1. CS3220 Web and Internet Programming RESTful Web Service
Chengyu Sun
California State University, Los Angeles

2. Example: Files and Folders
\ Documents
\ Users
\ John
\ Courses
\ CS3220
File.java
files.sql
\ CS5220
Homework1.pdf
contacts.xls
\ Jane
log.txt

3. The Need to Exchange Data Between Client and Server
Ajax Folder Expand
Client
Server
+ Documents
+ Users
log.txt
Folder ID
List of files
and subfolders
in the folder

4. Usage of RESTful Web Service
Applications
Mobile
Apps
Server
RESTful
Web Service
Desktop
Applications
Other
Web Services

5. A RESTful Web Service Example
Implementation
File
DbUtils
FileServlet
Request
Get file with id=1: /file/1
JSON Response
mapped to /file/* {
“id”: 1,
“name”: “Documents”,
“parentId”: null,
“folder”: true }

6. Is That Really A Web Service?
Why does it look like a web application?
Why is it called RESTful?

7. A Brief History of Web Service
Remote Procedure Call
Simplifies network programming
RPC
CORBA
Cross-platform RPC
(Traditional)
Web Services
Cross-platform RPC over HTTP
SOAP – complex and not efficient
RESTful
Web Services

8. Why Does It Look Like A Web Application?
Answer: it does, and it’s a good thing.
Now all web technologies/languages
can be used to create web services
(and you don’t have to implement
complex specifications like SOAP).

9. Why Is It Called RESTful?
REpresentational State Transfer
Introduced by Roy Fielding in his Ph.D. dissertation on network-base software architecture
Describes the common characteristics of scalable, maintainable, and efficient distributed software systems

10. The REST Constraints Client and server Stateless Support caching
Uniformly accessible
Layered
(Optional) support code-on-demand

11. RESTful Web Services Web applications for programs
Generate responses in formats to be read by machines (i.e. JSON and XML) rather than by humans (i.e. HTML)
Simulate how the static web (the largest REST system) works
Use URLs that look like URLs for static web pages
Utilize HTTP request methods and headers
Stateless, i.e. no session

12. RESTful Web Service Example
Files and folders
Get
Add
Update
Delete
List
All the top-level files and folders
All the files and folders under a folder

13. Create a RESTful Web Service
Identify resources and operations
Determine resource representation, i.e. data exchange format between the service and the clients
Design URL and request mapping
Implement the operations

14. Resource Representation
Data format should be easily “understandable” by all programming languages
XML
Already widely in use as a platform independent data exchange format
XML parsers are readily available in many languages
JSON
Much more concise than XML
Can be used directly in JavaScript

15. URL Design and Request Mapping Conventions (1)
Operation: get a file/folder
URL
/file/{id} or
/file/get?id={id}
Path variable based design is usually preferred to
request parameter based design.

16. URL Design and Request Mapping Conventions (2)
Operation: get a file/folder
Choose which data format to use to communicate with a client
Solution:
/file/{id}.{format}, or
Check the Accept request header

17. URL Design and Request Mapping Conventions (3)
Map HTTP Request Methods to CRUD operations
POST (or PUT)
GET
PUT (or POST)
DELETE
Create
Retrieve
Update
Delete

18. Request Mapping Example (I)
Operation
HTTP Request
Get a file
GET /file/1 HTTP 1.1
Delete a file
DELETE /file/1 HTTP 1.1
Update a file
PUT /file/1 HTTP 1.1
{ “id”: 1,
“name”: “Documents2”,
“parentId”: null,
“folder”: true }

19. Request Mapping Example (II)
Operation
HTTP Request
List top-level files
GET /files HTTP 1.1
List files under a folder
GET /files/1 HTTP 1.1
Add a file
POST /files HTTP 1.1
{ “id”: null,
“name”: “Lab1.pdf”,
“parentId”: 7,
“folder”: false }

20. Implement RESTful Web Service
In theory any web application technology would do, but in practice it should be
Easy to handle request methods and request/response headers
Easy to handle “path parameters” like /file/{id}
Easy to handle data in XML and/or JSON format

