Building Serverless APIs with Spring Boot, AWS Lambda and API Gateway

This post demonstrates how to expose a RESTful API implemented with Spring MVC in a Spring Boot application as a Lambda function to be deployed via AWS API Gateway. We will be using the aws-serverless-java-container package which supports native API gateway’s proxy integration models for requests and responses.

Project Setup

Create a new Spring Boot project e.g. using the Spring Initializer or modify an existing project to include the aws-serverless-java-container package dependency:

<dependency> 
      <groupId>com.amazonaws.serverless</groupId> 
      <artifactId>aws-serverless-java-container-spring</artifactId> 
      <version>1.1</version> 
</dependency>

We can remove the Spring Boot Maven Plugin from the pom file. Instead, add the Maven Shade Plugin and remove the embedded Tomcat from the deployed package:

<plugins> 
   <plugin> 
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-shade-plugin</artifactId>
      <configuration> 
        <createDependencyReducedPom>false</createDependencyReducedPom> 
      </configuration> 
      <executions> 
        <execution> 
          <phase>package</phase>
          <goals> 
            <goal>shade</goal> 
          </goals> 
          <configuration> 
             <artifactSet> 
                <excludes> 
                   <exclude>org.apache.tomcat.embed:*</exclude>
                </excludes> 
             </artifactSet>
          </configuration> 
        </execution>
      </executions> 
   </plugin>
</plugins>

Serverless API

1. HelloController

Implement RESTful APIs using Spring MVC as usual. For example:

package com.madman.lambda;
...
@RestController
public class HelloController {
 
     @RequestMapping(path = "/greeting", method = RequestMethod.GET) 
     public GreetingDto sayHello(@RequestParam String name) { 
          String message = "Hello " + name; 
          GreetingDto dto = new GreetingDto();
          dto.setMessage(message); return dto; 
     }

     ...
}

2. StreamLambdaHandler

To deploy Java codes to run as AWS Lambda function, it needs to implement the handler interface RequestStreamHandler. The aws-serverless-java-container library makes it rather straight forward:

...
public class StreamLambdaHandler implements RequestStreamHandler {
    private static Logger logger = LoggerFactory.getLogger(StreamLambdaHandler.class);     

    public static final SpringBootLambdaContainerHandler<AwsProxyRequest, AwsProxyResponse> handler;
 
    static { 
       try { 
           handler = SpringBootLambdaContainerHandler.getAwsProxyHandler(HelloLambdaApplication.class);
       } catch (ContainerInitializationException e) { 
           // if we fail here. We re-throw the exception to force another cold start 
           String errMsg = "Could not initialize Spring Boot application"; 
           logger.error(errMsg); 
           throw new RuntimeException("Could not initialize Spring Boot application", e); 
       } 
    }

    @Override 
    public void handleRequest(InputStream inputStream, OutputStream outputStream, Context context) throws IOException {
        handler.proxyStream(inputStream, outputStream, context);
        // just in case it wasn't closed 
        outputStream.close(); 
    }
}

The class StreamLambdaHandler implements the AWS Lambda predefined handler  interface RequestStreamHandler for handling events.

Note the handling of the Lambda events is delegated to the class SpringBootLambdaContainerHandler.

3. HelloLambdaApplication

Note the SpringBootLambdaContainerHandler.getAwsProxyHandler method is provided with a Spring web application initializer interface, which is implemented by the main Spring Boot Application class by extending the implementing class SpringBootServletInitializer :

@SpringBootApplication
@ComponentScan(basePackages = "com.madman.lambda.controller")
public class HelloLambdaApplication extends SpringBootServletInitializer {
 
     public static void main(String[] args) { 
           SpringApplication.run(HelloLambdaApplication.class, args);
     }
}

4. HelloControllerTest

The aws-serverless-java-container library also supports integration testing the proxy API. Below is integration test for HelloController:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = { HelloLambdaApplication.class })
@WebAppConfiguration
public class HelloControllerTest {
    private MockLambdaContext lambdaContext;
    private SpringBootLambdaContainerHandler<AwsProxyRequest, AwsProxyResponse> handler;
    
    @Autowired 
    private ObjectMapper mapper;
 
    public HelloControllerTest() { 
       lambdaContext = new MockLambdaContext(); 
       this.handler = StreamLambdaHandler.handler; 
    }

