BACKED UP MEMORIES

Invoking secured web services with WSO2 Mashup Server

2011-12-02T06:20:00.000-08:00

WSO2 Mashup Server is based on WSO2 Carbon Platform which is then built on top of Apache Axis2 engine. Apache Rampart is the security module of Axis2. It secures SOAP messages according to specifications in the WS-Security stack. When you create a complex mashup which invokes many enterprise level web services, then WS* security will be a key concern.

Using WSRequest hostobject of the Mashup Server, you can easily access web services secured with many security scenarios. You can either dynamically pick the policy from the service wsdl or set it manually.

In both cases, you can set all the rampart related configurations using a simple json object notation. In this post, I have described how you can use WSO2 Mashup Server to invoke secured services from a mashup.

All the samples described here can be deployed on WSO2 Mashup Server 2.3.3 or above which can be downloaded from here.

Structure of the Keystores

Lets consider an encryption scenario as below.

Request Flow

When, client invokes the service, it encrypt the payload using client’s private key. Then at the server, it should have client’s public key certificate in order to decrypt the payload.

Response Flow

When server sends back the response to the client, server uses its private key to encrypt the response. Then the client who invoked the secured service should have the public key certificate of the server to decrypt the response.

Likewise, depending on the security policies being used between client and server, it will need to have client’s public key certificate in at the server and server’s public key certificate at the client. But for several other scenarios, a trusted third party certificate might be used.

Anyway, we are going to have the following structure in our client and server keystore as it will be used to test all the scenarios available via Mashup Server’s management console.

client.jks (password - client)

alias	key
client	client's private key (password - client)
server	server's public key

server.jks (password - server)

alias	key
server	server's private key (password - server)
client	client's public key

Generating keystores

Please follow this post and create client.jks and server.jks with the structure
described above.

Creating a sample mashup to be used as the service

In this tutorial, I will use a simple mashup as the secured service. i.e A mashup which takes a string name as the input and responds a greeting for that name, will be created and deployed in WSO2 Mashup Server. Once we deployed any mashup in WSO2 Mashup Server, it will behave as any other Axis2 service. Then, we can easily do most of the administrative tasks we want using management console.

So, please create a mashup with the content below.

this.serviceName = "helloService";
    function sayHello(name) {
    return "Hello " + name "!";
}

Creating mashup client

Introduction to WSRequest Hostobject

The WSRequest object is similar to the XMLHTTPRequest object. Its usage typically involves specifying the endpoint address and setting up options on how to frame the message, invoking the operation with a specific XML payload, and then checking and extracting information from the result.

It can also be considered as the Javascript wrapper for Axis2 ServiceClient which allows to do web service invocation. So, in WSO2 Mashup Server, the Web Service client is WSRequest. You can invoke services either synchronously or asynchronous, send custom HTTP/SOAP headers and even secure services invocation from a mashup with the help of WSRequest Hostobject.

Following is the Javascript interface of the WSRequest Hostobject. For more information please refer this.

{
    property EventListener onreadystatechange;
    property unsigned short readyState;
    function void open ( object options | String httpMethod, String url [, boolean async [, String username[, String password]]]);
    function void send ( XML payload | XMLString payload ); // To be used when the open method of WSRequest is used
    function void openWSDL ( String wsdlURL, ?boolean async, [Object options,[QName serviceName, [String endpointName]]]);
    function void send ( String operationName | QName operationName, XML payload | XMLString payload ); //To be used when the openWSDL method of WSRequest is used
    readonly property String responseText;
    readonly property Document responseXML;
    readonly property XML responseE4X;
    readonly property WebServiceError error;
}

Invoking the sample Service

Here I will describe how you can use WSRequest Hostobject to invoke a web service. You can find more information about service invocation using WSRequest Hostobject at Mashup Server’s documentation pages. But it would be better to write the client mashup to work with a normal service before extending it to access a secured service.

Following code fragment will invoke the above deployed HelloService and return the response. In the following client, the payload has been hard coded for the simplicity.

function invokeService(){
    var client = new WSRequest();
    var options = new Array();
    options["useSOAP"] = 1.2;
    options["action"] = "urn:sayHello";

    var payload =
    <sayHello>
        <name>Ruchira</name>
    </sayHello>;

    var result;

    try {
        client.open(options,"http://localhost:9763/services/admin/helloService", false);
        client.send(payload);
        result = client.responseE4X;
    } catch (e) {
        system.log(e.toString(),"error");
        return e.toString();
    }
    return result;
}

Create a file named helloClient.js in repository/deployment/server/jsservice/admin directory and add the above code fragment. Once you invoke the "Tryit" page of the newly created service, you should get the "Hello Ruchira!" greeting from the service.

Once you succeed with the above step, you can move to the next step which secures the helloService and modifies helloClient to invoke the secured service.

Secure Services

Secured Web services can be categorized into following forms depending on the method they used.

HTTP Basic Auth

Your service might have been secured using HTTP Basic Authentication. In that case, you can simply pass the username and password into the open() method of WSRequest Hostobject and invoke the service.

WS-Security

In most of the Enterprise level use-cases, HTTP Basic Authentication might not be a good solution, then WS-Security comes into the picture. Using WS-Security, you can have a greater flexibility with your service security. So, most of the today’s services are based on WS-Security.

Likewise, a web service can be secured either with HTTP Basic Authentication or using WS-Security. WSRequest hostobject can be used to invoke services secured with any of the above methods.

Securing the mashup service

Uploading Keystore into WSO2 Mashup Server
1. Go to Configure > Keystores
2. Go through "Add New Key store" wizard and add the server.jks created above
Apply a security scenario using Management Console
1. Go to Main > Manage > Web Services > List
2. Select the above created service i.e. "helloService" and click on "Unsecured" link on the service listing
3. Go through the security engaging wizard and engage one of the scenarios listed there
View the WSDL
1. If you view the WSDL 1.0 or 2.0 of the service now, you will be able to see the newly applied policy in
  the WSDL.

Invoking secured service

WSRequest Hostobject offers two methods to deal with security. If you know the policy being used in the service, then you can use open() method and set the policy manually. If you don’t, then you can use openWSDL() method which will then extract the policy definition from the given WSDL and invoke the service. But performance wise, open() method is more better than openWSDL() as openWSDL method always read the WSDL before invoking the service.

open() method

Method signature is as bellow.

function void open ( object options | String httpMethod, String url [, boolean async [, String username[, String password]]])

When you use this method to invoke a secured service, then you have two options as below.

