Download - Building Web Services
Building Web Services
Jussi Pohjolainen
Communica9on between Apps
• Implemen9ng RPCs can be a difficult task • DCOM, CORBA, RMI … firewalls and proxy servers can block binary
• Using HTTP for RPCs you can bypass this problem
Web Service
• Communica9on between devices over Web – W3C defines "Web Service" as a technology that uses WSDL, SOAP, HTTP and XML to create the communica9on
• Two types – XML Web Services – Web API
XML Web Services
• XML Web services uses XML messages that follow SOAP standard for crea9ng the communica9on
• Services are wriRen using WSDL – Web Services Descrip9on Language (WSDL)
• Web Services are integrated very well to .NET and Java (6 -‐>)
Web API (Rest)
• Emphasis to simpler communica9on – Representa)onal state transfer (REST)
• Do not require SOAP, WSDL • Simple Web API – hRp://www.something.com/twiRerthis.php?msg=hello!
• If the Web API is implemented using certain constraints, it's rest API – hRp://www.something.com/clients/client17
XML WEB SERVICE
SOAP?
• SOAP is a XML-‐based protocol to let apps exchange informa9on over HTTP
• SOAP is language independent and it's W3C recommenda9on
• Since SOAP is XML and it's text, it can be send easily through firewalls
SOAP Building Blocks <?xml version="1.0"?> <soap:Envelope xmlns:soap="http://www.w3.org/2001/12/soap-envelope" soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding"> <soap:Header> ... </soap:Header> <soap:Body> ... <soap:Fault> ... </soap:Fault> </soap:Body> </soap:Envelope>
SOAP Request <?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ns1="http://hello/">
<SOAP-ENV:Body>
<ns1:getArea><arg0>5.6</arg0></ns1:getArea>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>
SOAP Response <?xml version="1.0" ?>
<S:Envelope xmlns:S="http://schemas.xmlsoap.org/soap/envelope/">
<S:Body>
<ns2:getAreaResponse xmlns:ns2="http://hello/">
<return>98.5203456165759</return>
</ns2:getAreaResponse>
</S:Body>
</S:Envelope>
Client and Server
• "Soap Server" provides a WSDL – file to client • Client opens the WSDL file and discovers the methods and arguments of given service
• Client makes a invoca9on to server. The invoka9on is a soap message
• Server receives the soap message, parses it and invocates the method. Result is send back in SOAP envelope
Java 6: XML & Web Services
• Easy way of crea9ng Web Services • Expose web service with a simple annota9on
Web Service package hello; import javax.jws.WebService; @WebService public class CircleFunctions { public double getArea(double r) {
return java.lang.Math.PI * (r * r); } public double getCircumference(double r) { return 2 * java.lang.Math.PI * r; } }
Server package hello;
import javax.xml.ws.Endpoint; class Publish {
public static void main(String[] args) {
Endpoint.publish( "http://localhost:8080/circlefunctions", new CircleFunctions());
}
}
Generate Stub Files
• Generate stub files: – wsgen –classpath . hello.CircleFunctions
PHP Client <?php
$arguments = array (
"arg0" => "5.6",
);
// URI delivered to web service
$soapclient = new SoapClient("http://localhost:8080/circlefunctions?wsdl");
$result = $soapclient->getArea($arguments);
print($result->return);
?>
REST
REST Constraints • Client Server
– Interface separates clients from servers. Server and client can be replaced and developed independently
– Client? Browser, PHP script, Desktop app, Command line … • Statelessness
– Each request from any client contains all the informa9on necessary • Cacheable
– Clients can cache responses. Response indicate whether it is cacheable or not
• Uniform interface – Uniform interface between clients and servers. Four guiding principles
• Layered System – Client does not know is it connected directly to server or some
middleware
Guidelines for the Interface • Iden9fica9on of resources
– Resources are iden9fied via request using URIs – Server sends to client HTML, XML or JSON as result (does not send the
database) • Manipula9on of resources
– Client can delete or modify a resource when it holds a representa9on of the resource
• Self-‐descrip9ve messages – Message includes enough informa9on to describe how to process the
message • Hypermedia as the engine of applica9on state
– Client enters REST app using simple fixed URL. All future ac9ons the client may take can be discovered from the returned representa9on
Resources
• Resource can be anything: ar9cle, comment, user …
• Resources are accessed by URI – hRp://example.com/ar9cle/1 – hRp://example.com/comments/
RESTful Web APIs
PHP REST IMPLEMENTATION
Rewrite engine
• Rewrite engine is a sohware that modifies web URL's appearance – URL rewri9ng
• Usage – hRp://example.com/index.php?clien9d=123
• Can be altered – hRp://example.com/clients/client/123
• Apache HTTP Server has URL rewri9ng provided by mod_rewrite module
.htaccess # Let's use the mod_rewrite module
RewriteEngine On
# Set's the base URL for per-directory rewrites
RewriteBase /
# Defines a condition under which rewriting will
# take place
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
# Make the rule
RewriteRule ^(.*)$ /xampp/rest/index.php/$1 [L]
XAMPP windows
• Open apache/conf/extra/hRpd-‐xampp.conf – set AllowOverride All
Gekng info about Request and Path
<?php
$requestMethod = $_SERVER['REQUEST_METHOD'];
print("Request method: " . $requestMethod . "\n\n");
$urlPaths = $_SERVER['REQUEST_URI'] ;
print("Path: " . $urlPaths);
?>
Modifica9on <?php
$requestMethod = $_SERVER['REQUEST_METHOD'];
$urlPaths = $_SERVER['REQUEST_URI'] ;
$paths = explode("/", $urlPaths);
$paths = array_splice($paths, 3);
print_r($paths);
?>
Encoding and decoding
• Encode data to and decode from JSON – json_encode() – json_decode()
Tes9ng: Advanced REST Client Chrome App
Tes9ng
• PHP Script that makes hRp requests • CURL • Telnet…
