JAX-RS @QueryParam

last modified January 10, 2023

JAX-RS @QueryParam tutorial shows how use the @QueryParam annotation in a RESTful Java web application with Jersey framework.

Jersey

Jersey is a framework for developing RESTful Web Services in Java. It is a reference implementation of the Java API for RESTful Web Services (JAX-RS) specification. Another popular JAX-RS implementation is JBoss’ RESTEasy.

JAX-RS @QueryParam

The JAX-RS @QueryParam annotation binds the value(s) of a HTTP query parameter to a resource method parameter, resource class field, or resource class bean property.

JAX-RS @QueryParam example

The following example is a simple RESTful application, which returns some context related data to the client as plain text.

├── pom.xml └── src ├── main │ ├── java │ │ └── com │ │ └── zetcode │ │ ├── conf │ │ │ └── ApplicationConfig.java │ │ └── ws │ │ └── MyResource.java │ ├── resources │ └── webapp │ └── META-INF │ └── context.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>JerseyQueryParam</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>war</packaging>

<name>JerseyQueryParam</name>

<properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <maven.compiler.source>1.8</maven.compiler.source> <maven.compiler.target>1.8</maven.compiler.target> </properties>

<dependencies>
    <dependency>
        <groupId>org.glassfish.jersey.containers</groupId>
        <artifactId>jersey-container-servlet</artifactId>
        <version>2.25</version>
    </dependency>

    <dependency>
        <groupId>org.glassfish.jersey.core</groupId>
        <artifactId>jersey-server</artifactId>
        <version>2.25</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 the jersey-container-servlet and jersey-server.

context.xml

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

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

ApplicationConfig.java

package com.zetcode.conf;

import com.zetcode.ws.HelloResource; import java.util.HashSet; import java.util.Set; import javax.ws.rs.ApplicationPath; import javax.ws.rs.core.Application;

@ApplicationPath(“rest”) public class ApplicationConfig extends Application {

@Override
public Set<Class<?>> getClasses() {
    Set<Class<?>> set = new HashSet<>();
    set.add(MyResource.class);
    return set;
}

}

This is the application configuration class. Since Servlet 3.0 it is possible to deploy application without the web.xml file. The Application defines the components of a JAX-RS application and supplies additional meta-data. Here we register resource classes, providers, or properties the application needs.

@ApplicationPath(“rest”)

With the @ApplicationPath annotation, we set the path to RESTful web services.

@Override public Set<Class<?>> getClasses() { Set<Class<?>> set = new HashSet<>(); set.add(MyResource.class); return set; }

Inside the getClasses method, we add the resource classes. In our case, we have one MyResource class.

MyResource.java

package com.zetcode.ws;

import javax.ws.rs.DefaultValue; import javax.ws.rs.GET; import javax.ws.rs.Path; import javax.ws.rs.Produces; import javax.ws.rs.QueryParam; import javax.ws.rs.core.MediaType; import javax.ws.rs.core.Response;

@Path(“myresource”) public class MyResource {

@GET
@Produces(MediaType.TEXT_PLAIN)
public Response message(@DefaultValue("Guest") @QueryParam("name") String name,
        @DefaultValue("0") @QueryParam("age") int age) {

    StringBuilder builder = new StringBuilder();
    builder.append(name).append(" is ")
            .append(age).append(" years old");

    String output = builder.toString();

    return Response.status(200).entity(output).build();
}

}

This is the MyResource class.

@Path(“myresource”) public class MyResource {

The @Path specifies the URL to which the resource responds.

@GET @Produces(MediaType.TEXT_PLAIN)

The @GET annotation indicates that the annotated method responds to HTTP GET requests. With the @Produces annotation, we define that the method produces plain text.

public Response message(@DefaultValue(“Guest”) @QueryParam(“name”) String name, @DefaultValue(“0”) @QueryParam(“age”) int age) {

We use the @QueryParam annotations for method parameters. We expect two parameters: name and age. The @DefaultValue value provides default values for the parameters. They are used if the parameters are missing in the URL.

StringBuilder builder = new StringBuilder(); builder.append(name).append(” is “) .append(age).append(” years old”);

String output = builder.toString();

From the supplied parameter values, we build a message.

return Response.status(200).entity(output).build();

We send a response containing the message to the client.

$ curl “localhost:8084/JerseyQueryParam/rest/myresource?name=Peter&age=45” Peter is 45 years old

After the application is deployed to Tomcat, we send a GET request to the application with curl. The URL contains the two parameters.

In this tutorial, we have used the JAX-RS @QueryParam annotation.