Building RESTful Web Services with Jakarta REST

This chapter describes the REST architecture, RESTful web services, and the Jakarta RESTful Web Services.

Jakarta REST makes it easy for developers to build RESTful web services using the Java programming language.

What Are RESTful Web Services?

RESTful web services are loosely coupled, lightweight web services that are particularly well suited for creating APIs for clients spread out across the internet. Representational State Transfer (REST) is an architectural style of client-server application centered around the transfer of representations of resources through requests and responses. In the REST architectural style, data and functionality are considered resources and are accessed using Uniform Resource Identifiers (URIs), typically links on the Web. The resources are represented by documents and are acted upon by using a set of simple, well-defined operations.

For example, a REST resource might be the current weather conditions for a city. The representation of that resource might be an XML document, an image file, or an HTML page. A client might retrieve a particular representation, modify the resource by updating its data, or delete the resource entirely.

The REST architectural style is designed to use a stateless communication protocol, typically HTTP. In the REST architecture style, clients and servers exchange representations of resources by using a standardized interface and protocol.

The following principles encourage RESTful applications to be simple, lightweight, and fast:

Resource identification through URI: A RESTful web service exposes a set of resources that identify the targets of the interaction with its clients. Resources are identified by URIs, which provide a global addressing space for resource and service discovery. See The @Path Annotation and URI Path Templates for more information.
Uniform interface: Resources are manipulated using a fixed set of four create, read, update, delete operations: PUT, GET, POST, and DELETE. PUT creates a new resource, which can be then deleted by using DELETE. GET retrieves the current state of a resource in some representation. POST transfers a new state onto a resource. See Responding to HTTP Methods and Requests for more information.
Self-descriptive messages: Resources are decoupled from their representation so that their content can be accessed in a variety of formats, such as HTML, XML, plain text, PDF, JPEG, JSON, and other document formats. Metadata about the resource is available and used, for example, to control caching, detect transmission errors, negotiate the appropriate representation format, and perform authentication or access control. See Responding to HTTP Methods and Requests and Using Entity Providers to Map HTTP Response and Request Entity Bodies for more information.
Stateful interactions through links: Every interaction with a resource is stateless; that is, request messages are self-contained. Stateful interactions are based on the concept of explicit state transfer. Several techniques exist to exchange state, such as URI rewriting, cookies, and hidden form fields. State can be embedded in response messages to point to valid future states of the interaction. See Using Entity Providers to Map HTTP Response and Request Entity Bodies and Extracting Request Parameters in the Jakarta REST Overview document for more information.

Creating a RESTful Root Resource Class

Root resource classes are "plain old Java objects" (POJOs) that are either annotated with @Path or have at least one method annotated with @Path or a request method designator, such as @GET, @PUT, @POST, or @DELETE. Resource methods are methods of a resource class annotated with a request method designator. This section explains how to use Jakarta REST to annotate Java classes to create RESTful web services.

Developing RESTful Web Services with Jakarta REST

Jakarta REST is a Java programming language API designed to make it easy to develop applications that use the REST architecture.

The Jakarta REST API uses Java programming language annotations to simplify the development of RESTful web services. Developers decorate Java programming language class files with Jakarta REST annotations to define resources and the actions that can be performed on those resources. Jakarta REST annotations are runtime annotations; therefore, runtime reflection will generate the helper classes and artifacts for the resource. A Jakarta EE application archive containing Jakarta REST resource classes will have the resources configured, the helper classes and artifacts generated, and the resource exposed to clients by deploying the archive to a Jakarta EE server.

Summary of Jakarta REST Annotations lists some of the Java programming annotations that are defined by Jakarta REST, with a brief description of how each is used. Further information on the Jakarta REST APIs can be viewed at https://jakarta.ee/specifications/platform/9/apidocs/.

