Monday, January 17, 2022

Spring WebFlux Example using Functional Programming

      ,      No comments   

This article will focus on implementing a functional model based Spring WebFlux reactive programming example. In functional programming model, functions are used to route and handle requests and contracts are designed for immutability. It is an alternative to the annotation-based programming model. Introductory concepts around reactive programming and Spring WebFlux is explained in Reactive Programming with Spring WebFlux.

LoanInfoService example

In this example, we will implement a simple loan type handling service using Spring WebFlux. We expose a "/loans" endpoint and demonstrate the usage of functional model and reactive types Flux and Mono.

Spring Boot dependencies

Create a Spring starter project and include the Spring Reactive Web support (WebFlux), Spring Data MongoDB Reactive, Project Lombak and test modules as dependencies to the pom.xml. For more details on Project Lombak refer to this article "Introduction to Project Lombak". 
<dependencies>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-data-mongodb-reactive</artifactId>
	</dependency>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-webflux</artifactId>
	</dependency>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-test</artifactId>
		<scope>test</scope>
	</dependency>
	<dependency>
		<groupId>io.projectreactor</groupId>
		<artifactId>reactor-test</artifactId>
		<scope>test</scope>
	</dependency>
	<dependency>
		<groupId>org.projectlombok</groupId>
		<artifactId>lombok</artifactId>
		<version>1.18.22</version>
		<scope>provided</scope>
	</dependency>		
</dependencies>

Configure application.properties

Update the application.properties to specify the Mongo database. We are using a local Mongo database on port 27017 and the database would be "loans". 
spring.data.mongodb.host=localhost
spring.data.mongodb.port=27017
spring.data.mongodb.database=loans

Define the data object

We start with the LoanInfo POJO. We use the Lombok @Data annotation which generate the getters and setters needed. 
package com.stackstalk;

import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;

import lombok.AllArgsConstructor;
import lombok.Data;

@Data
@AllArgsConstructor
@Document
public class LoanInfo {

	@Id
	private String loanId;
	private String loanType;
	private Float interestRate;
	private Integer maxTermInMonths;
	private Float processingFee;
}

Define the repository

Now let us define the repository. Note that here we use the Mongo specific repositiry with reactive support. 
ppackage com.stackstalk;

import org.springframework.data.mongodb.repository.ReactiveMongoRepository;

public interface LoanInfoRepository extends ReactiveMongoRepository<LoanInfo, String> {

}

Define the Handler Function

In WebFlux.fn, an HTTP request is handled with a HandlerFunction: a function that takes ServerRequest and returns a delayed ServerResponse (i.e. Mono<ServerResponse>). HandlerFunction is the equivalent of the body of a @RequestMapping method in the annotation-based programming model. 
package com.stackstalk;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.MediaType;
import org.springframework.stereotype.Component;
import org.springframework.web.reactive.function.server.ServerRequest;
import org.springframework.web.reactive.function.server.ServerResponse;

import reactor.core.publisher.Mono;

@Component
public class LoanInfoHandler {

	@Autowired
	private LoanInfoRepository loanRepository;
	
	public Mono<ServerResponse> addLoanInfo(ServerRequest serverRequest) {
		return serverRequest.bodyToMono(LoanInfo.class)
				.flatMap(l -> {
					return ServerResponse.ok().contentType(MediaType.APPLICATION_JSON).body(loanRepository.save(l), LoanInfo.class);
				}).log();
	}

	public Mono<ServerResponse> getAllLoans(ServerRequest serverRequest) {
		return ServerResponse.ok().contentType(MediaType.APPLICATION_JSON).body(loanRepository.findAll(), 
				LoanInfo.class).log();	
	}

	public Mono<ServerResponse> updateLoanInfo(ServerRequest serverRequest) {
		return serverRequest.bodyToMono(LoanInfo.class)
				.flatMap(l -> {
					return ServerResponse.ok().contentType(MediaType.APPLICATION_JSON).body(loanRepository.save(l), LoanInfo.class);
				}).log();
	}

	public Mono<ServerResponse> deleteLoanInfo(ServerRequest serverRequest) {
		loanRepository.deleteById(serverRequest.pathVariable("loanId"));
		return ServerResponse.ok().build(Mono.empty());
	}
}

Define the Router Function

Incoming requests are routed to a handler function with a RouterFunction: a function that takes ServerRequest and returns a delayed HandlerFunction (i.e. Mono<HandlerFunction>). When the router function matches, a handler function is returned; otherwise an empty Mono. RouterFunction is the equivalent of a @RequestMapping annotation, but with the major difference that router functions provide not just data, but also behavior. 
package com.stackstalk;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.reactive.function.server.RequestPredicates;
import org.springframework.web.reactive.function.server.RouterFunction;
import org.springframework.web.reactive.function.server.RouterFunctions;
import org.springframework.web.reactive.function.server.ServerResponse;

