Java Servlet RESTFul client

last modified August 24, 2023

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

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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