AEM Invoke API – REST service using HTTP Client factory

Problem Statement:

How to make REST based calls from AEM to an external system? Is HTTP Client is the best way to handle HTTP requests?

Requirement:

Create an OSGi based REST service to integrate AEM with the external system, also provide config to provide endpoint options and client factory configurations.

Introduction:

As we all know AEM is REST based Web application, however, is there a way to integrate OSGi based service to make calls to the external system.

After going through the ACS commons based HTTP Client factory, I created a more feature-friendly and rich HTTP client factory.

Create HTTPClientFactory Service Interface:

This service provides the implementation for most of the basic HTTP REST based operations like GET, PUT, POST and DELETE operations.

package com.example.core.services;

import org.apache.http.client.fluent.Executor;
import org.apache.http.client.fluent.Request;

/**
 * Factory for building pre-configured HttpClient Fluent Executor and Request objects
 * based a configure host, port and (optionally) username/password.
 * Factories will generally be accessed by service lookup using the factory.name property.
 */
public interface HttpClientFactory {

    /**
     * Get the configured Executor object from this factory.
     *
     * @return an Executor object
     */
    Executor getExecutor();

    /**
     * Create a GET request using the base hostname and port defined in the factory configuration.
     *
     * @param partialUrl the portion of the URL after the port (and slash)
     *
     * @return a fluent Request object
     */
    Request get(String partialUrl);

    /**
     * Create a PUT request using the base hostname and port defined in the factory configuration.
     *
     * @param partialUrl the portion of the URL after the port (and slash)
     *
     * @return a fluent Request object
     */
    Request put(String partialUrl);

    /**
     * Create a POST request using the base hostname and port defined in the factory configuration.
     *
     * @param partialUrl the portion of the URL after the port (and slash)
     *
     * @return a fluent Request object
     */
    Request post(String partialUrl);

    /**
     * Create a DELETE request using the base hostname and port defined in the factory configuration.
     *
     * @param partialUrl the portion of the URL after the port (and slash)
     *
     * @return a fluent Request object
     */
    Request delete(String partialUrl);

    /**
     * Create a OPTIONS request using the base hostname and port defined in the factory configuration.
     *
     * @param partialUrl the portion of the URL after the port (and slash)
     *
     * @return a fluent Request object
     */
    Request options(String partialUrl);

    /**
     * Get External URI type is form the factory configuration.
     *
     * @return External URI Type
     */
    String getExternalURIType();

    /**
     * Get apiStoreLocatorHostName URI type is form the factory configuration.
     *
     * @return API StoreLocatorHost
     */
    String getApiStoreLocatorHostName();

    Request postWithAbsolute(String absolutelUrl);
}

Create HTTPClientFactoryConfig:

Add the required attributes to create the HTTPCLientFactory.

package com.example.services.config;

import org.osgi.service.metatype.annotations.AttributeDefinition;
import org.osgi.service.metatype.annotations.AttributeType;
import org.osgi.service.metatype.annotations.ObjectClassDefinition;
import com.example.constants.Constants;

@ObjectClassDefinition(name = "Http Client API Configuration", description = "Http Client API Configuration")
public @interface HttpClientFactoryConfig {

    @AttributeDefinition(name = "API Host Name", description = "API host name, e.g. https://example.com", type = AttributeType.STRING)
    String apiHostName() default Constants.DEFAULT_API_HOST_NAME;

    @AttributeDefinition(name = "API URI Type Path", description = "API URI type path, e.g. /services/int/v2", type = AttributeType.STRING)
    String uriType() default Constants.DEFAULT_API_URI_TYPE_PATH;

    @AttributeDefinition(name = "API URI Type Path", description = "API URI type path, e.g. /services/ext/v2", type = AttributeType.STRING)
    String uriExternalType() default Constants.DEFAULT_API_URI_EXTERNAL_TYPE_PATH;

