11 Programming RESTful Web Services

Overview of RESTful Web Services

Representational State Transfer (REST) describes any simple interface that transmits data over a standardized interface (such as HTTP) without an additional messaging layer, such as SOAP. REST provides a set of design rules for creating stateless services that are viewed as resources, or sources of specific information, and can be identified by their unique URIs. A client accesses the resource using the URI, a standardized fixed set of methods, and a representation of the resource is returned. The client is said to transfer state with each new resource representation.

When using the HTTP protocol to access RESTful resources, the resource identifier is the URL of the resource and the standard operation to be performed on that resource is one of the HTTP methods: GET, PUT, DELETE, POST, or HEAD.

You build RESTful endpoints using the invoke() method of the javax.xml.ws.Provider<T> interface (see http://java.sun.com/javaee/5/docs/api/javax/xml/ws/Provider.html). The Provider interface provides a dynamic alternative to building an service endpoint interface (SEI).

Programming RESTful Web Services: Main Steps

The procedure in this section describes how to program and compile the JWS file required to implement the RESTful Web service. The procedure shows how to create the JWS file from scratch; if you want to update an existing JWS file, you can also use this procedure as a guide.

It is assumed that you have set up an Ant-based development environment and that you have a working build.xml file to which you can add targets for running the jwsc Ant task and deploying the Web services. For more information, see Getting Started With JAX-WS Web Services for Oracle WebLogic Server.

<jwsc srcdir="." destdir="output/restEar">
      <jws file="NearbyCity.java" type="JAXWS"/>
    </jwsc>

prompt> ant build-rest

Programming Guidelines for the RESTful Web Service

The following example shows a simple JWS file that implements a RESTful Web service; see the explanation after the example for coding guidelines that correspond to the Java code in bold.

package examples.webservices.jaxws.rest;
import javax.xml.ws.WebServiceProvider;
import javax.xml.ws.BindingType;
import javax.xml.ws.Provider; 
import javax.xml.ws.WebServiceContext;
import javax.xml.ws.handler.MessageContext;
import javax.xml.ws.http.HTTPBinding;
import javax.xml.ws.http.HTTPException;
import javax.xml.transform.Source;
import javax.xml.transform.stream.StreamSource;
import javax.annotation.Resource;
import java.io.ByteArrayInputStream;
import java.util.StringTokenizer;

@WebServiceProvider(
   targetNamespace="http://example.org",
   serviceName = "NearbyCityService")
@BindingType(value = HTTPBinding.HTTP_BINDING) 

public class NearbyCity implements Provider<Source> { 
  @Resource(type=Object.class)
  protected WebServiceContext wsContext;

  public Source invoke(Source source)  { 
    try {
        MessageContext messageContext = wsContext.getMessageContext();

        // Obtain the HTTP mehtod of the input request.
        javax.servlet.http.HttpServletRequest servletRequest = 
          (javax.servlet.http.HttpServletRequest)messageContext.get(
           MessageContext.SERVLET_REQUEST);
        String httpMethod = servletRequest.getMethod();
        if (httpMethod.equalsIgnoreCase("GET"));
        {

            String query =
                 (String)messageContext.get(MessageContext.QUERY_STRING); 
            if (query != null && query.contains("lat=") &&
                query.contains("long=")) {
                return createSource(query); 
            } else {
                System.err.println("Query String = "+query);
                throw new HTTPException(404);
            }
            } catch(Exception e) {
              e.printStackTrace();
              throw new HTTPException(500);
            }
        }
        } else {
   // This operation only supports "GET"
       throw new HTTPException405);
   }
    private Source createSource(String str) throws Exception {
        StringTokenizer st = new StringTokenizer(str, "=&/");
        String latLong = st.nextToken();
        double latitude = Double.parseDouble(st.nextToken());
        latLong = st.nextToken();
        double longitude = Double.parseDouble(st.nextToken());
        City nearby = City.findNearBy(latitude, longitude);
        String body = nearby.toXML();
        return new StreamSource(new ByteArrayInputStream(body.getBytes()));
    }

