Java SDK reference

note

This SDK works with Harness Self-Managed Enterprise Edition (on premises).

This topic describes how to use the Harness Feature Flags Java SDK for your Java application.

For getting started quickly, you can use our sample code from the Java SDK README. You can also clone and run a sample application from the Java SDK GitHub Repository.

Before you begin

Make sure you read and understand:

• Feature Flags Overview
• Getting Started with Feature Flags
• Client-Side and Server-Side SDKs
• Communication Strategy Between SDKs and Harness Feature Flags

Version

Latest SDK version can be found on GitHub Release Page

Requirements

To use this SDK, make sure you:  

• Install JDK 8 or a newer version
• Install Maven, Gradle or an alternative build automation tool for your application
• Download the SDK from our GitHub repository
• Create a Java application, or clone our sample application.
• Create a Feature Flag on the Harness Platform. If you are following along with the SDK README sample code, make sure your flag is called harnessappdemodarkmode.
• Create an SDK key and make a copy of it

Install the SDK

Install the Feature Flag SDK as a dependency in your application using your application's dependency manager. You can use Maven, Gradle, SBT, etc. for your application. 

Below are the dependencies for Maven and Gradle that use Java SDK version 1.1.10 as an example:

Install using Maven

Add the following dependency in your project's pom.xml file:

<dependency>  
    <groupId>io.harness</groupId>  
    <artifactId>ff-java-server-sdk</artifactId>  
    <version>1.3.1</version>
</dependency>

If you are using the Harness Java sample application from the Java SDK GitHub repository, do not add the Maven dependency in the pom.xml file as it has already been added.

Install using Gradle

implementation group: 'io.harness', name: 'ff-java-server-sdk', version: '1.3.1'

Initialize the SDK

To initialize the Java SDK, you need to:

1. Add your Server SDK key to connect to your Harness Environment.
2. Add a Target that you want to Evaluate against a Feature Flag.
3. Configure the SDK options, if needed. For more details on what features you can configure for this SDK, go to Configure the SDK.
4. Complete the initialization with the SDK using the Server SDK Key, Target, and Configuration parameters you set.

Add the Server SDK Key

After installing the SDK, you must enter the server SDK key that you created in the Harness platform into the apiKey field, for example:

String apiKey = System.getProperty("FF_API_KEY", "<default api key>");

 

Add a Target

Details

What is a Target?

Targets are used to control which users see which Variation of a Feature Flag, for example, if you want to do internal testing, you can enable the Flag for some users and not others. When creating a Target, you give it a name and a unique identifier. Often Targets are users but you can create a Target from anything that can be uniquely identified, such as an app or a machine.

For more information about Targets, go to Targeting Users With Flags.

To add a Target, build it and pass in arguments for the following:

Parameter	Description	Required?	Example
identifier	Unique ID for the TargetRead Regex requirements for Target names and identifiers below for accepted characters.	Required	.identifier("HT_1")
name	Name for this Target. This does not have to be unique. Note: If you don’t provide a value, the name will be the same as the identifier.Read Regex requirements for Target names and identifiers below for accepted characters.	Optional Note: If you don't want to send a name, don't send the parameter. Sending an empty argument will cause an error.	.name("Harness_Target_1")
attributes	Additional data you can store for a Target, such as email addresses or location.	Optional	.attributes(new HashMap<String, Object>())

Regex requirements for Target names and identifiers

Identifier

Regex: ^[A-Za-z0-9.@_-]*$
Must consist of only alphabetical characters, numbers, and the following symbols:
. (period)
@ (at sign)
-(dash)
_ (underscore)

The characters can be lowercase or uppercase but cannot include accented letters, for example Cafe_789.

Name Regex: ^[\\p{L}\\d .@_-]*$

Must consist of only alphabetical characters, numbers, and the following symbols:
. (period)
@ (at sign)
-(dash)
_ (underscore)
(space)

The characters can be lowercase or uppercase and can include accented letters, for example Café_123.