Specify policy definition with rampart configuration as an E4X XML object in the options object using "policy" property. You can also use ${resources.dir} to specify the path of the resources folder in keystore paths. i.e. Assume your keystore named client.jks is in *.resources folder, then you can use ${resources.dir}/client.jks as the keystore path in your rampart configuration.
Specify policy definition using "policy" property and rampart configuration as a JSON object using "rampart" property. The structure of the rampart configuration JSON has been described under the section named "Rampart
Configuration" below. Here, you don’t need to specify rampart configuration in policy definition.

In both cases, you can also keep the policy definition as a separate XML file within your resources folder and set it to "policy" property by creating an XML object with the help of File Hostobject.

If you are invoking an HTTP Basic Authentication enabled service, then just passing the username and password as method parameters would be sufficient and "policy" and "rampart" properties won’t need to be specified.

var options = new Object();
…..
options["policy"] =
<Policy>.....</Policy>;
options["rampart"] = { ….. };
…..
wsRequest.open(options, serviceUrl, false);

Please refer WSRequest documentation at [2] for more information about other input parameters and properties of the options object.

openWSDL() method

function void openWSDL ( String wsdlURL, ?boolean async, [Object options,[QName serviceName, [String endpointName]]]);

When openWSDL() method is used, you need to specify the URL of the secured service WSDL. Then it will read the WSDL and find the attached policy definitions from it. In this case, you only need to specify the "rampart" property in your options object.

Specifying "policy" property too, will override the policy definition extracted from the WSDL.

Rampart Configuration

Following is the format of the rampart configuration JSON. Dummy values and comments have been added to explain it more precisely.

{ 
    user : "admin", //username for to use UT and other scenarios
    userPassword : "admin", //in UT, this is the user password
    keyPassword : "client", //private key password
    userCertAlias : "client",
    stsAlias : "sts",
    encryptionUser : "server",
    timestampTTL : "10000",
    timestampMaxSkew : "10",
    timestampPrecisionInMilliseconds : "100",
    signatureCrypto : {
        type : "jks", //keystore type
        file : "client.jks", //keystore file relative to resource folder
        password : "client", //keystore password
        enableCryptoCaching : true,
        cacheRefreshInterval : 3000
    },
    encryptionCrypto : {
        type : "jks", //keystore type
        file : "client.jks", //keystore file relative to resource folder
        password : "client", //keystore password
        enableCryptoCaching : true,
        cacheRefreshInterval : 3000
    },
    decryptionCrypto : {
        type : "jks", //keystore type
        file : "client.jks", //keystore file relative to resource folder
        password : "client" //keystore password
    },
    stsCrypto : {
        type : "jks", //keystore type
        file : "client.jks", //keystore file relative to resource folder
        password : "client" //keystore password
    },
    kerberosConfig : {
        /**
        "key" : "value" properties, you can also use ${resources.dir}
        in property values
        */
        "client.principal.name" : "client",
        "client.principal.password" : "client",
        "service.principal.name" : "service",
        "java.security.auth.login.config" : "jassconfig",
        "javax.security.auth.useSubjectCredsOnly" : "true",
        "kdc.des.aes.factor" : "4",
        "java.security.krb5.conf" : "/home/ruchira/wso2/conf"
    }
}

Secure Client using Open() method
(you need to set the correct scenario xml there in the line number 6)

function invokeSecureServiceOpen() {
    /**
    * Reads the policy.xml from resources folder and creates
    * E4X XML object from it
    */
    var policyFile = new File("scenarios/scenario2-policy.xml");
    policyFile.openForReading();
    var policy = new XML(policyFile.readAll());

    var client = new WSRequest();
    var options = new Array();
    options["useSOAP"] = 1.2;
    options["action"] = "urn:sayHello";
    options["policy"] = policy;
    options["rampart"] = {
        user : "admin", //username for to use UT and other scenarios
        userPassword : "admin", //in UT, this is the user password
        keyPassword : "client", //private key password
        userCertAlias : "client",
        encryptionUser : "server",
        signatureCrypto : {
            type : "jks", //keystore type
            file : "client.jks", //keystore file relative to resource folder
            password : "client", //keystore password
            enableCryptoCaching : true,
            cacheRefreshInterval : 3000
        },
        encryptionCrypto : {
            type : "jks", //keystore type
            file : "client.jks", //keystore file relative to resource folder
            password : "client", //keystore password
            enableCryptoCaching : true,
            cacheRefreshInterval : 3000
        },
        decryptionCrypto : {
            type : "jks", //keystore type
            file : "client.jks", //keystore file relative to resource folder
            password : "client" //keystore password
        },
        stsCrypto : {
            type : "jks", //keystore type
            file : "client.jks", //keystore file relative to resource folder
            password : "client" //keystore password
        }
    };

    var payload =
    <sayHello>
        <name>Ruchira</name>
    </sayHello>;

    var result;

    try {
        client.open(options,"http://localhost:9763/services/admin/helloService", false);
        client.send(payload);
        result = version.responseE4X;
    } catch (e) {
        system.log(e.toString(),"error");
        return e.toString();
    }
    return result;
}

Secure Client using openWSDL() method

function invokeSecureServiceOpenWSDL() {
    var client = new WSRequest();
    var options = new Array();
    options["useSOAP"] = 1.2;
    options["action"] = "urn:sayHello";
    options["rampart"] = {
    user : "admin", //username for to use UT and other scenarios
    userPassword : "admin", //in UT, this is the user password, else private key
    keyPassword : "client", //private key password
    userCertAlias : "client",
    encryptionUser : "server",
    signatureCrypto : {
            type : "jks", //keystore type
            file : "client.jks", //keystore file relative to resource folder
            password : "client", //keystore password
            enableCryptoCaching : true,
            cacheRefreshInterval : 3000
        },
        encryptionCrypto : {
            type : "jks", //keystore type
            file : "client.jks", //keystore file relative to resource folder
            password : "client", //keystore password
            enableCryptoCaching : true,
            cacheRefreshInterval : 3000
        },
        decryptionCrypto : {
            type : "jks", //keystore type
            file : "client.jks", //keystore file relative to resource folder
            password : "client" //keystore password
        },
        stsCrypto : {
            type : "jks", //keystore type
            file : "client.jks", //keystore file relative to resource folder
            password : "client" //keystore password
        }
    };

    var payload =
    <sayHello>
        <name>Ruchira</name>
    </sayHello>;

    var result;

    try {
        var service = new QName("http://services.mashup.wso2.org/helloService","helloService");
        request.openWSDL("http://localhost:9763/services/admin/helloService?wsdl", false, options, service, "SOAP12Endpoint");
        request.send("sayHello", payload);
        result = version.responseE4X;
    } catch (e) {
        system.log(e.toString(),"error");
        return e.toString();
    }
    return result;
}

Testing the service

After successfully created the two operations with open and openWSDL methods, now you can invoke the client service using it’s tryit page which will then invoke the secured "helloService".

