JAX-RS - Resource Field and Property Injection

In previous tutorials, we saw JAX-RS annotation can be used with resource methods parameters and with constructor parameter as well. There's a third option which we should be aware of i.e. using those annotation on field/property levels; the JAX-RS runtime will automatically inject their corresponding values.

Field injection

Following example shows how to use field injection:

@Path("/")
public class MyResource {
    @Context
    UriInfo uriInfo;
    @PathParam("num")
    int pathNum;
    @QueryParam("q")
    String qValue;

    @GET
    @Path("/test{num:[1-9]{0,1}}")
    public String handleRequest() {
        URI uri = uriInfo.getRequestUri();
        return String.format(" response from: %s%n PathNum: %s%n query paramMyResource: %s%n",
                uri, pathNum, qValue);
    }
}

mvn tomcat7:run

Testing above resource with JAX-RS client:

public class MyClient {
    public static void main(String[] args) {
        Client client = ClientBuilder.newClient();
        WebTarget target = client.target("http://localhost:8080/test9");
        String response = target.queryParam("q", "testVal")
                                .request()
                                .get(String.class);
        System.out.println(response);
    }
}

Output

 response from: http://localhost:8080/test9?q=testVal
 PathNum: 9
 q: testVal

Property Injection

@Path("/property/")
public class MyResource1 {
    UriInfo uriInfo;
    int pathNum;
    String myParam;

    @GET
    @Path("/test{num:[1-9]{0,1}}")
    public String handleRequest() {
        URI uri = uriInfo.getRequestUri();
        return String.format("response from: %s%nPathNum: %s%nmyParam: %s%n",
                uri, pathNum, myParam);
    }

    @Context
    public void setUriInfo(UriInfo uriInfo) {
        this.uriInfo = uriInfo;
    }

    @PathParam("num")
    public void setPathNum(int pathNum) {
        this.pathNum = pathNum;
    }

    @QueryParam("q")
    public void setMyParam(String myParam) {
        this.myParam = myParam;
    }
}

public class MyClient1 {
    public static void main(String[] args) {
        Client client = ClientBuilder.newClient();
        WebTarget target = client.target("http://localhost:8080/property/test5");
        String response = target.queryParam("q", "testVal")
                                .request()
                                .get(String.class);
        System.out.println(response);
    }
}

Output

response from: http://localhost:8080/property/test5?q=testVal
PathNum: 5
myParam: testVal

Field/Property injection with singleton resources

Only @Context annotation is allowed on singleton resources:

@Path("/static/")
public class MyResource2 {
    @Context
    UriInfo uriInfo;

    @Context
    HttpHeaders headers;

    @GET
    @Path("/test2")
    public String handleRequest() {
        return String.format("handleRequest, path: %s, headers: %s%n",
                uriInfo.getPath(),
                headers.getRequestHeader("myHeader"));
    }

    @GET
    @Path("/test3")
    public String handleRequest2() {
        return String.format("handleRequest2, path: %s, headers: %s%n",
                uriInfo.getPath(),
                headers.getRequestHeader("myHeader2"));
    }
}

@ApplicationPath("/")
public class MyRestApp extends Application {
    .............
    @Override
    public Set<Object> getSingletons() {
        Set<Object> set = new HashSet<>();
        set.add(new MyResource2());
        return set;
    }
}

public class MyClient2 {
    public static void main(String[] args) {
        Client client = ClientBuilder.newClient();
        WebTarget target = client.target("http://localhost:8080/static/test2");
        String response = target.request().header("myHeader", "header-value")
                                .get(String.class);
        System.out.println(response);

        //second request
        target = client.target("http://localhost:8080/static/test3");
        response = target.request().header("myHeader2", "header-value2")
                         .get(String.class);
        System.out.println(response);
    }
}

Output

handleRequest, path: static/test2, headers: [header-value]

handleRequest2, path: static/test3, headers: [header-value2]

Attempting to use other annotations will end up with an exception during startup time:

@Path("/static/")
public class MyResource2 {
    .....
    @QueryParam("q")
    String qValue;
    .....
}

Output

java.lang.IllegalStateException: Not inside a request scope.
	at jersey.repackaged.com.google.common.base.Preconditions.checkState(Preconditions.java:173)
	at org.glassfish.jersey.process.internal.RequestScope.current(RequestScope.java:233)
   ....

Example Project

Dependencies and Technologies Used:

• jersey-container-servlet 2.25.1: Jersey core Servlet 3.x implementation.
• JDK 1.8
• Maven 3.3.9