Since version 5.8.0, Tapestry provides out-of-the-box support for writing REST endpoints as regular event handler methods in page classes. They work in the same way the
activate event (i.e.
onActivate() methods) work, including how event handler method parameters work. The
@RequestBody annotation was created so event handler methods can access the request body. The @StaticActivationContextValue annotation was created so you can write event handler methods that are only called when one or more parts of the URL path match given values. Both annotations are not REST-specific and can be used in any event handler method. A new subproject/JAR, tapestry-rest-jackson, automates the use of Jackson Databind to make JSON conversions. tapestry-Swagger/OpenAPI 3.0 descriptions are generated automatically and can be easily customized. A new subproject/JAR, tapestry-openapi-viewer, provides an out-of-the-box viewer for the generated OpenAPI description using Swagger UI. For a Tapestry REST support example project, check out https://github.com/thiagohp/tapestry-rest-example.
Some important warnings:
- Tapestry's REST support isn't an implementation of JAX-RS, so they expect any of its concepts to work here. It's REST implemented in a Tapestry way.
- REST endpoint event handler methods in components are ignored just like
The following HTTP methods are supported:
|HTTP method||Tapestry event name|
Writing REST endpoints
Writing a REST endpoint in Tapestry is exactly the same as writing
onActivate() method in a page class. Everything is the same: parameter handling, returned value processing, precedence rules, class inheritance, URLs, etc. If you know how to write
onActivate() methods, you already know almost everything you need how to write a REST endpoint event handler. There are only 2 small differences between
onActivate() and REST endpoint event handler methods:
- REST event handler methods are invoked after the
- The event name is different, according to the HTTP method to be handled.
So, for example, if you want a REST endpoint with URL /userendpoint/[id], supposing the id is a
Long, handling the
GET HTTP method, you can just write the following page class and event handler:
The example above could also be written using the
@OnEvent annotation and would work the same:
Reading the request body with
Many times, specially with POST, PUT and PATCH requests, the data is sent through the request body. To get this data, the event handler method needs to add a parameter with the
@RequestBody annotation. It has a single property,
false as its default value, which defines whether an empty request body is empty. If not, an exception will be thrown.
The following types are supported out-of-the-box:
- Primitive types and their wrapper types
The actual conversion logic is implemented in the
HttpRequestBodyConverter service, which is defined is an ordered configuration of
HttpRequestBodyConverter instances. The service calls all contributed instances until one of them returns a non-null value. If none of them returns a non-null value, it falls back to trying to find a coercion, direct or indirect, from
HttpServletRequest to the desired type.
Here's one example of implementing an new
HttpRequestBodyConverter then the code added to
AppModule or any other Tapestry-IoC module class to have it used by
Answering REST requests
Just like any other Tapestry event handler method, the returned value defines what gets to be sent to the user agent making the request. This logic is written in
ComponentEventResultProcessor implementations, usually but not necessarily one per return type/class, which are contributed to the
ComponentEventResultProcessor service. These implementations can also set additional HTTP headers and set the HTTP status code.
REST requests responses usually fall into 2 types: ones just returning HTTP status and and headers (for example,
DELETE requests) and ones returning that and also content (for example,
GET, sometimes other methods too).
For content responses, Tapestry has out-of-the-box support for
StreamResponse (mostly binary content),
TextStreamResponse (simple text content),
JSONArray (since Tapestry 5.8.0) and
JSONObject (since 5.8.0). Here's one example for adding support for a class,
User, converting it to the JSON format:
For responses without content, just HTTP status and headers, and also for simple String responses, Tapestry 5.8.0 introduced the
HttpStatus class. You can create instances of it by either using its utility static methods that match HTTP status names like
forbidden() or using one of its constructors. In both cases, you can customize the response further by using a fluent interface with methods for header-specific methods like
withContentLocation(url) or the generic
withHttpHeader(String name, String value). Check the
HttpStatus JavaDoc for the full list of methods.