XML to JSON and JSON to XML Conversion in Javascript

2011-06-16T03:19:00.000-07:00

When we deal with today's highly ajax based web application developments, dealing with XMLs within your page might be a little bit tedious task. As all of us know, JavaScript doesn't have a proper way to deal with XMLs(although recent specs supports E4X, it hasn't implemented in all browsers). If we can convert the XML into a JSON format, then it will be a great relief for web developers.

Although there are many XML to JSON notations available, all of them tends to ignore xml namespaces, but Badgerfish. So, I thought of writing a JavaScript code which does the XML to JSON conversion and wise-versa. If you want to get the Javascript code for XML to JSON, then go though my blog post XML to BadgerFish Conversion in Javascript. In this post, I will give you the function which converts JSON back to it's original XML.

Using these xml2bf and bf2xml functions, you will get the most flexibility with XML in your web developments.

function bf2xml(json) {
    if (typeof json !== "object") return null;
    var cloneNS = function(ns) {
        var nns = {};
        for (var n in ns) {
            if (ns.hasOwnProperty(n)) {
                nns[n] = ns[n];
            }
        }
        return nns;
    };
    var processLeaf = function(lname, child, ns) {
        var body = "";
        if (child instanceof Array) {
            for (var i = 0; i < child.length; i++) {
                body += processLeaf(lname, child[i], cloneNS(ns));
            }
            return body;
        } else if (typeof child === "object") {
            var el = "<" + lname;
            var attributes = "";
            var text = "";
            if (child["@xmlns"]) {
                var xmlns = child["@xmlns"];
                for (var prefix in xmlns) {
                    if (xmlns.hasOwnProperty(prefix)) {
                        if (prefix === "$") {
                            if (ns[prefix] !== xmlns[prefix]) {
                                attributes += " " + "xmlns=\"" + xmlns[prefix] + "\"";
                                ns[prefix] = xmlns[prefix];
                            }
                        } else if (!ns[prefix] || (ns[prefix] !== xmlns[prefix])) {
                            attributes += " xmlns:" + prefix + "=\"" + xmlns[prefix] + "\"";
                            ns[prefix] = xmlns[prefix];
                        }
                    }
                }
            }
            for (var key in child) {
                if (child.hasOwnProperty(key) && key !== "@xmlns") {
                    var obj = child[key];
                    if (key === "$") {
                        text += obj;
                    } else if (key.indexOf("@") === 0) {
                        attributes += " " + key.substring(1) + "=\"" + obj + "\"";
                    } else {
                        body += processLeaf(key, obj, cloneNS(ns));
                    }
                }
            }
            body = text + body;
            return (body !== "") ? el + attributes + ">" + body + "</" + lname + ">" : el + attributes + "/>"
        }
    };
    for (var lname in json) {
        if (json.hasOwnProperty(lname) && lname.indexOf("@") == -1) {
            return processLeaf(lname, json[lname], {});
        }
    }
    return null;
}

How to increase JVM Heap Size and Perm Gen space

2011-04-28T06:35:00.000-07:00

If you are dealing with applications which have large code bases, then you might quickly run out of Java memory. Probably you might get either java.lang.OutOfMemoryError: PermGen or java.lang.OutOfMemoryError: Java heap space. In order to fix that, just having sufficient memory in your machine is not sufficient. So you need to increase the JVM Heap size and Permanent Generation space.

Setting the following environment variable before starting your application, you can increase them easily.

Unix

export JAVA_OPTS="-Xms512m -Xmx1024m -XX:MaxPermSize=1024m"

Windows

set JAVA_OPTS="-Xms512m -Xmx1024m -XX:MaxPermSize=1024m"

How to Remote Debug on Apache Tomcat

2011-04-28T06:28:00.000-07:00

If you want to debug on your application on Apache Tomcat, then you might need to set the following environment variables and start Tomcat using the command below where 8000 is the port that you are going to connect from your IDE.

Windows

set JPDA_ADDRESS=8000
set JPDA_TRANSPORT=dt_socket

bin/catalina.bat jpda start

Unix

export JPDA_ADDRESS=8000
export JPDA_TRANSPORT=dt_socket

bin/catalina.sh jpda start

Parse XML String into DOM with Javascript

2011-02-22T05:07:00.000-08:00

You can use following function to convert any XML string into a DOM object from a browser.

function parseXML(xml) {
    xml = xml.replace(/^[\s\n\r\t]*[<][\?][xml][^<^>]*[\?][>]/, "");
    var doc;
    if (window.ActiveXObject) {
        doc = new ActiveXObject("Microsoft.XMLDOM");
        doc.async = false;
        doc.loadXML(xml);
    } else
        doc = (new DOMParser()).parseFromString(xml, "application/xml");
    return doc;
}

Online XML to JSON Converter using Badgerfish Notation

2011-02-22T04:47:00.000-08:00

I have hosted an online XML to JSON converter at http://gogooog.com. It has been implemented purely with Javascript. You can read about the xml to badgerfish conversion at http://ruchirawageesha.blogspot.com/2011/01/xml-to-badgerfish-converter-in.html.

XML to BadgerFish Conversion in Javascript

2011-01-28T02:52:00.000-08:00

Recently I came across the need of converting an xml into a JSON format. There I used BadgerFish notation to transform the xml into JSON.