Summary of Jakarta REST Annotations
Annotation	Description
`@Path`	The `@Path` annotation’s value is a relative URI path indicating where the Java class will be hosted: for example, `/helloworld`. You can also embed variables in the URIs to make a URI path template. For example, you could ask for the name of a user and pass it to the application as a variable in the URI: `/helloworld/{username}`.
`@GET`	The `@GET` annotation is a request method designator and corresponds to the similarly named HTTP method. The Java method annotated with this request method designator will process HTTP GET requests. The behavior of a resource is determined by the HTTP method to which the resource is responding.
`@POST`	The `@POST` annotation is a request method designator and corresponds to the similarly named HTTP method. The Java method annotated with this request method designator will process HTTP POST requests. The behavior of a resource is determined by the HTTP method to which the resource is responding.
`@PUT`	The `@PUT` annotation is a request method designator and corresponds to the similarly named HTTP method. The Java method annotated with this request method designator will process HTTP PUT requests. The behavior of a resource is determined by the HTTP method to which the resource is responding.
`@DELETE`	The `@DELETE` annotation is a request method designator and corresponds to the similarly named HTTP method. The Java method annotated with this request method designator will process HTTP DELETE requests. The behavior of a resource is determined by the HTTP method to which the resource is responding.
`@HEAD`	The `@HEAD` annotation is a request method designator and corresponds to the similarly named HTTP method. The Java method annotated with this request method designator will process HTTP HEAD requests. The behavior of a resource is determined by the HTTP method to which the resource is responding.
`@OPTIONS`	The `@OPTIONS` annotation is a request method designator and corresponds to the similarly named HTTP method. The Java method annotated with this request method designator will process HTTP OPTIONS requests. The behavior of a resource is determined by the HTTP method to which the resource is responding.
`@PATCH`	The `@PATCH` annotation is a request method designator and corresponds to the similarly named HTTP method. The Java method annotated with this request method designator will process HTTP PATCH requests. The behavior of a resource is determined by the HTTP method to which the resource is responding.
`@PathParam`	The `@PathParam` annotation is a type of parameter that you can extract for use in your resource class. URI path parameters are extracted from the request URI, and the parameter names correspond to the URI path template variable names specified in the `@Path` class-level annotation.
`@QueryParam`	The `@QueryParam` annotation is a type of parameter that you can extract for use in your resource class. Query parameters are extracted from the request URI query parameters.
`@Consumes`	The `@Consumes` annotation is used to specify the MIME media types of representations a resource can consume that were sent by the client.
`@Produces`	The `@Produces` annotation is used to specify the MIME media types of representations a resource can produce and send back to the client: for example, `"text/plain"`.
`@Provider`	The `@Provider` annotation is used for anything that is of interest to the Jakarta REST runtime, such as `MessageBodyReader` and `MessageBodyWriter`. For HTTP requests, the `MessageBodyReader` is used to map an HTTP request entity body to method parameters. On the response side, a return value is mapped to an HTTP response entity body by using a `MessageBodyWriter`. If the application needs to supply additional metadata, such as HTTP headers or a different status code, a method can return a `Response` that wraps the entity and that can be built using `Response.ResponseBuilder`.
`@ApplicationPath`	The `@ApplicationPath` annotation is used to define the URL mapping for the application. The path specified by `@ApplicationPath` is the base URI for all resource URIs specified by `@Path` annotations in the resource class. You may only apply `@ApplicationPath` to a subclass of `jakarta.ws.rs.core.Application`.

Overview of a Jakarta REST Application

The following code sample is a very simple example of a root resource class that uses Jakarta REST annotations:

package ee.jakarta.tutorial.hello;

import jakarta.ws.rs.Consumes;
import jakarta.ws.rs.GET;
import jakarta.ws.rs.PUT;
import jakarta.ws.rs.Path;
import jakarta.ws.rs.Produces;
import jakarta.ws.rs.core.Context;
import jakarta.ws.rs.core.UriInfo;

/**
 * Root resource (exposed at "helloworld" path)
 */
@Path("helloworld")
public class HelloWorld {
    @Context
    private UriInfo context;

    /** Creates a new instance of HelloWorld */
    public HelloWorld() {
    }

    /**
     * Retrieves representation of an instance of helloWorld.HelloWorld
     * @return an instance of java.lang.String
     */
    @GET
    @Produces("text/html")
    public String getHtml() {
        return "<html lang=\"en\"><body><h1>Hello, World!!</h1></body></html>";
    }
}

The following sections describe the annotations used in this example.

The @Path annotation’s value is a relative URI path. In the preceding example, the Java class will be hosted at the URI path /helloworld. This is an extremely simple use of the @Path annotation, with a static URI path. Variables can be embedded in the URIs. URI path templates are URIs with variables embedded within the URI syntax.
The @GET annotation is a request method designator, along with @POST, @PUT, @DELETE, and @HEAD, defined by Jakarta REST and corresponding to the similarly named HTTP methods. In the example, the annotated Java method will process HTTP GET requests. The behavior of a resource is determined by the HTTP method to which the resource is responding.
The @Produces annotation is used to specify the MIME media types a resource can produce and send back to the client. In this example, the Java method will produce representations identified by the MIME media type "text/html".
The @Consumes annotation is used to specify the MIME media types a resource can consume that were sent by the client. The example could be modified to set the message returned by the getHtml method, as shown in this code example:
```
@POST
@Consumes("text/plain")
public void postHtml(String message) {
    // Store the message
}
```

The @Path Annotation and URI Path Templates

The @Path annotation identifies the URI path template to which the resource responds and is specified at the class or method level of a resource. The @Path annotation’s value is a partial URI path template relative to the base URI of the server on which the resource is deployed, the context root of the application, and the URL pattern to which the Jakarta REST runtime responds.

