Distributed Programming in Java

Transcription

1 Distributed Programming in Java Web Services (3) Tracing SOAP Messages Enable trace messages by enabling the electric.logging property or using Log.startLogging Run the client with SOAP logging enabled 2/41 Logging CATEGORY COMMAND COMMENT ERROR EXCEPTION HTTP JMS MAPPING ONEWAY SOAP SOURCE A general comment MEANING Generated when line in a command file executed Generated when internal GLUE exception occurs Generated when a SOAPException constructed Generated by any SOAP-related HTTP traffic Generated when a JMS warning occurs Generated when a map file is read Generated when an exception for oneway msg occurs Generated by any remote SOAP requests or SOAP responses Generated when the source of a Java interface cannot be found 3/41 1

2 Tracing using In-code Logging public class ExchangeClient { public static void main(string args[]) throws Exception { // bind to web service from WSDL at the specified URL String url = " IExchange exchange = (IExchange) Registry.bind(url, IExchange.class); // Start Logging SOAP messages (using text from table) Log.startLogging("SOAP"); } // invoke the web service via its proxy double rate = exchange.getrate("canada", "usa"); System.out.println("canada/usa exchange rate = " + rate); } 4/41 Anatomy of a SOAP Request 5/41 HTTP Request LOG.HTTP: outbound request to tcp:// :8004 POST /soap/exchange HTTP/1.1 Host: :8004 Content-Type: text/xml; charset=utf-8 User-Agent: GLUE/2.1 Connection: Keep-Alive SOAPAction: "getrate" Content-Length: 534 < material deleted > 6/41 2

3 SOAP Message Model Header: optional, 1 or more header entries Body: 0 or more body entries 0 or more non-standard elements 7/41 SOAP Request LOG.SOAP: request to <?xml version='1.0' encoding='utf-8'?> <soap:envelope xmlns:xsi=' xmlns:xsd=' xmlns:soap=' xmlns:soapenc=' soap:encodingstyle=' <soap:body> <n:getrate xmlns:n=' <country1 xsi:type='xsd:string'>canada</country1> <country2 xsi:type='xsd:string'>usa</country2> </n:getrate> </soap:body> </soap:envelope> 8/41 Anatomy of a SOAP Response 9/41 3

4 HTTP Response LOG.HTTP: <?xml version='1.0' encoding='utf-8'?> <soap:envelope xmlns:xsi=' xmlns:xsd=' xmlns:soap=' xmlns:soapenc=' soap:encodingstyle=' '><soap:body><n:getrateresponse xmlns:n=' xsi:type='xsd:double'> </result></n:getrater esponse></soap:body></soap:envelope> 10/41 SOAP Response LOG.SOAP: response from <?xml version='1.0' encoding='utf-8'?> <soap:envelope xmlns:xsi=' xmlns:xsd=' xmlns:soap=' xmlns:soapenc=' soap:encodingstyle=' <soap:body> <n:getrateresponse xmlns:n=' <Result xsi:type='xsd:double'> </result> </n:getrateresponse> </soap:body> </soap:envelope> 11/41 Envelope-Message 12/41 4

5 WSDL Web Service Description Language Neutral format for services to advertise themselves on the network In future, can choose between competing providers of same service (price, etc.) GLUE generates WSDL file automatically 13/41 WSDL 14/41 WSDL Messages Request Response 15/41 5

6 WSDL Port Type Defines operations offered by a service 16/41 WSDL Binding How messages will be handled 17/41 WSDL Service Definition How to access the service (defines port, binding, and service URL) 18/41 6

7 Web Service Design Considerations Transport Protocol HTTP -- firewall friendly, unreliable. Tends to be used synchronously for request/response. Asynchronous/Synchronous Messaging Synchronous: connection remains open until response sent. Servers have to maintain multiple concurrent messages -- complex. Server has to do error handling WS-ReliableMessaging designed to address reliable delivery and message processing 19/41 Web Service Design Considerations Encoding style: Encoded: primitive (standard) mapping of objects and parameters to XML. Literal: external specification provided for wire representation. Style is mostly encoded Binding style: RPC: Receiver must interpret message as a procedure call (rules are SOAP-specified) Document: XML document is delivered Summary: most Web Services uses SOAP encoding with synchronous, RPC binding; i.e., looks just like RMI, CORBA requests. 20/41 Apache Axis Open source web service framework Client programming model of Axis provides components for client to invoke a service endpoint and receive the response message Server programming model based on a listener for each transport protocol, a set of message handlers, and service handlers Let us have a closer look at its architecture 21/41 7

8 Axis Engine Architecture HTTP, JMS, etc. SOAP, XML-RPC java:rpc /41 Axis Architecture Framework made up of handlers: Invoked in order depending on configuration Whether client or server accessing framework Handlers grouped in chains: request and response 3 chains: Transport Global Service Reference 23/41 Service Activator Activator handles all messaging details and invokes the service like any client. Service can be POJO. 24/41 8

9 Techniques for Deploying Web Services in Axis Automatic Deployment Using a Web Services Deployment Descriptor (WSDD) Generate proxies from an existing WSDL document 25/41 Automatic Deployment Write business logic as Java Web Service file (*.jws) Deploy SOURCE file into webapps directory of Axis server File name forms part of endpoint that axis server exposes as a Web Service: WSDL is automatically generated, as is the location Can also generate client stub classes (like GLUE) Cannot set deployment parameters though 26/41 Creating a Service Implement the service in a web service agnostic manner (as a regular class) 27/41 9

10 Deploying the Service In Axis you use a Web Service Deployment Descriptor (WSDD) to tell Axis how to route requests to the correct target class SmallCompanyImpl.wsdd 28/41 Starting the Axis Server Two options for running Axis: as a servlet from within a servlet engine (eg Tomcat): code in webapps/axis as a standalone server (for testing and simple applications only) Invoking the standalone server 29/41 Deploying the Service Make the service available to clients by deploying it using the AdminClient If deploying to the standalone Axis server, also supply the port number Now we are ready to invoke the service 30/41 10

11 Create the Client Again two options: Dynamic web service client: create a Call object for each method at runtime Static web service client: generate a proxy from a WSDL description First we will use the dynamic option Most interesting from the perspective of understanding low level operation 31/41 Client 32/41 Appendix This appendix collects information you may find useful setting up Apache Axis Apache Axis requires Tomcat (or other servlet container) 33/41 11

12 Tomcat Servlet container, provides reference implementation for Java Servlet and JavaServer pages technologies. Good release is Download and install Create start_tomcat, stop_tomcat shell scripts ==> 34/41 Startup script: Tomcat Scripts Shutdown script: 35/41 Configuring Tomcat Port Edit server.xml in $CATALINA_HOME/conf Change 8080 to required value 36/41 12

13 Axis Installation Download Apache Axis from website Latest stable v1 release is axis-1_4.zip Also have axis 2, supports SOAP 2, REST, Install in a directory and put the jar files in the axis/lib directory into your classpath Can also install in Eclipse by adding all jar files to the Eclipse project Should also set default output directory to put compiled classes into webapps/axis 37/41 Setting up Axis in Tomcat Axis as a servlet Install axis subdir. from dist n into tomcat webapps directory Set up classpath as shown in appendix Services classes in WEB-INF/classes 38/41 Axis is Running! After configuration, type 39/41 13

14 Setting up the Classpath 40/41 Axis User Guide 41/41 14