ZetCode

Java Servlet RESTFul client

last modified July 14, 2020

In Java Servlet RESTFul client tutorial, we create a RESTFul client in a Java Servlet with JAX-RS.

Java API for RESTful Web Services (JAX-RS) is a Java API specification that provides support in creating web services according to the Representational State Transfer (REST) architectural pattern.

RESTEasy is a Java RESTful Web Services Framework and a JAX-RS implementation from JBoss.

Servlet is a Java class which responds to a particular type of network request - most commonly an HTTP request. Java servlets are used to create web applications. They run in servlet containers such as Tomcat or Jetty. Modern-day Java web development uses frameworks that are built on top of servlets.

Java Servlet application

The following web application creates a request to the api.randomuser.me site, which is a random user generator.

The Java servlet uses ClientBuilder to create a Client, which is the main entry point to the fluent API used to build and execute client requests in order to consume responses returned.

pom.xml
src
├── main
│   ├── java
│   │   └── com
│   │       └── zetcode
│   │           ├── model
│   │           │   ├── Location.java
│   │           │   ├── Name.java
│   │           │   ├── Person.java
│   │           │   └── PersonsList.java
│   │           ├── service
│   │           │   └── PersonService.java
│   │           └── web
│   │               └── MyServlet.java
│   ├── resources
│   └── webapp
│       ├── index.html
│       └── show.jsp
└── 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>JavaServletRestClient</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>14</maven.compiler.source>
        <maven.compiler.target>14</maven.compiler.target>
    </properties>

    <dependencies>

        <dependency>
            <groupId>jstl</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>

        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>org.jboss.resteasy</groupId>
            <artifactId>resteasy-servlet-initializer</artifactId>
            <version>4.5.5.Final</version>
        </dependency>

        <dependency>
            <groupId>org.jboss.resteasy</groupId>
            <artifactId>resteasy-client</artifactId>
            <version>4.5.5.Final</version>
        </dependency>

        <dependency>
            <groupId>org.jboss.resteasy</groupId>
            <artifactId>resteasy-jackson2-provider</artifactId>
            <version>4.5.5.Final</version>
        </dependency>


    </dependencies>

    <build>
        <plugins>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>3.3.0</version>
            </plugin>

            <plugin>
                <groupId>org.eclipse.jetty</groupId>
                <artifactId>jetty-maven-plugin</artifactId>
                <version>9.4.30.v20200611</version>
            </plugin>
        </plugins>
    </build>

</project>

This is the Maven POM file. We have the following artifacts: javax.servlet-api for servlets, jstl for the standard JSP tags library, resteasy-servlet-initializer for integrating RESTEasy with servlets, resteasy-client for the RESTFul core client implementation and resteasy-jackson2-provide for JSON/Java model data binding.

In the application, we have three model classes; these models will be filled with data from the response.

com/zetcode/model/Location.java
package com.zetcode.model;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;

@JsonIgnoreProperties(ignoreUnknown = true)
public class Location {

    private String city;
    private String state;
    private String postcode;

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state;
    }

    public String getPostcode() {
        return postcode;
    }

    public void setPostcode(String postcode) {
        this.postcode = postcode;
    }

    @Override
    public String toString() {
        final StringBuilder sb = new StringBuilder("Location{");
        sb.append("city='").append(city).append('\'');
        sb.append(", state='").append(state).append('\'');
        sb.append(", postcode='").append(postcode).append('\'');
        sb.append('}');
        return sb.toString();
    }
}

The Location stores the address of the user.

@JsonIgnoreProperties(ignoreUnknown = true)

With the @JsonIgnoreProperties annotation we tell the Jackson to ignore properties not listed in the Person.

com/zetcode/model/Name.java
package com.zetcode.model;

public class Name {

    private String first;
    private String last;
    private String title;

    public String getFirst() {
        return first;
    }

    public void setFirst(String firstName) {
        first = firstName;
    }

    public String getLast() {
        return last;
    }

    public void setLast(String lastName) {
        last = lastName;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    @Override
    public String toString() {

        StringBuilder sb = new StringBuilder();
        sb.append(title).append(" ").append(first)
                .append(" ").append(last);
        return sb.toString();
    }
}

The Name stores the user name details.

com/zetcode/model/Person.java
package com.zetcode.model;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;

@JsonIgnoreProperties(ignoreUnknown = true)
public class Person {

    private Name name;
    private Location location;
    private String email;
    private String gender;

    public void setName(Name name) {
        this.name = name;
    }

    public Name getName() {
        return name;
    }    

    public Location getLocation() {
        return location;
    }

    public void setLocation(Location location) {
        this.location = location;
    }
    
    public void setEmail(String email) {
        this.email = email;
    }

    public String getEmail() {
        return email;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    @Override
    public String toString() {

