Android chapter18c Consuming Web Services Using KSOAP (on IIS) and REST (on Apache Tomcat)

14 Consuming Web Services Example 1 – TUTORIAL – Android Application 14 The WebServiceCall class negotiates the transporting of request/response objects as well as preparation of serial

Android

Consuming Web Services

Using KSOAP (on IIS) and REST (on Apache Tomcat)

18C

Victor Matos

Cleveland State University

Notes are based on:

Android Developers

http://developer.android.com/index.html

2

Consuming Web Services

2

Web Services

• Support machine-to-machine collaboration

• They can be described, published, located, and invoked over a

data network

• Web services are used to implement the notion of a

service-oriented architecture (SOA)

SOA applications are independent of specific programming languages

or operating systems

• Web services rely on existing transport technologies, such as

HTTP, and XML, for invoking the implementation.

3

Consuming Web Services

3

Web Services

The interface describing the format of services can be done using

the Web Services Description Language (WSDL)

According to W3C there are two major types of web services

• REST-compliant which use XML to represent its Web

resources, and offers a "stateless" set of operations; and

• Arbitrary solutions, in which the service may expose a

heterogeneous set of operations

4

Consuming Web Services

4

Web Services - Implementations

Two widely used architectures supporting Web services are

Representational State Transfer (REST) Closely tie to the HTTP protocol by

associating its operation to the common GET, POST, PUT, DELETE for HTTP

Remote Procedure Call (RPC) Web services are directly implemented as

language-specific functions or method calls In this category we find

1 Object Management Group's (OMG) Common Object Request Broker

Architecture ( CORBA ),

2 Microsoft's Distributed Component Object Model ( DCOM ) and

3 Sun Microsystems's Java/Remote Method Invocation ( RMI )

5

Consuming Web Services

5

Web Services

6

Consuming Web Services

6

How Android Applications Consume WebServices?

We will present two examples of how an Android application can request services hosted in a

(1) IIS webserver (RPC discrete function oriented approach)

(2) Apache-Tomcat 7.0 (REST state oriented approach)

The examples are exhaustive and include details of how the

server-side methods are constructed (you may skip this portion based on your previous experience)

7

Consuming Web Services

7

Example 1 - How NET Web Services Are Called?

Services are passive server-side pieces of code waiting for

incoming messages to do some work Clients initiate the interaction

by sending a message to server-services requesting action

Services expose one or more endpoints where messages can be

sent Each endpoint consists of

address (where to send messages)

binding (how to send messages )

contract (what messages contain)

Clients can use WSDL to know this information before accessing a service

8

Consuming Web Services

8

Example 1 - How NET Web Services Are Called?

Windows Communication Foundation (WCF) uses the information found in the service contract to perform dispatching and

serialization

Dispatching is the process of deciding which method to call for

an incoming SOAP message

Serialization is the process of mapping between the data found

in a SOAP message and the corresponding NET objects used in the method

9

Consuming Web Services

9

Example 1 - How NET Web Services Are Called?

Our example code consists of two fragments which implement the server and client side of the application

Server Side:

to create a simple Web service running on a Windows IIS-Server We

have chosen to expose our collection of methods on the free host

Client Side:

We use the KSOAP 2.0 platform to request a sequence of remote

procedure calls to the IIS server hosting our service code The methods include functions taking zero, or more simple/object-complex inputs that return simple/object-complex results

Consuming Web Services Example 1 – TUTORIAL – IIS Server Side Code

Android App accessing

all services available

at the IIS server

supports synchronous, asynchronous, and complex-routing

communication schemes

Our implementation includes three classes

1 Main webcalls are assembled

2 EnglishDistance (Serialized)

3 WebServiceCall deals with HTTP

transporting of the request/response and envelope objects

Consuming Web Services Example 1 – TUTORIAL – Android Application

A fragment of the Main class follows

// add two numbers - get int result

int intResult = webServiceCall.AddService(11, 22);

txtMsg append( "\nAdd RESULT= " + intResult );

}

All the intelligent work is done by the WebServiceCall class

14

Consuming Web Services Example 1 – TUTORIAL – Android Application

14

The WebServiceCall class negotiates the transporting of request/response objects as well

as preparation of serialization of complex data elements ( 1/4 )

private static final String SOAP_ACTION = "http://tempuri1.org/" ;

private static final String NAMESPACE = "http://tempuri1.org/" ;

private static final String URL =

"http://iamok.somee.com/MathService.asmx" ;

protected Object call( String soapAction,

SoapSerializationEnvelope envelope)