For example:

Target target = Target.builder()  
                   .name("Harness_Target_1")  
                   .attributes(new HashMap<String, Object>())  
                   .identifier("HT_1")  
                   .build();

Configure the SDK

You can configure the following features of the SDK through the baseConfig:

Name	Example	Description	Default Value
configUrl	HarnessConfig.configUrl("https://config.ff.harness.io/api/1.0")	The URL used to fetch Feature Flag Evaluations. When using the Relay Proxy, change this to: http://localhost:7000	https://config.ff.harness.io/api/1.0
eventUrl	HarnessConfig.eventUrl("https://events.ff.harness.io/api/1.0")	The URL for posting metrics data to the Feature Flag service. When using the Relay Proxy, change this to: http://localhost:7000	https://events.ff.harness.io/api/1.0
pollIntervalInSeconds	BaseConfig.pollIntervalInSeconds(60))	The interval in seconds that we poll for changes when you are not using stream mode.	60 (seconds)
streamEnabled	BaseConfig.streamEnabled(false)	Set to true to enable streaming mode.Set to false to disable streaming mode.	true
analyticsEnabled	BaseConfig.analyticsEnabled(true)	Set to true to enable analytics.Set to false to disable analytics.Note: When enabled, analytics data is posted every 60 seconds.	true
frequency	BaseConfig.frequency(60))	The interval in seconds of how often to send metrics data.	60

For example:  
// Create Options  
BaseConfig options = BaseConfig.builder()  
        .pollIntervalInSeconds(60)  
        .streamEnabled(true)  
        .analyticsEnabled(true)  
        .build();

 

When initializing the SDK, you can also configure it to use the Harness Relay Proxy, for more information about how to do this, go to Use the Relay Proxy. 

Complete the initialization

To complete the initialization, create an instance of the cfClient and pass in the Server SDK key, Target, and configuration options. 

Sample of initializing the SDK

// Connector Config  
HarnessConfig connectorConfig = HarnessConfig.builder()  
        .configUrl("https://config.ff.harness.io/api/1.0")  
        .eventUrl("https://events.ff.harness.io/api/1.0")  
        .build();  
  
// Create Options  
BaseConfig options = BaseConfig.builder()  
        .pollIntervalInSeconds(60)  
        .streamEnabled(true)  
        .analyticsEnabled(true)  
        .build();  
  
// Create the client  
CfClient cfClient = new CfClient(new HarnessConnector(apiKey, connectorConfig), options);

Evaluate a Flag

Evaluating a Flag is when the SDK processes all Flag rules and returns the correct Variation of that Flag for the Target you provide. 

If a matching Flag can’t be found, or the SDK can’t remotely fetch flags, the default value is returned. 

There are different methods for the different Variation types and for each method you need to pass in:

• Identifier of the Flag you want to evaluate
• The Target object you want to evaluate against
• The default Variation

For example:

Evaluate a boolean Variation

boolean result = cfClient.boolVariation("sample_boolean_flag", target, false);

Evaluate a number Variation

double result = cfClient.numberVariation("sample_number_flag", target, 0);

Evaluate a string Variation

String result = cfClient.stringVariation("sample_string_flag", target, "");

Evaluate a json Variation

JsonObject result = cfClient.jsonVariation("sample_json_flag", target, new JsonObject());

Test your app is connected to Harness

When you receive a response showing the current status of your Feature Flag, go to the Harness Platform and toggle the Flag on and off. Then, check your app to verify if the Flag Variation displayed is updated with the Variation you toggled.

note

The SDK must run for at least 60 seconds before it sends metrics. Please ensure metrics have not been disabled in the SDK.

Close the SDK client

In most applications, you won't need to close the SDK client.

However, you should close the SDK client if:

• Your application is about to terminate. Closing the client ensures that all associated resources are released.
• You have determined that you do not need to evaluate flags again in your application lifecycle.

important

The SDK does not evaluate flags after the client is closed.

