XML-RPC

The Quickest Way to Web Services

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XML-RPC

XML-RPC is an attempt to implement conventional Remote Procedure Call (RPC) concepts using XML to transmit the RPC information

Traffic on wire in XML format

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XML-RPC

You are specifying that a particular object method be called on a remote host with the arguments passed in, and a given return type.

There may be several types of method calls: blocking, non-blocking, fire-and-forget, etc.

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Implementations

There are several implementations out there (Userland, Sun, Apache).

Some implementations have extensions that make your life easier, but are non-standard.

http://ws.apache.org/xmlrpc/ for the apache implementation; I used 3.x

You’ll also need commons codec jar file in the classpath if building from scratch

See https://movesinstitute.org/~mcgredo/WebServices/rpcExample.tar.gz for a pre-packaged example

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Example

POST /RPC2 HTTP/1.0 User-Agent: Frontier/5.1.2 (WinNT) Host: betty.userland.com Content-Type: text/xml Content-length: 181

<?xml version="1.0"?> <methodCall> <methodName>Calculator.add</methodName> <params> <param> <value><i4>41</i4></value> </param> <param> <value><i4>17</i4></value> </param> </params> </methodCall>

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Apache XML-RPC

On the client side the code is relatively straightforward:

XmlRpcClientConfigImpl config = new XmlRpcClientConfigImpl(); XmlRpcClient client = new XmlRpcClient(); Object[] params = new Object[]{new Integer(1), new Integer(2)};System.out.println("preparing execute"); Integer result = (Integer) client.execute("Calculator.add", params);

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Server Side

The server side is trickier. There should be java object receiving messages, but how to do this?

The apache implementation uses a properties file and a default implementation of a class called XmlRpcServlet to do this

XmlRpcServlet handles decoding the XML and encoding the response back

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XmlRpcServlet

XmlRpcServlet

XML

Java Object

Some Method

ResponseXML Response

XMLRpcServlet is responsible for handling the conversion from and to XML, and calling the Java object that actuallyimplements the functionality

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XmlRpcServlet

XmlRpcServlet accepts the HTTP, extracts the XML, and converts the XML into what is necessary to call the method on the local object. It accepts the return value from the object, converts it into XML-RPC, and places it into an HTTP response

You don’t have to write any of this code

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XmlRpcServlet

To specify the object, you need to modify the xmlrpc-server-3.0.jar file.

• Extract the contents of the jar file in a temporary directory: jar -xvf xmlrpc-server-3.0.jar

• Add a file called XmlRpcServlet.properties in org/apache/xmlrpc/webserver

Contents are “objectName=fullyQualifiedClassName”• Repackage the jar file: “jar -cvf xmlrpc-server-3.0.jar

org”• Replace the old jar file with the new one

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Set up servlet

Deploying the servlet is a little tricky. The environment in which a servlet program lives is standardized

AppName WEB-INF web.xml (config file) classes (your classes) lib (supporting jar files)

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Web.xml

Contained inside of WEB-INF, describes the servlets, security, etc.

The example web.xml file works. It includes a subclass of XmlRpcServlet that adds logging capability

The ugly config stuff is done for you if you just use the example distribution

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Example

The example distribution includes an Ant file that • Generates a xmlRpcExample.war file in the dist

directory• Runs a client that connects to the servletTo deploy the servlet, remove the old copy from

the Tomcat webapps directory , copy dist/xmlRpcExmaple.war it to the Tomcat /webapps directory, and restart Tomcat

The war file will be automatically unpacked and the servlet started

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Data Types

You can pass Integer, Boolean, String, Double, Date, byte[], Map and Arrays of these

With enabledForExtensions switched on, you can pas Byte, Float, Long, XML DOM Node, Short, Serializable, BigDecimal, BigInteger, and Calendar objects

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Modifying

To modify the example to do what you want:• Unpack the xmlrpc-server-3.0.jar file• Modify XmlRpcServlet.properties file with object name

on the LHS and fully qualified class name on the RHS• Repackage the jar file and replace the old jar file• Implement the class with a no-args constructor and

public methods that take only legal data types• ant dist, copy war file to tomcat webapps directory,

stop and restart tomcat