You can use following Javascript function to convert any DOM node into the relevant BadgerFish notation. You can convert any XML string into a DOM object using method described at Parse XML String into DOM with Javascript

Please find the hosted version of XML to Badgerfish converter at gogooog.com

function xml2bf(node) {
    var json = {};
    var cloneNS = function(ns) {
        var nns = {};
        for (var n in ns) {
            if (ns.hasOwnProperty(n)) {
                nns[n] = ns[n];
            }
        }
        return nns;
    };
    var process = function (node, obj, ns) {
        if (node.nodeType === 3) {
            if (!node.nodeValue.match(/[\S]+/)) return;
            if (obj["$"] instanceof Array) {
                obj["$"].push(node.nodeValue);
            } else if (obj["$"] instanceof Object) {
                obj["$"] = [obj["$"], node.nodeValue];
            } else {
                obj["$"] = node.nodeValue;
            }
        } else if (node.nodeType === 1) {
            var p = {};
            var nodeName = node.nodeName;
            for (var i = 0; node.attributes && i < node.attributes.length; i++) {
                var attr = node.attributes[i];
                var name = attr.nodeName;
                var value = attr.nodeValue;
                if (name === "xmlns") {
                    ns["$"] = value;
                } else if (name.indexOf("xmlns:") === 0) {
                    ns[name.substr(name.indexOf(":") + 1)] = value;
                } else {
                    p["@" + name] = value;
                }
            }
            for (var prefix in ns) {
                if (ns.hasOwnProperty(prefix)) {
                    p["@xmlns"] = p["@xmlns"] || {};
                    p["@xmlns"][prefix] = ns[prefix];
                }
            }
            if (obj[nodeName] instanceof Array) {
                obj[nodeName].push(p);
            } else if (obj[nodeName] instanceof Object) {
                obj[nodeName] = [obj[nodeName], p];
            } else {
                obj[nodeName] = p;
            }
            for (var j = 0; j < node.childNodes.length; j++) {
                process(node.childNodes[j], p, cloneNS(ns));
            }
        } else if (node.nodeType === 9) {
            for (var k = 0; k < node.childNodes.length; k++) {
                process(node.childNodes[k], obj, cloneNS(ns));
            }
        }
    };
    process(node, json, {});
    return json;
}

All about Javascript Functions

2011-01-26T22:00:00.000-08:00

If you're a Javascript fan, it's worth reading JavaScript, 5 ways to call a function which nicely explains must to know concepts behind Javascript functions.

How to build mod_v8 in Ubuntu

2010-10-02T21:32:00.000-07:00

mod_v8 is a simple Apache module which enable Server Side JavaScript(SSJS) support in Apache Server. It uses Google V8 engine for the JavaScript execution. What this module basically does is, it adds a Handler for a particular file extension(.v8) and then, those files are treated as SSJS files which then get executed via V8 engine.

While I was building this amazing mod_v8 module, I had to do small modification to the process. So I though it might be worth to have a post with the steps I followed.

1. Checkout V8 development branch

svn checkout http://v8.googlecode.com/svn/branches/bleeding_edge/ v8

2. Build V8 using scons with the library=shared option. Optionally you might need to add arch option too. You can find more info about it at Building V8 in Ubuntu 64 bit

scons library=shared arch=x64

3. Assuming your v8 checkout is at /home/wageesha/v8, building process will create following obj, libv8.so etc.. directories and files within v8 directory. You need to copy this libv8.so into /usr/lib.

cp ~/wageesha/v8/libv8.so /usr/lib

4. Checkout mod_v8 code

svn checkout https://svn.i-want-a-pony.com/repos/mod_v8/trunk/ mod_v8

5. Build mod_v8 using scons. Depending on your scons version, you might need to change

opts = Options('build.py') into opts = Variables('build.py')

and

opts.Add(PathOption(....)) into opts.Add(PathVariable(....))

in the SConstruct. Further, if you haven't copied libv8.so into the /usr/lib directory as in step 3, build process will fail saying

/usr/bin/ld: cannot find -lv8

6. Then open /etc/apache2/apache2.conf and add following lines, with the correct path to libmod_v8.so

LoadModule v8_module /home/wageesha/mod_v8/trunk/libmod_v8.so

<IfModule mod_v8.cpp>
#Adds the v8 handler
AddHandler v8-script .v8
</IfModule>

7. Copy /home/wageesha/mod_v8/trunk/test.v8 into /var/www folder.

8. Restart apache and access test.v8

http://localhost/test.v8

which will then print

Hello World!

in the browser.

Building V8 in Ubuntu 64 bit

2010-10-01T00:11:00.000-07:00

If you are trying to build Google V8 in a Ubuntu 64bit machine you might get

/usr/include/gnu/stubs.h:7:27: error: gnu/stubs-32.h: No such file or directory

error when you ran scons with default arguments. When default arguments are used, it tries to guess the OS. In my case it failed to detect the correct architecture (i.e. x64). So you can specify arch argument when you run the scons to manually set the architecture. i.e.

scons arch=x64

arch argument accepts any of arm, ia32, x64 or mips

JSON to XML and XML to JSON convertion using Javascript

2010-07-30T00:18:00.000-07:00

Following link will provide you a better implementation to convert JSON data into XML and vice versa just using Javascript.

http://goessner.net/download/prj/jsonxml/

Regular Expressions with Javascript

2010-07-29T22:42:00.000-07:00

Here is an excellent demonstration of Regular Expression usage in Javascript.

http://lawrence.ecorp.net/inet/samples/regexp-format.php

How to Create Client/Server Keystores using Java Keytool

2010-07-08T00:15:00.000-07:00

Here I have described how to create client/server keystores which can be used to secure Axsi2 webservices and invoke Axis2 secured webservices. i.e. It can be easily used with any WSO2 Product to experience security scenarios.More detailed explanation on creating client/server keystores using openssl including Certificate Authority(CA) Requests, can be found at http://wso2.org/library/174.

Java keytool stores the keys and certificates in a keystore, protected by a keystore password. Further, it protects private key again with another password. A Java keystore contains private-public key pair and multiple trusted certificate entries. All entries in a keystore are referred by aliases. Both private key and self signed public key is referred by one alias while any other trusted certificates are referred by different individual aliases.

As the first step, let's create a keystore for server. In order to do it, execute following command in a terminal. "server" in the following command corresponds to the private key/self signed public key certificate alias in the keystore while "server.jks" is the name of the creating keystore file.

keytool -genkey -alias server -keyalg RSA -keystore server.jks

when you execute the above command it will first prompt you to specify a password which is corresponded to the keystore password. Then it will prompt several questions. You can give answers that you wish. At the end it will ask for a password again, which will be used to secure the generated private key.

Enter keystore password:  
Re-enter new password: 
What is your first and last name?
[Unknown]:  Ruchira Wageesha
What is the name of your organizational unit?
[Unknown]:  Mashup Server
What is the name of your organization?
[Unknown]:  WSO2
What is the name of your City or Locality?
[Unknown]:  Ahangama
What is the name of your State or Province?
[Unknown]:  Southern
What is the two-letter country code for this unit?
[Unknown]:  LK
Is CN=Ruchira Wageesha, OU=Mashup Server, O=WSO2, L=Ahangama, ST=Southern, C=LK correct?
[no]: yes
Enter key password for 
(RETURN if same as keystore password):

Once you successfully completed this, java keytool will create a file named "server.jks". In the same way, you can create a client keystore named "client.jks" with the alias "client" using following command.

keytool -genkey -alias client -keyalg RSA -keystore client.jks

Now, you have two files named client.jks and server.jks. You can view the content of these keystore files using the following command. Replacess "ruchira" with the keystore password you entered while creating the keystore.

keytool -list -v -keystore server.jks -storepass ruchira

This will list something like this.