This is a service which provides a list of mapped entities. They're usually classes which are mapped to other formats like JSON and XML and used to represent data received or sent to or from external processes, for example REST endpoints. Contributions are done by package and all classes inside the contributed ones are considered mapped entities. The
[root package]. rest.entities package is automatically contributed.
This service is used by Tapestry code, including the OpenAPI description generator and tapestry-rest-jackson, to know which classes should be considered part of the webapp's external APIs.
Here's an example contribution:
Integration with Jackson Databind with tapestry-rest-jackson
JSON has been widely used as a data interchange format in REST endpoints, while Jackson Databind is maybe the mostly used Java library for JSON mapping. tapestry-rest-jackson
automates the usage of Jackson Databind in Tapestry, defining an
ObjectMapperSource service, contributing
HttpRequestBodyConverter implementations for all mapped entity classes (as defined by the
MappedEntityManager service) and implementing the generation of JSON schemas for OpenAPI descriptions of mapped entity classes using victools/jsonschema-generator.
ObjectMapperSource service defines how tapestry-rest-jackson will get an
ObjectMapper instance to use for a given entity class. It has an ordered configuration of
ObjectMapperSource. It has a single method,
ObjectMapper get(Class<?> clasz). When it's called, it goes through all the contributed instances calling the same method on them until one returns a non-null value. When a non-null value is returned, the service method returns it. If none is found, the fallback is always returning the same object returned by
new ObjectMapper(). Any customizations to the
ObjectMapper instance should be done as contributions to the
ObjectMapperSource service. Here's one example that defines which date format should be used for all entity classes:
Automatic generation of OpenAPI 3.0 (Swagger) descriptions
Tapestry provides an out-of-the-box OpenAPI 3.0 (Swagger) description generator driven by the REST endpoints event handlers (i.e. the ones handling the events listed in the table in the top of this page), configuration symbols and internationalization messages (i.e. app.properties). The description is in the JSON format.
It's disabled by default. It's enabled by setting the
SymbolConstants.PUBLISH_OPENAPI_DEFINITON) configuration symbol to
true. If enabled, it will be available at the
/openapi.json URL. This is configurable by using the
SymbolConstants.OPENAPI_DESCRIPTION_PATH) configuration symbol.
All the entity classes returned by MappedEntityManager.getEntities() are automatically added to the schemas section of the generated description.
Customizing names, summaries and descriptions using messages and configuration symbols
Summaries, names and descriptions and messages are taken from messages first, configuration symbol second, except for the OpenAPI version, which is only taken from the
SymbolConstants.OPENAPI_VERSION) symbol and has a default value of
3.0.0. Given a message key, the corresponding configuration symbol is
tapestry.[message key] format.
HTTP method names are lowercased.
When building a message key, if it's based on a path, the starting slash is not removed. For example, the summary for the
/something endpoint for the POST method is
You can see which messages and symbols are being looked up by setting the debug level of the
org.apache.tapestry5.internal.services.rest.DefaultOpenApiDescriptionGenerator class to
Customizing the consumed and produced MIME content types of an endpoint with
@RestInfo annotation allows you to define, just for OpenAPI description generation purposes, what are the accepted MIME content types accepted by a REST endpoint event handler method, the produced types and what's the actual returned value type of the method when its execution succeeds. Many REST event handler methods usually have a return type of
Object so it can return an
HttpStatus instance of something goes wrong and a mapped entity class entity when the call is successful.
Here's one example:
The generated description can be further customized by implementing the
OpenApiDescriptionGenerator interface and contributing it to the
OpenApiDescriptionGenerator service. The
JSONObject generate(JSONObject documentation) method will receive the generated description and it can be changed by using the
JSONObject methods. The return value should be the same object received as a parameter.
The tapestry-openapi-viewer Tapestry subproject/JAR embeds the open source Swagger-UI OpenAPI/Swagger and makes it available at the
/openapiviewer URL. No configuration is needed other than including the JAR in the classpath.