alexkasko/rest-handlers

Library for creating REST HTTP services

Library for creating REST services

Note: if you are happy with JAX-RS (JSR311) you probably don't need this library

Thin library over servlet API, eases request dispatching with regular expressions. Uses extended regular expression library with named groups support (for JDK6) to create clean URLs.

Library depends on named-regexp.

Javadocs for the latest release are available here.

Usage

Maven dependency (available in central repository):

<dependency>
    <groupId>com.alexkasko.rest</groupId>
    <artifactId>rest-handlers</artifactId>
    <version>1.1</version>
</dependency>

Request processing is split between transport-level (TransportHandler) and application level (RestHandler) classes. Transport handlers may be singletones, one for each transport type. They take all input parameters from servlet, additional parameters from URL matching (e.g. id for GET requests) and RestHandler class. Rest handler instance may be instantiated or obtained from some kind of DI.

JSON TransportHandler example:

public class JsonTransportHandler implements TransportHandler<JsonHandler> {
    // may be preconfigured
    private static final Gson gson = new Gson();

    public void handle(Class<? extends JsonHandler> handlerClass, HttpServletRequest request,
                       HttpServletResponse response, Map<String, String> urlParams) throws Exception {
        // set proper content-type
        response.setContentType("application/json");
        // obtain handler instance, may be singleton, from DI etc
        JsonHandler ha = handlerClass.newInstance();
        // parse input object from request body
        Object in = gson.fromJson(request.getReader(), ha.inputClass());
        // fire handler
        Object out = ha.handle(in);
        // write results to client
        gson.toJson(out, response.getWriter());
    }
}

Application RestHandler example (may have any methods definition, only called from its TransportHandler):

public class JsonHandler implements RestHandler {
    // sends text message back untouched (any application logic here)
    public OutputMessage handle(InputMessage input) {
        return new OutputMessage(input.getText());
    }

    // inpup message class to be instantiated by transport handler
    public Class<InputMessage> inputClass() {
        return InputMessage.class;
    }
}

Setup example (web.xml):

<servlet>
    <servlet-name>dispatcherServlet</servlet-name>
    <servlet-class>com.alexkasko.rest.handlers.HandlersDispatcherServlet</servlet-class>
    <init-param>
        <param-name>dispatcherKeyInServletContext</param-name>
        <param-value>dispatcher</param-value>
    </init-param>
</servlet>
<servlet-mapping>
    <servlet-name>dispatcherServlet</servlet-name>
    <url-pattern>/rest/*</url-pattern>
</servlet-mapping>
<listener>
    <listener-class>com.myapp.InitListener</listener-class>
</listener>

Dispather init from servlet listener:

// create dispatcher instance with some handlers
HandlersDispatcher dispatcher = HandlersDispatcher.builder()
    .addGet("^/status/jobid/(?<jobid>\\d+)$", new MyTransportHandler(), JobStatusHandler.class)
    .addPost("^/echo$", new JsonTransportHandler(), EchoHandler.class)
    .build();
// add dispatcher to servlet context so dispatcherServlet will be able to access it
sce.getServletContext().setAttribute("dispatcher", dispatcher);

Call with curl:

curl http://127.0.0.1:8080/rest/status/jobid/42

Url parameter matched with (?<jobid>\\d+) will be provided to handler as Map<String, String> - jobid:42

Working example with JSON may be found here, example javadocs.

Classes description

• HandlersDispatcher - regexp-based dispatcher, GET, POST and PUT requests are registered separately
• HandlersDispatcherServlet - servlet, delegate all work to dispatcher (gets it from ServletContext by dispatcherKeyInServletContext key)
• TransportHandler - transport part of request handler, implementation should get nessessary parameters from requests and delegates processing to application level handler (with clean method definitions, from DI with decalarative transactions etc)
• RestHandler - application level marker-interface for calling from TransportHandler
• NotFoundHandler - will be called if no other handlers matched
• DefaultNotFoundHandler - default implementation, returns 404 with available handlers list
• ExceptionHandler - will be called on exception during requst processing
• DefaultExceptionHandler - default implementation, returns 500 with stacktrace

License information

This project is released under the Apache License 2.0

Changelog

1.2.1 (2015-04-01)

• HEAD support

1.2 (2015-03-30)

• DELETE support

1.1 (2013-11-20)

• sub-dispatchers (submappings) support

1.0.2 (2013-07-14)

• dispatcher building composition support

1.0.1 (2013-05-22)

• formatting of list of all available handlers on missed request

1.0 (2012-11-13)

• initial version