Edison HAL

Library to produce and consume application/hal+json representations of REST resources using Jackson.

1. Status

2. About

At otto.de, microservices should only communicate via REST APIs with other microservices. HAL is a nice format to implement the HATEOAS part of REST. Edison-HAL is a library to make it easy to produce and consume HAL representations for your REST APIs.

Currently, there are only a couple of libraries supporting HAL and even less that support the full media type including all link properties, curies (compact URIs) and embedded resources.

Spring HATEOAS, for example, is lacking many link properties, such as title, name, type and others.

3. Features

Creating HAL representations:

• Links with all specified attributes like rel, href, profile, type, name, title, etc. pp.
• Embedded resources, even deeply nested
• Curies in links and embedded resources
• Generation of HAL representations using Jackson annotations

Parsing HAL representations:

• Mapping application/hal+json to Java classes using Jackson. This also works for deeply nested embedded items.
• Simple domain model to access links, embedded resources etc.
• Curies are automatically resolved: Given a curi with name=ex and href=http://example.com/rels/{rel}, links and embedded items can be access either in curied format ex:foo, or expanded format http://exampl.com/rels/foo

Traversion of HAL representations:

• Simple client-side navigation through linked and embedded REST resources using Traverson API
• Embedded resources are transparantly used, if present.
• Curies are resolved transparantly, too. Clients of the Traverson API do not need to know anything about curies or embedded resources.

4. Usage

Before using this library, you should have a good understanding of the Hypertext Application Language (HAL):

• Read Mike's article about HAL and
• the current draft of the RFC.

4.1 Include edison-hal into your project:

    dependencies {
        compile "de.otto.edison:edison-hal:1.0.0",
        ...
    }

4.2 Provide a class for the representation of your REST API

If your representation does not need additional attributes beside of the properties defined in application/hal+json, you can create a HalRepresentations like this:

    final HalRepresentation representation = new HalRepresentation(
            linkingTo(
                    self("http://example.org/test/bar")),
            embeddedBuilder()
                    .with("foo", asList(
                            new HalRepresentation(linkingTo(self("http://example.org/test/foo/01"))),
                            new HalRepresentation(linkingTo(self("http://example.org/test/foo/02")))))
                    .with("bar", asList(
                            new HalRepresentation(linkingTo(self("http://example.org/test/bar/01"))),
                            new HalRepresentation(linkingTo(self("http://example.org/test/bar/02")))))
                    .build());

Otherwise, you can derive a class from HalRepresentation to add extra attributes:

    public class MySpecialHalRepresentation extends HalRepresentation {
        @JsonProperty("someProperty")
        private String someProperty;
        @JsonProperty("someOtherProperty")
        private String someOtherProperty;
        
        // ...
    }

4.3 Multiple Links

A resource may have multiple links that share the same link relation.

For link relations that may have multiple links, we use an array of links.

{
    "_links": {
        "item": [
            { "href": "http://example.com/items/foo" },
            { "href": "http://example.com/items/bar" }
        ]
    }
}

Note: If you're unsure whether the link should be singular, assume it will be multiple. If you pick singular and find you need to change it, you will need to create a new link relation or face breaking existing clients.

[text + example taken from http://stateless.co/hal_specification.html)

By default, links with link-relation type curies, item, and items are serialized as an array of links.

Using Edison HAL, you can override this default behaviour when you build a HalRepresentation:

    final HalRepresentation representation = new HalRepresentation(
            linkingTo(
                    link("foo", "http://example.org/test/foo")
                    link("bar", "http://example.org/test/bar")
            ),
            RelRegistry.relRegistry("foo", "bar")
    );

Curies, however, are always rendered as an array.

4.4 Serializing HalRepresentations

To convert your representation class into a application/hal+json document, you can use Jackson's ObjectMapper directly:

    final ObjectMapper mapper = new ObjectMapper();
    
    final String json = mapper.writeValueAsString(representation);

4.5 Curies

The semantics of links in application/hal+json documents are specified by the link-relation type (rel). It is recommended to use predfined and documented rels like, for example, self, prev or next.

In case of custom link-relation types, fully qualified URIs should be used: a link to a product, for example, could be specified by something like http://spec.example.com/link-relations/product. The URI should be resolvable, pointing to some human readable documentation.

