Rump

Rump is a REST client for Java that attempts to resemble Axios from JavaScript.

Install with Maven

<dependency>
  <groupId>dev.yasper</groupId>
  <artifactId>rump</artifactId>
  <version>1.0.6</version>
</dependency>

Why

I was working on a project and none of the currently available REST clients for Java seemed to match my needs. I am a pretty big fan of Axios for JavaScript so I decided to make a version of that for Java that would fit my needs.

Features

Create rest requests synchronously
Create rest requests asynchronously
Custom response mapper support by modifying request config (By default Rump uses Jackson)
Customer request body mapper support (By default Rump uses Jackson)
Request transformation before sending it out
Intercept requests/responses to modify them
Canceling of requests by using a request interceptor
Canceling of responses by using a response interceptor
Creation of instances is fast and easy due to chaining of calls, and the ability to have multiple configs per request

Basic Usage

There's three different ways of making REST api calls with Rump:

1. Via the Rump class you can make requests directly.

a) Synchronous

try {
    HttpResponse<Post> res = Rump.get("https://jsonplaceholder.typicode.com/posts/1", Post.class);
    Post post = res.getBody();
    // Do something with post
} catch (IOException e) {
    e.printStackTrace();
}

b) Asynchronous

Rump.getAsync("https://jsonplaceholder.typicode.com/posts/1", Post.class).thenAccept(res -> {
    Post post = res.getBody();
    // Do something with post
});

2. Synchronously using a DefaultRestClient instance

RequestConfig config = new RequestConfig()
                .setBaseURL("https://jsonplaceholder.typicode.com/");
DefaultRestClient drs = Rump.createDefault(config);

try {
    HttpResponse<Post> res = drs.get("posts/1", Post.class);
    Post post = res.getBody();
    // Do something with post
} catch (IOException e) {
    e.printStackTrace();
}

3. Asynchronously using an AsyncRestClient instance

RequestConfig config = new RequestConfig()
                .setBaseURL("https://jsonplaceholder.typicode.com/");
AsyncRestClient ars = Rump.createAsync(config, Executors.newFixedThreadPool(1));
ars.get("posts/1", Post.class).thenAccept(res -> {
    Post post = res.getBody();
    // Do something with post
});

Request Configuration

Requests are configured using the RequestConfig class. By default request config supports most configuratble options for a HttpURLConnection however any option not supported by this class can be modified using the connectionConsumer in RequestConfig. I can also add more options to the request configuration, just create an issue.

HttpResponse

The HttpResponse contains the following values:

The response code
The response message
The config used for the request that generated this response
The headers that the server responded with
The response body mapped as the type you requested

The HttpResponse object will also be returned in case of an error, however the response body will not be mapped to your requested type but will be kept as a string.

Overriding config values

Sometimes your default config values, whether they come from a constructed instance or simply the default values supplied by Rump, are not enough for a specific request.

This is where config overriding comes in. Rump supports config overriding by appending any number of configs to a request. A call could look like this: Rump.get("https://jsonplaceholder.typicode.com/posts/1", Post.class, config1, config2, config3);. In this example the precedence taken is whatever config supplies the value last. For example, if the default config, config1, config2 and config3 all have a different value set for reqeust params then the values of config3 will be used in the request.

To make it easier to construct config instances based of certain configurable request values, Rump gives you the option to convert a certain configurable instance such as RequestHeaders to a RequestConfig instance. An example could look like this:

RequestConfig params = new RequestParams()
                .add("test", 1)
                .toConfig();

RequestConfig headers = new RequestHeaders()
        .setAuthentication("Bearer token")
        .setContentType(RequestHeaders.ContentType.JSON)
        .setUserAgent("Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.116 Safari/537.36")
        .toConfig();

try {
    // Params from default config are now overridden and headers from default config are now merged together
    HttpResponse<Post> res = Rump.get("https://jsonplaceholder.typicode.com/posts/1", Post.class, params, headers);
    Post post = res.getBody();  
    // Do something with post
} catch (IOException e) {
    e.printStackTrace();
}

Overriding config defaults

With an instance created by Rump you can set the defaults yourself by the RequestConfig instance you passed. If you want to modify the defaults used by the backing instance for the static methods inside Rump.java then you can modify the constant Rump.DEFAULT_CONFIG. If you want to change the default base url for all static methods for example:

Rump.DEFAULT_CONFIG.setBaseURL("https://www.new-default.org");

Mappers

Rump supports configurable object mapping, but by default it uses Jackson. You can map request bodies using the RequestTransformer interface and overriding the config value. You can map response bodies by using the ResponseTransformer interface and overriding the config value. You can look at JacksonRequestTransformer and JacksonResponseTransformer for examples.

Interceptors

Interceptors can be used to intercept requests before they are fired and intercept responses before they are returned. For the request this can be used to modify the config or cancel the request completely. For the response these can be used to add a default error handler or a default response data transformation.

Request interceptor

A request interceptor could look like this:

RequestConfig config = new RequestConfig()
        .addRequestInterceptor((mergedURL, connection, config1) -> {
            if (mergedURL.startsWith("https://www.mydomain.com")) {
                connection.setRequestProperty("Authorization", "Bearer myDomainToken");
            }
            return true;
        });
DefaultRestClient drs = Rump.createDefault(config);

Here we check if the domain we are sending a request to matches https://www.mydomain.com and if so we will append our authorization token for this domain to the header of that specific request. Please note that Rump applies the config values before calling the request interceptor so modifying the config values will have no effect on the request. Unless you added a response specific config value such as adding a response interceptor at this stage.

Response interceptor

A response interceptor could look like this:

RequestConfig config = new RequestConfig()
        .setBaseURL("https://jsonplaceholder.typicode.com/")
        .addResponseInterceptor(res -> {
            Object body = res.getBody();
            if (body instanceof Post) {
                Post post = (Post) body;
                post.setTitle(String.format("[INTERCEPTED] %s", post.getTitle()));
            }
            return true;
        });

DefaultRestClient drs = Rump.createDefault(config);

Now whenever the response body is of type Post the interceptor will activate and modify the post's title appending [INTERCEPTED]. A sample request could be like this:

HttpResponse<Post> res = drs.get("posts/1", Post.class);
System.out.println(res.getBody().getTitle());

Output:

[INTERCEPTED] sunt aut facere repellat provident occaecati excepturi optio reprehenderit

Error handling

Response status errors (any response status code above 299) are thrown as HttpStatusCodeException. These are thrown as completion errors within the async functionality of Rump. You are able to modify what status codes are considered as errors by adjusting ignoreStatusCode in RequestConfig. For example:

RequestConfig config = new RequestConfig()
        .setIgnoreStatusCode((code) -> code < 400);

Config now doesn't throw an error if the status code is between 300 and 399.

The HttpStatusCodeException contains a HttpResponse<String> where the error body is of string value. You can therefore easily inspect values of the error response the same way you would check values of a successful response.

RequestConfig also has a value exceptionHandler that can be modified to change the default exception behaviour. DefaultExceptionHandler is the default exception handler that simply thros the HttpStatusCodeException that it is passed.

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