    @AttributeDefinition(name = "Relaxed SSL", description = "Defines if self-certified certificates should be allowed to SSL transport", type = AttributeType.BOOLEAN)
    boolean relaxedSSL() default Constants.DEFAULT_RELAXED_SSL;

    @AttributeDefinition(name = "Store Locator API Host Name", description = "Store Locator API host name, e.g. https://example.com", type = AttributeType.STRING)
    String apiStoreLocatorHostName() default Constants.DEFAULT_STORE_LOCATOR_API_HOST_NAME;

    @AttributeDefinition(name = "Maximum number of total open connections", description = "Set maximum number of total open connections, default 5", type = AttributeType.INTEGER)
    int maxTotalOpenConnections() default Constants.DEFAULT_MAXIMUM_TOTAL_OPEN_CONNECTION;

    @AttributeDefinition(name = "Maximum number of concurrent connections per route", description = "Set the maximum number of concurrent connections per route, default 5", type = AttributeType.INTEGER)
    int maxConcurrentConnectionPerRoute() default Constants.DEFAULT_MAXIMUM_CONCURRENT_CONNECTION_PER_ROUTE;

    @AttributeDefinition(name = "Default Keep alive connection in seconds", description = "Default Keep alive connection in seconds, default value is 1", type = AttributeType.LONG)
    int defaultKeepAliveconnection() default Constants.DEFAULT_KEEP_ALIVE_CONNECTION;

    @AttributeDefinition(name = "Default connection timeout in seconds", description = "Default connection timout in seconds, default value is 30", type = AttributeType.LONG)
    long defaultConnectionTimeout() default Constants.DEFAULT_CONNECTION_TIMEOUT;

    @AttributeDefinition(name = "Default socket timeout in seconds", description = "Default socket timeout in seconds, default value is 30", type = AttributeType.LONG)
    long defaultSocketTimeout() default Constants.DEFAULT_SOCKET_TIMEOUT;

    @AttributeDefinition(name = "Default connection request timeout in seconds", description = "Default connection request timeout in seconds, default value is 30", type = AttributeType.LONG)
    long defaultConnectionRequestTimeout() default Constants.DEFAULT_CONNECTION_REQUEST_TIMEOUT;
}

Create HttpClientFactoryImpl Service implementation:

This provides the implementation class for HTTPClientFactory Service and during @Activate/@Modified we are trying to create a new Apache Closable HTTP Client using OSGi based HttpClientBuilderFactory.

HTTP client is like a dish, and you can taste it better if your recipe is great and if you prepare it well, before making calls to the external system.

Close all Connection:

Make sure to close the existing connection if any after bundle get activated or modified

Preparing Request Configuration:

Create Request Config Object and set Connection timeout, socket timeout and request timeout based on the service configurations

Pooling HTTP Connection:

PoolingHttpClientConnectionManager maintains a pool of HttpClientConnections and is able to service connection requests from multiple execution threads. Connections are pooled on a per route basis. A request for a route that already the manager has persistent connections for available in the pool will be serviced by leasing a connection from the pool rather than creating a brand new connection.

Hence set max pool size and number default max per route (per endpoint)

Things to be aware of before pooling connection is, are you making HTTPS calls to the external system if yes? Then create an SSLConnectionSocketFactory with NOOP based verifier and add all the trusted certificates.

Default Keep Alive Strategy:

If the Keep-Alive header is not present in the response, HttpClient assumes the connection can be kept alive indefinitely. However, many HTTP servers in general use are configured to drop persistent connections after a certain period of inactivity to conserve system resources, often without informing the client. In case the default strategy turns out to be too optimistic, one may want to provide a custom keep-alive strategy.

HTTP Client Builder OSGi Service:

Get the reference to OSGi-based httpClientBuilderFactory service, prepare a new builder, set the request configuration, and add a connection manager with pooling connection.