    @Test public void testGreetingApi() throws JsonParseException, JsonMappingException, IOException {
       AwsProxyRequest request = new AwsProxyRequestBuilder("/greeting", "GET").queryString("name", "John").build(); 
       AwsProxyResponse response = handler.proxy(request, lambdaContext);
      
       assertThat(response.getStatusCode(), equalTo(200)); 
       GreetingDto responseBody = mapper.readValue(response.getBody(), GreetingDto.class);
       asserThat(responseBody.getMessage(), equalTo("Hello John")); 
    }
}

Deploying to AWS

The full source codes can be found in GitHub here. Run Maven to build the jar file and deploy it as Lambda function. I use the AWS Toolkit for Eclipse to deploy the jar package to AWS. Refer to AWS documentation for more options and information on deploying Lambda applications.

To setup AWS API Gateway as trigger for the Lambda function:

  1. Create a New API
  2. Create Resource
    1. Configure as proxy resource
    2. Resource Name: greeting
  3. Create Method
    1. Get
    2. Integration type: Lambda Function
    3. Use Lambda Proxy Integration: true
    4. Lambda Function: <Name of Lambda function>

You should then be able to test the API with the AWS console (as screenshot below).

blog_apigateway

A couple of things to note:

  1. Cold start – the Java container takes a good few seconds. The latency is ok once it’s warmed up
  2. Fat jar – the Spring Boot jar in this example is around 13MB which is still ok for Lambda (limit 50MB)
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Hello Angular 6 Elements

Yet another blog post on Angular 6 elements.

Quick Start

A starter “hello world” project can be found in GitHub. To build the element, checkout the project and run the following command:

>npm run build:elements

This should generate the file hello-world.js in the elements folder. To use the newly created Angular element, embed the javascript file in a html file:

<!DOCTYPE html>
<body>
 <hello-world></hello-world>
 <scr\ipt type="text/javascript" src="hello-world.js"></script>
</body>
</html>

NgModule

The hello-world element is implemented as a Angular component the same way as in an Angular app. To use it as a custom element outside of Angular, it is bootstrapped a bit differently in the app module file (app.module.ts)

...
import { createCustomElement } from '@angular/elements';
import { HelloWorldComponent } from './hello-world/hello-world.component';
@NgModule({  
     declarations: [HelloWorldComponent],
     imports: [BrowserModule],
     entryComponents: [HelloWorldComponent],
     providers: []})
export class AppModule {
 constructor(private injector: Injector) {
 }
 ngDoBootstrap() { 
     const el = createCustomElement(HelloWorldComponent, {
          injector: this.injector }); 
     customElements.define('hello-world', el); 
 }
}

Note the missing bootstrap attribute in the @NgModule definition for an Angular app. Instead the component is registered with the browser as a custom element in the ngDoBootstrap() method using the createCustomElement() API exported by @angular/elements package.

The building and export of custom elements in Angular 6 is still a work in progress. A custom script and build task (build:elements) from this blog post is used here to concatenate the output javascript files into the single hello-world.js file.

RouteReuseStrategy for Route Caching in Angular

This post explains how to implement RouteReuseStrategy to support custom control of route snapshot caching in Angular. Typical use case is a list page which a user can search for a list of items and then select and navigates to a particular item’s detail pages. When the user clicks the back button in the browser, the Angular app should return to the list page displaying the same items as before, using the previous search criteria.

Other advantages of caching route for rendering is faster page load and reduce network traffic.

To achieve the above in Angular, we need to implement the RouteReuseStrategy to tell Angular not to destroy a component but to save it for re-rendering. There are few blog posts online already with example implementations. This blog will focus more on describing the mechanics of the interface and its methods

RouteReuseStretagy

Below is a skeleton implementation of a custom RouteReuseStrategy:

import { Injectable } from '@angular/core';
import { RouteReuseStrategy, ActivatedRouteSnapshot, DetachedRouteHandle } from '@angular/router';

