delete all comments of
Message 10
GET /messages
POST /messages/10/comments create a new comment for
message 10
PUT /message/20/comments replace all comments for
message 20 with new list

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Method Idempotence
• PUT Vs POST
• put- is for update
• POST-> create

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HTTP Methods
• GET  READ ONLY
• does not make any changes on server.
• Write
• PUTupdate
• DELETEdelete
• POSTcreate
• cannot make multiple calls/duplicate calls

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Java code example
• count = 100;
• count =100;
• count = 100;
Methods are repeatable
vs
Non repeatable

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Java code example
• count = 100;
• count =100;
• count = 100;
Methods are repeatable
vs
Non repeatable

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DELETE
• making repeated calls to delete.
• /message/20
• does not make any changes because the message is deleted.
• delete is safe

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PUT ( UPDATE )
• making repeated calls to put.( update)
• /message/20
• updates the message 20
• repeated calls makes update same messages. ( Net effect is same ).

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POST( CREATE )
• /messages
• every time a post is made it creates a new message.
• data on server is inserted on each call .
• its not safe to make multiple calls using POST method
• .

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Idempotence
• Idempotence is the property of certain operations in mathematics and computer science, that can be
applied multiple times without changing the result beyond the initial application
• Idempotent
• GET
• PUT
• DELETE
• NON Idempotent
• POST

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Resource creation
• resource creation should be non-idempotent.
• update, delete, put should be idempotent

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Cache Get Responses
CACHE

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Browser Refresh
• browser refresh last request.
• if it was a post.
• browser protects from submitting duplicate request by prompting the user with an information
message.

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HTTP Response
CLIENT
REQUEST URI
response

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WebApplication
CLIENT REQUEST URIresponse
HTML

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RESTful Web Services
CLIENT REQUEST URIresponse
XML/JSON

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JSON
• A Client to REST API is browser which makes REST API calls
• sending response in JSON makes its easy for the JavaScript client to convert the response(JSON) to
JavaScript object
• text format
• xml format

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Message Entity
public class MessageEntity
{
private int longId;
private String message;
private Date dateCreated;
private String author;
}

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JSON Object returned in response to request
{
“id”: 10,
“message”:”Hello Tom”,
“created”: “2015-09-10”
“author”:”Jack”
}

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XML response
<messageEntity>
<id>10</id>
<message>Hello john</message>
<dateCreated>10-09-2015</dateCreated>
<author>John</author>
</messageEntity>

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Responses
<messageEntity>
<id>10</id>
<message>Hello john</message>
<dateCreated>10-09-2015</dateCreated>
<author>John</author>
</messageEntity>
{
“id”: 10,
“message”:”Hello Tom”,
“created”: “2015-09-10”
“author”:”Jack”
}
MESSAGE ID : 10

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REST
Representational State transfer
we are sending or receiving representation of resources
different representation for the same resources.
JSON
XML
TEXT

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HTTP Headers
HTTP HEADERS
BODY
conent length
MIME TYPE
content Type

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Error Mesages
• status codes
200 OK
404 NOT FOUND
100-------------------------599

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classes of Error codes
1xx Informational Codes
2XX Success
200 OK
201 CREATED
204 NO CONTENT ( Eg: delete request, send an
acknowledgment without body)
3XX Redirection codes.
used by the server to redirect the client
300
304 not modified
400 Client error
client makes an error in request
forbidden access
404 Not found

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classes of Error codes
1xx Informational Codes
500 Internal Server error
200 OK
201 CREATED
204 NO CONTENT ( Eg: delete request, send an
acknowledgment without body)
3XX Redirection codes.
used by the server to redirect the client
300
304 not modified
400 Client error
client makes an error in request
forbidden access
404 Not found

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HATEOAS
• H-HyperMedia
• A-As
• T-The
• E-Engine
• O-Of
• A-Application
• S-State

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No SERVICE
DEFINITIONS

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Web Application
CLIENT REQUEST URIresponse
HTML

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Accessing Messages
{
“id”: 10,
“message”:”Hello Tom”,
“created”: “2015-09-10”
“author”:”Jack”
“commentsUri”:”api/messages/10/comments”
“likesUri”:”api/messages/10/likes”
“sharesUri”:”api/messages/10/shares”
}
CLIENT REQUEST URIresponse

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Accesesing Messages-- /messages
[
{
“id”: 10,
“message”:”Hello Tom”,
“created”: “2015-09-10”
“author”:”Jack”
},
{
”id”: 10,
“message”:”Hello Tom”,
“created”: “2015-09-10”
“author”:”Jack”
}
]

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Thank You