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.

pom.xml

<?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.

context.xml

<?xml version=“1.0” encoding=“UTF-8”?> <Context path="/RestEasyTomcatCdi”/>

In the Tomcat’s context.xml configuration file, we define the application context path.

beans.xml

<?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.

City.java

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.

AppConfig.java

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.

ICityService.java

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.

CityService.java

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.

MyResource.java

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.