[Android] Web services

Android Programming

Lesson 10

Web services
NGUYEN The Linh

Android Programming

Contents

1 Overview

2 Working with SOAP services

3 Working with XML

4 Using KSoap2 Library

2

Android Programming

Web services

Overview

3

Android Programming

Overview

 What is a web service?
 A Web service is a method of communication between two
electronic devices over the World Wide Web.

 The most important factor to the success and popularity of web
services is the fact that its backbone is XML.

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Android Programming

Overview

 What is a web service?(cont.)

5

Android Programming

Overview

 What is a web service?(cont.)
Request -> POST

XML

Web
services

Response

XML
6

Android Programming

Web services

Working with SOAP services

7

Android Programming


 What is SOAP?
 SOAP stands for Simple Object Access Protocol

 SOAP is a communication protocol

 SOAP is for communication between applications

 SOAP is a format for sending messages

 SOAP communicates via Internet
8

Android Programming


 What is SOAP? (cont.)
 SOAP is platform independent

 SOAP is language independent

 SOAP is based on XML

 SOAP is simple and extensible

 SOAP is a W3C recommendation
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Android Programming


 Why is SOAP Needed?
 It is important for application development to allow Internet
communication between programs.

 HTTP is supported by all Internet browsers and servers.

 SOAP provides a way to communicate between applications
running on different operating systems, with different technologies
and programming languages.

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Android Programming


 SOAP Building Blocks

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Android Programming


 SOAP Building Blocks (cont.)
 An Envelope element that identifies the XML document as a
SOAP message.

 A Header element that contains header information.

 A Body element that contains call and response information.

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Android Programming


13

Android Programming


14

Android Programming

Web services

Working with XML

15

Android Programming

Working with XML

 What is XML?
 XML stands for EXtensible Markup Language
 XML is a markup language much like HTML

 XML was designed to carry data, not to display data
 XML tags are not predefined. You must define your own tags
 XML is designed to be self-descriptive

 XML is a W3C Recommendation

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Android Programming

Working with XML

 What is XML Parser?
 A parser is a piece of program that takes a physical representation
of some data and converts it into an in-memory form for the
program as a whole to use.

 Parsers are used everywhere in software.

 An XML Parser is a parser that is designed to read XML and
create a way for programs to use XML.

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Android Programming

Working with XML

 The main types of parsers?
 The main types of parsers are known by some names:
• SAX
• DOM
• Pull

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Android Programming

Working with XML

 What is SAX parser?
 A SAX (Simple API for XML) parser does not create any internal
structure. Instead, it takes the occurrences of components of an
input document as events, and tells the client what it reads as it
reads through the input document.

 A SAX parser serves the client application always only with
pieces of the document at any given time.

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Android Programming

Working with XML

 What is SAX parser? (cont.)
 A SAX parser, however, is much more space efficient in case of a
big input document (because it creates no internal structure).
What’s more, it runs faster and is easier to learn than DOM
parser because its API is really simple.

 But from the functionality point of view, it provides a fewer
functions, which means that the users themselves have to take
care of more, such as creating their own data structures.

20

Android Programming

Working with XML

21

Android Programming

Working with XML

22

Android Programming

Working with XML

 What is DOM parser?
 A DOM (Document Object Model) parser creates a tree structure
in memory from an input document and then waits for requests
from client.

 A DOM parser always serves the client application with the entire
document no matter how much is actually needed by the client.

23

Android Programming

Working with XML

 What is DOM parser? (cont.)
 A DOM parser is rich in functionality.

 It creates a DOM tree in memory and allows you to access any
part of the document repeatedly and allows you to modify the
DOM tree.

 But it is space inefficient when the document is huge, and it takes
a little bit longer to learn how to work with it.

24

Android Programming

Working with XML

25

Android Programming

Working with XML

 What is Pull parser?
 SAX is a push parser, since it pushes events out to the calling
application.

 Pull parsers, on the other hand, sit and wait for the application to
come calling. They ask for the next available event, and the
application basically loops until it runs out of XML.

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Android Programming

Working with XML

 What is Pull parser? (cont.)
 Pull parsers are useful in streaming applications, which are areas
where either the data is too large to fit in memory.

 It is designed to be used with large data sources, and unlike SAX
which returns every event, the pull parser can choose to skip
events that it is not interested in.

27

Android Programming

Working with XML

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Android Programming

Working with XML

 What is Pull parser? (cont.)
 The above example will generate the following output:
• Start document
• Start tag contact
• Text Nguyen Van A
• End tag contact
• End document

29

Android Programming

Working with XML

 Example 10.1
 GetLove App
 http://nikmesoft.com/apis/J4FServices/
index.php

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Android Programming

Web services

Using KSoap2 Library

31

Android Programming


 What is KSoap2?
 KSOAP is a SOAP web service client library for constrained
Java environments such as Applets or J2ME applications (CLDC /
CDC / MIDP).

 The ksoap2-android project provides a lightweight and efficient
SOAP client library for the Android platform.

 http://code.google.com/p/ksoap2-android/

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Android Programming


 Why is KSoap2 Needed?

Send
Request
(XML)
Get
Response
(XML)

Parsing
XML

33

Android Programming



Send
Request
(XML)
Get
Response
(XML)

Parsing
XML

34

Android Programming


Parsing
Send XML
Request
KSOAP2
(XML)

Get
Response All In One
(XML)

35

Android Programming


 Example 10.2
 Using KSoap2

36

[Android] Web services

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