Java Rest

Java/J2ee Programming Training
Java Rest

Classification: Restricted
Agenda
• Roy fielding has authored REST specification.
• REST webservices

• 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.

HTTPExchange
CLIENT SERVERHTTP
Request
CLIENT SERVER
HTTP
Response

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.

Resource Locations
• REST API have URI and address
CLIENT SERVERDATA

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

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;

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

HTTP Methods
• GET
• PUT
• POST
• DELETE

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.

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.

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

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

Diagram

Restful Resource based URI
• Web Application URI…

Restful Resource based URI
• best practices

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

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

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.

RESOURCE URI for RELATIONS

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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
• .

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

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

Cache Get Responses
CACHE

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.

HTTP Response
CLIENT
REQUEST URI
response

WebApplication
CLIENT REQUEST URIresponse
HTML

RESTful Web Services
XML/JSON

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

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

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

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

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

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

HTTP Headers
HTTP HEADERS
BODY
conent length
MIME TYPE
content Type

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

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

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

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

No SERVICE
DEFINITIONS

Web Application
HTML

Accessing Messages
{
“id”: 10,
“created”: “2015-09-10”
“commentsUri”:”api/messages/10/comments”
“likesUri”:”api/messages/10/likes”
“sharesUri”:”api/messages/10/shares”
}

Accesesing Messages-- /messages
[
{
“id”: 10,
“created”: “2015-09-10”
},
{
”id”: 10,
“created”: “2015-09-10”
}
]

Thank You

Java Rest

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