@Injectable()
export class AppRouteReuseStrategyService implements RouteReuseStrategy {

     handles: {[key: string]: DetachedRouteHandle} = {};

     constructor() { }

     shouldDetach(route: ActivatedRouteSnapshot): boolean {
           // To Be Implemented
     }

     store(route: ActivatedRouteSnapshot, handle: DetachedRouteHandle): void {
           // To Be Implemented
     }

     shouldAttach(route: ActivatedRouteSnapshot): boolean {
           // To Be Implemented
     }

      retrieve(route: ActivatedRouteSnapshot): DetachedRouteHandle {
          // To Be Implemented
      }

      shouldReuseRoute(future: ActivatedRouteSnapshot, curr: ActivatedRouteSnapshot): boolean {
          // To Be Implemented
      }
}

shouldReuseRoute()

This is the first method to consider. If returns true, none of the other methods will be called. For example, when we are already reusing the current route snapshot. Note the future argument refers to the route that you come from previously. For example if the app navigates from item list page to item details page, curr would refer to the route for the item detail page and future to the route for the item list page.

shouldDetach() and store()

If the method shouldRouteReuse returns false, the method shouldDetach will be called to determine whether the current route snapshot should be detached and stored. If it returns true, the store method will be called. A handle to the detached route snapshot (of type DetachedRouteHandle) is provided as argument to the method so it can store it for later use.

Note if a null handle is provided to the method, it should erase the stored value for the input route. See the API documentation here.

Note once a route snapshot is detached, it is the developer’s responsibility to manage its lifecycle and perform any clean up as needed for proper memory management.

shouldAttach() and retrieve()

Similar to above,

If the method shouldReuseRoute returns false, the method shouldAttach will be called to determine if a cached route should be used. If it returns true, the method retrieve will be called to retrieve the saved handle to the detached route previously stored.

Note the shouldAttach method is also a good place to clean up any stored snapshots. For example when a user has logged out or the snapshot has got staled, in which case we should not be rendering the store snapshot. The method should then return false and the stored handle to route snapshot should be removed from storage.

That’s it. Hope above gives some clarity on what the class RouteReuseStrategy does.

Spring for Apache Kafka Quick Start

In this blog, I setup a basic Spring Boot project for developing Kafka based messaging system using Spring for Apache Kafka. The project also includes basic Spring config required for publishing and listening to messages from Kafka broker.

Project Setup

The following tools and versions are used here:

  1. Maven 3.x
  2. Spring Kafka 1.3.2 (current release version)
  3. Kafka client 0.11.0.2
  4. Spring Boot 1.5.9

The current Spring Boot release version (1.5.9) has Spring Kafka version  1.1.7 as the managed version. I have to override this to use 1.3.2. My Maven pom file fragment as below:

 <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>1.5.9.RELEASE</version>
      <relativePath /> <!-- lookup parent from repository -->
 </parent>

 <dependencies>
      <dependency>
           <groupId>org.springframework.kafka</groupId>
           <artifactId>spring-kafka</artifactId>
           <version>1.3.2.RELEASE</version>
      </dependency>
      
      <dependency>
           <groupId>org.springframework.kafka</groupId>
           <artifactId>spring-kafka-test</artifactId>
           <version>1.3.2.RELEASE</version>
           <scope>test</scope>
      </dependency>

      <dependency>
           <groupId>org.apache.kafka</groupId>
           <artifactId>kafka-clients</artifactId>
           <version>0.11.0.2</version>
      </dependency>

Producer Config

Spring Boot provides auto configuration for connecting to Kafka but I find it useful to setup the beans myself. Spring Kafka adopts the same approach to Kafka as in other message brokers such as ActiveMQ. For publishing message a template, KafkaTemplate, as to be configured as with JmsTemplate for ActiveMQ.