    static class City {
         String city;
         String state;
         double latitude;
         double longitude;
         City(String city, double lati, double longi, String st) {
             this.city = city;
             this.state = st;
             this.latitude = lati;
             this.longitude = longi;
         }

         double distance(double lati, double longi) {
            return Math.sqrt((lati-this.latitude)*(lati-this.latitude) + 
                (longi-this.longitude)*(longi-this.longitude)) ;
         }

         static final City[] cities = {
            new City("San Francisco",37.7749295,-122.4194155,"CA"),
            new City("Columbus",39.9611755,-82.9987942,"OH"),
            new City("Indianapolis",39.7683765,-86.1580423,"IN"),
            new City("Jacksonville",30.3321838,-81.655651,"FL"),
            new City("San Jose",37.3393857,-121.8949555,"CA"),
            new City("Detroit",42.331427,-83.0457538,"MI"),
            new City("Dallas",32.7830556,-96.8066667,"TX"),
            new City("San Diego",32.7153292,-117.1572551,"CA"),
            new City("San Antonio",29.4241219,-98.4936282,"TX"),
            new City("Phoenix",33.4483771,-112.0740373,"AZ"),
            new City("Philadelphia",39.952335,-75.163789,"PA"),
            new City("Houston",29.7632836,-95.3632715,"TX"),
            new City("Chicago",41.850033,-87.6500523,"IL"),
            new City("Los Angeles",34.0522342,-118.2436849,"CA"),
            new City("New York",40.7142691,-74.0059729,"NY")};
        static City findNearBy(double lati, double longi) {
            int n = 0;
            for (int i = 1; i < cities.length; i++)  {
                if (cities[i].distance(lati, longi) <  
                     cities[n].distance(lati, longi)) {
                    n = i;
                }
            }
            return cities[n];
        }

        public String toXML() {
             return "<ns:NearbyCity xmlns:ns=\"http://example.org\"><City>"
                  +this.city+"</City><State>"+ this.state+"</State><Lat>"
                  +this.latitude +
                  "</Lat><Lng>"+this.longitude+"</Lng></ns:NearbyCity>";
        }
    }
}

Follow these guidelines when programming the JWS file that implements the RESTful Web service. Code snippets of the guidelines are shown in bold in the preceding example.

• Import the packages required to implement the RESTful Web service.

  import javax.xml.ws.WebServiceProvider;
  import javax.xml.ws.BindingType;
  import javax.xml.ws.Provider;
  

• Annotate the Provider implementation class and set the binding type to HTTP.

  @WebServiceProvider(
     targetNamespace="http://example.org",
     serviceName = "NearbyCityService")
  @BindingType(value = HTTPBinding.HTTP_BINDING)
  

• Implement the invoke() method of the Provider interface.

  public class NearbyCity implements Provider<Source> {
    @Resource(type=Object.class)
    protected WebServiceContext wsContext;
  
    public Source invoke(Source source)  {
    ...
    }
  

• Get the request string using the QUERY_STRING field in the javax.xml.ws.handler.MessageContext for processing (see message URL http://java.sun.com/javase/6/docs/api/javax/xml/ws/handler/MessageContext.html). The query string is then passed to the createSource() method that returns the city, state, longitude, and latitude that is closest to the specified values.

  String query =
               (String)messageContext.get(MessageContext.QUERY_STRING); 
  .
  .
  .
  return createSource(query);
  

Accessing the RESTful Web Service from a Client

To access a RESTful Web service from a Web service client, use the resource URI. For example:

URL url = new URL (http://localhost:7001/NearbyCity/NearbyCityService?lat=35&long=-120);
HttpURLConnection conn = (HttpURLConnection)url.openConnection();
connection.setRequestMethod("POST");
// Get result
InputStream is = connection.getInputStream();

In this example, you set the latitude (lat) and longitude (long) values, as required, to access the required resource.

Securing RESTful Web Services

You can secure RESTful Web services using the same methods that you use to secure Web applications. For more information, see "Options for Securing Web Application and EJB Resources" in Securing Resources Using Roles and Policies for Oracle WebLogic Server.