Tips to solve DS and Algorithm related problems.

Whilst facing the interview, don’t jump into the solution of the problem immediately. Instead think of a data structure which can be applicable to solve the problem. Given below is the list of data structure and algorithms/approaches, you can think of and it is recommended to have all these on your tip as well –

  • Brute Force (For/while Loops) => Complexity (exponential, n^k, etc)
  • Sorting and Searching => Complexity ( n^k, n, logn etc)
  • HashMap, HashTable, HashSet => Complexity ( n, 1 etc)
  • Stack(LIFO), Queue(FIFO) => Complexity ( n etc)
  • Heap, PriorityQueue => Complexity ( nlogn, n, logn, etc)
  • Recursion and DP => Complexity ( exponential, n^k tc)
  • Tree, BST, Tree traversal, Tries =>Complexity ( n, logn, k etc)
  • Graphs (DFS {Stack}, BFS {Queue}, Topological) => Complexity ( E+Vlogv, V+E etc)
  • LinkedList, DoublyLinkedList=> Complexity (n etc)
  • Bitwise Operation  => Complexity (n, k, 1 etc)

Note* : In the online coding test, you may come across the situation in which you will have to write too many lines of code. Even these lengthy questions are asked to test your thinking whether you leave these questions or start wasting your time keeping other problems unattended. It’s not like that you don’t need to solve these lengthy problem but spare your time in the last only when all the other easy problems are solved.  Moreover, the point I would like to highlight is that in the face to face interview, you will always be asked the basic question having 15 to 20 lines of code max as this kind of f2f interview goes around 45 minutes min or 1 hour max.  Happy coding and learning 🙂

Generate Swagger UI through Grizzly and Jersey Application.

Statement : Generate Swagger UI for the listing of all the REST APIs through Grizzly and Jersey Application.

  • Add following dependency in pom.xml –

<dependency>

<groupId>io.swagger</groupId>

<artifactId>swagger-jersey2-jaxrs</artifactId>

<version>1.5.9</version>

</dependency>

  • Bundle Swagger UI and docs folder through you main application class using the below code –

package com.main;

import java.io.IOException;

import java.net.URI;

import org.glassfish.grizzly.http.server.CLStaticHttpHandler;

import org.glassfish.grizzly.http.server.HttpServer;

import org.glassfish.grizzly.http.server.ServerConfiguration;

import org.glassfish.jersey.grizzly2.httpserver.GrizzlyHttpServerFactory;

import org.glassfish.jersey.jackson.JacksonFeature;

import org.glassfish.jersey.server.ResourceConfig;

import com.fasterxml.jackson.jaxrs.json.JacksonJsonProvider;

import io.swagger.jaxrs.config.BeanConfig;

public class MainApp {

// Base URI the Grizzly HTTP server will listen on

public static final URI BASE_URI = URI.create(http://0.0.0.0:8080&#8221;);

public static HttpServer getLookupServer() {

String resources = “com.main”;

BeanConfig beanConfig = new BeanConfig();

beanConfig.setVersion(“1.0.1”);

beanConfig.setSchemes(new String[] { “http” });

beanConfig.setBasePath(“”);

beanConfig.setResourcePackage(resources);

beanConfig.setScan(true);

final ResourceConfig resourceConfig = new ResourceConfig();

resourceConfig.packages(resources);

resourceConfig.register(io.swagger.jaxrs.listing.ApiListingResource.class);

resourceConfig.register(io.swagger.jaxrs.listing.SwaggerSerializers.class);

resourceConfig.register(JacksonFeature.class);

resourceConfig.register(JacksonJsonProvider.class);

return GrizzlyHttpServerFactory.createHttpServer(BASE_URI, resourceConfig);

}

public static void main(String[] args) throws IOException {

final HttpServer server = getLookupServer();

server.start();

ClassLoader loader = MainApp.class.getClassLoader();

CLStaticHttpHandler docsHandler = new CLStaticHttpHandler(loader, “swagger-ui/”);

docsHandler.setFileCacheEnabled(false);

ServerConfiguration cfg = server.getServerConfiguration();

cfg.addHttpHandler(docsHandler, “/docs/”);

}

}

  • Take the latest code of swagger-ui. Copy all the content of the dist folder and create a folder named  swagger-ui inside src/main/resources and paste all the copied contents. Now change the url in index.file which is inside the copied folder like below –

    url: http://0.0.0.0:8080/swagger.json

  • Lastly, annotate your controller with @Api and @ApiOperation.

Hope it works. Now to run your Grizzly Jersey Application, go to browser and type localhost:8080/docs/. You will see Swagger UI having all the details of your REST APIs.

Happy coding and sharing as well. 🙂 You can find the git repo for the above implementation.

Generate Swagger UI through Spring Boot Application.

Statement : Generate Swagger UI for the listing of all the REST APIs through Spring Boot Application.

