Feature flags

*Turn feature up or down live by using feature flag also known as feature flipping or feature toggle

Inspired by Flickr and Launchpad.
The main goal is to decouple code delivery in production from feature activation.

See the demo

Requirements

• Java SE 5 (for enum)
• slf4j 1.6.1 (for logging)
• Servlet API 2.4

Features

• Flag created and used as enum
• RESTful API
• HTML Dashboard
• Manage different state per user or user group (since 1.1.0)
• Persist flags state in case of reboot (since 1.2.0)

Roadmap

• Distribute flags state across servers
• Manage different state per server
• ...

How To Use

First: dependencies
Add feature flag jar and dependencies to your classpath

• featureflags-1.2.2.jar (Use "save link as")
• slf4-api-1.6.1.jar
• slf4-simple-1.6.1.jar

Second: create a FeatureFlags enum
Create an enum like the one below to host all your feature flags.

package org.featureflags.demo;

import org.featureflags.FeatureFlags;
import org.featureflags.FlagManager.FlagState;

public enum Flags implements FeatureFlags {

	//Create your own feature flags
    ONE("First Feature Flag"),
    TWO("Second Feature Flag", FlagState.UP),
    THREE("Third Feature Flag");
    
    //Don't change anything below
    private String description;
    private static FlagManager flagManager;
    
    private Flags(String description) {
	this(description, FlagState.DOWN);
    }

    private Flags(String description, FlagState flagState) {
	initFlag(description, flagState);
    }

    public void initFlag(String description, FlagState flagState) {
	this.description = description;
	flagManager = FlagManager.get(this.getClass());
	flagManager.setFlagStateTo(this, flagState);
    }
    
    public boolean isUp() {
	    return flagManager.isUp(this);
    }

    public String getDescription() {
        return description;
    }
    
}

Third: Use Feature Flags in your code

if(Flags.ONE.isUp()) { 
	// Do the new stuff
} else {
	// Keep doing the old stuff
}

Fourth: Configure FeatureFlag servlet

Add this to your web.xml (replace filter-class and param-value with your own)

	<servlet>
		<servlet-name>featureFlags</servlet-name>
		<servlet-class>org.featureflags.FlagServlet</servlet-class>
		<init-param>
			<param-name>featureFlagsClassName</param-name>
			<param-value>org.featureflags.demo.Flags</param-value>
			<description>Full class name of your Feature flags class. REQUIRED</description>
		</init-param>
	</servlet>

	<servlet-mapping>
		<servlet-name>featureFlags</servlet-name>
		<url-pattern>/flags/*</url-pattern>
	</servlet-mapping>

Optional: add a servlet filter to enable flag per user/group

Create a servletFilter:

public class FeatureFlagFilter implements Filter {

    private FlagManager flagManager;
    
    public void init(FilterConfig filterConfig) throws ServletException {
		String featureFlagsClassName = filterConfig.getInitParameter("featureFlagsClassName");
		flagManager = FlagManager.get(featureFlagsClassName);
    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		// Replace this your code to get the current user or user group name
		String username = request.getParameter("username");
		flagManager.setThreadUserName(username);
		chain.doFilter(request, response);
		flagManager.resetThreadUserName();

    }

    public void destroy() {
    }

}

Add this to your web.xml (replace filter-class and param-value with your own)

<filter>
	<filter-name>featureFlagsFilter</filter-name>
	<filter-class>org.featureflags.demo.FeatureFlagFilter</filter-class>
	<init-param>
		<param-name>featureFlagsClassName</param-name>
		<param-value>org.featureflags.demo.Flags</param-value>
		<description>Full class name of your Feature flags class. REQUIRED</description>
	</init-param>
</filter>

<filter-mapping>
	<filter-name>featureFlagsFilter</filter-name>
	<url-pattern>/*</url-pattern>
</filter-mapping>