To close the SDK client:

• Call the following function>

  cfClient.close();

Additional options

Develop on your local environment

By default, you are connected to the Harness environment but you can use a local connector to develop in your local environment. To do this: 

1. Create three folders to contain the data for your  flags, segments and metrics, for example:
   local/flags
local/segments
local/metrics
2. In the flags folder, create files with a json extension and the following structure:

{  
  "project": "string",  
  "environment": "string",  
  "feature": "string",  
  "state": "on",  
  "kind": "boolean",  
  "variations": [  
    {  
      "identifier": "off-variation",  
      "value": true,  
      "name": "Off Variation",  
      "description": "string"  
    }  
  ],  
  "rules": [  
    {  
      "ruleId": "string",  
      "priority": 1,  
      "clauses": [  
        {  
          "id": 32434243,  
          "attribute": "identifier",  
          "op": "starts_with",  
          "values": [  
            "string"  
          ],  
          "negate": false  
        }  
      ],  
      "serve": {  
        "distribution": {  
          "bucketBy": "string",  
          "variations": [  
            {  
              "variation": "off-variation",  
              "weight": 50  
            }  
          ]  
        },  
        "variation": "string"  
      }  
    }  
  ],  
  "defaultServe": {  
    "distribution": {  
      "bucketBy": "string",  
      "variations": [  
        {  
          "variation": "off-variation",  
          "weight": 50  
        }  
      ]  
    },  
    "variation": "string"  
  },  
  "offVariation": "string",  
  "prerequisites": [  
    {  
      "feature": "string",  
      "variations": [  
        "string"  
      ]  
    }  
  ],  
  "variationToTargetMap": [  
    {  
      "variation": "off-variation",  
      "targets": [  
        {  
          "identifier": "string",  
          "name": "string"  
        }  
      ],  
      "targetSegments": [  
        "string"  
      ]  
    }  
  ],  
  "version": 0  
}

3. In the segments folder, create files with a json extension and the following structure:

{  
   "identifier": "string",  
   "name": "Beta Testers",  
   "environment": "Production",  
   "tags": [  
     {  
       "name": "string",  
       "value": "string"  
     }  
   ],  
   "included": [  
     {  
       "identifier": "john-doe",  
       "account": "abcXDdffdaffd",  
       "org": "string",  
       "environment": "string",  
       "project": "string",  
       "name": "John Doe",  
       "anonymous": true,  
       "attributes": {  
         "age": 20,  
         "location": "Belfast"  
       },  
       "createdAt": 0,  
       "segments": [  
         null  
       ]  
     }  
   ],  
   "excluded": [  
     {  
       "identifier": "john-doe",  
       "account": "abcXDdffdaffd",  
       "org": "string",  
       "environment": "string",  
       "project": "string",  
       "name": "John Doe",  
       "anonymous": true,  
       "attributes": {  
         "age": 20,  
         "location": "Belfast"  
       },  
       "createdAt": 0,  
       "segments": [  
         null  
       ]  
     }  
   ],  
   "rules": [  
     {  
       "id": 32434243,  
       "attribute": "identifier",  
       "op": "starts_with",  
       "values": [  
         "string"  
       ],  
       "negate": false  
     }  
   ],  
   "createdAt": 0,  
   "modifiedAt": 0,  
   "version": 1  
 }

 

4. Leave the metrics folder empty.
5. Create an instance of LocalConnector and pass in the location of your folders.
6. Pass the instance into the cfClient when initializing the SDK.

For example: 

LocalConnector connector = new LocalConnector(path);  
CfClient client = new CfClient(connector, BaseConfig.builder().build())

 

Configure your logger

You can provide your own logger to the SDK and configure it using the standard logging configuration. 

Log4j logger

If using Log4j you can add the following log4j2.xml to your project, for example:

<?xml version="1.0" encoding="UTF-8"?>  
<Configuration status="INFO" monitorInterval="30">  
    <Properties>  
        <Property name="LOG_PATTERN">%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1} SDK=${sys:SDK} flag=${sys:version} target=%mdc{target} - %m%n</Property>  
    </Properties>  
  
     <Appenders>  
        <Console name="console" target="SYSTEM_OUT" follow="true">  
            <PatternLayout pattern="${LOG_PATTERN}"/>  
        </Console>  
    </Appenders>  
   
    <Loggers>  
        <Root level="debug">  
            <AppenderRef ref="console"/>  
        </Root>  
    </Loggers>  
</Configuration>

  

Use the Relay Proxy

To use the Relay Proxy, you need to change the following URLs in the HarnessConfig class when initializing the SDK to http://localhost:7000.