A curi (compact URI) is a feature in HAL+JSON that is helpful to use URIs while keeping the link-relation types compact. For example:

{
  "_links" : {
    "http://spec.example.com/link-relations/product" : [
      {"href" : "http://example.com/products/1"},
      {"href" : "http://example.com/products/1"}
    ],
    "http://spec.example.com/link-relations/shoppingcart" :
      {"href" : "http://example.com/shoppingcart/42"},
    "http://spec.example.com/link-relations/wishlist" :
      {"href" : "http://example.com/wishlist/0815"}
  },
  "_embedded" : {
    "http://spec.example.com/link-relations/product" : [
      {
        "_links" : {
          "http://spec.example.com/link-relations/similar-articles" : 
            {"href" : "http://example.com/recommendations/similar-articles?productId=1"}
        },
        "title" : "Jeans", 
        "more" : "attributes"
      },
      {
        "_links" : {
          "http://spec.example.com/link-relations/similar-articles" : 
            {"href" : "http://example.com/recommendations/similar-articles?productId=2"}
        },
        "title" : "Shirt", 
        "more" : "attributes"
      }
    ]  
  }
}

By specifying a curi, the same document would look like this:

{
  "_links" : {
    "curies" : [
      {"name" : "ex", "href" : "http://spec.example.com/link-relations/{rel}", "templated" : true}
    ],
    "ex:product" : [
      {"href" : "http://example.com/products/1"},
      {"href" : "http://example.com/products/1"}
    ],
    "ex:shoppingcart" :
      {"href" : "http://example.com/shoppingcart/42"},
    "ex:wishlist" :
      {"href" : "http://example.com/wishlist/0815"}
  },
  "_embedded" : {
    "ex:product" : [
      {
        "_links" : {
          "ex:similar-articles" : 
            {"href" : "http://example.com/recommendations/similar-articles?productId=1"}
        },
        "title" : "Jeans", 
        "more" : "attributes"
      },
      {
        "_links" : {
          "ex:similar-articles" : 
            {"href" : "http://example.com/recommendations/similar-articles?productId=2"}
        },
        "title" : "Shirt", 
        "more" : "attributes"
      }
    ]  
  }
}

Curies are fully supported by edison-hal: By just adding a curi to the links of a HalRepresentation, the library takes care of matching link-relation types and replaces them during serialization:

final HalRepresentation representation = new HalRepresentation(
        linkingTo(
                curi("x", "http://example.org/rels/{rel}"),
                curi("y", "http://example.com/rels/{rel}"),
                link("http://example.org/rels/foo", "http://example.org/test"),
                link("http://example.com/rels/bar", "http://example.org/test")),
        
);

...will be rendered as

{
  "_links" : {
    "curies" : [
      {"name" : "x", "href" : "http://example.org/rels/{rel}", "templated" : true},
      {"name" : "y", "href" : "http://example.com/rels/{rel}", "templated" : true}
    ],
    "x:foo" : {"href" : "http://example.org/test"},
    "y:bar" : {"href" : "http://example.org/test"}
  }
}

In the same way, curies are automatically applied to link-relation types in embedded resources, even if the embedded resources have nested embedded resources.

{
  "_links" : {
    "curies" : [
      {"name" : "x", "href" : "http://example.org/rels/{rel}", "templated" : true},
      {"name" : "y", "href" : "http://example.com/rels/{rel}", "templated" : true}
    ],
    "x:foo" : {"href" : "http://example.org/test"},
    "y:bar" : {"href" : "http://example.org/test"}
  },
  "_embedded" : {
    "x:deeply-embedded" : {
      "_links" : {
        "x:foobar" : {"href" : "http://example.org/test"},
        "y:barbar" : {"href" : "http://example.org/test"}
      },
      "_embedded" : {
        "x:even-deeper" : {
          "_links" : {
            "x:barfoo" : {"href" : "http://example.org/test"},
            "y:foofoo" : {"href" : "http://example.org/test"}
          }
        }      
      }
    }
  }
}

4.6 Parsing application/hal+json documents

A HAL document can be parsed using Jackson, too:

    @Test public void shouldParseHal() {
        // given
        final String json =
                "{" +
                    "\"someProperty\":\"1\"," +
                    "\"someOtherProperty\":\"2\"," +
                    "\"_links\":{\"self\":{\"href\":\"http://example.org/test/foo\"}}," +
                    "\"_embedded\":{\"bar\":[" +
                        "{" +
                            "\"_links\":{\"self\":{\"href\":\"http://example.org/test/bar/01\"}}" +
                        "}" +
                    "]}" +
                "}";
        