Add default headers and keepAlive strategy, so that we don’t have to create a new connection

Finally, create the HTTP Client out of this builder and set the client to Apache fluent Executor.

the fluent executor makes an arbitrary HttpClient instance and executes the request.

package com.example.core.services.impl;

import java.io.IOException;
import java.security.KeyManagementException;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.TimeUnit;
import org.apache.commons.lang3.StringUtils;
import org.apache.http.Header;
import org.apache.http.HttpResponse;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.fluent.Executor;
import org.apache.http.client.fluent.Request;
import org.apache.http.config.Registry;
import org.apache.http.config.RegistryBuilder;
import org.apache.http.conn.ConnectionKeepAliveStrategy;
import org.apache.http.conn.socket.ConnectionSocketFactory;
import org.apache.http.conn.socket.PlainConnectionSocketFactory;
import org.apache.http.conn.ssl.NoopHostnameVerifier;
import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.conn.ssl.TrustAllStrategy;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.apache.http.message.BasicHeader;
import org.apache.http.osgi.services.HttpClientBuilderFactory;
import org.apache.http.protocol.HttpContext;
import org.apache.http.ssl.SSLContextBuilder;
import org.osgi.service.component.annotations.Activate;
import org.osgi.service.component.annotations.Component;
import org.osgi.service.component.annotations.Deactivate;
import org.osgi.service.component.annotations.Modified;
import org.osgi.service.component.annotations.Reference;
import org.osgi.service.metatype.annotations.Designate;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.example.core.services.HttpClientFactory;
import com.example.core.services.config.HttpClientFactoryConfig;

/**
 * Implementation of @{@link HttpClientFactory}.
 * <p>
 * HttpClientFactory provides service to handle API connection and executor.
 */
@Component(service = HttpClientFactory.class)
@Designate(ocd = HttpClientFactoryConfig.class)
public class HttpClientFactoryImpl implements HttpClientFactory {

    private static final Logger log = LoggerFactory.getLogger(HttpClientFactoryImpl.class);

    private Executor executor;
    private String baseUrl;
    private String uriExternalType;
    private String apiStoreLocatorHostName;
    private CloseableHttpClient httpClient;
    private HttpClientFactoryConfig config;

    @Reference
    private HttpClientBuilderFactory httpClientBuilderFactory;

    @Activate
    @Modified
    protected void activate(HttpClientFactoryConfig config) throws Exception {

        log.info("########### OSGi Configs Start ###############");
        log.info("API Host Name : {}", config.apiHostName());
        log.info("URI Type: {}", config.uriType());
        log.info("########### OSGi Configs End ###############");

        closeHttpConnection();

        this.config = config;
        if (this.config.apiHostName() == null) {
            log.debug("Configuration is not valid. Both hostname is mandatory.");
            throw new IllegalArgumentException("Configuration is not valid. Both hostname is mandatory.");
        }

        this.uriExternalType = this.config.uriExternalType();
        this.apiStoreLocatorHostName = this.config.apiStoreLocatorHostName();
        this.baseUrl = StringUtils.join(this.config.apiHostName(), config.uriType());

        initExecutor();
    }

    private void initExecutor() throws Exception {

        PoolingHttpClientConnectionManager connMgr = null;

        RequestConfig requestConfig = initRequestConfig();

        HttpClientBuilder builder = httpClientBuilderFactory.newBuilder();
        builder.setDefaultRequestConfig(requestConfig);

        if (config.relaxedSSL()) {

            connMgr = initPoolingConnectionManagerWithRelaxedSSL();

        } else {

            connMgr = new PoolingHttpClientConnectionManager();
        }

        connMgr.closeExpiredConnections();

        connMgr.setMaxTotal(config.maxTotalOpenConnections());
        connMgr.setDefaultMaxPerRoute(config.maxConcurrentConnectionPerRoute());

        builder.setConnectionManager(connMgr);

        List<Header> headers = new ArrayList<>();
        headers.add(new BasicHeader("Accept", "application/json"));
        builder.setDefaultHeaders(headers);
        builder.setKeepAliveStrategy(keepAliveStratey);

        httpClient = builder.build();

        executor = Executor.newInstance(httpClient);
    }

    private PoolingHttpClientConnectionManager initPoolingConnectionManagerWithRelaxedSSL()
            throws NoSuchAlgorithmException, KeyStoreException, KeyManagementException {

