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JAX-RS @Context tutorial

JAX-RS @Context tutorial shows how use the @Context 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 @Context

The JAX-RS @Context annotation allows to inject context related information into a class field, bean property or method parameter.

JAX-RS @Context example

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

$ tree
.
├── nb-configuration.xml
├── 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>JerseyContext</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>

    <name>JerseyContext</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>
        
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.0</version>
            <scope>provided</scope>
        </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, jersey-server, and javax.servlet dependencies.

context.xml
<?xml version="1.0" encoding="UTF-8"?>
<Context path="/JerseyContext"/>

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.inject.Inject;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
import javax.ws.rs.core.UriInfo;

@Path("myresource")
public class MyResource {
    
    @Context
    private UriInfo info;
    
    @Context
    private HttpServletRequest servletRequest;    
    
    @Context 
    private ServletContext servletContext;

    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public Response message() {

        StringBuilder builder = new StringBuilder();
        
        String baseUri = info.getBaseUri().toASCIIString();
        String method = servletRequest.getMethod();
        String serverInfo = servletContext.getServerInfo();
        
        builder.append("Base uri: ").append(baseUri)
                .append("; HTTP method: ").append(method)
                .append("; Server info: ").append(serverInfo);
        
        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.

@Context
private UriInfo info;

@Context
private HttpServletRequest servletRequest;    

@Context 
private ServletContext servletContext;

Here we inject UriInfo, HttpServletRequest, and ServletContext into class fields with @Context.

@GET
@Produces(MediaType.TEXT_PLAIN)
public Response message() {

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.

StringBuilder builder = new StringBuilder();

String baseUri = info.getBaseUri().toASCIIString();
String method = servletRequest.getMethod();
String serverInfo = servletContext.getServerInfo();

builder.append("Base uri: ").append(baseUri)
        .append("; HTTP method: ").append(method)
        .append("; Server info: ").append(serverInfo);

String output = builder.toString();

From the injected classes, we get the base URI, HTTP method, and server info. We build an output from the gathered information.

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

We send a response containing the information to the client.

$ curl localhost:8084/JerseyContext/rest/myresource
Base uri: http://localhost:8084/JerseyContext/rest/; HTTP method: GET; 
Server info: Apache Tomcat/8.0.27

After the application is deployed on Tomcat, we send a GET request to the application with curl.

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

You might also be interested in the following related tutorials: Java tutorial, JAX-RS @PathParam tutorial, JAX-RS @QueryParam tutorial, Jersey Hello World tutorial, Spring Boot Jersey tutorial, Jersey application with embedded Jetty, and Web URL in a Jersey application.