        StringBuilder sb = new StringBuilder();
        sb.append("Name: ").append(name)
                .append("Address: ").append(location)
                .append("Email ").append(email)
                .append("Gender: ").append(gender);
        return sb.toString();
    }
}

The Person class stores data about the user, including name, address, email, and gender.

com/zetcode/PersonsList.java
package com.zetcode.model;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import java.util.List;

@JsonIgnoreProperties(ignoreUnknown = true)
public class PersonsList {

    private List<Person> results;

    public List<Person> getResults() {
        return results;
    }

    public void setResults(List<Person> result) {
        results = result;
    }
}

This is the list of Person objects. The web service fills this list with data.

com/zetcode/web/MyServlet.java
package com.zetcode.web;

import com.zetcode.model.Person;
import com.zetcode.service.PersonService;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;

@WebServlet(name = "MyServlet", urlPatterns = {"/MyServlet"})
public class MyServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html;charset=UTF-8");

        List<Person> people = PersonService.fetchPeople(0, 50);

        request.setAttribute("people", people);
        request.getRequestDispatcher("show.jsp").forward(request, response);
    }
}

The MyServlet servlet calls the PersonService.fetchPeople(), which returns a list of Person objects. The list is stored as an attribute and the processing is dispatched to the show.jsp page. The JSP page renders the list of Person objects.

com/zetcode/service/PersonService.java
package com.zetcode.service;

import com.zetcode.model.Person;
import com.zetcode.model.PersonsList;
import java.util.List;

import javax.ws.rs.client.ClientBuilder;
import javax.ws.rs.client.WebTarget;
import javax.ws.rs.core.MediaType;

public class PersonService {

    private static WebTarget resource = ClientBuilder.newBuilder()
            .build().target("https://api.randomuser.me/");
 
    public static List<Person> fetchPeople(int offset, int num) {
        PersonsList res = resource.queryParam("seed", 1)
                .queryParam("results", num).queryParam("page", 1)
                .request(MediaType.APPLICATION_JSON).get(PersonsList.class);
        return res.getResults();
    }      
}

PersonService contains a fetchPeople() method to perform a query on api.randomuser.me web service. The service returns randomly user objects.

private static WebTarget resource = ClientBuilder.newBuilder()
        .build().target("https://api.randomuser.me/");

With the ClientBuilder, we create a web resource target. The api.randomuser.me website returns randomly a list of users.

public static List<Person> fetchPeople(int offset, int num) {
    PersonsList res = resource.queryParam("seed", 1)
            .queryParam("results", num).queryParam("page", 1)
            .request(MediaType.APPLICATION_JSON).get(PersonsList.class);
    return res.getResults();
}    

We send a query to the web resouce; the data is stored in PersonsList.

webapp/index.html
<!DOCTYPE html>
<html>
    <head>
        <title>Home Page</title>
        <meta charset="UTF-8">
    </head>
    <body>
        <a href="MyServlet">List people</a>
    </body>
</html>

This is the home page. It contains a link to call the MyServlet.

webapp/show.jsp
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>Show people</title>
    </head>
    <body>
        <table>
            <thead>
                <tr>
                    <th>Title</th>
                    <th>First name</th>
                    <th>Last name</th>
                    <th>City</th>
                    <th>State</th>
                    <th>Postcode</th>
                    <th>Email</th>
                    <th>Gender</th>
                </tr>
            </thead>
            <tbody>

                <c:forEach var="per" items="${people}">
                    <tr>
                        <td><c:out value="${per.name.title}"/></td>
                        <td><c:out value="${per.name.first}"/></td>
                        <td><c:out value="${per.name.last}"/></td>
                        <td><c:out value="${per.location.city}"/></td>
                        <td><c:out value="${per.location.state}"/></td>
                        <td><c:out value="${per.location.postcode}"/></td>
                        <td><c:out value="${per.email}"/></td>
                        <td><c:out value="${per.gender}"/></td>
                    </tr>
                </c:forEach>
            </tbody>
        </table>
    </body>    
</html>

The show.jsp page displays data in a HTML table using c:forEach and c:out tags from the JSTL library.

$ mvn jetty:run 

We start the application and locate to localhost:8080.

In this tutorial, we created a RESTEasy client request to a web service that generates randomly users. The request was sent from a Java servlet.

List all Java Servlet tutorials.