        // when
        final TestHalRepresentation result = new ObjectMapper().readValue(json.getBytes(), TestHalRepresentation.class);
        
        // then
        assertThat(result.someProperty, is("1"));
        assertThat(result.someOtherProperty, is("2"));
        
        // and
        final Links links = result.getLinks();
        assertThat(links.getLinkBy("self").get(), is(self("http://example.org/test/foo")));
        
        // and
        final List<HalRepresentation> embeddedItems = result.getEmbedded().getItemsBy("bar");
        assertThat(embeddedItems, hasSize(1));
        assertThat(embeddedItems.get(0).getLinks().getLinkBy("self").get(), is(link("self", "http://example.org/test/bar/01")));
    }

4.6.1 Configuring the ObjectMapper

There are some special cases, where it is required to configure the ObjectMapper as follows:

    final ObjectMapper mapper = new ObjectMapper();
    mapper.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);

This will be necessary, if there are single embedded items for a link-relation type, instead of an array of items:

{
    "_embedded" : {
        "item" : {
            "msg" : "This item can not be parsed without the ObjectMapper configuration",
            "_links" : { "self" : {"href" : "http://example.com/a-single-embedded-item"}}
        },
        "multipleItems": [
          {"foo" : 42},
          {"foo" : 4711}
        ]
    }
}

4.6.2 Using the HalParser

If you want to parse embedded resources as a sub-class of HalRepresentation, you need to use the HalParser:

    @Test
    public void shouldParseEmbeddedItemsWithSpecificType() throws IOException {
        // given
        final String json =
                "{" +
                        "\"_embedded\":{\"bar\":[" +
                        "   {" +
                        "       \"someProperty\":\"3\"," +
                        "       \"someOtherProperty\":\"3\"," +
                        "       \"_links\":{\"self\":[{\"href\":\"http://example.org/test/bar/01\"}]}" +
                        "   }" +
                        "]}" +
                        "}";
        
        // when
        final HalRepresentation result = HalParser
                .parse(json)
                .as(HalRepresentation.class, withEmbedded("bar", EmbeddedHalRepresentation.class));
        
        // then
        final List<EmbeddedHalRepresentation> embeddedItems = result
                .getEmbedded()
                .getItemsBy("bar", EmbeddedHalRepresentation.class);
        
        assertThat(embeddedItems, hasSize(1));
        assertThat(embeddedItems.get(0).getClass(), equalTo(EmbeddedHalRepresentation.class));
        assertThat(embeddedItems.get(0).getLinks().getLinkBy("self").get(), is(link("self", "http://example.org/test/bar/01")));
    }

4.6.3 Nested embedded resources

The HalParser is also able to parse nested embedded resources into different subclasses of HalRepresentation. For example, you could parse a shopping-cart document with embedded shopping-cart items, which in turn have embedded products:

{
  "_links" : {"self" : {"href" : "http://shop.example.com/shoppingcarts/42"}},
  "_embedded" : {
    "http://example.com/rels/customer" : {
      "_links" : {"self" : {"href" : "http://shop.example.com/customers/1234"}},
      "customerId" : "some customer id",
      "name" : "Max Mustermann"
    },
    "item" : [
      {
        "_links" : {"self" : {"href" : "http://shop.example.com/shoppingcarts/42/item/1"}},
        "_embedded" : {
          "item" : [
            {
              "_links" : {"self" : {"href" : "http://shop.example.com/products/0815"}},
              "count" : 2
            },
            {
              "_links" : {"self" : {"href" : "http://shop.example.com/products/4711"}},
              "count" : 2
            }
          ]
        }
      },
      {
      "more" : "shopping-cart items..."
      }
    ]
  }
}

This shopping-cart document could be parsed into some java ShoppingCart object containing embedded Customerand ShoppingCartItems, which in turn have embedded Products like this:

final ShoppingCart cart = HalParser
        .parse(json)
        .as(ShoppingCart.class, 
            withEmbedded("http://example.com/rels/customer", Customer.class),
            withEmbedded("item", ShoppingCartItem.class,
                withEmbedded("item", Product.class)
            )
        );

EmbeddedTypeInfo.withEmbedded() is a factory method used to specify the types of embedded items. By nesting the type infos, you can tell the HalParser about the types of any embedded item type, event deeply nested in complex HAL representations.