@Configuration
public class LoanInfoRouter {
	
	@Bean
	public RouterFunction<ServerResponse> routes(LoanInfoHandler handler) {
		return RouterFunctions.route(RequestPredicates.GET("/loans"), handler::getAllLoans)
				.andRoute(RequestPredicates.POST("/loans"), handler::addLoanInfo)
				.andRoute(RequestPredicates.PUT("/loans"), handler::updateLoanInfo)
				.andRoute(RequestPredicates.DELETE("/loans/{loanId}"), handler::deleteLoanInfo);
	}
}

Define the application

Finally let us define the application. 
package com.stackstalk;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class LoanInfoServiceApplication {

	public static void main(String[] args) {
		SpringApplication.run(LoanInfoServiceApplication.class, args);
	}

}

Putting it all together and testing

Now, let us test the application and examine. On starting the application observe that Netty server is being started on port 8080. Also see the usage of reactive MongoDB repository. 
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
[32m :: Spring Boot :: [39m              [2m (v2.6.2)[0;39m

[2m2022-01-17 18:41:14.149[0;39m [32m INFO[0;39m [35m13172[0;39m [2m---[0;39m [2m[           main][0;39m [36mc.stackstalk.LoanInfoServiceApplication [0;39m [2m:[0;39m Starting LoanInfoServiceApplication using Java 16.0.2 on MYHOST-M-ABCD with PID 13172 (/Users/itsme/Documents/workspace-spring-tool-suite-4-4.12.0.RELEASE/BookInfoService/target/classes started by itsme in /Users/itsme/Documents/workspace-spring-tool-suite-4-4.12.0.RELEASE/LoanInfoService)
[2m2022-01-17 18:41:14.151[0;39m [32m INFO[0;39m [35m13172[0;39m [2m---[0;39m [2m[           main][0;39m [36mc.stackstalk.LoanInfoServiceApplication [0;39m [2m:[0;39m No active profile set, falling back to default profiles: default
[2m2022-01-17 18:41:14.565[0;39m [32m INFO[0;39m [35m13172[0;39m [2m---[0;39m [2m[           main][0;39m [36m.s.d.r.c.RepositoryConfigurationDelegate[0;39m [2m:[0;39m Bootstrapping Spring Data Reactive MongoDB repositories in DEFAULT mode.
[2m2022-01-17 18:41:14.689[0;39m [32m INFO[0;39m [35m13172[0;39m [2m---[0;39m [2m[           main][0;39m [36m.s.d.r.c.RepositoryConfigurationDelegate[0;39m [2m:[0;39m Finished Spring Data repository scanning in 119 ms. Found 1 Reactive MongoDB repository interfaces.
[2m2022-01-17 18:41:15.136[0;39m [32m INFO[0;39m [35m13172[0;39m [2m---[0;39m [2m[           main][0;39m [36morg.mongodb.driver.cluster              [0;39m [2m:[0;39m Cluster created with settings {hosts=[localhost:27017], mode=SINGLE, requiredClusterType=UNKNOWN, serverSelectionTimeout='30000 ms'}
[2m2022-01-17 18:41:15.492[0;39m [32m INFO[0;39m [35m13172[0;39m [2m---[0;39m [2m[localhost:27017][0;39m [36morg.mongodb.driver.connection           [0;39m [2m:[0;39m Opened connection [connectionId{localValue:2, serverValue:96}] to localhost:27017
[2m2022-01-17 18:41:15.492[0;39m [32m INFO[0;39m [35m13172[0;39m [2m---[0;39m [2m[localhost:27017][0;39m [36morg.mongodb.driver.connection           [0;39m [2m:[0;39m Opened connection [connectionId{localValue:1, serverValue:95}] to localhost:27017
[2m2022-01-17 18:41:15.492[0;39m [32m INFO[0;39m [35m13172[0;39m [2m---[0;39m [2m[localhost:27017][0;39m [36morg.mongodb.driver.cluster              [0;39m [2m:[0;39m Monitor thread successfully connected to server with description ServerDescription{address=localhost:27017, type=STANDALONE, state=CONNECTED, ok=true, minWireVersion=0, maxWireVersion=7, maxDocumentSize=16777216, logicalSessionTimeoutMinutes=30, roundTripTimeNanos=235134928}
[2m2022-01-17 18:41:15.667[0;39m [32m INFO[0;39m [35m13172[0;39m [2m---[0;39m [2m[           main][0;39m [36mo.s.b.web.embedded.netty.NettyWebServer [0;39m [2m:[0;39m Netty started on port 8080
[2m2022-01-17 18:41:15.675[0;39m [32m INFO[0;39m [35m13172[0;39m [2m---[0;39m [2m[           main][0;39m [36mc.stackstalk.LoanInfoServiceApplication [0;39m [2m:[0;39m Started LoanInfoServiceApplication in 1.848 seconds (JVM running for 2.549)