URI path templates are URIs with variables embedded within the URI syntax. These variables are substituted at runtime in order for a resource to respond to a request based on the substituted URI. Variables are denoted by braces ({ and }). For example, look at the following @Path annotation:

@Path("/users/{username}")

In this kind of example, a user is prompted to type his or her name, and then a Jakarta REST web service configured to respond to requests to this URI path template responds. For example, if the user types the user name "Galileo," the web service responds to the following URL:

http://example.com/users/Galileo

To obtain the value of the user name, the @PathParam annotation may be used on the method parameter of a request method, as shown in the following code example:

@Path("/users/{username}")
public class UserResource {

    @GET
    @Produces("text/xml")
    public String getUser(@PathParam("username") String userName) {
        ...
    }
}

By default, the URI variable must match the regular expression "[^/]+?". This variable may be customized by specifying a different regular expression after the variable name. For example, if a user name must consist only of lowercase and uppercase alphanumeric characters, override the default regular expression in the variable definition:

@Path("users/{username: [a-zA-Z][a-zA-Z_0-9]*}")

In this example, the username variable will match only user names that begin with one uppercase or lowercase letter and zero or more alphanumeric characters and the underscore character. If a user name does not match that template, a 404 (Not Found) response will be sent to the client.

A @Path value isn’t required to have leading or trailing slashes (/). The Jakarta REST runtime parses URI path templates the same way, whether or not they have leading or trailing slashes.

A URI path template has one or more variables, with each variable name surrounded by braces: { to begin the variable name and } to end it. In the preceding example, username is the variable name. At runtime, a resource configured to respond to the preceding URI path template will attempt to process the URI data that corresponds to the location of {username} in the URI as the variable data for username.

For example, if you want to deploy a resource that responds to the URI path template http://example.com/myContextRoot/resources/{name1}/{name2}/, you must first deploy the application to a Jakarta EE server that responds to requests to the http://example.com/myContextRoot URI and then decorate your resource with the following @Path annotation:

@Path("/{name1}/{name2}/")
public class SomeResource {
    ...
}

In this example, the URL pattern for the Jakarta REST helper servlet, specified in web.xml, is the default:

<servlet-mapping>
      <servlet-name>jakarta.ws.rs.core.Application</servlet-name>
      <url-pattern>/resources/*</url-pattern>
</servlet-mapping>

A variable name can be used more than once in the URI path template.

If a character in the value of a variable would conflict with the reserved characters of a URI, the conflicting character should be substituted with percent encoding. For example, spaces in the value of a variable should be substituted with %20.

When defining URI path templates, be careful that the resulting URI after substitution is valid.

Examples of URI Path Templates lists some examples of URI path template variables and how the URIs are resolved after substitution. The following variable names and values are used in the examples:

name1: james
name2: gatz
name3:
location: Main%20Street
question: why

The value of the name3 variable is an empty string.

Examples of URI Path Templates
URI Path Template	URI After Substitution
http://example.com/{name1}/{name2}/	http://example.com/james/gatz/
http://example.com/{question}/{question}/{question}/	http://example.com/why/why/why/
http://example.com/maps/{location}	http://example.com/maps/Main%20Street
http://example.com/{name3}/home/	http://example.com//home/

Responding to HTTP Methods and Requests

The behavior of a resource is determined by the HTTP methods (typically, GET, POST, PUT, or DELETE) to which the resource is responding.

The Request Method Designator Annotations

Request method designator annotations are runtime annotations, defined by Jakarta REST, that correspond to the similarly named HTTP methods. Within a resource class file, HTTP methods are mapped to Java programming language methods by using the request method designator annotations. The behavior of a resource is determined by which HTTP method the resource is responding to. Jakarta REST defines a set of request method designators for the common HTTP methods GET, POST, PUT, DELETE, and HEAD; you can also create your own custom request method designators. Creating custom request method designators is outside the scope of this document.

The following example shows the use of the PUT method to create or update a storage container:

@PUT
public Response putContainer() {
    System.out.println("PUT CONTAINER " + container);

    URI uri =  uriInfo.getAbsolutePath();
    Container c = new Container(container, uri.toString());

    Response r;
    if (!MemoryStore.MS.hasContainer(c)) {
        r = Response.created(uri).build();
    } else {
        r = Response.noContent().build();
    }

    MemoryStore.MS.createContainer(c);
    return r;
}

By default, the Jakarta REST runtime will automatically support the methods HEAD and OPTIONS if not explicitly implemented. For HEAD, the runtime will invoke the implemented GET method, if present, and ignore the response entity, if set. For OPTIONS, the Allow response header will be set to the set of HTTP methods supported by the resource. In addition, the Jakarta REST runtime will return a Web Application Definition Language (WADL) document describing the resource; see https://www.w3.org/Submission/wadl/ for more information.