4.6.4 Unmapped attributes

HalRepresentation supports access to attributes, that could not be mapped to properties. For example:

{
  "foo" : "Hello World",
  "bar" : [
    "Hello",
    "World"
  ]
}

Using HalParser or Jackson's ObjectMapper, this plain json document can be parsed into a HalRepresentation:

        HalRepresentation resource = HalParser.parse(json).as(HalRepresentation.class);

Because HalRepresentation does neither have foo nor barproperties, the values of these properties can only be accessed using HalRepresentation.getAttributes or HalRepresentation.getAttribute(name) The values of such attributes are Jackson JsonNode objects:

        assertThat(
                resource.getAttributes().keySet(), 
                containsInAnyOrder("foo", "bar"));
        assertThat(
                resource.getAttribute("foo").asText(), 
                is("Hello World"));
        assertThat(
                resource.getAttribute("bar").at("/0").asText(), 
                is("Hello"));
        assertThat(
                resource.getAttribute("bar").at("/1").asText(), 
                is("World"));

4.7 Using HAL in Spring controllers

Using Spring MVC, you can directly return HalRepresentations from you controller methods:

    @RequestMapping(
            value = "/my/hal/resource",
            produces = {
                    "application/hal+json",
                    "application/json"},
            method = GET
    )
    public TestHalRepresentation getMyHalResource() {    
        return new TestHalRepresentation(getTheInputData());
    }

4.8 Using the Traverson

Traverson is a utility to make it easy to traverse linked and/or embedded resources using link-relation types:

    class ProductHalJson extends HalRepresentation {
        @JsonProperty String price;
    }
    
    void printProducts(final String query) {
        traverson(this::getHalJson)
                .startWith(HOME_URI)
                .follow(REL_SEARCH, withVars("q", query))
                .follow(REL_PRODUCT)
                .streamAs(ProductHalJson.class)
                .forEach(product->{
                    System.out.println(product.title + ": " + product.price);
                });
    }
    
    String getHalJson(final Link link) {
        try {
            final HttpGet httpget = new HttpGet(HOST + link.getHref());
            if (link.getType().isEmpty()) {
                httpget.addHeader("Accept", "application/hal+json");
            } else {
                httpget.addHeader("Accept", link.getType());
            }
            final HttpEntity entity = httpclient.execute(httpget).getEntity();
            return EntityUtils.toString(entity);
        } catch (final IOException e) {
            throw new RuntimeException(e.getMessage(), e);
        }
    }

The Traverson is automatically taking care of embedded resources: if a linked resource is already embedded, it is used instead of resolving the link. Only if it is not embedded, the Traverson is following the links.

4.9 Selecting Links

In some situations, there are multiple links to the same resource, but with different profile, name or type attributes. The type, for example, could be used to distinguish links to a web page from links pointing to a JSON representation of the resource:

{
    "_links": {
        "user": [
            { "href": "http://example.com/users/42.json", "type": "application/json"},
            { "href": "http://example.com/users/42.html", "type": "text/html"}
        ]
    }
}

The Traverson can be used to navigate linked resources using predicates to select one of multiple links:

User user = traverson(this::getHalJson)
        .startWith("http://example.com/baskets/4711")
        .follow("user", LinkPredicates.havingType("application/json"))
        .getResourceAs(User.class);

Because Traverson.follow() only expects a java.util.function.Predicate<Link>, you are free to write your own predicates, of simply compose them:

Predicate<Link> selectJsonOrHal = havingType("application/json").or(havingType("application/hal+json"));

...
traverson.follow("user", selectJsonOrHal)
...

4.10 Paging over HAL resources

Iterating over pages of items is supported by the Traverson, too. Traverson.paginateNext() can be used to iterate pages by following 'next' links. The callback function provided to paginateNext() is called for every page, until either false is returned from the callback, or the last page is reached.

The Traverson parameter of the callback function is then used to traverse the items of the page.

        traverson(this::getHalJson)
                .startWith("/example/products")
                // Page of products by following link-relation type 'next':
                .paginateNext((Traverson pageTraverson) -> {
                    // Follow all 'item' links
                    pageTraverson
                            .follow("item")
                            .streamAs(ProductHalRepresentation.class)
                            .forEach(product->{
                                System.out.println(product.title + ": " + product.price);
                            };
                    // proceed to next page of products:
                    return true;
                });

It is also possible to page by following other link-relation types using Traverson.paginatePrev (for 'prev') or Traverson.paginate() for other rels.

