====== Lesson 2 - REST, JAX-RS, Jersey======

===== Lesson plan =====
  * Homework check
  * REST intro
  * JAX-RS application with Glassfish/Jersey example

===== REST =====

See the presentation describing[[http://old.kwarc.info/projects/students/papers/Rest.ppt | REST]].

===== Simple example =====

The example may be downloaded here: {{:courses:a4m36aos:cviceni:jersey-sample.zip|}}

Check the sample, see how it works. The application is inspired by the sample [[http://https://www.nabisoft.com/tutorials/java-ee/producing-and-consuming-json-or-xml-in-java-rest-services-with-jersey-and-moxy|REST]] application. The application provides two resources - a message resource and a person resource. The application supports just GET method for both resources, therefore you are able to get person and message resources.

==== Jersey maven ====
The following are the dependencies we are using:

<code>
<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>${version.servlet.api}</version>
    <scope>provided</scope>
</dependency>
                    
<!-- Jersey -->		
<dependency>
    <groupId>org.glassfish.jersey.containers</groupId>
    <artifactId>jersey-container-servlet</artifactId>
    <version>${version.jersey}</version>
</dependency>

<dependency>
     <groupId>org.glassfish.jersey.media</groupId>
     <artifactId>jersey-media-moxy</artifactId>
     <version>${version.jersey}</version>
</dependency>
</code>   

==== Descriptor ====
To deploy the application the minimal web.xml descriptor must be used:
<code>
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" 
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" 
    id="WebApp_ID" version="3.1">    
  <session-config>
    <session-timeout>30</session-timeout>
    <cookie-config>
      <name>SESSIONID</name>
    </cookie-config>
  </session-config>
</web-app>
</code>
   
==== Message resource ====

<code>
@Path("/message")
public class MessageResource {
    
    @GET
    @Path("ping")
    public String getServerTime() {
        return "received ping on "+new Date().toString();
    }
    
    @GET
    @Produces({MediaType.APPLICATION_JSON})  //add MediaType.APPLICATION_XML if you want XML as well (don't forget @XmlRootElement)
    public List<Message> getAllMessages() throws Exception{
        List<Message> messages = new ArrayList<>();
        
        Message firstMessage = new Message();
        firstMessage.setDate(new Date());
        firstMessage.setFirstName("Nabi");
        firstMessage.setAge(30);
        firstMessage.setText("Hello World!");
        messages.add(firstMessage);

        Message secondMessage = new Message();
        secondMessage.setDate(new Date());
        secondMessage.setFirstName("Francis");
        secondMessage.setAge(31);
        secondMessage.setText("It's in the game.");
        messages.add(secondMessage);

        return messages; //do not use Response object because this causes issues when generating XML automatically
    }

    @GET
    @Produces({MediaType.APPLICATION_JSON})  //add MediaType.APPLICATION_XML if you want XML as well (don't forget @XmlRootElement)
    @Path("text/{textParam}")
    public Message getMessage(@PathParam("textParam") String textParam) throws Exception{
        Message message = new Message();
        message.setDate(new Date());
        message.setFirstName("Vladimir");
        message.setAge(35);
        message.setText(textParam);

        return message;
    }
}
</code>

==== Client for testing ====

For testing, you can use one of the following clients:
  * Simple REST client - Chrome
  * REST client - Firefox

Deploy the application to web server and go to the address http://localhost:8080/rest/:

==== Tasks ====
  * Modify the resources such that they return not only JSON, but also XML (remember to call them with correct headers: Content-type: application/xml}
  * Find out how to implement PUT, POST and DELETE methods
  * Find out how to implement Query parameters - use [[https://jersey.java.net/documentation/latest/|Jersey Guide]]