The following is my Java Config for a KafkaTemplate to publish message to the Kafka broker

@Configuration
public class KafkaProducerConfig {

     @Value("${spring.kafka.bootstrap-servers}") // (1)
     private String brokerAsString;
 
     @Bean
     public ProducerFactory<Integer, String> producerFactory() {
          return new DefaultKafkaProducerFactory<>(producerConfigs());
     }

     @Bean
     public Map<String, Object> producerConfigs() {
          Map<String, Object> props = new HashMap<>();
          props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, brokerAsString);
          props.put(ProducerConfig.RETRIES_CONFIG, 0);
          props.put(ProducerConfig.BATCH_SIZE_CONFIG, 16384);
          props.put(ProducerConfig.LINGER_MS_CONFIG, 1);
          props.put(ProducerConfig.BUFFER_MEMORY_CONFIG, 33554432);
          props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, IntegerSerializer.class);
          props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
          return props;
      }

     @Bean
     public KafkaTemplate<Integer, String> kafkaTemplate() {
          return new KafkaTemplate<Integer, String>(producerFactory());
     }
}

Note:

  1. The broker address is set using the property spring.kafka.bootstrap-servers defined in the application.properties (or yml) file. For example,
// application.properties
spring.kafka.bootstrap-servers=http://localhost:9092

Consumer Config

Consuming messages from Kafka using Spring Kafka is similar to consuming messages from Active MQ using Spring JMS support. We need to define container factory and message listener. Below is my Java Config for message listener factory.

@Configuration
public class KafkaConsumerConfig {
 
     @Value("${spring.kafka.bootstrap-servers}")
     private String brokerAsString;

     @Value("${spring.kafka.consumer.group-id}")
     private String groupId;
 
     @Value("${spring.kafka.consumer.auto-offset-reset}")
     private String autoOffsetReset;
 
     @Bean
     ConcurrentKafkaListenerContainerFactory<Integer, String> kafkaListenerContainerFactory() {
          ConcurrentKafkaListenerContainerFactory<Integer, String> factory = new ConcurrentKafkaListenerContainerFactory<>();
          factory.setConsumerFactory(consumerFactory());
          return factory;
     }

     @Bean
     public ConsumerFactory<Integer, String> consumerFactory() {
         return new DefaultKafkaConsumerFactory<>(consumerConfigs());
     }

     @Bean
     public Map<String, Object> consumerConfigs() {
         Map<String, Object> props = new HashMap<>();
         props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, brokerAsString);
         props.put(ConsumerConfig.GROUP_ID_CONFIG, groupId);
         props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, autoOffsetReset);
         props.put(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG, true);
         props.put(ConsumerConfig.AUTO_COMMIT_INTERVAL_MS_CONFIG, "100");
         props.put(ConsumerConfig.SESSION_TIMEOUT_MS_CONFIG, "15000");
         props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, IntegerDeserializer.class);
         props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
         return props;
     }
}

Now we can listen to a Kafka topic by using the annotation @KafkaListener. For example

@Service
public class GreetingsTopicListener {

 private Logger logger = LoggerFactory.getLogger(getClass());
 
 @KafkaListener(topics = "greetings")
 public void listen(ConsumerRecord<?,?> cr) throws Exception {
      logger.info(cr.toString());
 }
}

@KafkaListener will use the default listener container factory defined in class ConsumerConfig above to create the message listener. It is also possible to override this by settig the containerFactory attribute in the annotation. See javadoc for more details.

Creating Topics

It is also possible to automatically add topics to the broker by defining @Beans using the new 0.11.0.x client library class AdminClient as in the Spring Kafka reference documentation

@Configuration
public class KafkaTopicConfig {
 
 @Value("${spring.kafka.bootstrap-servers}")
 private String brokerAsString;
 
 @Bean
 public KafkaAdmin admin() {
   Map<String, Object> configs = new HashMap<>();
   configs.put(AdminClientConfig.BOOTSTRAP_SERVERS_CONFIG, brokerAsString);
   return new KafkaAdmin(configs);
 }

 @Bean
 public NewTopic topic1() {
   return new NewTopic("foo", 10, (short) 2);
 }

 @Bean
 public NewTopic topic2() {
   return new NewTopic("bar", 10, (short) 2);
 }
}

That’s about it. The codes included in this blog should be sufficient for setting up a Spring Boot project for a messaging system using Spring Kafka.