Methods decorated with request method designators must return void, a Java programming language type, or a jakarta.ws.rs.core.Response object. Multiple parameters may be extracted from the URI by using the @PathParam or @QueryParam annotations, as described in Extracting Request Parameters. Conversion between Java types and an entity body is the responsibility of an entity provider, such as MessageBodyReader or MessageBodyWriter. Methods that need to provide additional metadata with a response should return an instance of the Response class. The ResponseBuilder class provides a convenient way to create a Response instance using a builder pattern. The HTTP PUT and POST methods expect an HTTP request body, so you should use a MessageBodyReader for methods that respond to PUT and POST requests.

Both @PUT and @POST can be used to create or update a resource. POST can mean anything, so when using POST, it is up to the application to define the semantics. PUT has well-defined semantics. When using PUT for creation, the client declares the URI for the newly created resource.

PUT has very clear semantics for creating and updating a resource. The representation the client sends must be the same representation that is received using a GET, given the same media type. PUT does not allow a resource to be partially updated, a common mistake when attempting to use the PUT method. A common application pattern is to use POST to create a resource and return a 201 response with a location header whose value is the URI to the newly created resource. In this pattern, the web service declares the URI for the newly created resource.

Using Entity Providers to Map HTTP Response and Request Entity Bodies

Entity providers supply mapping services between representations and their associated Java types. The two types of entity providers are MessageBodyReader and MessageBodyWriter. For HTTP requests, the MessageBodyReader is used to map an HTTP request entity body to method parameters. On the response side, a return value is mapped to an HTTP response entity body by using a MessageBodyWriter. If the application needs to supply additional metadata, such as HTTP headers or a different status code, a method can return a Response that wraps the entity and that can be built by using Response.ResponseBuilder.

Types Supported for HTTP Request and Response Entity Bodies shows the standard types that are supported automatically for HTTP request and response entity bodies. You need to write an entity provider only if you are not choosing one of these standard types.

Types Supported for HTTP Request and Response Entity Bodies
Java Type	Supported Media Types
`byte[]`	All media types (`/`)
`java.lang.String`	All text media types (`text/*`)
`java.io.InputStream`	All media types (`/`)
`java.io.Reader`	All media types (`/`)
`java.io.File`	All media types (`/`)
`jakarta.activation.DataSource`	All media types (`/`)
`javax.xml.transform.Source`	XML media types (`text/xml`, `application/xml`, and `application/*+xml`)
`jakarta.xml.bind.JAXBElement` and application-supplied Jakarta XML Binding classes	XML media types (`text/xml`, `application/xml`, and `application/*+xml`)
`MultivaluedMap<String, String>`	Form content (`application/x-www-form-urlencoded`)
`StreamingOutput`	All media types (`/`), `MessageBodyWriter` only

The following example shows how to use MessageBodyReader with the @Consumes and @Provider annotations:

@Consumes("application/x-www-form-urlencoded")
@Provider
public class FormReader implements MessageBodyReader<NameValuePair> { }

The following example shows how to use MessageBodyWriter with the @Produces and @Provider annotations:

@Produces("text/html")
@Provider
public class FormWriter implements
        MessageBodyWriter<Hashtable<String, String>> { }

The following example shows how to use ResponseBuilder:

@GET
public Response getItem() {
    System.out.println("GET ITEM " + container + " " + item);

    Item i = MemoryStore.MS.getItem(container, item);
    if (i == null)
        throw new NotFoundException("Item not found");
    Date lastModified = i.getLastModified().getTime();
    EntityTag et = new EntityTag(i.getDigest());
    ResponseBuilder rb = request.evaluatePreconditions(lastModified, et);
    if (rb != null)
        return rb.build();

    byte[] b = MemoryStore.MS.getItemData(container, item);
    return Response.ok(b, i.getMimeType()).
            lastModified(lastModified).tag(et).build();
}

Using @Consumes and @Produces to Customize Requests and Responses

The information sent to a resource and then passed back to the client is specified as a MIME media type in the headers of an HTTP request or response. You can specify which MIME media types of representations a resource can respond to or produce by using the following annotations:

jakarta.ws.rs.Consumes
jakarta.ws.rs.Produces

By default, a resource class can respond to and produce all MIME media types of representations specified in the HTTP request and response headers.

The @Produces Annotation

The @Produces annotation is used to specify the MIME media types or representations a resource can produce and send back to the client. If @Produces is applied at the class level, all the methods in a resource can produce the specified MIME types by default. If applied at the method level, the annotation overrides any @Produces annotations applied at the class level.

If no methods in a resource are able to produce the MIME type in a client request, the Jakarta REST runtime sends back an HTTP "406 Not Acceptable" error.

