RESTEasy Tomcat CDI tutorial
last modified January 10, 2023
RESTEasy Tomcat CDI tutorial shows how to create a RESTful web application with RESTEasy, Tomcat, and CDI.
RESTEasy
RESTEasy is a framework for developing RESTful Web Services in Java. It is a fully certified and portable implementation of the JAX-RS 2.0 specification. JAX-RS 2.0 specification is a JCP (Java Community Process) specification that provides a Java API for RESTful Web Services over the HTTP protocol.
RESTEasy can run in any Servlet container. It contains a rich set of providers, such as XML, JSON, YAML, Fastinfoset, Multipart, XOP, and Atom.
CDI
Contexts and Dependency Injection (CDI) defines a powerful set of complementary services that help improve the structure of application code. CDI allows to bind the lifecycle and interactions of stateful components to well-defined but extensible lifecycle contexts and to inject components into an application in a typesafe way. The advantages of CDI are: loose coupling, easier testing, better layering, interface-based design promotion, and dynamic proxies.
JBoss Weld is a reference implementation of the CDI specification.
RESTEasy Tomcat CDI example
The following example is a simple RESTful application, which returns some context related data to the client as JSON data. The application uses Weld and is deployed on Tomcat.
$ tree
.
├── nb-configuration.xml
├── pom.xml
└── src
├── main
│ ├── java
│ │ └── com
│ │ └── zetcode
│ │ ├── conf
│ │ │ └── AppConfig.java
│ │ ├── model
│ │ │ └── City.java
│ │ ├── resource
│ │ │ └── MyResource.java
│ │ └── service
│ │ ├── CityService.java
│ │ └── ICityService.java
│ ├── resources
│ └── webapp
│ ├── META-INF
│ │ └── context.xml
│ └── WEB-INF
│ └── beans.xml
└── test
└── java
This is the project structure.
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.zetcode</groupId>
<artifactId>RestEasyTomcatCdi</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>war</packaging>
<name>RestEasyTomcatCdi</name>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>11</maven.compiler.source>
<maven.compiler.target>11</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>org.jboss.resteasy</groupId>
<artifactId>resteasy-jaxrs</artifactId>
<version>3.1.4.Final</version>
</dependency>
<dependency>
<groupId>org.jboss.resteasy</groupId>
<artifactId>resteasy-servlet-initializer</artifactId>
<version>3.1.4.Final</version>
</dependency>
<dependency>
<groupId>org.jboss.weld.servlet</groupId>
<artifactId>weld-servlet-shaded</artifactId>
<version>3.0.2.Final</version>
</dependency>
<dependency>
<groupId>org.jboss.resteasy</groupId>
<artifactId>resteasy-jackson-provider</artifactId>
<version>3.1.0.Final</version>
</dependency>
<dependency>
<groupId>org.jboss.resteasy</groupId>
<artifactId>resteasy-cdi</artifactId>
<version>3.1.4.Final</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<version>2.3</version>
<configuration>
<failOnMissingWebXml>false</failOnMissingWebXml>
</configuration>
</plugin>
</plugins>
</build>
</project>
This is the Maven POM file. It contains dependencies for RESTEasy, Weld, and Jackson provider.
<?xml version="1.0" encoding="UTF-8"?> <Context path="/RestEasyTomcatCdi"/>
In the Tomcat's context.xml configuration file, we define
the application context path.
<?xml version="1.0"?>
<beans xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/beans_1_1.xsd"
version="1.1" bean-discovery-mode="all">
</beans>
Applications that use CDI must have a beans.xml file defined. It can
be empty, like in our case. For web applications, the beans.xml file
must be in the WEB-INF directory. For EJB modules or JAR files, the
beans.xml file must be in the META-INF directory.
package com.zetcode.model;
import java.util.Objects;
public class City {
private Long id;
private String name;
private int population;
public City() {
}
public City(Long id, String name, int population) {
this.id = id;
this.name = name;
this.population = population;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getPopulation() {
return population;
}
public void setPopulation(int population) {
this.population = population;
}
@Override
public int hashCode() {
int hash = 3;
hash = 71 * hash + Objects.hashCode(this.id);
hash = 71 * hash + Objects.hashCode(this.name);
hash = 71 * hash + this.population;
return hash;
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
final City other = (City) obj;
if (this.population != other.population) {
return false;
}
if (!Objects.equals(this.name, other.name)) {
return false;
}
return Objects.equals(this.id, other.id);
}
@Override
public String toString() {
return "City{" + "id=" + id + ", name=" + name
+ ", population=" + population + '}';
}
}
This is a City model class. It contains three attributes:
id, name, and population.
package com.zetcode.conf;
import javax.ws.rs.ApplicationPath;
import javax.ws.rs.core.Application;
@ApplicationPath("rest")
public class AppConfig extends Application {
}
This is the application configuration class. The Application
defines the components of a JAX-RS application and supplies additional meta-data.
@ApplicationPath("rest")
With the @ApplicationPath annotation, we set the path to RESTful web services.
package com.zetcode.service;
import com.zetcode.model.City;
import java.util.List;
public interface ICityService {
public List<City> findAll();
}
ICityService contains the findAll contract method.
package com.zetcode.service;
import com.zetcode.model.City;
import java.util.ArrayList;
import java.util.List;
public class CityService implements ICityService {
@Override
public List<City> findAll() {
List<City> cities = new ArrayList<>();
cities.add(new City(1L, "Bratislava", 432000));
cities.add(new City(2L, "Budapest", 1759000));
cities.add(new City(3L, "Prague", 1280000));
cities.add(new City(4L, "Warsaw", 1748000));
cities.add(new City(5L, "Los Angeles", 3971000));
cities.add(new City(6L, "New York", 8550000));
cities.add(new City(7L, "Edinburgh", 464000));
cities.add(new City(8L, "Berlin", 3671000));
return cities;
}
}
CityService contains the implementation for the findAll
method. It simply returns a list of cities. This is usually retrieved from a data source
such as database.
package com.zetcode.resource;
import com.zetcode.model.City;
import com.zetcode.service.ICityService;
import java.util.List;
import javax.inject.Inject;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;
@Path("cities")
public class MyResource {
@Inject
private ICityService cityService;
@GET
@Produces(MediaType.APPLICATION_JSON)
public List<City> message() {
List<City> cities = cityService.findAll();
return cities;
}
}
This is the MyResource class.
@Path("cities")
public class MyResource {
The @Path specifies the URL to which the resource responds.
@Inject private ICityService cityService;
With the @Inject annotation, we inject the city service object
into the cityService field.
@GET
@Produces(MediaType.APPLICATION_JSON)
public List<City> message() {
List<City> cities = cityService.findAll();
return cities;
}
The @GET annotation indicates that the annotated method responds to
HTTP GET requests. With the @Produces annotation, we define that
the method produces JSON. We call a service method and return a list of cities.
The message body writer converts the Java classes to JSON and writes it to the
response body.
$ curl localhost:8084/RestEasyTomcatCdi/rest/cities
[{"id":1,"name":"Bratislava","population":432000},{"id":2,"name":"Budapest","population":1759000},
{"id":3,"name":"Prague","population":1280000},{"id":4,"name":"Warsaw","population":1748000},
{"id":5,"name":"Los Angeles","population":3971000},{"id":6,"name":"New York","population":8550000},
{"id":7,"name":"Edinburgh","population":464000},{"id":8,"name":"Berlin","population":3671000}]
After the application is deployed on Tomcat, we send a GET request to the
application with curl. We get JSON data.
In this tutorial, we have created a simple RESTFul application with RESTEasy and Weld. The application was deployed on Tomcat.