JarCastingTrafficante : Strongly Typed API Server
Trafficante library introduces a very simple and intuitive way to construct a strongly typed server with spring boot and swagger within seconds. Trafficante requires JDK 1.8 or higher.
Latest Release
The most recent release is Trafficante 1.0.2, released May, 2017.
To add a dependency on Trafficante Library using Maven, use the following:
<dependency>
<groupId>io.github.avivcarmis</groupId>
<artifactId>trafficante</artifactId>
<version>1.0.2</version>
</dependency>
To add a dependency on Trafficante Library using Gradle, use the following:
compile 'io.github.avivcarmis:trafficante:1.0.2'
Getting Started
Trafficante library divides the server into different Endpoints. Each endpoint is responsible to handle requests with certain HTTP method and path (i.e. POST /get_users), and defines strongly typed request and response entities. Let's implement some example endpoint:
public class GetUserById extends BasicEndpoint<GetUserById.Request, GetUserById.Response, GetUserById.Response> {
public GetUserById() {
super(RequestMethod.GET, true);
}
@Override
protected Response handle(Request request) throws APIException {
Integer userId = request.userId;
User user = // ...acquire user using userId
return new Response(user.getFirstName(), user.getLastName(), user,getWebsiteURL());
}
@Override
protected Response wrapResponse(Response response) {
return response;
}
@Override
protected Response wrapFailure(Throwable throwable) {
return new Response(null, null, null);
}
public static class Request {
private Integer userId;
}
public static class Response {
private final String firstName;
private final String lastName;
private final String websiteURL;
public Response(String firstName, String lastName, String websiteURL) {
this.firstName = firstName;
this.lastName = lastName;
this.websiteURL = websiteURL;
}
}
}
So what's going on here? Our endpoint class extends abstract BasicEndpoint, declares it's request and response entity to be Request and Response classes (just ignore the third generic type for the moment). The request and response classes are nestedly defined, but they don't need to be and it's entirely up to your own coding style. Then it declares the HTTP method it expects and whether or not to log the traffic in the super constructor. The path of the endpoint is automatically derived from the class name, so the above endpoint will be registered to handle calls to GET /getUserById or GET /get_user_by_id or any other custom naming strategy you initially define (more on naming strategies in a moment). Then it defines it's business logic, what actually the endpoint class does to process a request and produce a response, using the implemented handle method. And let's also ignore those wrapResponse and wrapFailure for the moment.
That's it! We have our first endpoint ready! Now we need to create a main class and start a new Trafficante server:
public class Main {
public static void main(String[] args) {
Trafficante.start(
"com.example", // base package name containing all my endpoint classes
ServerNamingStrategy.SNAKE_CASE, // property naming strategy to be used server-wide
"0.0.0.0", // host name to be registered - "0.0.0.0" to allow all
8080, // port to be used
true, // whether or not to enable swagger - should typically be `false` in production environments
true, // whether or not to enable JMX support
args // program arguments - may be null
);
}
}
Now our server is up and running.
Let's Dive Deeper
So we've seen the minimal code required to construct a Trafficante server, now let's explore the recommended setting. Endpoint classes support response wrapping, to allow client a easy parsing of the response in case of either success and failure, and across the entire server. Let's, for example, consider this JSON structure to be responded for each and every server request:
{
"success": true,
"result": {},
"error": null
}
where result may be any response entity, and in case of failure:
{
"success": false,
"result": null,
"error": "string describing the error"
}
To achieve this we need to follow a few simple steps:
- Declare response wrapping entity.
- Define a standard endpoint class.
- Define additional error handler.
So first, let's declare our wrapping entity. The Java version of the JSON above can be achieved using:
public class APIResponse<T> {
private final boolean success;
private final T result;
private final String error;
private APIResponse(boolean success, T result, String error) {
this.success = success;
this.result = result;
this.error = error;
}
public static <T> APIResponse<T> success(T result) {
return new APIResponse<>(true, result, null);
}
public static <T> APIResponse<T> failure(Throwable t) {
return new APIResponse<>(false, null, t.getMessage());
}
}
This is simple, next, we can easily define a standard abstract endpoint class to be used across the entire server:
abstract public class Endpoint<REQ, RES> extends BasicEndpoint<REQ, RES, APIResponse<RES>> {
public Endpoint(RequestMethod httpMethod, boolean enableFlowLogging) {
super(httpMethod, enableFlowLogging);
}
@Override
protected APIResponse<RES> wrapResponse(RES response) {
return APIResponse.success(response);
}
@Override
protected APIResponse<RES> wrapFailure(Throwable t) {
return APIResponse.failure(t);
}
}
So as you now can see, the third generic type of the BasicEndpoint class expects the type of the response wrapper. Since we previously didn't wrap our response, we just passed the same type twice. In the current case we wire the APIResponse class to be generated both on failure and on success of the endpoint.