Follow the below steps to generate the Swagger UI  through Spring Boot application –

  1. Add following dependency in pom.xml –

<dependency>

<groupId>io.springfox</groupId>

<artifactId>springfox-swagger2</artifactId>

<version>2.6.1</version>

</dependency>

<dependency>

<groupId>io.springfox</groupId>

<artifactId>springfox-swagger-ui</artifactId>

<version>2.6.1</version>

</dependency>

  1.  Add the following piece of code in your main application class having the @EnableSwagger2 annotation.

@EnableSwagger2

@SpringBootApplication

public class MyApp {

public static void main(String[] args) {

SpringApplication.run(MyApp.class, args);

}

@Bean

  public Docket api() {

    return new Docket(DocumentationType.SWAGGER_2).select()

        .apis(RequestHandlerSelectors.withClassAnnotation(Api.class)).paths(PathSelectors.any()).build()

        .pathMapping(“/”).apiInfo(apiInfo()).useDefaultResponseMessages(false);

  }

  @Bean

  public ApiInfo apiInfo() {

    final ApiInfoBuilder builder = new ApiInfoBuilder();

    builder.title(“My Application API through Swagger UI”).version(“1.0”).license(“(C) Copyright Test”)

        .description(“List of all the APIs of My Application App through Swagger UI”);

    return builder.build();

  }

}

  1. Add the below RootController class in your code to redirect to the Swagger UI page. In this way, you don’t need to put the dist folder of Swagger-UI in your  resources directory.

import org.springframework.stereotype.Controller;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RequestMethod;

@Controller

@RequestMapping(“/”)

public class RootController {

@RequestMapping(method = RequestMethod.GET)

public String swaggerUi() {

return “redirect:/swagger-ui.html”;

}

}

  1. Being a final steps, add the @Api and @ApiOperation notation in all your RESTControllers like below –

import static org.springframework.web.bind.annotation.RequestMethod.GET;

import org.springframework.http.HttpStatus;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RequestMethod;

import org.springframework.web.bind.annotation.ResponseStatus;

import org.springframework.web.bind.annotation.RestController;

import io.swagger.annotations.Api;

import io.swagger.annotations.ApiOperation;

@RestController

@RequestMapping(“/hello”)

@Api(value = “hello”, description = “Sample hello world application”)

public class TestController {

@ApiOperation(value = “Just to test the sample test api of My App Service”)

@RequestMapping(method = RequestMethod.GET, value = “/test”)

// @Produces(MediaType.APPLICATION_JSON)

public String test() {

return “Hello to check Swagger UI”;

}

@ResponseStatus(HttpStatus.OK)

@RequestMapping(value = “/test1”, method = GET)

@ApiOperation(value = “My App Service get test1 API”, position = 1)

public String test1() {

System.out.println(“Testing”);

if (true) {

return “Tanuj”;

}

return “Gupta”;

}

}

Now your are done. Now to run your Spring Boot Application, go to browser and type localhost:8080. You will see Swagger UI having all the details of your REST APIs.

Happy Coding 🙂 Enjoy the source code of the above implementation in my git repo.

Continue reading “Generate Swagger UI through Spring Boot Application.”

Dockerize Java RESTful Application

Please follow the below steps to dockerize your java RESTful application –

Prerequisites : Please insure that Docker, java and mvn is installed on your machine.

  1. Create Dockerfile : Go to the root of the application where pom.xml is contained. Below is the content of my Dockerfile –

cd yourProjectFolder -> vi Dockerfile

#Fetch the base Jav8 image

FROM java:8

#Expose the local application port

EXPOSE 8088

#Place the jar file to the docker location

ADD /target/lookupService-1.0-SNAPSHOT.jar lookupService-1.0-SNAPSHOT.jar

#Place the config file as a part of application

ADD /src/main/java/com/test/config/config.properties config.properties

#execute the application

ENTRYPOINT [“java”,”-jar”,”yourService-1.0-SNAPSHOT.jar”]

  1.  Build Docker Image :

docker build -f Dockerfile -t yourservice .

  1. Run the Docker Image :

docker run -p 8088:8088 -tyourservice

Option -p publishes or maps host system port 18080 to container port 8080.

Note* Please don’t forget to change your base uri that is localhost:8088 to 0.0.0.0:8080 network interface created inside the container listen to all available address.

Few important commands of docker to know :

  1. To find the Id of your running container –

docker ps

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                    NAMES

77558fabec6c       yourservice       “java -jar lookupS…”   38 minutes ago      Up 38 minutes       0.0.0.0:8088->8088/tcp   affectionate_brahmagupta

  1. To kill the process inside the docker using container is –

docker container kill 77558fabec6c(Container Id)

Now you can test your RESt call on port 0.0.0.0:8080 using any of the REST client . Hope it helps 🙂