The value of @Produces is an array of String of MIME types or a comma-separated list of MediaType constants. For example:

@Produces({"image/jpeg,image/png"})

The following example shows how to apply @Produces at both the class and method levels:

@Path("/myResource")
@Produces("text/plain")
public class SomeResource {
    @GET
    public String doGetAsPlainText() {
        ...
    }

    @GET
    @Produces("text/html")
    public String doGetAsHtml() {
        ...
    }
}

The doGetAsPlainText method defaults to the MIME media type of the @Produces annotation at the class level. The doGetAsHtml method’s @Produces annotation overrides the class-level @Produces setting and specifies that the method can produce HTML rather than plain text.

@Produces can also use the constants defined in the jakarta.ws.rs.core.MediaType class to specify the media type. For example, specifying MediaType.APPLICATION_XML is equivalent to specifying "application/xml".

@Produces(MediaType.APPLICATION_XML)
@GET
public Customer getCustomer() { ... }

If a resource class is capable of producing more than one MIME media type, the resource method chosen will correspond to the most acceptable media type as declared by the client. More specifically, the Accept header of the HTTP request declares what is most acceptable. For example, if the Accept header is Accept: text/plain, the doGetAsPlainText method will be invoked. Alternatively, if the Accept header is Accept: text/plain;q=0.9, text/html, which declares that the client can accept media types of text/plain and text/html but prefers the latter, the doGetAsHtml method will be invoked.

More than one media type may be declared in the same @Produces declaration. The following code example shows how this is done:

@Produces({"application/xml", "application/json"})
public String doGetAsXmlOrJson() {
    ...
}

The doGetAsXmlOrJson method will get invoked if either of the media types application/xml or application/json is acceptable. If both are equally acceptable, the former will be chosen because it occurs first. The preceding examples refer explicitly to MIME media types for clarity. It is possible to refer to constant values, which may reduce typographical errors. For more information, see the API documentation for the constant field values of jakarta.ws.rs.core.MediaType.

The @Consumes Annotation

The @Consumes annotation is used to specify which MIME media types of representations a resource can accept, or consume, from the client. If @Consumes is applied at the class level, all the response methods accept the specified MIME types by default. If applied at the method level, @Consumes overrides any @Consumes annotations applied at the class level.

If a resource is unable to consume the MIME type of a client request, the Jakarta REST runtime sends back an HTTP 415 ("Unsupported Media Type") error.

The value of @Consumes is an array of String of acceptable MIME types, or a comma-separated list of MediaType constants. For example:

@Consumes({"text/plain,text/html"})

This is the equivalent of:

@Consumes({MediaType.TEXT_PLAIN,MediaType.TEXT_HTML})

The following example shows how to apply @Consumes at both the class and method levels:

@Path("/myResource")
@Consumes("multipart/related")
public class SomeResource {
    @POST
    public String doPost(MimeMultipart mimeMultipartData) {
        ...
    }

    @POST
    @Consumes("application/x-www-form-urlencoded")
    public String doPost2(FormURLEncodedProperties formData) {
        ...
    }
}

The doPost method defaults to the MIME media type of the @Consumes annotation at the class level. The doPost2 method overrides the class level @Consumes annotation to specify that it can accept URL-encoded form data.

If no resource methods can respond to the requested MIME type, an HTTP 415 ("Unsupported Media Type") error is returned to the client.

The HelloWorld example discussed previously in this section can be modified to set the message by using @Consumes, as shown in the following code example:

@POST
@Consumes("text/html")
public void postHtml(String message) {
    // Store the message
}

In this example, the Java method will consume representations identified by the MIME media type text/plain. Note that the resource method returns void. This means that no representation is returned and that a response with a status code of HTTP 204 ("No Content") will be returned.

Extracting Request Parameters

Parameters of a resource method may be annotated with parameter-based annotations to extract information from a request. A previous example presented the use of the @PathParam parameter to extract a path parameter from the path component of the request URL that matched the path declared in @Path.

You can extract the following types of parameters for use in your resource class:

Query
URI path
Form
Cookie
Header
Matrix

Query parameters are extracted from the request URI query parameters and are specified by using the jakarta.ws.rs.QueryParam annotation in the method parameter arguments. The following example demonstrates using @QueryParam to extract query parameters from the Query component of the request URL:

@Path("smooth")
@GET
public Response smooth(
        @DefaultValue("2") @QueryParam("step") int step,
        @DefaultValue("true") @QueryParam("min-m") boolean hasMin,
        @DefaultValue("true") @QueryParam("max-m") boolean hasMax,
        @DefaultValue("true") @QueryParam("last-m") boolean hasLast,
        @DefaultValue("blue") @QueryParam("min-color") ColorParam minColor,
        @DefaultValue("green") @QueryParam("max-color") ColorParam maxColor,
        @DefaultValue("red") @QueryParam("last-color") ColorParam lastColor
        ) { ... }

If the query parameter step exists in the query component of the request URI, the value of step will be extracted and parsed as a 32-bit signed integer and assigned to the step method parameter. If step does not exist, a default value of 2, as declared in the @DefaultValue annotation, will be assigned to the step method parameter. If the step value cannot be parsed as a 32-bit signed integer, an HTTP 400 ("Client Error") response is returned.