Name	Example	Description	Default Value
baseUrl	HarnessConfig.configUrl("https://config.ff.harness.io/api/1.0")	The URL used to fetch Feature Flag Evaluations. When using the Relay Proxy, change this to: http://localhost:7000	https://config.ff.harness.io/api/1.0
eventUrl	HarnessConfig.eventUrl("https://events.ff.harness.io/api/1.0")	The URL for posting metrics data to the Feature Flag service. When using the Relay Proxy, change this to: http://localhost:7000	https://events.ff.harness.io/api/1.0

For example: 

HarnessConfig connectorConfig = HarnessConfig.builder()  
        .configUrl("http://localhost:7000")  
        .eventUrl("http://localhost:7000")  
        .build();

Sample code for a Java application

Here is a sample code for integrating with the Java SDK:

package io.harness.ff.examples;  
  
import io.harness.cf.client.api.*;  
import io.harness.cf.client.dto.Target;  
   
import java.util.concurrent.Executors;  
import java.util.concurrent.ScheduledExecutorService;  
  
import java.util.concurrent.TimeUnit;  
  
public class GettingStarted {  
    // API Key - set this as an env variable  
    private static String apiKey = getEnvOrDefault("FF_API_KEY", "");  
   
    // Flag Identifier  
  
    private static String flagName = getEnvOrDefault("FF_FLAG_NAME", "harnessappdemodarkmode");  
  
    private static final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);  
  
   
    public static void main(String[] args) {  
        System.out.println("Harness SDK Getting Started");  
   
        try {  
            //Create a Feature Flag Client  
            CfClient cfClient = new CfClient(apiKey);  
            cfClient.waitForInitialization();  
   
            // Create a target (different targets can get different results based on rules.  This includes a custom attribute 'location')  
  
            final Target target = Target.builder()  
                    .identifier("javasdk")  
                    .name("JavaSDK")  
                    .attribute("location", "emea")  
                    .build();  
  
   
            // Loop forever reporting the state of the flag  
            scheduler.scheduleAtFixedRate(  
                    () -> {  
                        boolean result = cfClient.boolVariation(flagName, target, false);  
                        System.out.println("Boolean variation is " + result);  
                    },  
                    0,  
                    10,  
                    TimeUnit.SECONDS);  
   
        } catch (Exception e) {  
            e.printStackTrace();  
  
        } finally {  
            // Close the SDK  
            CfClient.getInstance().close();  
        }  
    }  
   
    // Get the value from the environment or return the default  
    private static String getEnvOrDefault(String key, String defaultValue) {  
        String value = System.getenv(key);  
        if (value == null || value.isEmpty()) {  
            return defaultValue;  
        }  
        return value;  
    }  
}

Known issues

Error when importing the SDK JAR file

If you're using the Java server SDK version 1.2.2 or earlier, you may see the following error when importing the SDK JAR file:

Missing artifact com.github.heremaps:oksse:jar:0.9.0

If you get this error, then add the Maven repository https://jitpack.io to your build system as follows:

If using Gradle:

repositories {
  maven {
    url 'https://jitpack.io'
  }
}

If using Maven:

<repository>
  <url>https://jitpack.io</url>
  ...
</repository>

Troubleshooting

The SDK logs the following codes for certain lifecycle events, for example authentication, which can aid troubleshooting.

Code	Description	Log Level
1000	Successfully initialized	Info
1001	Failed to initialize due to authentication error	Error
1002	Failed to initialize due to a missing or empty API key	Error
1003	WaitForInitialization configuration option was provided and the SDK is waiting for initialization to finish	Info
2000	Successfully authenticated	Info
2001	Authentication failed with a non-recoverable error	Error
2002	Authentication failed and is retrying	Warn
2003	Authentication failed and max retries have been exceeded	Error
3000	SDK closing	Info
3001	SDK closed successfully	Info
4000	Polling service started	Info
4001	Polling service stopped	Info
5000	Streaming connected	Info
5001	Streaming disconnected	Warn
5002	Streaming event received	Debug
5003	Streaming disconnected and is retrying to connect	Info
5004	Streaming service stopped	Info
5005	Stream is still retrying to connect after 4 attempts	Warn
6000	Evaluation was successful	Debug
6001	Evaluation failed and the default value was returned	Info
7000	Metrics service has started	Info
7001	Metrics service has stopped	Info
7002	Metrics posting failed	Warn
7003	Metrics posting success	Debug