Gmugra/net.cactusthorn.routing

Lightweight JAX-RS implementation for HTTP requests routing

net.cactusthorn.routing

Lightweight JAX-RS implementation.

Motivation

The Java API for RESTful web services (JAX-RS) makes developing RESTful web services in Java simple and intuitive. It's also nice that the API defines a powerful, flexible and easy-to-use routing mechanism (mapping HTTP requests to Java object methods), that more than suitable for any web-application (not only for RESTful web services).

However, the specification contains requirements (such as e.g. XML support) that inevitably turn any full implementation into a multi-megabyte-sized framework with dozen(s) of dependencies on other libraries. And often, most of these features are never used in a particular application. (For example, think of a very typical use case: a microservice that should only handle a few JSON requests / responses).

The idea behind this project is to get a slightly limited, but lightweight JAX-RS implementation without big, not always necessary features, but with all the core features as per the spec.

Goals

1. Intended to be used in conjunction with the embedded java servlet container (e.g. Jetty, Tomcat, Undertow)
2. Don't use any dependencies other than rs-api & annotation-api
3. Implement JAX-RS specification as much as possible

Non-Goals

Be a complete implementation of the JAX-RS.

Limitations

MessageBodyReaders & MessageBodyReaders

The library do not provide "complex" MessageBodyReaders/Writers out of the box. So, to get support for XML or JSON it need to provide an implementation of MessageBodyReaders/Writers.

However, such implementations are trivial issue:

• json-gson module as example of application/json MessageBodyReaders & MessageBodyWriter using GSON
• thymeleaf module as example of text/html MessageBodyWriter using Thymeleaf

ComponentProvider

The library requires an implementation of the ComponentProvider interface, which exposes JAX-RS resource instances. It seems that such an implementation is a tricky problem because you need "scopes" (Request, Session, Singletons etc.). But it's not. All of that is natural features of any good dependency injection framework (e.g. Dagger 2, Guice, HK2 ). It's anyway good idea to use dependency injection in the application, so all what is need for ComponentProvider: link it with dependency injection framework which you are using.

Example:

• demo-jetty module is Demo Application: it uses Dagger 2 for dependency injection and as the basis for the ComponentProvider implementation.

Usage

Usual JAX-RS resources, e.g:

@Path("/my")
public class MyEntryPoint {

    @GET
    @Path("something/{ id : \\d{6} }/{var1}-{var2}")
    @Produces(MediaType.APPLICATION_JSON)
    public MySomething getIt(
        @PathParam("id") int id,
        @PathParam("var1") String var1,
        @PathParam("var2") String var2,
        @QueryParam("qval") List<Integer> qval) {

        return new MySomething(...);
    }
}

Provide list of the annotated classes to the servlet and plug the servlet in the servlet-container. In combination with embedded Jetty it's looks like that:

import net.cactusthorn.routing.*;
import net.cactusthorn.routing.gson.*;
import net.cactusthorn.routing.thymeleaf.*;

import org.eclipse.jetty.server.*;
import org.eclipse.jetty.servlet.*;

import javax.servlet.MultipartConfigElement;

public class Application {

    public static void main(String... args) {

        ComponentProvider myComponentProvider = new MyComponentProvider(...);
        Collection<Class<?>> resources = ...

        RoutingConfig config =
            RoutingConfig.builder(myComponentProvider)
            .addResource(MyResource.class)
            .addResource(resources)
            .addMessageBodyWriter(SimpleGsonBodyWriter.class)
            .addMessageBodyReader(SimpleGsonBodyReader.class)
            .addMessageBodyWriter(new SimpleThymeleafBodyWriter("/thymeleaf/"))
            .addParamConverterProvider(LocalDateParamConverterProvider.class)
            .addExceptionMapper(UnsupportedOperationExceptionMapper.class)
            .setParametersValidator(SimpleParametersValidator.class)
            .build();

        MultipartConfigElement mpConfig = new MultipartConfigElement("/tmp", 1024 * 1024, 1024 * 1024 * 5, 1024 * 1024 * 5 * 5);

        ServletHolder servletHolder = new ServletHolder(new RoutingServlet(config));
        servletHolder.setInitOrder(0);
        servletHolder.getRegistration().setMultipartConfig(mpConfig);

        ServletContextHandler servletContext = new ServletContextHandler(ServletContextHandler.SESSIONS);
        servletContext.setContextPath("/");
        servletContext.addServlet(servletHolder, "/*");

        Server jetty = new Server(8080);
        jetty.setHandler(servletContext);
        jetty.start();
        jetty.join();
    }
}

Supported features

Request to resource matching

1. URI template matched to request URI according JAX-RS rules
2. If no one resource found then HTTP response with status 404 send back to client.
3. If some resources was found, but @Consumes-annotation of no one of them fit Content-Type request-header: HTTP response with status 415 send back to client.
4. If some resources was found, but @Produces-annotation of no one of them fit Accept request-header: HTTP response with status 406 send back to client.