        PoolingHttpClientConnectionManager connMgr;
        SSLContextBuilder sslbuilder = new SSLContextBuilder();
        sslbuilder.loadTrustMaterial(new TrustAllStrategy());
        SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(sslbuilder.build(),
                NoopHostnameVerifier.INSTANCE);
        Registry<ConnectionSocketFactory> socketFactoryRegistry = RegistryBuilder.<ConnectionSocketFactory>create()
                .register("http", PlainConnectionSocketFactory.getSocketFactory()).register("https", sslsf).build();
        connMgr = new PoolingHttpClientConnectionManager(socketFactoryRegistry);
        return connMgr;
    }

    private RequestConfig initRequestConfig() {

        return RequestConfig.custom()
                .setConnectTimeout(Math.toIntExact(TimeUnit.SECONDS.toMillis(config.defaultConnectionTimeout())))
                .setSocketTimeout(Math.toIntExact(TimeUnit.SECONDS.toMillis(config.defaultSocketTimeout())))
                .setConnectionRequestTimeout(
                        Math.toIntExact(TimeUnit.SECONDS.toMillis(config.defaultConnectionRequestTimeout())))
                .build();
    }

    @Deactivate
    protected void deactivate() {
        closeHttpConnection();
    }

    private void closeHttpConnection() {
        if (null != httpClient) {
            try {
                httpClient.close();
            } catch (final IOException exception) {
                log.debug("IOException while clossing API, {}", exception.getMessage());
            }
        }
    }

    @Override
    public Executor getExecutor() {
        return executor;
    }

    @Override
    public Request get(String partialUrl) {
        String url = baseUrl + partialUrl;
        return Request.Get(url);
    }

    @Override
    public Request post(String partialUrl) {
        String url = baseUrl + partialUrl;
        return Request.Post(url);
    }

    @Override
    public Request postWithAbsolute(String absolutelUrl) {
        return Request.Post(absolutelUrl);
    }

    @Override
    public Request put(String partialUrl) {
        String url = baseUrl + partialUrl;
        return Request.Put(url);
    }

    @Override
    public Request delete(String partialUrl) {
        String url = baseUrl + partialUrl;
        return Request.Delete(url);
    }

    @Override
    public Request options(String partialUrl) {
        String url = baseUrl + partialUrl;
        return Request.Options(url);
    }

    @Override
    public String getExternalURIType() {
        return uriExternalType;
    }

    @Override
    public String getApiStoreLocatorHostName() {
        return apiStoreLocatorHostName;
    }

    ConnectionKeepAliveStrategy keepAliveStratey = new ConnectionKeepAliveStrategy() {

        @Override
        public long getKeepAliveDuration(HttpResponse response, HttpContext context) {
            /*
             * HeaderElementIterator headerElementIterator = new BasicHeaderElementIterator(
             * response.headerIterator(HTTP.CONN_KEEP_ALIVE));
             *
             * while (headerElementIterator.hasNext()) { HeaderElement headerElement =
             * headerElementIterator.nextElement(); String param = headerElement.getName();
             * String value = headerElement.getValue(); if (value != null &&
             * param.equalsIgnoreCase("timeout")) { return
             * TimeUnit.SECONDS.toMillis(Long.parseLong(value)); } }
             */

            return TimeUnit.SECONDS.toMillis(config.defaultKeepAliveconnection());
        }
    };
}
OSGi configuration

References:

https://github.com/kiransg89/AEM-REST-Integration

How to use HTTP Client Factory?

Check this out URI

AEM Scheduler – Best Practices

Problem statement:

Best way to create OSGI scheduler using best practices

Requirement:

What is new with the AEM scheduler with OSGi R7/8 annotations?

How to use scheduler service?