User-defined Java programming language types may be used as query parameters. The following code example shows the ColorParam class used in the preceding query parameter example:

public class ColorParam extends Color {
    public ColorParam(String s) {
        super(getRGB(s));
    }

    private static int getRGB(String s) {
        if (s.charAt(0) == '#') {
            try {
                Color c = Color.decode("0x" + s.substring(1));
                return c.getRGB();
            } catch (NumberFormatException e) {
                throw new WebApplicationException(400);
            }
        } else {
            try {
                Field f = Color.class.getField(s);
                return ((Color)f.get(null)).getRGB();
            } catch (Exception e) {
                throw new WebApplicationException(400);
            }
        }
    }
}

The constructor for ColorParam takes a single String parameter.

Both @QueryParam and @PathParam can be used only on the following Java types.

All primitive types except char.
All wrapper classes of primitive types except Character.
Any class with a constructor that accepts a single String argument.
Any class with the static method named valueOf(String) that accepts a single String argument.
List<T>, Set<T>, or SortedSet<T>, where T matches the already listed criteria. Sometimes, parameters may contain more than one value for the same name. If this is the case, these types may be used to obtain all values.

If @DefaultValue is not used in conjunction with @QueryParam, and the query parameter is not present in the request, the value will be an empty collection for List, Set, or SortedSet; null for other object types; and the default for primitive types.

URI path parameters are extracted from the request URI, and the parameter names correspond to the URI path template variable names specified in the @Path class-level annotation. URI parameters are specified using the jakarta.ws.rs.PathParam annotation in the method parameter arguments. The following example shows how to use @Path variables and the @PathParam annotation in a method:

@Path("/{username}")
public class MyResourceBean {
    ...
    @GET
    public String printUsername(@PathParam("username") String userId) {
        ...
    }
}

In the preceding snippet, the URI path template variable name username is specified as a parameter to the printUsername method. The @PathParam annotation is set to the variable name username. At runtime, before printUsername is called, the value of username is extracted from the URI and cast to a String. The resulting String is then available to the method as the userId variable.

If the URI path template variable cannot be cast to the specified type, the Jakarta REST runtime returns an HTTP 400 ("Bad Request") error to the client. If the @PathParam annotation cannot be cast to the specified type, the Jakarta REST runtime returns an HTTP 404 ("Not Found") error to the client.

The @PathParam parameter and the other parameter-based annotations (@MatrixParam, @HeaderParam, @CookieParam, and @FormParam) obey the same rules as @QueryParam.

Cookie parameters, indicated by decorating the parameter with jakarta.ws.rs.CookieParam, extract information from the cookies declared in cookie-related HTTP headers. Header parameters, indicated by decorating the parameter with jakarta.ws.rs.HeaderParam, extract information from the HTTP headers. Matrix parameters, indicated by decorating the parameter with jakarta.ws.rs.MatrixParam, extract information from URL path segments.

Form parameters, indicated by decorating the parameter with jakarta.ws.rs.FormParam, extract information from a request representation that is of the MIME media type application/x-www-form-urlencoded and conforms to the encoding specified by HTML forms, as described in https://www.w3.org/TR/html401/interact/forms.html#h-17.13.4.1. This parameter is very useful for extracting information sent by POST in HTML forms.

The following example extracts the name form parameter from the POST form data:

@POST
@Consumes("application/x-www-form-urlencoded")
public void post(@FormParam("name") String name) {
    // Store the message
}

To obtain a general map of parameter names and values for query and path parameters, use the following code:

@GET
public String get(@Context UriInfo ui) {
    MultivaluedMap<String, String> queryParams = ui.getQueryParameters();
    MultivaluedMap<String, String> pathParams = ui.getPathParameters();
}

The following method extracts header and cookie parameter names and values into a map:

@GET
public String get(@Context HttpHeaders hh) {
    MultivaluedMap<String, String> headerParams = hh.getRequestHeaders();
    Map<String, Cookie> pathParams = hh.getCookies();
}

In general, @Context can be used to obtain contextual Java types related to the request or response.

