Stack Activity 1 - Spring

• Creating An Application
• Creating Endpoints
• Result
• Config
• Autowired

Creating An Application

package com.example;

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

Creating Endpoints

In Spring we map HTTP Rest Calls to Endpoints by creating methods inside of a class marked as @RestController

Basic Endpoint

package com.example.rest;

@RestController
public class MyApiController
{
    @GetMapping("/hello")
    public String helloWorld()
    {
        return "Hello world";
    }
}

Using ResponseEntity

package com.example.rest;

@RestController
public class MyApiController
{
    @GetMapping("/hello")
    public ResponseEntity<String> helloWorld()
    {
        return ResponseEntity.status(HttpStatus.OK)
                             .body("Hello World");
    }
}

Taking Query Arguments

package com.example.rest;

@RestController
public class MyApiController
{
    @GetMapping("/hello")
    public ResponseEntity<String> helloWorld(@RequestParam String name)
    {
        return ResponseEntity.status(HttpStatus.OK)
                             .body("Hello " + name + "!");
    }
}

Taking Path Arguments

package com.example.rest;

@RestController
public class MyApiController
{
    @GetMapping("/hello/{name}")
    public ResponseEntity<String> helloWorld(@PathVariable String name)
    {
        return ResponseEntity.status(HttpStatus.OK)
                             .body("Hello " + name + "!");
    }
}

Taking a JSON Body Argument

package com.example.model.request;

public class PojoRequestModel
{
    private Integer name;
    
    public Integer getName() { return name; }
    
    public void setName(Integer name) { this.name = name; }
    
}

Maps to:

{
    "name": "Example Name"
}

package com.example.rest;

@RestController
public class MyApiController
{
    @PostMapping("/hello")
    public ResponseEntity<String> helloWorld(@RequestBody PojoRequestModel request)
    {
        return ResponseEntity.status(HttpStatus.OK)
                             .body("Hello " + request.getName() + "!");
    }
}

Returning a JSON Body

package com.example.model.response;

public class PojoResponseModel
{
    private Integer name;
    
    public Integer getName() { return name; }
    
    public void setName(Integer name) { this.name = name; }
    
}

Maps to:

{
    "name": "Example Name"
}

package com.example.rest;

@RestController
public class MyApiController
{
    @GetMapping("/hello")
    public ResponseEntity<PojoResponseModel> helloWorld()
    {
        PojoResponseModel response = new PojoResponseModel();
        response.setName("Example");
        
        return ResponseEntity.status(HttpStatus.OK)
                             .body(response);
    }
}

Result

Building your own Response Model

Every endpoint will require creating and returning a JSON. All of these JSON's will have at the very least a single Result that describes the endpoints result.

package com.example.model.response;

public class ResultSuccessResponse
{
    private Result result;
    private Integer sum;
    
    //setters and getters
}

package com.example.rest;

@GetMapping("/result/sum")
public ResponseEntity<ResultBasicResponse> detail(
    @RequestParam("numX") Integer numX,
    @RequestParam("numY") Integer numY)
{
    ResultBasicResponse response = new ResultBasicResponse()
        .setResult(BasicResults.CALCULATION_SUCCESSFUL)
        .setSum(numX + numY);

    return ResponseEntity
        .status(response.getResult().status())
        .body(response);
}

For numX=1&numY=2 returns:

{
    "result": {
        "code": 30,
        "message": "Calculation successful"
    },
    "sum": 3
}

Exiting early

In the cases where you need to exit early and the only thing that needs to be returned is a Result you can throw a ResultError with the correct Result as a argument and it will automatically return the correct Result and HttpStatus to the user.

This is made for our convience for this project.

package com.example.rest;

@GetMapping("/result/sum")
public ResponseEntity<ResultBasicResponse> detail(
    @RequestParam("numX") Integer numX,
    @RequestParam("numY") Integer numY)
{
    if (numX < 0 || numY < 0) {
        throw new ResultError(BasicResults.DATA_CONTAINS_INVALID_INTEGERS);
    }

    ResultBasicResponse response = new ResultBasicResponse()
        .setResult(BasicResults.CALCULATION_SUCCESSFUL)
        .setSum(numX + numY);

    return ResponseEntity
        .status(response.getResult().status())
        .body(response);
}

For numX=-1&numY=2 returns:

{
    "result": {
        "code": 32,
        "message": "Data contains invalid integers"
    }
}

Using ResponseModel

Since all of our Responses will require a Result we can go ahead and just extend the provided ResponseModel abstract class which comes with the Result varaible and corrosponding getter and setter already implemented. This also comes with a convient toResponse() method that will automatically create a ResponseEntity with the ResponseModel as the body and the HttpStatus in Result as the status.

package com.example.rest;

@GetMapping("/result/sum")
public ResponseEntity<ResultSuccessResponse> detail(
    @RequestParam("numX") Integer numX,
    @RequestParam("numY") Integer numY)
{
    if (numX < 0 || numY < 0) {
        throw new ResultError(BasicResults.DATA_CONTAINS_INVALID_INTEGERS);
    }

    ResultSuccessResponse response  = new ResultSuccessResponse()
        .setResult(BasicResults.CALCULATION_SUCCESSFUL)
        .setSum(numX + numY);

    return response.toResponse();
}

For numX=1&numY=2 returns:

{
    "result": {
        "code": 30,
        "message": "Calculation successful"
    },
    "sum": 3
}

Config

You can take custom parameters from your application.yml file and map them to a class marked with @ConfigurationProperties(prefix = <your config prefix>) annotation.

config:
  default-hello: "Hello There Client!"

Maps automatically to:

@ConstructorBinding // Tells spring to use the constructor rather than setters
@ConfigurationProperties(prefix = "config")
public class SpringServiceConfig
{
    private final String defaultHello;

    public SpringServiceConfig(String defaultHello)
    {
        this.defaultHello = defaultHello;
    }

    public String getDefaultHello()
    {
        return defaultHello;
    }
}

Autowired

Spring will automatically create instances of classes with specific annotations for you when the application runs.
The annotations we will be using in this course that spring will create for us are:

• @RestController
• @ConfigurationProperties
• @Component

While @RestController classes are automatically being used to create the endpoints, the other two @ConfigurationProperties and @Component are up to us to use as needed, and we can request them by using the @Autowired marked constructor in any class marked those three annotations

For example:

@Component
public Validate
{
    public void validateNumber(int number)
    {
        if (number < 0) 
            throw new ResultError(BasicResults.DATA_CONTAINS_INVALID_INTEGERS);
    }
}

@ConstructorBinding
@ConfigurationProperties(prefix = "config")
public class SpringServiceConfig
{
    private final String defaultHello;

    public SpringServiceConfig(String defaultHello)
    {
        this.defaultHello = defaultHello;
    }

    public String getDefaultHello()
    {
        return defaultHello;
    }
}

@RestController
public class MathController
{
    private final SpringServiceConfig config;
    private final Validate            validate;
    
    @Autowired
    public HelloController(
            SpringServiceConfig config, 
            Validate validate            // If validate was not marked as @Component this would not work 
    ) 
    {
        this.config = config;
        this.validate = validate;
    }
}