Why is enable/disable important on a scheduler?

Introduction:

A scheduler to schedule time/cron based jobs. A job is an object that is executed/fired by the scheduler. The object should either implement the Job interface or the Runnable interface. A job can be scheduled either by creating a ScheduleOptions instance through one of the scheduler methods and then calling schedule(Object, ScheduleOptions) or by using the whiteboard pattern and registering a Runnable service with either the PROPERTY_SCHEDULER_EXPRESSION or PROPERTY_SCHEDULER_PERIOD property. If both properties are specified, only PROPERTY_SCHEDULER_PERIOD is considered for scheduling. Services registered by the whiteboard pattern can by default run concurrently, which usually is not wanted. Therefore it is advisable to also set the PROPERTY_SCHEDULER_CONCURRENT property with Boolean.FALSE. Jobs started through the scheduler API are not persisted and are not restarted after a bundle restart. If the client bundle is stopped, the scheduler will stop all jobs started by this bundle as well. However, the client bundle does not need to keep a reference to the scheduler service.

Create Scheduler Config – OCD

Create package for config for adding Scheduler related OCD
Creating separate configs will help in the long run if more configs are required for the scheduler

Things to keep in mind:
  1. Always provide enabled boolean attribute to start or stop the scheduler (sometimes scheduler takes a long time to run hence this helps to remove those schedulers)
  2. Add the scheduler based on the condition in @Activate, @Modified method
package com.mysite.core.schedulers.config;

import org.osgi.service.metatype.annotations.AttributeDefinition;
import org.osgi.service.metatype.annotations.AttributeType;
import org.osgi.service.metatype.annotations.ObjectClassDefinition;

@ObjectClassDefinition(name="A scheduled task", description = "Simple demo for cron-job like task with properties")
public @interface SimpleScheduledTaskConfig {

    @AttributeDefinition(name = "Cron-job expression")
    String schedulerExpression() default "*/30 * * * * ?";

    @AttributeDefinition(name = "Concurrent task", description = "Whether or not to schedule this task concurrently")
    boolean schedulerConcurrent() default false;

    @AttributeDefinition(name = "A parameter", description = "Can be configured in /system/console/configMgr")
    String myParameter() default "";

    @AttributeDefinition(name = "Enabled", description = "True, if scheduler service is enabled", type = AttributeType.BOOLEAN)
    public boolean enabled() default true;
}

Creates Schduler

Create a scheduler using OSGi Component Service DS with service has runnable

Reference Scheduler service and sling setting to make sure the scheduler runs only in author is recommended and override the run method

Make sure the scheduler runs in

  • author mode during @Activate @Modified method
  • get the class simple name and use it has a scheduler ID
@Activate
@Modified
protected void activate(SimpleScheduledTaskConfig simpleScheduledTaskConfig) {
  if (isAuthor()) {
    /**
     * Creating the scheduler id
     */
    this.schedulerJobName = this.getClass().getSimpleName();
    addScheduler(simpleScheduledTaskConfig);
    this.myParameter = simpleScheduledTaskConfig.myParameter();
  }
}

Add the scheduler to the scheduler service

private void addScheduler(SimpleScheduledTaskConfig simpleScheduledTaskConfig) {
  /**
   * Check if the scheduler is enabled
   */
  if (simpleScheduledTaskConfig.enabled()) {

    /**
     * Scheduler option takes the cron expression as a parameter and run accordingly
     */
    ScheduleOptions scheduleOptions = scheduler.EXPR(simpleScheduledTaskConfig.schedulerExpression());

    /**
     * Adding some parameters
     */
    scheduleOptions.name(schedulerJobName);
    scheduleOptions.canRunConcurrently(simpleScheduledTaskConfig.schedulerConcurrent());

    /**
     * Scheduling the job
     */
    scheduler.schedule(this, scheduleOptions);

    logger.info("{} Scheduler added", schedulerJobName);
  } else {
    logger.info("Scheduler is disabled");
    removeScheduler();
  }
}