Keystore type: JKS
Keystore provider: SUN

Your keystore contains 1 entry

Alias name: server
Creation date: Jul 8, 2010
Entry type: PrivateKeyEntry
Certificate chain length: 1
Certificate[1]:
Owner: CN=Ruchira Wageesha, OU=Mashup Server, O=WSO2, L=Ahangama, ST=Southern, C=LK
Issuer: CN=Ruchira Wageesha, OU=Mashup Server, O=WSO2, L=Ahangama, ST=Southern, C=LK
Serial number: 4c356225
Valid from: Thu Jul 08 10:59:09 IST 2010 until: Wed Oct 06 10:59:09 IST 2010
Certificate fingerprints:
MD5:  60:0B:48:0D:DB:56:8C:68:8C:2D:94:4A:D6:DA:04:B8
SHA1: A7:CE:57:10:70:87:C1:2C:C0:9D:1D:90:8C:BB:69:B6:66:26:97:13
Signature algorithm name: SHA1withRSA
Version: 3


*******************************************
*******************************************

The next step is, getting server's self signed public key certificate and storing it in client's keystore. And getting and storing client's self signed public key certificate in server's keystore. In order to do that, first we need to export both server and client public key certificates into files. Using the following command, you can export server's public key certificate into server.cert file and client's public key certificate into client.cert file.

keytool -export -file server.cert -keystore server.jks -storepass ruchira -alias server
keytool -export -file client.cert -keystore client.jks -storepass ruchira -alias client

Now you have server.cert and client.cert. You can use following commands to view certificate contents.

keytool -printcert -v -file server.cert
keytool -printcert -v -file client.cert

As the last step, we need to import server.cert into client keystore and client.cert into server keystore. As I mentioned earlier, each entry of a Java Keystore is stored against an alias. So, we need to specify aliases here, which will be used to refer the certificates that we are going to store.

keytool -import -file client.cert -keystore server.jks -storepass ruchira -alias client

Above command will store client's self signed public key certificate(client.cert) in server.jks against the alias "client". So, using "client" alias on server.jks, we can refer client's certificate anytime. Likewise, following command will store server.cert within client.jks against the alias "server".

keytool -import -file server.cert -keystore client.jks -storepass ruchira -alias server

After all, please view the content of both keystore again using following commands.

keytool -list -v -keystore server.jks -storepass ruchira
keytool -list -v -keystore client.jks -storepass ruchira

It will give you something like bellow for server.jks

Keystore type: JKS
Keystore provider: SUN

Your keystore contains 2 entries

Alias name: server
Creation date: Jul 8, 2010
Entry type: PrivateKeyEntry
Certificate chain length: 1
Certificate[1]:
Owner: CN=Ruchira Wageesha, OU=Mashup Server, O=WSO2, L=Ahangama, ST=Southern, C=LK
Issuer: CN=Ruchira Wageesha, OU=Mashup Server, O=WSO2, L=Ahangama, ST=Southern, C=LK
Serial number: 4c3562a0
Valid from: Thu Jul 08 11:01:12 IST 2010 until: Wed Oct 06 11:01:12 IST 2010
Certificate fingerprints:
MD5:  AB:77:72:F1:0D:09:55:E3:B6:D3:DC:A6:4D:D4:39:36
SHA1: D7:C1:60:5C:7E:34:40:A9:0B:E4:2C:65:6C:E0:79:7C:EE:37:A7:19
Signature algorithm name: SHA1withRSA
Version: 3


*******************************************
*******************************************


Alias name: client
Creation date: Jul 8, 2010
Entry type: trustedCertEntry

Owner: CN=Ruchira Wageesha, OU=Mashup Server, O=WSO2, L=Ahangama, ST=Southern, C=LK
Issuer: CN=Ruchira Wageesha, OU=Mashup Server, O=WSO2, L=Ahangama, ST=Southern, C=LK
Serial number: 4c356225
Valid from: Thu Jul 08 10:59:09 IST 2010 until: Wed Oct 06 10:59:09 IST 2010
Certificate fingerprints:
MD5:  60:0B:48:0D:DB:56:8C:68:8C:2D:94:4A:D6:DA:04:B8
SHA1: A7:CE:57:10:70:87:C1:2C:C0:9D:1D:90:8C:BB:69:B6:66:26:97:13
Signature algorithm name: SHA1withRSA
Version: 3


*******************************************
*******************************************

something like below for client.jks

Keystore type: JKS
Keystore provider: SUN

Your keystore contains 2 entries

Alias name: server
Creation date: Jul 8, 2010
Entry type: trustedCertEntry

Owner: CN=Ruchira Wageesha, OU=Mashup Server, O=WSO2, L=Ahangama, ST=Southern, C=LK
Issuer: CN=Ruchira Wageesha, OU=Mashup Server, O=WSO2, L=Ahangama, ST=Southern, C=LK
Serial number: 4c3562a0
Valid from: Thu Jul 08 11:01:12 IST 2010 until: Wed Oct 06 11:01:12 IST 2010
Certificate fingerprints:
MD5:  AB:77:72:F1:0D:09:55:E3:B6:D3:DC:A6:4D:D4:39:36
SHA1: D7:C1:60:5C:7E:34:40:A9:0B:E4:2C:65:6C:E0:79:7C:EE:37:A7:19
Signature algorithm name: SHA1withRSA
Version: 3


*******************************************
*******************************************


Alias name: client
Creation date: Jul 8, 2010
Entry type: PrivateKeyEntry
Certificate chain length: 1
Certificate[1]:
Owner: CN=Ruchira Wageesha, OU=Mashup Server, O=WSO2, L=Ahangama, ST=Southern, C=LK
Issuer: CN=Ruchira Wageesha, OU=Mashup Server, O=WSO2, L=Ahangama, ST=Southern, C=LK
Serial number: 4c356225
Valid from: Thu Jul 08 10:59:09 IST 2010 until: Wed Oct 06 10:59:09 IST 2010
Certificate fingerprints:
MD5:  60:0B:48:0D:DB:56:8C:68:8C:2D:94:4A:D6:DA:04:B8
SHA1: A7:CE:57:10:70:87:C1:2C:C0:9D:1D:90:8C:BB:69:B6:66:26:97:13
Signature algorithm name: SHA1withRSA
Version: 3


*******************************************
*******************************************

If everything went well, you might have successfully created server.jks and client.jks which can be used to secure Axis2 Services and access those secured services.