Path matching precedence rules

The JAX-RS specification has defined strict sorting and precedence rules for matching URI expressions and is based on a most specific match wins algorithm. The JAX-RS provider gathers up the set of deployed URI expressions and sorts them based on the following logic:

1. The primary key of the sort is the number of literal characters in the full URI matching pattern. The sort is in descending order.
2. The secondary key of the sort is the number of template expressions embedded within the pattern (e.g. {id} or {id : .+}). This sort is in descending order.
3. The tertiary key of the sort is the number of nondefault template expressions. A default template expression is one that does not define a regular expression (e.g. {id}).

Method parameter types converting

The type of the annotated parameter must either:

1. Be a primitive type
2. Have a constructor that accepts a single String argument
3. Have a static method named valueOf or fromString that accepts a single String argument (see, for example, Integer.valueOf(String))
   1. If both methods are present then valueOf used unless the type is an enum in which case fromString used.
4. Have a registered implementation of javax.ws.rs.ext.ParamConverterProvider JAX-RS extension SPI that returns a ParamConverter instance capable of a "from string" conversion for the type.
5. Be List<T>, Set<T> or SortedSet<T>, where T satisfies 2, 3 or 4 above. The resulting collection is read-only.

Supported JAX-RS features

1. @Path for class and/or method
   • path-parameters (with regular expressions support)
2. @GET @POST @DELETE @HEAD @OPTIONS @PATCH @PUT for method
3. @PathParam, @QueryParam, @FormParam, @CookieParam, @HeaderParam, @FormPart for method parameters.
4. @DefaultValue
5. @Consumes for class and/or method
   • default(if not present) is "*/*"
6. @Produces for class and/or method
   • default(if not present) is "text/plain"
7. @Context for method parameters. The following types are currently supported:
   • javax.servlet.http.HttpServletRequest
   • javax.servlet.http.HttpServletResponse
   • javax.servlet.ServletContext
   • javax.ws.rs.core.SecurityContext
   • javax.ws.rs.core.HttpHeaders
   • javax.ws.rs.core.UriInfo
   • javax.ws.rs.ext.Providers
   • javax.ws.rs.core.Application
8. javax.ws.rs.core.Response
9. javax.ws.rs.ext.ExceptionMapper
10. javax.ws.rs.ext.ParamConverterProvider
11. javax.ws.rs.core.UriBuilder
12. javax.ws.rs.core.Link.Builder
13. javax.ws.rs.core.Variant.VariantListBuilder
14. javax.ws.rs.core.Form

Extensions

1. ParametersValidator interface to integrate additional validations e.g. javax.validation
   • Implemetation example is validation-javax module
2. javax.annotation.security.RolesAllowed method annotation
   1. to check entry point against request.isUserInRole(...)
   2. Implemetation example exists in demo-jetty module
3. @Template annotation, Templated-class and TemplatedMessageBodyWriter to implement message body writers for html-template-engines (e.g. FreeMarker, Thymeleaf )
   • Implemetation example is thymeleaf module
4. Default parameter name
   1. Only when project compiled with javac -parameters
   2. Parameters annotation can be used with empty-string as name, e.g: @QueryParam("") List<Integer> qval. In this case paramener name will be used to match parameter in request.

ParamConverterProvider

Default(if the annotation is not present) priority is javax.ws.rs.Priorities.USER

Example:

@javax.annotation.Priority(3000)
public class LocalDateParamConverterProvider implements javax.ws.rs.ext.ParamConverterProvider {

    private static final DateTimeFormatter FORMATTER = DateTimeFormatter.ofPattern("ddMMyyyy");

    private static final javax.ws.rs.ext.ParamConverter<LocalDate> CONVERTER = new javax.ws.rs.ext.ParamConverter<LocalDate>() {

        @Override
        public LocalDate fromString(String value) {
            if (value == null || value.trim().isEmpty()) {
                return null;
            }
            return LocalDate.parse(value, FORMATTER);
        }

        @Override
        public String toString(LocalDate value) {
            if (value == null) {
                return null;
            }
            return value.format(FORMATTER);
        }
    };