{

Consuming Web Services Example 1 – TUTORIAL – Android Application

WebServiceCall class (continuation 2/4)

Object result = null ;

final HttpTransportSE transportSE = new HttpTransportSE( URL );

transportSE debug = false ;

// call and Parse Result

16

Consuming Web Services Example 1 – TUTORIAL – Android Application

16

Fragment of the WebServiceCall class called to add two numbers Here input parameters

and output values resulting from the webservice are sent and received (cont 3/4)

public int AddService( int v1, int v2){

// indicate webservice (endpoint) to be called

final String webMethod = "Add" ;

// Create the outgoing request message

final SoapObject requestObject = new SoapObject( NAMESPACE ,

webMethod);

// add outgoing parameters (name-type must agree with endpoint) requestObject.addProperty( "v1" , v1);

requestObject.addProperty( "v2" , v2);

// Create soap envelope for NET server

final SoapSerializationEnvelope envelope =

envelope dotNet = true ;

// place in envelope the outgoing request object

envelope.setOutputSoapObject(requestObject);

Consuming Web Services Example 1 – TUTORIAL – Android Application

The WebServiceCall class (continuation 4/4)

try

{

// call webmethod and parse returning response object

final Object response = (Object) this call(

18

Consuming Web Services Example 1 – TUTORIAL – IIS Server Side Code

18

Transferring Complex Data Objects to/from Server

The previous fragment illustrates the sending of simple pieces of primitive data (int, strings, …) between client and server

When complex objects are exchanged the sender and receiver

must deal with the serialization of the objects in transit

Serializing requires the client’s Java definition of the class to

implement the KvmSerializable interface The server must also mark the corresponding class as [Serializable]

Consuming Web Services Example 1 – TUTORIAL – IIS Server Side Code

Transferring Complex Data Objects to/from Server ( 1 of 5)

In the following fragment an EnglishDistance class is defined in the client (Java)

and server (C#) The following fragments of Android code illustrates the defining

of the class and the calling mechanism to send/receive this complex data type

// Calling DotNET Webservices running on an IIS server

// This class represents a KvmSerializable version of an

// EnglishDistance(fett, inches) Observe the required

// methods: getProperty, setProperty, getPropertyCount

// Author: Victor Matos - April 2011

public class EnglishDistance implements KvmSerializable {

private int _feet ;

private int _inches ;

this _feet = Integer.parseInt(obj.getProperty( "feet" ).toString());

}

public String showDistance(){

return _feet + "\" " + _inches + "\' " ;

Consuming Web Services Example 1 – TUTORIAL – IIS Server Side Code

Transferring Complex Data Objects to/from Server ( 3 of 5 )

@Override

public Object getProperty( int index) {

Object object = null ;

return object;

}

Needed by interface

Consuming Web Services Example 1 – TUTORIAL – IIS Server Side Code

Transferring Complex Data Objects to/from Server ( 5 of 5 )

24

Consuming Web Services Example 1 – TUTORIAL – IIS Server Side Code

24

Transferring Data Objects - NET Code – IIS Server Definition 1/2

The following fragment shows the Server side definition of the EnglishDistance

class Notice the server needs to agree with the client’s definition on attributes (name, type); however it does not need to include the same methods

namespace MathService

{

[ Serializable]

public class EnglishDistance {

private int _feet = 0;

private int _inches = 0;

Consuming Web Services Example 1 – TUTORIAL – IIS Server Side Code

Transferring Data Objects Server Definition 2/2

public String ShowEnglishDistance() {

return _feet + "\" " + _inches + "\' ";

}

{

get { return this._feet; }

set { _feet = value; }

26

Consuming Web Services Example 1 – TUTORIAL – Android Code

26

Android – Sending / Receiving Objects from Web Services ( 1 of 3)

This fragment is from the Android’s app Main class It creates an instance of an EnglishDistance and sends it to the server to be increased by half a foot

Transferring of the object requires its serialization

// make a local EnglishDistance object & pass it to webservice

// get the modified object back from service (6 more inches)

EnglishDistance ed1 = new EnglishDistance(6, 16);

txtMsg append( "\nMake ED ed1= " + ed1.showDistance() );

EnglishDistance ed2 = (EnglishDistance)webServiceCall.AddHalfFoot(ed1);

Consuming Web Services Example 1 – TUTORIAL – Android Code

Android – Sending / Receiving Objects from Web Services ( 2 of 3)