Background geolocation in Ionic app

This blog show an example on how to implement background geolocation in an Ionic app using the background geolocation plugin.  to capture user locations for building location aware applications

Install plugin

First add the cordova plugin to the Ionic app:

cordova plugin add cordova-plugin-mauron85-background-geolocation

Implement background geolocation service

Next, implement an Angular service:

var app = angular.module('starter');
app.factory('BackgroundGeolocationService', ['$q', '$http', function ($q, $http) { 
      var callbackFn = function(location) {
          postLocation(location);
          backgroundGeoLocation.finish();  
      },
      failureFn = function(error) {
          console.log('BackgroundGeoLocation error ' + JSON.stringify(error));  
      },

      //Enable background geolocation  
      start = function () {      
          //save settings (background tracking is enabled) in local storage    
          window.localStorage.setItem('bgGPS', 1);
          backgroundGeoLocation.configure(callbackFn, failureFn, {
               desiredAccuracy: 10,      
               stationaryRadius: 10,
               distanceFilter: 10,
               locationProvider: 'ANDROID_ACTIVITY_PROVIDER',
               interval: 10000,      
               fastestInterval: 5000,      
               stopOnStillActivity: false,
               debug: false,      
               stopOnTerminate: false
         });
         backgroundGeoLocation.start();
      };
     // Send location to a backend server, e.g. for location tracking
     postLocation = function post(location) {
         return $http(      
           {        
              method: 'POST',
              headers: {
                   "Content-Type": "application/json"
                    },
              url: 'http://<location server DNS>/location',
              data: {          
                    lat : location.latitude,
                    lng : location.longitude        
                    }      
           }).then(function (response) {
                   return response.data;      
           });  
       }
  
       return {    
            start: start,
            // Stop data tracking    
            stop: function () {
                window.localStorage.setItem('bgGPS', 0);
                backgroundGeoLocation.stop();    
            }  
      }
}]);

The codes above are largely based on this blog article.  I have modified the plugin configuration (see notes below). Details about each configuration parameter can be found in the plugin documentation. I am setting it up and tested for Android here. A few notes or tips below:

  1. Two location providers are supported in Android – Android_distance_filter_provider and Android_activity_provider. I end up using the 2nd one to adjust the intervals in which the app gets location update by setting the parameters interval and fastinterval (to 10 and 5 seconds respectively).
  2. Debug is your friend. Set this to true will trigger a sound and notification when the app receives a location update.
  3. I use a combination of parameters desiredAccuracy, stationaryRadius and distanceFilter to define how often the app should receive location update events. The values set here seems to strike a good balance between accuracy/frequency and battery usage but its largely depends on the app’s use cases and phones.
  4. The plugin includes a url paramter where you can set to the backend server to post the locations. It is also possible, and more flexible, to just implement your own method and call it in the callback function callbackFn 

To kick start the plugin, call init() method in the app.js :

angular.module('app', ['ionic', ...])
.run(function($ionicPlatform, $http, BackgroundGeolocationService) {
   $ionicPlatform.ready(function() {    
       if(window.StatusBar) {
          StatusBar.styleDefault();
       }
       BackgroundGeolocationService.init();
   });
});

Now the Ionic app can send geolocations events when it is in the background, it is rather straight forward to implement a backend server to track and display users’ current locations. Below is a screenshot of a Java app I build, for example:

blog_track.png

 

Integrate Docker with Maven for Spring Boot projects

This blog will demonstrate how to setup in Maven using a number of plugins to integrate Docker in a Spring Boot Maven project. The objective here is to rebuild the docker image for the project seamlessly whenever Maven is run to build and release a new jar file.

The source codes for this project can be found in here

POM File

The project pom.xml file build life cycle is updated to include 3 plugins as shown below:

<build>
 <plugins>
    <plugin>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-maven-plugin</artifactId>
    </plugin>
    <plugin>
       <artifactId>maven-resources-plugin</artifactId>
       <executions>
          <execution>
             <id>copy-resources</id>
             <phase>process-resources</phase>
             <goals>
                 <goal>copy-resources</goal>
             </goals>
             <configuration>
               <outputDirectory>${basedir}/target</outputDirectory>
               <resources>
                  <resource>
                     <directory>src/main/resources/docker</directory>
                     <includes>
                        <include>Dockerfile</include>
                     </includes>
                  </resource>
               </resources>
             </configuration>
           </execution>
        </executions>
     </plugin>
     <plugin>
        <groupId>com.google.code.maven-replacer-plugin</groupId>
        <artifactId>replacer</artifactId>
        <version>1.5.3</version>
        <executions>
            <execution>
               <phase>prepare-package</phase>
               <goals>
                   <goal>replace</goal>
               </goals>
            </execution>
        </executions>
        <configuration>
             <file>${basedir}/target/Dockerfile</file>
             <replacements>
                 <replacement>
                     <token>IMAGE_VERSION</token>
                     <value>${project.version}</value>
                 </replacement>
             </replacements>
         </configuration>
     </plugin>
     <plugin>
         <groupId>com.spotify</groupId>
         <artifactId>dockerfile-maven-plugin</artifactId>
         <version>${version.dockerfile-maven}</version>
    <executions>
       <execution>
       <id>default</id>
       <goals>
          <goal>build</goal>
          <goal>push</goal>
       </goals>
       </execution>
     </executions>
     <configuration>
          <contextDirectory>${project.build.directory}</contextDirectory>
          <repository>image name here</repository>
          <tag>${project.version}</tag>
     </configuration>
    </plugin>
  </plugins>
</build>