For form parameters, it is possible to do the following:

@POST
@Consumes("application/x-www-form-urlencoded")
public void post(MultivaluedMap<String, String> formParams) {
    // Store the message
}

Configuring Jakarta REST Applications

A Jakarta REST application consists of at least one resource class packaged within a WAR file. The base URI from which an application’s resources respond to requests can be set one of two ways:

Using the @ApplicationPath annotation in a subclass of jakarta.ws.rs.core.Application packaged within the WAR
Using the servlet-mapping tag within the WAR’s web.xml deployment descriptor

Configuring a Jakarta REST Application Using a Subclass of Application

Create a subclass of jakarta.ws.rs.core.Application to manually configure the environment in which the REST resources defined in your resource classes are run, including the base URI. Add a class-level @ApplicationPath annotation to set the base URI.

@ApplicationPath("/webapi")
public class MyApplication extends Application { ... }

In the preceding example, the base URI is set to /webapi, which means that all resources defined within the application are relative to /webapi.

By default, all the resources in an archive will be processed for resources. Override the getClasses method to manually register the resource classes in the application with the Jakarta REST runtime.

@Override
public Set<Class<?>> getClasses() {
    final Set<Class<?>> classes = new HashSet<>();
    // register root resource
    classes.add(MyResource.class);
    return classes;
}

Configuring the Base URI in web.xml

The base URI for a Jakarta REST application can be set using a servlet-mapping tag in the web.xml deployment descriptor, using the Application class name as the servlet.

<servlet-mapping>
    <servlet-name>jakarta.ws.rs.core.Application</servlet-name>
    <url-pattern>/webapi/*</url-pattern>
</servlet-mapping>

This setting will also override the path set by @ApplicationPath when using an Application subclass.

<servlet-mapping>
   <servlet-name>com.example.rest.MyApplication</servlet-name>
   <url-pattern>/services/*</url-pattern>
</servlet-mapping>

Example Applications for Jakarta REST

This section provides an introduction to creating, deploying, and running your own Jakarta REST applications. This section demonstrates the steps that are needed to create, build, deploy, and test a very simple web application that uses Jakarta REST annotations.

Creating a Simple RESTful Web Service

This section explains how to use NetBeans IDE to create a RESTful web service using a Maven archetype. The archetype generates a skeleton for the application, and you simply need to implement the appropriate method.

You can find a version of this application at jakartaee-examples/tutorial/rest/hello/.

To Create a RESTful Web Service Using NetBeans IDE

Ensure you have installed the tutorial archetypes as described in Installing the Tutorial Archetypes.
In NetBeans IDE, create a simple web application using the jaxrs-service-archetype Maven archetype. This archetype creates a very simple "Hello, World" web application.
1. From the File menu, choose New Project.
2. From Categories, select Maven. From Projects, select Project From Archetype. Click Next.
3. Under Search enter rest-service, select the rest-service-archetype, and click Next.
4. Under Project Name enter HelloWorldApplication, set the Project Location, and set the Package name to ee.jakarta.tutorial.hello, and click Finish.
  
  The project is created.
In HelloWorld.java, find the getHtml() method. Replace the //TODO comment with the following text, so that the finished product resembles the following method:
```
@GET
@Produces("text/html")
public String getHtml() {
    return "<html lang=\"en\"><body><h1>Hello, World!!</body></h1></html>";
}
```
Because the MIME type produced is HTML, you can use HTML tags in your return statement.
Right-click the HelloWorldApplication project in the Projects pane and select Run.

This will build and deploy the application to GlassFish Server.
In a browser, open the following URL:
```
http://localhost:8080/HelloWorldApplication/HelloWorldApplication
```
A browser window opens and displays the return value of Hello, World!!

For other sample applications that demonstrate deploying and running Jakarta REST applications using NetBeans IDE, see The rsvp Example Application and Your First Cup: An Introduction to the Jakarta EE Platform at https://eclipse-ee4j.github.io/jakartaee-firstcup/toc.html. You may also look at the tutorials on the NetBeans IDE tutorial site, such as the one titled "Getting Started with RESTful Web Services" at https://netbeans.apache.org/kb/docs/websvc/rest.html. This tutorial includes a section on creating a CRUD application from a database. Create, read, update, and delete (CRUD) are the four basic functions of persistent storage and relational databases.

The rsvp Example Application

The rsvp example application, located in the jakartaee-examples/tutorial/rest/rsvp/ directory, allows invitees to an event to indicate whether they will attend. The events, people invited to the event, and the responses to the invite are stored in Apache Derby using Jakarta Persistence. The Jakarta REST resources in rsvp are exposed in a stateless session enterprise bean.

Components of the rsvp Example Application

The three enterprise beans in the rsvp example application are rsvp.ejb.ConfigBean, rsvp.ejb.StatusBean, and rsvp.ejb.ResponseBean.

ConfigBean is a singleton session bean that initializes the data in the database.