Lastly, we want to be able to control the response of failure that don't get to reach a specific endpoint class, like 404, or 405 HTTP errors for example. To this end, we need to inherit BasicErrorHandler class:
public class ErrorHandler extends BasicErrorHandler<APIResponse<?>> {
@Override
protected APIResponse<?> wrapFailure(Throwable t) {
return APIResponse.failure(t);
}
}
Now let's get back to our original endpoint example, and re-implement it using our newly create Endpoint class:
public class GetUserById extends Endpoint<GetUserById.Request, GetUserById.Response> {
public GetUserById() {
super(RequestMethod.GET, true);
}
@Override
protected Response handle(Request request) throws APIException {
Integer userId = request.userId;
User user = // ...acquire user using userId
return new Response(user.getFirstName(), user.getLastName(), user,getWebsiteURL());
}
public static class Request {
private Integer userId;
}
public static class Response {
private final String firstName;
private final String lastName;
private final String websiteURL;
public Response(String firstName, String lastName, String websiteURL) {
this.firstName = firstName;
this.lastName = lastName;
this.websiteURL = websiteURL;
}
}
}
That's a bit cleaner, but more importantly, now our server responds with the same object structure to each request, allowing the client for easy and intuitive consumption.
In order to read and write HTTP headers and status codes, you may call the thread-safe, static methods:
BasicEndpoint.requestHeader(String key)return the value of the given request header ornullif not found.BasicEndpoint.responseHeader(String key, String value)which writes a response header.BasicEndpoint.responseStatusCode(HttpStatus status)which alters the response code.
This methods may be called from anywhere in the code.
Validation, Naming and Further Customization
In real life, we would want to validate the GetUserById request. No need to manually trigger such a request. When the endpoint handle method is invoked the request object is already validated. In the above case we did not specify any validation and so any request will be valid. Trafficante supports a simple two types of validation approach to cover all your needs:
- Required fields should be annotated with an
@Requiredannotation. - Any additional validation is defined using the
Validatableinterface. Let's, for example, consider a valid request object to specify auserIdwith a positive sign integer. Then ourRequestclass should be altered this way:
public static class Request implements Validatable {
@Required
private Integer userId;
@Override
public void validate() throws BadRequestException {
if (userId < 0) {
throw new BadRequestException("user id must be >= 0");
}
}
}
The term Naming in the context of Trafficante refers to two concepts - method of mapping an endpoint class to path, and the naming of properties in the request and the response. By default, a server-wide naming strategy is picked up, and then all the magic happens. For the above example using snake case naming convention - a valid request may be GET /get_user_by_id?user_id=1, and it's response may be:
{
"success": true,
"result": {
"first_name": "john",
"last_name": "doe",
"website_url": "example.com"
},
"error": null
}
The above may be achieved using ServerNamingStrategy.SNAKE_CASE property naming when starting a new Trafficante server like in the example above. Trafficante offers 3 basic out of the box strategies to cover the common cases:
ServerNamingStrategy.SNAKE_CASEwhich translate naming from camel case to snake case.ServerNamingStrategy.CAMEL_CASEwhich translate naming from camel case to lower camel case. in this case, typically field names remain the same and class names receive a lowercase first character.ServerNamingStrategy.UNPROCESSEDwhich doesn't translate names at all.
To use any other naming, implement you own PropertyNamingStrategy, or preferably, the simpler PropertyNamingStrategyBase version.
To set custom name for a specific request or response field, annotate it using:
@JsonProperty("custom_external_name")
To set custom naming strategy to a request or a response class, annotate it using:
@JsonNaming(PropertyNamingStrategy.KebabCaseStrategy.class)
Endpoint may be further customized using the following method overrides:
defaultPathProvider- To be overridden in case path strategy should be changed. This let's you ignore the server naming strategy and the class name, and simply return the endpoint path.defaultInvocationWrapper- To be overridden in case some operations should be performed before and/or after handling the request. For example, measuring execution time, extra logging, etc...defaultParamsRequestConditionProvider,defaultHeadersRequestConditionProvider,defaultConsumesRequestConditionProvider,defaultProducesRequestConditionProviderwhich may be further explained in Spring documentation.