Remove the scheduler if the scheduler is disabled

/**
 * This method removes the scheduler
 */
private void removeScheduler() {
  logger.info("Removing scheduler: {}", schedulerJobName);
  /**
   * Unscheduling/removing the scheduler
   */
  scheduler.unschedule(String.valueOf(schedulerJobName));
}

Use the below template to create the AEM scheduler

package com.mysite.core.schedulers;

import org.apache.sling.commons.scheduler.ScheduleOptions;
import org.apache.sling.commons.scheduler.Scheduler;
import org.apache.sling.settings.SlingSettingsService;
import org.osgi.service.component.annotations.Activate;
import org.osgi.service.component.annotations.Component;
import org.osgi.service.component.annotations.Modified;
import org.osgi.service.component.annotations.Reference;
import org.osgi.service.metatype.annotations.Designate;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.mysite.core.schedulers.config.SimpleScheduledTaskConfig;
import com.mysite.core.services.ExampleService;

/**
 * A simple demo for cron-job like tasks that get executed regularly.
 * It also demonstrates how property values can be set. Users can
 * set the property values in /system/console/configMgr
 */
@Component(service=Runnable.class)
@Designate(ocd= SimpleScheduledTaskConfig.class)
public class SimpleScheduledTask implements Runnable {

    private final Logger logger = LoggerFactory.getLogger(getClass());

    /**
     * Id of the scheduler based on its name
     */
    private String schedulerJobName;

    @Reference
    private Scheduler scheduler;

    @Reference
    private SlingSettingsService slingSettings;

    @Reference
    private ExampleService exampleService;

    private String myParameter;
    
    @Override
    public void run() {
        logger.debug("SimpleScheduledTask is now running, myParameter='{}'", myParameter);
        exampleService.generateContentList(myParameter);
    }

    @Activate
    @Modified
    protected void activate(SimpleScheduledTaskConfig simpleScheduledTaskConfig) {
    	if (isAuthor()) {
            /**
             * Creating the scheduler id
             */
            this.schedulerJobName = this.getClass().getSimpleName();
            addScheduler(simpleScheduledTaskConfig);
            this.myParameter = simpleScheduledTaskConfig.myParameter();
        }
    }

    private void addScheduler(SimpleScheduledTaskConfig simpleScheduledTaskConfig) {
        /**
         * Check if the scheduler is enabled
         */
        if (simpleScheduledTaskConfig.enabled()) {
            /**
             * Scheduler option takes the cron expression as a parameter and run accordingly
             */
            ScheduleOptions scheduleOptions = scheduler.EXPR(simpleScheduledTaskConfig.schedulerExpression());
            /**
             * Adding some parameters
             */
            scheduleOptions.name(schedulerJobName);
            scheduleOptions.canRunConcurrently(simpleScheduledTaskConfig.schedulerConcurrent());
            /**
             * Scheduling the job
             */
            scheduler.schedule(this, scheduleOptions);
            logger.info("{} Scheduler added", schedulerJobName);
        } else {
            logger.info("Scheduler is disabled");
            removeScheduler();
        }
    }

    /**
     * This method removes the scheduler
     */
    private void removeScheduler() {
        logger.info("Removing scheduler: {}", schedulerJobName);
        /**
         * Unscheduling/removing the scheduler
         */
        scheduler.unschedule(String.valueOf(schedulerJobName));
    }

    /**
     * It is use to check whether AEM is running in Publish mode or not.
     * @return Returns true is AEM is in publish mode, false otherwise
     */
    public boolean isAuthor() {
        return this.slingSettings.getRunModes().contains("author");
    }
}

AEM OSGi Services – Best practices

Problem Statement:

What is the best way to write an OSGi service?