The pom file assumes the Dockerfile can be found in the source folder /src/resource/docker. You can define your own Dockerfile as needed for your project. For demo purpose, I am using, with minor modification, the sample Dockerfile found in this blog

FROM frolvlad/alpine-oraclejdk8:slim
VOLUME /tmp
ADD docker-maven-IMAGE_VERSION.jar app.jar
RUN sh -c 'touch /app.jar'
ENV JAVA_OPTS=""
ENTRYPOINT [ "sh", "-c", "java $JAVA_OPTS -Djava.security.egd=file:/dev/./urandom -jar /app.jar" ]

Note the tag IMAGE_VERSION, this will be replaced with the version of the jar file being built

The first step in the build is to copy the Dockerfile above to the /target, i.e. build output, folder using the resource plugin. This is needed for 2 reasons: (1) we need to set the filename to add to the image to match that of the version being built and (2) Docker does not allow in ADD source file outside of the context directory of the Dockerfile so we have to put it in same directory as the jar file.

The second step is to set in the Dockerfile just copied the correct version of the jar file to be included in the docker image. The Maven Replacer plugin is used to replace the tag IMAGE_VERSION in the Dockerfile with the Maven variable project.version.

Finally, we run the Spotify Dockerfile Maven plugin to build/push the docker image. The plugin allows you to set what repository to use. Note we set the tag to be that of the Maven variable project.version as in step 2 to make sure that the image tag matches that of the jar file.

Running Maven

Now whenever the project is build or deploy in Maven using the standard mvn install or mvn deploy, the corresponding docker image will also be build or pushed to the repository. This also works for mvn release:prepare and mvn release:prepare for releasing tag version of the jar file.

Note you would need to setup certificate required to access the Docker daemon. For example, include the following environment variables:

DOCKER_HOST // to <host ip address>
DOCKER_TLS_VERIFY = true
DOCKER_CERT_PATH = C:\Users\<username>\.docker\machine\certs

Consult Docker documentation for more details on secure access to the Docker daemon.

Below is an excerpt of what you would see in a console when running mvn install

[INFO] ------------------------------------------------------------------------
[INFO] Building docker-maven 0.0.1-SNAPSHOT
[INFO] ------------------------------------------------------------------------
...
[INFO] --- maven-resources-plugin:2.6:copy-resources (copy-resources) @ docker-maven ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 1 resource
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ docker-maven ---
...
[INFO] --- replacer:1.5.3:replace (default) @ docker-maven ---
[INFO] Replacement run on 1 file.
[INFO] 
[INFO] --- maven-jar-plugin:2.6:jar (default-jar) @ docker-maven ---
[INFO] Building jar: D:\src\blog_docker_maven\target\docker-maven-0.0.1-SNAPSHOT.jar
...
[INFO] Image will be built as <image name here>
[INFO] 
[INFO] Step 1/7 : FROM frolvlad/alpine-oraclejdk8:slim
[INFO] Pulling from frolvlad/alpine-oraclejdk8
...

Docker image for Oracle JDK

Oracle has deprecated their official Docker image for JDK a few years back. The only official image available is for open JDK (here). There are quite a few docker images available and here is another one I create.  It creates an image with JDK8(u131) under Oracle Linux and can be pulled in from Docker Hub using the following command

docker pull rhslee2000/docker_oraclejdk