21. Service Implementation – Know Your Libraries
Modern webapp frameworks like Spring
Jersey -
Convert between objects and XML/JSON
Jackson -
Gson, JAXB, Simple XML Serialization …

22. Serialization/Marshalling and Deserialization/Unmarshalling
Java
Object
XML/JSON
De-serialization/
Un-marshalling

23. Service Access – Libraries on the Client Side
HTTP client
Client-side JavaScript for web applications
Apache HttpClient for Java applications
HttpUrlConnection for Android apps
Various XML/JSON parsers, e.g. Jackson, XmlPullParser, JsonReader, …

24. Service Testing Browser addons/extensions Standalone clients
E.g. RESTClient for Firefox and Advanced REST Client for Chrome
Standalone clients
Full-featured test software like Selenium

25. Service Implementation Using Jersey
A Java library for creating and accessing RESTful web services
The reference implementation of the JAX-RS (Java API for RESTful Web Services) specification

26. Use Maven for Dependency Management
Convert an Eclipse Dynamic Web Project to a Maven Project: right click on project -> Configure -> Convert to Maven Project
Maven is a project management tool for Java
Project Object Model (POM)
Project Lifecycles
Dependency Management
Plugin Framework

27. Maven Coordinates groupId artifactId version packaging, default: jar
Name of the company, organization, team etc., usually using the reverse URL naming convention
artifactId
A unique name for the project under groupId
version
packaging, default: jar
classifier
Maven coordinates uniquely identifies a project.

28. Why Not Just Use Project Name
Rage-quit: Coder unpublished 17 lines of JavaScript and “broke the Internet”

29. Dependency Management
A dependency of a project is a library that the project depends on
Adding a dependency to a project is as simple as adding the coordinates of the library to pom.xml
Maven automatically downloads the library from an online repository and store it locally for future use

30. Dependency Example Add a dependency to pom.xml
<dependencies>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>jstl</artifactId>
<version>1.2</version>
</dependency>
</dependencies>
Add a dependency to pom.xml
Add a dependency in Eclipse

31. More About Dependency Management
Dependencies of a dependency are automatically included
Dependency conflicts are automatically resolved

32. Jersey Dependencies
org.glassfish.jersey.containers:jersey-container-servlet
org.glassfish.jersey.media:jersey-media-json-jackson

33. Example: Get File in Jersey
URL: /service/file/{id}
Basic Jersey terminology
Dispatcher servlet
Resource class
Resource method (i.e. sub-resource)
Provider
Entity Provider

34. Understand Request Routing in Jersey
/service/file/1
Request URI
Servlet mapping for the Jersey
dispatcher servlet in web.xml
/service/*
Path annotation for resource
class
@Path(“/file”)
Path annotation for resource
method (optional)
@Path(“/{id}”)

35. Common Jersey Annotations …
@Path
@PathParam
Map part of the path to an argument of a resource method

36. … Common Jersey Annotations
@Produces
Tell Jersey which data format the return value should be converted to
Help mapping a request to a resource method based on the Accept header in the request
Set the Content-Type header in response
@Consumes
Tell Jersey the data format of the data in the request body
Help mapping a request to a resource method based on the Content-Type header in the request

37. Example: RESTful Web Service Implementation and Access
Complete the rest of the operations
Test the operations
Implement AJAX Folder Expand

38. Run the Code Example
Download the zip file from
Unzip it to a local folder
In Eclipse, select File  Import  Existing Maven Project
Follow the instructions in README.md
In Eclipse, right click on the project and select Run As  Run on Server

39. Application Deployment
Deploy Application
Computer for
Development
Server Hosting the
Web Application

40. WAR Files Web application ARchive
A JAR file for packaging, distributing, and deploying Java web applications
Ways to create WAR files
The command line tool jar
Eclipse Export -> Web -> WAR file
mvn package

41. Deploy WAR Files to a Tomcat Server
Copy the WAR file to the webapps folder
Use the Manager App
Need a user with the manager-gui role
More options at