Requirement:

What is recommended way to register service? Recommendation as per R7/8 annotations

Introduction:

A Service Component is a Java class that can be optionally registered as an OSGi service and can optionally use OSGi services. The runtime for DS is called Service Component Runtime (SCR) and uses component descriptions in the bundle (in XML form) to instantiate and wire components and services together. The component descriptions are used by SCR as a performance choice so that SCR can avoid processing all classes in a bundle to search for annotations at runtime

As per Adobe’s best practices please start using OSGi R7/R8 annotations, avoid using felix based component annotations

OSGi R7/8

Create Services using Service Component

A Service Component is a Java class that can be optionally registered as an OSGi service and can optionally use OSGi services. The runtime for DS is called Service Component Runtime (SCR) and uses component descriptions in the bundle (in XML form) to instantiate and wire components and services together. The component descriptions are used by SCR as a performance choice so that SCR can avoid processing all classes in a bundle to search for annotations at runtime

Create Example Service – ExampleService

package com.mysite.core.services;

import java.util.Set;

public interface ExampleService {
    /**
     * Start generation content list
     *
     * @return result set
     */
    public Set<String> generateContentList(String path);
}

Create Example Service Object class definition – ExampleServiceConfig

  1. Creating a separate Interface annotation class will help in long run when we want to introduce more fields
  2. Service config name and description
  3. Attribute name, description, and type
package com.mysite.core.services.config;

import org.osgi.service.metatype.annotations.AttributeDefinition;
import org.osgi.service.metatype.annotations.AttributeType;
import org.osgi.service.metatype.annotations.ObjectClassDefinition;

@ObjectClassDefinition(name = "Example Content list generator Service", description = "Example Content list generator Service generates Set")
public @interface ExampleServiceConfig {

    @AttributeDefinition(name = "Enabled Generator", description = "True, to generate the list", type = AttributeType.BOOLEAN)
    boolean isEnabled() default false;
}

Create Service Implementation – ExampleServiceImpl

  1. Get OCD based configs @Activate without any method
  2. You can also get config inside @Modfied with method
  3. To get resource resolver inside service its recommended to use “try-with-resource” which helps to never forget to close a resource(avoids unclosed resource resolver warnings)
package com.mysite.core.services.impl;

import com.mysite.core.services.ExampleService;
import com.mysite.core.services.config.ExampleServiceConfig;
import org.apache.sling.api.resource.LoginException;
import org.apache.sling.api.resource.ResourceResolver;
import org.apache.sling.api.resource.ResourceResolverFactory;
import org.osgi.service.component.annotations.Activate;
import org.osgi.service.component.annotations.Component;
import org.osgi.service.component.annotations.Modified;
import org.osgi.service.component.annotations.Reference;
import org.osgi.service.metatype.annotations.Designate;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

@Component(service = ExampleService.class, immediate = true, name = "Example Content Generator Service")
@Designate(ocd = ExampleServiceConfig.class)
public class ExampleServiceImpl implements ExampleService {

    private static final Logger LOGGER = LoggerFactory.getLogger(ExampleServiceImpl.class);
    /** Service User name */
    private static final String SERVICE_USER = "exampleUset";
    private boolean serviceEnabled;

    @Reference
    private ResourceResolverFactory resolverFactory;

    //R8 Annotation
    @Activate
    ExampleServiceConfig exampleServiceConfig;

    //R7 Annotation but captures and @Modified configs
    @Modified
    protected void activate(final ExampleServiceConfig exampleServiceConfig) {
        this.exampleServiceConfig = exampleServiceConfig;
    }

    @Override
    public Set<String> generateContentList(String path) {
        if(exampleServiceConfig.isEnabled()){
            try (ResourceResolver resourceResolver = resolverFactory.getServiceResourceResolver(Collections.singletonMap(ResourceResolverFactory.SUBSERVICE, SERVICE_USER))){

            } catch (LoginException e) {
                LOGGER.error("Error Occured during Login", e.getMessage());
            }
        }
        return new HashSet<>();
    }
}

Project Structure

Code structure for best practices

Note: Make sure to add the config XML’s for the services and please don’t depend on the OCD default values.