    @Override @SuppressWarnings("unchecked")
    public <T> ParamConverter<T> getConverter(Class<T> rawType, Type genericType, Annotation[] annotations) {
        if (rawType == LocalDate.class) {
            return (ParamConverter<T>) CONVERTER;
        }
        return null;
    }
}

MessageBodyReaders

Default(if the annotation is not present) priority is javax.ws.rs.Priorities.USER

Default(if the annotation is not present) consumes is "*/*"

For the next types MessageBodyReaders are provided:

Type	Priority
java.io.InputStream	50
java.lang.String	50
Any convertable from String	9999

Simple

@javax.annotation.Priority(3000)
@javax.ws.rs.Consumes({MediaType.APPLICATION_JSON, MediaType.TEXT_HTML})
public class MyClassMessageBodyReader implements javax.ws.rs.ext.MessageBodyReader<MyClass> {

    @Override
    public boolean isReadable(Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {
        ...
    }

    @Override
    public MyClass readFrom(Class<InputStream> type, Type genericType, Annotation[] annotations, MediaType mediaType,
            MultivaluedMap<String, String> httpHeaders, InputStream entityStream) {
        ...
    }
}

Initializable

@javax.annotation.Priority(3000)
@javax.ws.rs.Consumes({MediaType.APPLICATION_JSON, MediaType.TEXT_HTML})
public class MyClassMessageBodyReader implements net.cactusthorn.routing.body.reader.InitializableMessageBodyReader<MyClass> {

    @Override
    public void init(ServletContext servletContext, RoutingConfig routingConfig) {
        ...
    }

    @Override
    public boolean isReadable(Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {
        ...
    }

    @Override
    public MyClass readFrom(Class<InputStream> type, Type genericType, Annotation[] annotations, MediaType mediaType,
            MultivaluedMap<String, String> httpHeaders, InputStream entityStream) {
        ...
    }
}

MessageBodyWriters

Default(if the annotation is not present) priority is javax.ws.rs.Priorities.USER

Default(if the annotation is not present) produces is "*/*"

For the next types MessageBodyReaders are provided:

Type	Priority
java.lang.String	50
java.lang.Object	9999

Simple

@javax.annotation.Priority(3000)
@javax.ws.rs.Produces({MediaType.APPLICATION_JSON, MediaType.TEXT_HTML})
public class MyClassMessageBodyWriter implements javax.ws.rs.ext.MessageBodyWriter<MyClass> {

    @Override
    public boolean isWriteable(Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {
        ...
    }

    @Override
    public void writeTo(MyClass entity, Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType,
            MultivaluedMap<String, Object> httpHeaders, OutputStream entityStream) throws IOException, WebApplicationException {
        ...
    }
}

Initializable

@javax.annotation.Priority(3000)
@javax.ws.rs.Produces({MediaType.APPLICATION_JSON, MediaType.TEXT_HTML})
public class MyClassMessageBodyWriter implements net.cactusthorn.routing.body.writer.InitializableMessageBodyWriter<MyClass> {

    @Override
    public void init(ServletContext servletContext, RoutingConfig routingConfig) {
        ...
    }

    @Override
    public boolean isWriteable(Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {
        ...
    }

    @Override
    public void writeTo(MyClass entity, Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType,
            MultivaluedMap<String, Object> httpHeaders, OutputStream entityStream) throws IOException, WebApplicationException {
        ...
    }
}

Templated

@Produces({MediaType.TEXT_HTML})
public class SimpleThymeleafBodyWriter implements net.cactusthorn.routing.body.writer.TemplatedMessageBodyWriter {

    @Override
    public void init(ServletContext servletContext, RoutingConfig routingConfig) {
        ...
    }

    @Override
    public boolean isWriteable(Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {
        ...
    }

    @Override
    public void writeTo(Templated templated, Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType,
            MultivaluedMap<String, Object> httpHeaders, OutputStream entityStream) throws IOException, WebApplicationException {
        ...
    }
}

ExceptionMappers

Default(if the annotation is not present) priority is javax.ws.rs.Priorities.USER

Example

@javax.annotation.Priority(3000)
public static class UnsupportedOperationExceptionMapper implements ExceptionMapper<UnsupportedOperationException> {

    @Override
    public Response toResponse(UnsupportedOperationException exception) {
        return Response.status(Response.Status.CONFLICT).build();
    }
}

DOWNLOAD

Maven Central Repository:

<dependency>
    <groupId>net.cactusthorn.routing</groupId>
    <artifactId>core</artifactId>
    <version>0.30</version>
</dependency>

Public Releases can be also downloaded from GitHub Releases or GitHub Packages

LICENSE

net.cactusthorn.routing is released under the BSD 3-Clause license. See LICENSE file included for the details.