Java Keytool Keystore Commands

2010-07-07T22:50:00.000-07:00

Create Keystore, Keys and Certificate Requests

Generate a Java keystore and key pair

keytool -genkey -alias mydomain -keyalg RSA -keystore keystore.jks -storepass password

Generate a certificate signing request (CSR) for an existing Java keystore

keytool -certreq -alias mydomain -keystore keystore.jks -storepass password -file mydomain.csr

Generate a keystore and self-signed certificate

keytool -genkey -keyalg RSA -alias selfsigned -keystore keystore.jks -storepass password -validity 360

Import Certificates

Import a root or intermediate CA certificate to an existing Java keystore

keytool -import -trustcacerts -alias root -file Thawte.crt -keystore keystore.jks -storepass password

Import a signed primary certificate to an existing Java keystore

keytool -import -trustcacerts -alias mydomain -file mydomain.crt -keystore keystore.jks -storepass password

Import New CA into Trusted Certs

keytool -import -trustcacerts -file /path/to/ca/ca.pem -alias CA_ALIAS -keystore $JAVA_HOME/jre/lib/security/cacerts

Export Certificates

Export a certificate from a keystore

keytool -export -alias mydomain -file mydomain.crt -keystore keystore.jks -storepass password

Check/List/View

Check a stand-alone certificate

keytool -printcert -v -file mydomain.crt

Check which certificates are in a Java keystore

keytool -list -v -keystore keystore.jks -storepass password

Check a particular keystore entry using an alias

keytool -list -v -keystore keystore.jks -storepass password -alias mydomain

List Trusted CA Certs

keytool -list -v -keystore $JAVA_HOME/jre/lib/security/cacerts

Delete Certificates

Delete a certificate from a Java Keytool keystore

keytool -delete -alias mydomain -keystore keystore.jks -storepass password

Change Passwords

Change a Java keystore password

keytool -storepasswd -new new_storepass -keystore keystore.jks -storepass password

Change a private key password

keytool -keypasswd -alias client -keypass old_password -new new_password -keystore client.jks -storepass password

Ubuntu - Copy Everything Except

2010-06-18T02:11:00.000-07:00

If you want to copy everything within a directory, except certain files or directories, you can use the following command.

cp -a `ls | grep -v yourexcludepattern` ../destinationdir/

Assume, you want to copy all files, except *.java within from the current directory to the foo directory. Then, the command would be,

cp -a `ls | grep -v *.java` /home/wageesha/foo

How to copy a file into multiple directories in Ubuntu

2010-06-11T00:44:00.000-07:00

Assume that you want to copy a file into multiple directories in the current directory, then all you have to do is, just entering following command in the terminal. Here, file.txt will be copied into all directories in the current directory. In case of a directory coping, replace file.txt with -rf [your dir].

for dir in *; do [ -d "$dir" ] && cp file.txt "$dir" ; done

for dir in *; do [ -d "$dir" ] && cp -rf /home/wageesha/images "$dir" ; done

WSO2 Stratos is LIVE

2010-06-01T08:43:00.000-07:00

WSO2 Stratos Alpha1 is live. You can register for any of the following WSO2 Cloud Services at http://cloud.wso2.com.

Mashup Server
Gadget Server
Application Server
Identity Server
Governance
BAM

WSO2 Mashup Server - Google Maps API Key Mashup

2010-05-23T09:18:00.000-07:00

If you are using Google Maps in your web site, you need to get an API key from Google.com. In order to do that, you need to login using an existing Google account, accept their terms and policies and finally you will be able to get the Google Maps API key. Although this is the usual procedure, if they provide a web service for it, it will be much useful in places where you want to get the key at runtime.

As an example, WSO2 Mashup Server has a Twitter Maps Mashup which shows recent tweets in a Google map. In order to have the proper functionality of this mashup independent of the domain where the server is running, it needs to dynamically generate an API key for that domain and use it within the Twitter map mashup. That was the original motivation towards this mashup.

You will need to deploy the following mashup in the WSO2 Mashup Server 2.0.2 or a newer one.

getAPIKey.inputTypes = { "username" : "string", "password" : "string", "url" : "string" };
getAPIKey.output = "string";
function getAPIKey(username, password, url) {
    var client = new HttpClient();
    var code = client.executeMethod("GET", "https://www.google.com/accounts/Login");
    if (code == 200) {
        var galx = client.cookies[0].value;
        var content = [
            { name : "Email", value : username },
            { name : "Passwd", value : password },
            { name : "signIn", value : "Sign in" },
            { name : "GALX", value : String(galx) },
            { name : "dsh", value : "5537526595243201224"},
            { name : "rmShown", value : "1"},
            { name : "PersistentCookie", value : "yes"}
        ];
        code = client.executeMethod("POST", "https://www.google.com/accounts/LoginAuth", content);
        if (code == 302 || code == 200) {
            code = client.executeMethod("GET", "http://code.google.com/apis/maps/signup/createkey", [
                { name : "referer", value : url }
            ]);
            if (code == 200) {
                var response = eval('(' + client.response + ')');
                client.releaseConnection();
                return response.generated_key;
            } else {
                client.releaseConnection();
                return new XML("" + code + "" + client.statusText + "");
            }
        } else {
            client.releaseConnection();
            return new XML("" + code + "" + client.statusText + "");
        }
    } else {
        client.releaseConnection();
        return new XML("" + code + "" + client.statusText + "");
    }
}

Subversion: How to revert to a previous revision

2010-04-23T02:34:00.000-07:00

Assume that your current revision is 100 and you want to revert the repository to the revision 90. Then you can use the following command,

$ svn merge -rHEAD:90 .

As you have used . at the end, it will revert your local repository. Once commited you will get a new revision such as 101 which is same as revision 90. You can do this directly to a remote repository as well. In that case, replace . with repository url.

