Kod do postu o Spring Boot i Swaggerze znajdującego się pod adresem https://blog.mloza.pl/spring-boot-swagger-ui/

Api.java

    @Operation(
            summary = "List all entries from database",
            description = "Returns all entries that was saved to our database"
    )
    @ApiResponses(value = {
            @ApiResponse(responseCode = "200", description = "Entry was added to database"),
            @ApiResponse(responseCode = "500", description = "Something went wrong, entry was not added")
    })
    @GetMapping("/api/list")
    public ListEntryResponse listObjects() {
        return new ListEntryResponse(database);
    }

    @Operation(
            summary = "Add entry to database",
            description = "Save entry to database. Keys and values can be duplicated."
    )
    @ApiResponses(value = {
            @ApiResponse(responseCode = "200", description = "Entry was added to database"),
            @ApiResponse(responseCode = "500", description = "Something went wrong, entry was not added")
    })
    @PostMapping("/api/add")
    public AddEntryResponse addEntry(@RequestBody AddEntryRequest addEntryRequest) {
        database.add(new Entry(addEntryRequest.getKey(), addEntryRequest.getValue()));
        return new AddEntryResponse("Success");
    }

    @Operation(
            summary = "Delete entry from database",
            description = "Deletes entry from database. If entries are duplicated, we delete only one instance." +
                    " Returns deleted entry"
    )
    @ApiResponses(value = {
            @ApiResponse(responseCode = "200", description = "Entry was removed from database"),
            @ApiResponse(responseCode = "500", description = "Something went wrong, entry was not added")
    })
    @DeleteMapping("/api/remove/{key}")
    public RemoveEntryResponse deleteEntry(@PathVariable String key) {
        Optional<Entry> entry = database.stream().filter(e -> e.getKey().equals(key)).findFirst();

        return entry.map(e -> {
            database.remove(e);
            return new RemoveEntryResponse(e);
        }).orElse(new RemoveEntryResponse());
    }

Main.java

package pl.mloza;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;
import pl.mloza.database.Entry;
import pl.mloza.rest.AddEntryRequest;
import pl.mloza.rest.AddEntryResponse;
import pl.mloza.rest.ListEntryResponse;

import java.util.ArrayList;
import java.util.List;

@SpringBootApplication
@RestController
public class Main {

    private final List<Entry> database = new ArrayList<>();

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

    public Main() {
        database.add(new Entry("one", "one"));
        database.add(new Entry("two", "two"));
        database.add(new Entry("three", "three"));
    }

    @GetMapping("/api/list")
    public ListEntryResponse listObjects() {
        return new ListEntryResponse(database);
    }

    @PostMapping("/api/add")
    public AddEntryResponse addEntry(@RequestBody AddEntryRequest addEntryRequest) {
        database.add(new Entry(addEntryRequest.getKey(), addEntryRequest.getValue()));
        return new AddEntryResponse("Success");
    }
}

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>pl.mloza</groupId>
    <artifactId>swagger-ui</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>15</maven.compiler.source>
        <maven.compiler.target>15</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <version>2.4.0</version>
        </dependency>
        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-boot-starter</artifactId>
            <version>3.0.0</version>
        </dependency>
    </dependencies>

</project>

SwaggerConfiguration.java

@Configuration
public class SwaggerConfiguration {
    public ApiInfo apiInfo() {
        return new ApiInfoBuilder()
                .title("API Demo")
                .description("Demo application API")
                .version("1.0.0")
                .build();
    }

    @Bean
    public Docket docket() {
        return new Docket(DocumentationType.OAS_30)
                .apiInfo(apiInfo())
                .enable(true)
                .select()
                .paths(PathSelectors.any())
                .build();
    }
}