Add a loan type with POST on /loans

This API is used to add a new loan type. 
curl --location --request POST 'http://localhost:8080/loans' \
> --header 'Content-Type: application/json' \
> --data-raw '{
>     "loanId": "4",
>     "loanType": "Education Loan",
>     "interestRate": 5.5,
>     "maxTermInMonths": 60,
>     "processingFee": 20
> }'
Returns the loan type added. 
{"loanId":"4","loanType":"Education Loan","interestRate":5.5,"maxTermInMonths":60,"processingFee":20.0}
In the logs observe usage of reactive signals with onSubscribe, request, onNext (once) and onComplete. 
[2m2022-01-17 19:09:42.690[0;39m [32m INFO[0;39m [35m18563[0;39m [2m---[0;39m [2m[ntLoopGroup-3-3][0;39m [36morg.mongodb.driver.connection           [0;39m [2m:[0;39m Opened connection [connectionId{localValue:3, serverValue:108}] to localhost:27017
[2m2022-01-17 19:10:49.384[0;39m [32m INFO[0;39m [35m18563[0;39m [2m---[0;39m [2m[ctor-http-nio-3][0;39m [36mreactor.Mono.FlatMap.2                  [0;39m [2m:[0;39m | onSubscribe([Fuseable] MonoFlatMap.FlatMapMain)
[2m2022-01-17 19:10:49.385[0;39m [32m INFO[0;39m [35m18563[0;39m [2m---[0;39m [2m[ctor-http-nio-3][0;39m [36mreactor.Mono.FlatMap.2                  [0;39m [2m:[0;39m | request(unbounded)
[2m2022-01-17 19:10:49.424[0;39m [32m INFO[0;39m [35m18563[0;39m [2m---[0;39m [2m[ctor-http-nio-3][0;39m [36mreactor.Mono.FlatMap.2                  [0;39m [2m:[0;39m | onNext(org.springframework.web.reactive.function.server.DefaultEntityResponseBuilder$DefaultEntityResponse@7afee938)
[2m2022-01-17 19:10:49.448[0;39m [32m INFO[0;39m [35m18563[0;39m [2m---[0;39m [2m[ctor-http-nio-3][0;39m [36mreactor.Mono.FlatMap.2                  [0;39m [2m:[0;39m | onComplete()

Query all loan types using GET on /loans

This API is used to query all added loan types. 
curl --location --request GET 'http://localhost:8080/loans'
Returns the loan type added. 
[{"loanId":"3","loanType":"Education Loan","interestRate":5.6,"maxTermInMonths":60,"processingFee":20.0},
 {"loanId":"4","loanType":"Education Loan","interestRate":5.5,"maxTermInMonths":60,"processingFee":20.0}]
In the logs observe usage of reactive signals with onSubscribe, request, onNext (multiple) and onComplete. 
[2m2022-01-17 19:09:42.561[0;39m [32m INFO[0;39m [35m18563[0;39m [2m---[0;39m [2m[ctor-http-nio-3][0;39m [36mreactor.Mono.MapFuseable.1              [0;39m [2m:[0;39m | onSubscribe([Fuseable] FluxMapFuseable.MapFuseableSubscriber)
[2m2022-01-17 19:09:42.564[0;39m [32m INFO[0;39m [35m18563[0;39m [2m---[0;39m [2m[ctor-http-nio-3][0;39m [36mreactor.Mono.MapFuseable.1              [0;39m [2m:[0;39m | request(unbounded)
[2m2022-01-17 19:09:42.564[0;39m [32m INFO[0;39m [35m18563[0;39m [2m---[0;39m [2m[ctor-http-nio-3][0;39m [36mreactor.Mono.MapFuseable.1              [0;39m [2m:[0;39m | onNext(org.springframework.web.reactive.function.server.DefaultEntityResponseBuilder$DefaultEntityResponse@8061ac0)
[2m2022-01-17 19:09:42.666[0;39m [32m INFO[0;39m [35m18563[0;39m [2m---[0;39m [2m[ctor-http-nio-3][0;39m [36mreactor.Mono.MapFuseable.1              [0;39m [2m:[0;39m | onComplete()
[2m2022-01-17 19:09:42.690[0;39m [32m INFO[0;39m [35m18563[0;39m [2m---[0;39m [2m[ntLoopGroup-3-3][0;39m [36morg.mongodb.driver.connection           [0;39m [2m:[0;39m Opened connection [connectionId{localValue:3, serverValue:108}] to localhost:27017
Get access to the full source code of this example in GitHub.

0 comments:

Post a Comment

Popular Posts