Знакомство со Spring Boot

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.1.1.RELEASE</version>
</parent>

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
        </plugin>
    </plugins>
</build>

<packaging>jar</packaging>

<?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>springboot.topjava.ru</groupId>
    <artifactId>SpringBootRestService</artifactId>
    <version>1.0</version>
    <packaging>jar</packaging>

    <properties>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.1.RELEASE</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

package springboot.topjava.ru;

public class PaymentRequest {

    private int userId;
    private String itemId;
    private double discount;

    public String getItemId() {
        return itemId;
    }

    public void setItemId(String itemId) {
        this.itemId = itemId;
    }

    public double getDiscount() {
        return discount;
    }

    public void setDiscount(double discount) {
        this.discount = discount;
    }

    public int getUserId() {
        return userId;
    }

    public void setUserId(int userId) {
        this.userId = userId;
    }
}

package springboot.topjava.ru;

public class BaseResponse {

    private final String status;
    private final Integer code;

    public BaseResponse(String status, Integer code) {
        this.status = status;
        this.code = code;
    }

    public String getStatus() {
        return status;
    }

    public Integer getCode() {
        return code;
    }
}

package springboot.topjava.ru;

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

@RestController
@RequestMapping("/payment")
public class PaymentController {
    
    private final String sharedKey = "SHARED_KEY";
    
    private static final String SUCCESS_STATUS = "success";
    private static final String ERROR_STATUS = "error";
    private static final int CODE_SUCCESS = 100;
    private static final int AUTH_FAILURE = 102;

    @GetMapping
    public BaseResponse showStatus() {
        return new BaseResponse(SUCCESS_STATUS, 1);
    }

    @PostMapping("/pay")
    public BaseResponse pay(@RequestParam(value = "key") String key, @RequestBody PaymentRequest request) {
        
        final BaseResponse response;
        
        if (sharedKey.equalsIgnoreCase(key)) {
            int userId = request.getUserId();
            String itemId = request.getItemId();
            double discount = request.getDiscount();
            // Process the request
            // ....
            // Return success response to the client.
            response = new BaseResponse(SUCCESS_STATUS, CODE_SUCCESS);
        } else {
            response = new BaseResponse(ERROR_STATUS, AUTH_FAILURE);
        }
        return response;
    }
}

package springboot.topjava.ru;

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

@SpringBootApplication
public class Application {

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