StatusBean exposes a Jakarta REST resource for displaying the current status of all invitees to an event. The URI path template is declared first on the class and then on the getEvent method:

@Stateless
@Named
@Path("/status")
public class StatusBean {
    ...
    @GET
    @Produces({MediaType.APPLICATION_XML, MediaType.APPLICATION_JSON})
    @Path("{eventId}/")
    public Event getEvent(@PathParam("eventId") Long eventId) {
         ...
    }
}

The combination of the two @Path annotations results in the following URI path template:

@Path("/status/{eventId}/")

The URI path variable eventId is a @PathParam variable in the getEvent method, which responds to HTTP GET requests and has been annotated with @GET. The eventId variable is used to look up all the current responses in the database for that particular event.

ResponseBean exposes a Jakarta REST resource for setting an invitee’s response to a particular event. The URI path template for ResponseBean is declared as follows:

@Path("/{eventId}/{inviteId}")

Two URI path variables are declared in the path template: eventId and inviteId. As in StatusBean, eventId is the unique ID for a particular event. Each invitee to that event has a unique ID for the invitation, and that is the inviteId. Both of these path variables are used in two Jakarta REST methods in ResponseBean: getResponse and putResponse. The getResponse method responds to HTTP GET requests and displays the invitee’s current response and a form to change the response.

The ee.jakarta.tutorial.rsvp.rest.RsvpApplication class defines the root application path for the resources by applying the jakarta.ws.rs.ApplicationPath annotation at the class level.

@ApplicationPath("/webapi")
public class RsvpApplication extends Application {
}

An invitee who wants to change his or her response selects the new response and submits the form data, which is processed as an HTTP POST request by the putResponse method. The new response is extracted from the HTTP POST request and stored as the userResponse string. The putResponse method uses userResponse, eventId, and inviteId to update the invitee’s response in the database.

The events, people, and responses in rsvp are encapsulated in Jakarta Persistence entities. The rsvp.entity.Event, rsvp.entity.Person, and rsvp.entity.Response entities respectively represent events, invitees, and responses to an event.

The rsvp.util.ResponseEnum class declares an enumerated type that represents all the possible response statuses an invitee may have.

The web application also includes two CDI managed beans, StatusManager and EventManager, which use the Jakarta REST Client API to call the resources exposed in StatusBean and ResponseBean. For information on how the Client API is used in rsvp, see The Client API in the rsvp Example Application.

Running the rsvp Example Application

Both NetBeans IDE and Maven can be used to deploy and run the rsvp example application.

To Run the rsvp Example Application Using NetBeans IDE

If the database server is not already running, start it by following the instructions in Starting and Stopping Apache Derby.
Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).
From the File menu, choose Open Project.
In the Open Project dialog box, navigate to:
```
jakartaee-examples/tutorial/rest
```
Select the rsvp folder.
Click Open Project.
In the Projects tab, right-click the rsvp project and select Run.

The project will be compiled, assembled, and deployed to GlassFish Server. A web browser window will open to the following URL:
```
http://localhost:8080/rsvp/index.xhtml
```
In the web browser window, click the Event status link for the Duke’s Birthday event.

You’ll see the current invitees and their responses.
Click the current response of one of the invitees in the Status column of the table, select a new response, and click Update your status.

The invitee’s new status should now be displayed in the table of invitees and their response statuses.

To Run the rsvp Example Application Using Maven

If the database server is not already running, start it by following the instructions in Starting and Stopping Apache Derby.
Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).
In a terminal window, go to:
```
jakartaee-examples/tutorial/rest/rsvp/
```
Enter the following command:
```
mvn install
```
This command builds, assembles, and deploys rsvp to GlassFish Server.
Open a web browser window to the following URL:
```
http://localhost:8080/rsvp/
```
In the web browser window, click the Event status link for the Duke’s Birthday event.

You’ll see the current invitees and their responses.
Click the current response of one of the invitees in the Status column of the table, select a new response, and click Update your status.

The invitee’s new status should now be displayed in the table of invitees and their response statuses.

Real-World Examples

Most blog sites use RESTful web services. These sites involve downloading XML files, in RSS or Atom format, that contain lists of links to other resources. Other websites and web applications that use REST-like developer interfaces to data include Twitter and Amazon S3 (Simple Storage Service). With Amazon S3, buckets and objects can be created, listed, and retrieved using either a REST-style HTTP interface or a SOAP interface. The examples that ship with Jersey include a storage service example with a RESTful interface.

Further Information about Jakarta REST

For more information about RESTful web services and Jakarta REST, see

"Fielding Dissertation: Chapter 5: Representational State Transfer (REST)":
https://www.ics.uci.edu/~fielding/pubs/dissertation/rest_arch_style.htm
RESTful Web Services, by Leonard Richardson and Sam Ruby, available from O’Reilly Media at https://www.oreilly.com/library/view/restful-web-services/9780596529260/
Jakarta RESTful Web Services 3.0 specification:
https://jakarta.ee/specifications/restful-ws/3.0/
Jersey project:
https://eclipse-ee4j.github.io/jersey/