If the page is needed as a subtype of HalRepresentation (for example, if it contains required extra attributes), paginateNextAs() or paginatePrevAs() can be used:

        traverson(this::getHalJson)
                .startWith("/example/products")
                // Paginate using next. Pages are parsed as ProductPageHalRepresentation:
                .paginateNextAs(ProductPageHalRepresentation.class, (Traverson pageTraverson) -> {
                    // Fetch the page resource:
                    pageTraverson
                            .getResourceAs(ProductPageHalRepresentation.class)
                            .ifPresent((page) -> {
                                System.out.println(productPage.pageTitle);
                            });
                    // Process linked items of the page:
                    pageTraverson
                            .follow("item")
                            .streamAs(ProductHalRepresentation.class)
                            .forEach(product->{
                                System.out.println(product.title + ": " + product.price);
                            };
                    return true;
                });

If the paged items may be embedded into the page, it is necessary to specify the type of the embedded items:

        traverson(this::getHalJson)
                .startWith("/example/products")
                .paginateNext(
                        withEmbedded("item", ProductHalRepresentation.class),
                        (Traverson pageTraverson) -> { ... }
                );

5. Building edison-hal

If you want to build edison-hal using Gradle, you might want to use the included Gradle wrapper:

    bin/go build

or

    bin/gradlew build

An IntelliJ IDEA Workspace can be created using

    bin/go idea

If you do not want to use the provided gradle wrapper, please make sure that you are using an up-to-date version of Gradle (>= 2.12.0).

6. Running the examples

Currently, there are two examples:

• One for the server side, using Spring Boot
• One for the client side, which is a simple Java application using an Apache HttpClient to access the example server.

The server can be started using Gradle:

    gradle :example-springboot:bootRun

Alternatively, you can simply run the class Server in your favorite IDE.

Open 'http://localhost:8080' in your Browser and navigate to the included HAL Browser to play around with the example.

The client can be started like this:

    gradle :example-client:run

It requires the server to be running. The REST resources are traversed in different ways.

7. Version History

2.0.0-m1

Breaking Changes

• The error handling in the Traverson API has been changed in that exceptions are now thrown instead of catching them and exposing a Traverson.getLastError(). In 1.0.0, the client had to check for the last error. This is rather unusual and is easy to overlook. Beginning with 2.0.0, getLastError is removed and the following method-signatures are now throwing java.io.IOException:
  • Traverson.paginateNext()
  • Traverson.paginateNextAs()
  • Traverson.paginatePrev()
  • Traverson.paginatePrevAs()
  • Traverson.stream()
  • Traverson.streamAs()
  • Traverson.getResource()
  • Traverson.getResourceAs()
• The static factory method Traverson.traverson() does not accept a java.util.function.Function<Link,String> anymore. Instead, a de.otto.edison.hal.traverson.LinkResolver was introduced. The major difference between the new PageHandler and the previous Function is that the PageHandler.apply(Link) is now throwing IOException while Function does not allow this.
• For the same reasons (being able to throw IOExceptions), the different paginate* methods now expect a de.otto.edison.hal.traverson.PageHandler instead of a java.util.function.Function<Traverson,Boolean>. Beside of this, using dedicated functional interfaces instead of generic Functions is a little easier to understand.

New Features / API extensions

• The Traverson now supports traversing linked resources while ignoring embedded resources: instead of returning an embedded item, clients are now able to force the Traverson to follow the links instead. This is especially helpful, if only a reduced set of attributes is embedded into a resource. A set of Traverson.followLink() methods was added to support this.
• Added new methods Traverson.paginate() and Traverson.paginateAs() to paginate over paged resources using link-relation types other than next or prev.
• Added a CuriTemplate helper to expand / shorten link-relation types using a CURI.

1.0.0 (CURRENT RELEASE)

New Features / API extensions

• It is now possible to configure the link-relation types that are serialized as an array of links.
• Parsing of nested embedded items
• Support for curies in deeply nested embedded items
• The HalParser now supports multiple type infos so more than one link-relation type can be configured with the type of the embedded items.
• Support for parsing and accessing attributes that were not mapped to properties of HalRepresentations
• Added TRACE logging to Traverson to make it easier to analyse the behaviour of the Traverson.