GCE O/L, A/L and Grade V Examination Results

2010-04-07T21:09:00.000-07:00

Do you want to view O/L, A/L and Grade V results a bit earlier than http://www.doenets.lk lets us. I have tried it when it says, "New Await Results". You can do this using firebug addon on firefox.

www.doenets.lk lets us to check previous result too. These are displayed by the "New Await Results" table. So what you need to do is first select one of those forms and change action url to exam_OL.jsp, exam_AL.jsp or exam_GV.jsp as appropriate. You would also need to change the size/maxLength of the inputput field as well. Otherwise it won't let us to insert our full index number. That's all, fill it with your index number, submit and get your results. You can also do a http POST using your own form as well.

Attention : I am not responsible for the accuracy of results as www.doenets.lk might not have officialy released the results when you use this.

How to enable mod rewrite on Apache

2010-03-21T09:40:00.000-07:00

Tired up trying to enable mode rewrite on apache? Try this link which explains it quite well.
http://drupal.org/node/134439

Serialize Javascript to PHP

2009-12-06T03:37:00.000-08:00

When interacting Javascript with PHP, you might need to serialise any Javascript data type into the PHP serialized format, where it can be unserialized using PHP. The following function will serialize any Javascript data.

function serialize(mixed_value) {
    var _getType = function(inp) {
        var type = typeof inp, match;
        var key;
        if (type == 'object' && !inp) {
            return 'null';
        }
        if (type == "object") {
            if (!inp.constructor) {
                return 'object';
            }
            var cons = inp.constructor.toString();
            match = cons.match(/(\w+)\(/);
            if (match) {
                cons = match[1].toLowerCase();
            }
            var types = ["boolean", "number", "string", "array"];
            for (key in types) {
                if (cons == types[key]) {
                    type = types[key];
                    break;
                }
            }
        }
        return type;
    };
    var type = _getType(mixed_value);
    var val, ktype = '';

    switch (type) {
        case "function":
            val = "";
            break;
        case "null":
        case "undefined":
            val = "N";
            break;
        case "boolean":
            val = "b:" + (mixed_value ? "1" : "0");
            break;
        case "number":
            val = (Math.round(mixed_value) == mixed_value ? "i" : "d") + ":" + mixed_value;
            break;
        case "string":
            val = "s:" + mixed_value.length + ":\"" + mixed_value + "\"";
            break;
        case "array":
        case "object":
            val = "a";
            var count = 0;
            var vals = "";
            var okey;
            var key;
            for (key in mixed_value) {
                ktype = _getType(mixed_value[key]);
                if (ktype == "function") {
                    continue;
                }

                okey = (key.match(/^[0-9]+$/) ? parseInt(key, 10) : key);
                vals += serialize(okey) +
                        serialize(mixed_value[key]);
                count++;
            }
            val += ":" + count + ":{" + vals + "}";
            break;
    }
    if (type != "object" && type != "array") {
        val += ";";
    }
    return val;
}

The code fragment below will do the serializing in Javascript and the later code will unserialize it in PHP.

var array = ["ruchira", "wageesha"];
//serialize value
var serialize_array = serialize(array);

$array = unserialize($_POST['array']);

Javascript Popup - close after redirect

2009-09-11T13:12:00.000-07:00

If you want to redirect the popup window to another location (a page or a file download) and then close the window, you can simply use the following javascript.

<script type="text/javascript">
    window.opener.location = "new_page.htm";
    window.close();
</script>

Find and Replace using grep and sed

2009-08-30T11:40:00.000-07:00

Following command finds all the occurences of <br> in all .xml files in the current directory, and replace those <br> with <br/> . Please note that < and > have been surrounded with [ and ] in the sed command. / in the <br/> tag has been escaped using \. If you want to replace foo with bar, then you can just use those words.

find . -iname "*.xml" | xargs grep -l "<br>" | xargs sed -i -e 's/[<]br[>]/<br\/>/g'

find . -iname "*.xml" | xargs grep -l "<br>" | xargs sed -i -e 's/foo/bar/g'

A more general form of the expression would be

find . \( -name "*.php" -or -name "*.html" \) | xargs grep -l 'TEXT TO SEARCH' | xargs sed -i -e 's/TEXT TO REPLACE/REPLACEMENT STRING/g'

Rename Files with find command in linux

2009-08-27T11:58:00.000-07:00

If you want to rename files recusivelly using linux find command, here are two example usage of it with exec and xargs. This command will convert all the *.xml files into *.html files.

Using xags

find . | xargs rename 's/\.xml$/\.html/i'

Using exec

find . -exec rename 's/\.xml$/\.html/i' {} +

Above commands recurrsively replace files within inner directories too. If you want to do it for current directory only you can use -prune.
i.e

find . -prune | xargs rename 's/\.xml$/\.html/i'

find . -prune -exec rename 's/\.xml$/\.html/i' {} +

Multiple Joins on the same table

2009-08-10T12:44:00.000-07:00

Here are few example queries which shows how to use multiple inner joins with sql.

SELECT Fruit1, F1FruitName = F1.FruitName, F1FruitCost = F1.FruitCost,
Fruit2, F2FruitName = F2.FruitName, F2FruitCost = F2.FruitCost
FROM T1
JOIN T2 F1 ON Fruit1 = F1.Fruit_ID
JOIN T2 F2 ON Fruit2 = F2.Fruit_ID

If you want each fruit on it's on line(Record set), then it looks like

SELECT UserID, Fruit1 AS FruitID, FruitName, FruitCost
FROM T1
JOIN T2 ON Fruit1 = Fruit_ID
UNION
SELECT UserID, Fruit2 AS FruitID, FruitName, FruitCost
FROM T1
JOIN T2 ON Fruit2 = Fruit_ID

Here is two equivalent queries where one of them uses join and other doesn't.

SELECT codice, 
other1.value AS value_one, 
other2.value AS value_two
FROM main
LEFT OUTER JOIN other as other1 ON (main.id = other1.id_main AND type = 'type_one')
LEFT OUTER JOIN other as other2 ON (main.id = other2.id_main AND type = 'type_two)

is equivalent to

SELECT codice,
(SELECT value FROM other WHERE id_main = id AND type = 'type_one') AS value_one,
(SELECT value FROM other WHERE id_main = id AND type = 'type_two') AS value_two
FROM codice

Query below will give you a clear idea about how to use mutliple joins in the same query. Hope this will help you to understand the usage.

