The following code sample is a very simple example of a root resource class that uses JAX-RS annotations:
package com.dineshonjava.ws.rest; import javax.ws.rs.GET; import javax.ws.rs.Produces; import javax.ws.rs.Path; // The Java class will be hosted at the URI path "/helloworld" @Path("/helloworld") public class HelloWorldResource { // The Java method will process HTTP GET requests @GET // The Java method will produce content identified by the MIME Media // type "text/plain" @Produces("text/plain") public String getClichedMessage() { // Return some cliched textual content return "Hello World!!! Dinesh on Java"; } }
The following sections describe the annotations used in this example.
@POST @Consumes("text/plain") public void postClichedMessage(String message) { // Store the message }
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 JAX-RS 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 JAX-RS 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 JAX-RS runtime parses URI path templates the same whether or not they have leading or trailing spaces.
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 deploy the application to a Java 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 { ... }
References
1. JAVA REST Web Services
2. Wikipedia for REST Web Service
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