Dynamically replacing values in JSON response with Spring Boot and Thymeleaf-CodePudding

Using Spring Boot I'd like to implement a mock service for an external API. As this mock is only used for testing, I'd like to keep things as simple as possible. The external API returns a JSON similar to this one:

{
  "customer": {
    "email": "[email protected]"
  },
  "result": {
    "status_code": 100
  },
  "transaction": {
    "amount": 100,
    "currency": "EUR",
    "order_no": "123456"
  }
}

And the controller:

@Value("classpath:/sample.json")
private Resource sampleResource;

@GetMapping(value = "/api")
public String mockMethod() throws IOException {
    final InputStream inputStream = sampleResource.getInputStream();
    final String sampleResourceString = StreamUtils.copyToString(sampleResource, StandardCharsets.UTF_8);
    return sampleResourceString;
}

So basically, the application loads a JSON string from a file and returns it in the response. Now I'd like to replace the amount and the order_no in the JSON with a dynamic value, like this:

{
  "customer": {
    "email": "[email protected]"
  },
  "result": {
    "status_code": 100
  },
  "transaction": {
    "amount": ${amount},
    "currency": "EUR",
    "order_no": "${orderNumber}"
  }
}

My first idea was to use Thymeleaf for this, so I created the following configuration:

@Configuration
@RequiredArgsConstructor
public class TemplateConfiguration {

    private final ApplicationContext applicationContext;

    @Bean
    public SpringResourceTemplateResolver templateResolver() {
        final SpringResourceTemplateResolver templateResolver = new SpringResourceTemplateResolver();
        templateResolver.setApplicationContext(applicationContext);
        templateResolver.setPrefix("/templates");
        templateResolver.setSuffix(".json");
        templateResolver.setTemplateMode(TemplateMode.TEXT);
        return templateResolver;
    }

    @Bean
    public SpringTemplateEngine templateEngine() {
        final SpringTemplateEngine templateEngine = new SpringTemplateEngine();
        templateEngine.setTemplateResolver(templateResolver());
        return templateEngine;
    }
}

But I'm stuck how I can actually "run" the templating so that the sampleResourceString is replaced with the dynamic values.

Or is Thymeleaf maybe actually some kind of "overkill" for this?

CodePudding user response：

Considering that the JSON has quite a simple structure, I would map them out to classes and use Jackson. For example:

public class DummyResponse {
    private DummyResponseCustomer customer;
    private DummyResponseTransaction transaction;
    private DummyResponseResult result;
    // TODO: Getters   Setters   ...
}

public class DummyResponseTransaction  {
    private BigDecimal amount;
    private String currency;
    @JsonProperty("order_no")
    private String orderNumber;
    // TODO: Getters   Setters   ...
}

And then you could write a controller like this:

@ResponseBody // You need the @ResponseBody annotation or annotate the controller with @RestController
@GetMapping(value = "/api")
public DummyResponse mockMethod() {
    return new DummyResponse(
        new DummyResponseCustomer("[email protected]"),
        new DummyResponseResult(100),
        new DummyResponseTransaction(new BigDecimal("100"), "EUR", "123456")
    );
}

This makes it fairly easy to come up with dynamic values and without having to use a templating engine (like Thymeleaf) or having to handle I/O. Besides that, you probably have these classes somewhere already to consume the external API.

CodePudding user response：

Maybe just use String.replace() ?

@GetMapping(value = "/api")
public String mockMethod() throws IOException {
    final InputStream inputStream = sampleResource.getInputStream();
    final String sampleResourceString = StreamUtils.copyToString(sampleResource, StandardCharsets.UTF_8);
    String replacedString = sampleResourceString.replace("${amount}", ...)
                                                .replace("${orderNumber}", ...);
    return replacedString;
}