SELECT u1.displayname AS Player1
, u2.displayname AS Player2
, u3.displayname AS Player3
, u4.displayname AS Player4
, u5.displayname AS Player5
, u6.displayname AS Player6
FROM (
(
(
(
(
DCMLeagues AS L
INNER 
JOIN Users AS u1 
ON u1.userid = L.player1
)
INNER 
JOIN Users AS u2
ON u2.userid = L.player2
)
INNER 
JOIN Users AS u3 
ON u3.userid = L.player3
)
INNER 
JOIN Users AS u4 
ON u4.userid = L.player4
)
INNER 
JOIN Users AS u5 
ON u5.userid = L.player5
)
INNER 
JOIN Users as u6 
ON u6.userid = L.player6

find command - search content of a file

2009-06-25T02:06:00.000-07:00

find in Unix is a very powerful tool for users which give you a very good flexibility. find command has a very broad usage among users. Here is the way how you can use find command to search files and content within files.

In order to search for a particular file named "test.txt" in /home directory, use

find /home -name "test.txt" -print

Search all the .txt files in /home directory, use

find /home -name "*.txt" -print

if you want to search for a string through all the files .txt files, there are two ways

find /home -name "*.txt" -exec grep -q "string-to-be-searched" '{}' \; -print

find /home -name "*.txt" | xargs grep "string-to-be-searched"

second one is more fast and efficient. Removal of -q in the first command will output the text segment where the specified string is. If you want to search all files for the string, just remove -name "*txt" option.

How to Increase JVM(Java) Heap Size

2009-06-25T01:52:00.000-07:00

If you're building a big project using ant/maven then your jvm heap size may not sufficient and give you a java.lang.OutOfMemoryError: PermGen space exception. Increasing of maven/ant heap size might not sufficient enough for that and an increase of jvm heap size might also needed. When you're starting an application through command line, you can do it by specifying

java -Xms32m -Xmx128m your_application

it will be a temporary increase of heap size and if you want to increase it permanently set the following environment variable as needed.

export _JAVA_OPTIONS="-Xms64m -Xmx128m"

-Xms64m is the startup size(64MB) and -Xmx128m is the maximum size(128MB)

PNG Tranparency in IE6

2009-05-25T18:34:00.000-07:00

1 . First Download this Zip file and unzip

2 . Copy and paste iepngfix.htc and blank.gif into your website folder.

3 . Copy and paste this into your website's CSS or HTML:

<style type="text/css">
    img, div { behavior: url(iepngfix.htc) }
</style>

That CSS selector must include the tags/elements on which you want PNG support -- basically, give it a comma-separated list of tags you use. It must also include the correct path to the .HTC relative to the HTML document location (not relative to the CSS document!). For instance, yours may look like this:

<style type="text/css">
    img, div, a, input { behavior: url(/css/resources/iepngfix.htc) }
</style>

4 . If your site uses subfolders, open the .HTC file in a text editor like Windows Notepad and change the blankImg variable to include a correct path to blank.gif like so:

IEPNGFix.blankImg = '/images/blank.gif';

Again the path is relative to the HTML file. Otherwise, you will see a "broken image" graphic!

5 . If you want support for CSS1 background-repeat and background-position, make sure you include the add-on .JS file in your <head>:

<script type="text/javascript" src="iepngfix_tilebg.js"></script>

Otherwise, background images will work but won't repeat or position.

You can view two other methods at
http://jquery.andreaseberhard.de/pngFix/
http://koivi.com/ie-png-transparency/

Add, Multiply, Divide Numbers in Fractional Format

2009-01-10T01:11:00.000-08:00

Here is a way to do fractional calculations in Java. This might be useful when you want to get the exact values for some arithmetic operations like division. You can keep the result as a fractional number and to the operations what ever you like. i.e. add, subtract, multiply and divide.

Here are two classes named Fraction.java and Util.java. As an example you can create the fractional number 7/8 using the constructor Fraction("8", "7"). There are many other constructors too in the Fraction class. If you want to get 10 as a fractional number, i.e. 10/1, you can use the contructor new Fraction("10").

In order to add two fractional numbers a and b, you can use Util.add(a, b) method. Likewise you can to subtraction, multiplication and division. Please refer the code, it might be useful to understand the usage.

Fraction.java

public class Fraction {
   
    private Long denominator;
    private Long numerator;
    /** Creates a new instance of Fraction */
    public Fraction(String denominator, String numerator) {
        this(new Long(denominator), new Long(numerator));
    }
   
    public Fraction(Long denominator, Long numerator) {
        long gcd = Util.gcd(denominator, numerator);       
        this.denominator = denominator / gcd;
        this.numerator = numerator /gcd;
    }
   
    public Fraction(String number) {
        this.denominator = new Long("1");
        this.numerator = new Long(number);
    }
   
    public Fraction(long number) {
        this.denominator = new Long("1");
        this.numerator = new Long(number);
    }

    public Long getDenominator() {
        return denominator;
    }

    public Long getNumerator() {
        return numerator;
    }
}

Util.java

public class Util {
   
    /** Creates a new instance of Util */
    public Util() {
    }
  
    public static long gcd(Long a, Long b) {      
        if (b==0)
            return a;
        else
            return gcd(b, a % b);
    }
   
    public static long lcm(Long a, Long b) {
        return (a/gcd(a, b))*b;
    }
   
    // (a + b)
    public static Fraction add(Fraction a, Fraction b) {
       
        Long denominator = lcm(a.getDenominator(), b.getDenominator());
        Long numerator = a.getNumerator()*(denominator/a.getDenominator()) +
                b.getNumerator()*(denominator/b.getDenominator());
        return new Fraction(denominator, numerator);
    }
   
    // (a - b)
    public static Fraction substract(Fraction a, Fraction b) {
       
        Long denominator = lcm(a.getDenominator(), b.getDenominator());
        Long numerator = a.getNumerator()*(denominator/a.getDenominator()) -
                b.getNumerator()*(denominator/b.getDenominator());
        return new Fraction(denominator, numerator);
    }
   
    // (a * b)
    public static Fraction multiply(Fraction a, Fraction b) {
        return new Fraction(a.getDenominator() * b.getDenominator(), a.getNumerator() * b.getNumerator());
    }
   
    // (a / b)
    public static Fraction divide(Fraction a, Fraction b) {
        return new Fraction(a.getDenominator() * b.getNumerator(), a.getNumerator() * b.getDenominator());
    }
   
}

How to find gcd and lcm in Java

2009-01-10T00:11:00.000-08:00

Here is the easiest and efficient way to get the Greatest Common Divisor(gcd) and Least Common Multiple(lcm) in Java. This algorithm could be used for any language. Here I have used Long data type. You can use integer as needed.

public static long gcd(long a, long b) {      
    if (b==0)
        return a;
    else
        return gcd(b, a % b);
}

public static long lcm(long a, long b) {
    return (a / gcd(a, b)) * b;
}