1.0.0.RC5

Bugfixes

• Fixed signature of HalRepresentation.withEmbedded(): using List<? extends HalRepresentation instead of List<HalRepresentation

1.0.0.RC4

New Features / API extensions

• Added support for traversal auf HAL documents with relative hrefs.

1.0.0.RC3

New Features / API extensions

• Added Traverson.getResourceAs(Class<T>, EmbeddedTypeInfo) and `Traverson.streamAs(Class, EmbeddedTypeInfo> so it is possible to specify the type of embedded items of a resource using Traversons.
• Added support for client-side traversal of paged resources using
  • Traverson.paginateNext()
  • Traverson.paginateNextAs()
  • Traverson.paginatePrev()
  • Traverson.paginatePrevAs()
  • Traverson.paginate()
  • Traverson.paginateAs()

1.0.0.RC2

Bugfixes

• Fixed traversion of links using predicates
• Fixed parsing of embedded items, where a rel has only only a single item instead of a list of items.
• Fixed getter for SkipLimitPaging.hasMore

1.0.0.RC1

New Features / API extensions

• New Traverson methods to select links matching some given predicate.

0.7.0

Breaking Changes

• Deprecated NumberedPaging.numberedPaging().

New Features / API extensions

• Introduced support for 1-based paging.
• New builder methods NumberedPaging.zeroBasedNumberedPaging() and NumberedPaging.oneBasedNumberedPaging()

0.6.2

Bugfixes

• The constructors of NumberedPaging are now protected instead of final. This prevented changing the names of the page/pageSize variables used in collection resources.
• Fixed numbering of last-page links in NumberedPaging.

New Features / API extensions

• Added NumberedPaging.getLastPage()

0.6.1

Bugfixes

• Fixed a bug that prevented the use of paging for empty collections.

0.6.0

Breaking Changes

• Moved Traverson classes to package de.otto.edison.hal.traverson

Bugfixes

• Fixed shortening of embedded links using curies when adding links to a HalResource after construction.

New Features / API extensions

• Added Link.getHrefAsTemplate()
• Added helpers to create links for paged resources: NumberedPaging and SkipLimitPaging

0.5.0

Breaking Changes

• Renamed Link.Builder.fromPrototype() and Links.Builder.fromPrototype() to copyOf()

New Features / API extensions

• Added Link.isEquivalentTo(Link)
• Link.Builder is not adding equivalent links anymore
• Added HalRepresentation.withEmbedded() and HalRepresentation.withLinks() so links and embedded items can be added after construction.

0.4.1

New Features / API extensions

• Added Traverson.startWith(HalRepresentation) to initialize a Traverson from a given resource.

Bufixes

• JsonSerializers and -Deserializers for Links and Embedded are now public to avoid problems with some testing szenarios in Spring.

0.4.0

Breaking Changes

• Simplified creation of links by removing unneeded factory methods for templated links. Whether or not a link is templated is now automatically identified by the Link.
• Removed duplicate factory method to create a Link.Builder.

New Features / API extensions

• Added a Traverson API to navigate through HAL resources.

0.3.0

Bugfixes

• curies are now rendered as an array of links instead of a single link document

New Features / API extensions

• Added factory method Link.curi() to build CURI links.
• Support for curies in links and embedded resources.
• Improved JavaDoc
• Added Links.getRels()
• Added Links.stream()
• Added Embedded.getRels()
• Added simple example for a client of a HAL service.

0.2.0

Bugfixes

• Fixed generation + parsing of non-trivial links
• Fixed type and name of 'deprecation' property in links
• Fixed rendering of empty embedded items
• Fixed rendering of empty links

Breaking Changes

• Renamed Link.LinkBuilder to Link.Builder
• Renamed Embedded.EmbeddedItemsBuilder to Embedded.Builder
• Renamed Embedded.Builder.withEmbedded() to Embedded.Builder.with()
• Renamed Embedded.Builder.withoutEmbedded() to Embedded.Builder.without()
• Added getter methods to Link instead of public final attributes

New Features / API extensions

• Introduced factory methods for Embedded.Builder
• Improved JavaDoc
• Added Spring-Boot example aplication incl HAL Browser
• Added Links.linkingTo(List links)
• Added Links.Builder
• Added Embedded.isEmpty()

0.1.0

• Initial Release
• Full support for all link properties specified by https://tools.ietf.org/html/draft-kelly-json-hal-08
• Full support for embedded resources.
• Serialization and deserialization of HAL resources.