This fragment is from the Android’s app WebServiceCall class It prepares the

request object and its EnglishDistance object parameter, calls the service and picks the returned object

public EnglishDistance AddHalfFoot(EnglishDistance inputEd){

// indicate webservice (endpoint) to be called

final String webMethod = "AddHalfFoot" ;

// Create the outgoing request object

final SoapObject requestObject = new SoapObject( NAMESPACE , webMethod);

// add outgoing parameter (name-type) must agree with endpoint

requestObject.addProperty( "inputEd" , inputEd);

// Create soap envelope for IIS server

final SoapSerializationEnvelope envelope =

new SoapSerializationEnvelope(SoapEnvelope. VER11 );

envelope dotNet = true ;

28

Consuming Web Services Example 1 – TUTORIAL – Android Code

28

Android – Sending / Receiving Objects from Web Services ( 3 of 3)

This fragment is from the Android’s app WebServiceCall class It prepares the

request object and its EnglishDistance object parameter, calls the service and picks the returned object

// call webservice and parse returning response object

EnglishDistance outputEd = null ;

final Object response = this call( SOAP_ACTION + webMethod, envelope );

Consuming Web Services Example 2 – TUTORIAL – Android Code

HttpServletRequest: the request object

Represents a client's request This object gives a servlet access to incoming information such as HTML form data and HTTP request headers

HttpServletResponse: the response object

Represents the servlet's response The servlet uses this object to return data

to the client such as HTTP errors (200, 404, and others), response headers (Content-Type, Set-Cookie, and others), and output data by writing to the response's output stream or output writer

Consuming Web Services Example 2 – TUTORIAL – Android Code

REST Protocol – Android & Apache Server

Use the container login mechanism configured for the ServletContext to authenticate the user

making this request

Consuming Web Services Example 2 – TUTORIAL – Android Code

REST Protocol – Android & Apache Server

Returns any extra path information after the servlet name but before the query string, and

translates it to a real path

getQueryString()

Returns the query string that is contained in the request URL after the path

getRemoteUser()

Returns the login of the user making this request, if the user has been authenticated, or null if the

user has not been authenticated

getRequestedSessionId ()

Returns the session ID specified by the client

Gets the AsyncContext that was created or reinitialized by the most recent invocation of startAsync() or

startAsync(ServletRequest,ServletResponse) on this request

getAttribute(java.lang.String name)

Returns the value of the named attribute as an Object, or null if no attribute of the given name exists

Returns an Enumeration of Locale objects indicating, in decreasing order starting with the preferred locale, the locales

that are acceptable to the client based on the Accept-Language header

getLocalName()

Returns the host name of the Internet Protocol (IP) interface on which the request was received

Consuming Web Services Example 2 – TUTORIAL – Android Code

REST Protocol – Android & Apache Server

Reference: http://download.oracle.com/javaee/6/api/javax/servlet/http/HttpServletRequest.html

Interface ServletRequest

getLocalPort()

Returns the Internet Protocol (IP) port number of the interface on which the request was received

getParameter(java.lang.String name)

Returns the value of a request parameter as a String, or null if the parameter does not exist

getParameterMap()

Returns a java.util.Map of the parameters of this request

getParameterNames()

Returns an Enumeration of String objects containing the names of the parameters contained in this request

getParameterValues(java.lang.String name)

Returns an array of String objects containing all of the values the given request parameter has, or null if the parameter

does not exist

getProtocol()

Returns the name and version of the protocol the request uses in the form protocol/majorVersion.minorVersion, for

example, HTTP/1.1

getReader()

Retrieves the body of the request as character data using a BufferedReader

getRealPath(java.lang.String path)

Deprecated As of Version 2.1 of the Java Servlet API, use ServletContext#getRealPath instead

Returns a boolean indicating whether this request was made using a secure channel, such as HTTPS

removeAttribute(java.lang.String name)

Removes an attribute from this request

setAttribute(java.lang.String name, java.lang.Object o)

Stores an attribute in this request

setCharacterEncoding(java.lang.String env)

Overrides the name of the character encoding used in the body of this request

startAsync()

Puts this request into asynchronous mode, and initializes its AsyncContext with the original (unwrapped)

ServletRequest and ServletResponse objects

startAsync(ServletRequest servletRequest, ServletResponse servletResponse)

Puts this request into asynchronous mode, and initializes its AsyncContext with the given request and response

objects