REST - Using Apache Wink (Part 01) [Starting JAX-RS Web Services - 01]

GitHub Link (Code Samples from the Article & More)
https://github.com/sumithpuri/skp-code-marathon-hochiminh

I built this Product Web Service using Apache Wink. It can add, update, delete and retrieve products in memory, and I intend to explain the basics of REST using Apache Wink and this service. REST stands for Representational State Transfer and is based on the concepts of Roy Fielding’s dissertation work as part of his thesis. It works on HTTP and has the following differences when compared to SOAP:

• Works on HTTP protocol, as compared to SOAP, which has its own protocol.
• Uses HTTP GET, PUT, POST, and DELETE as compared to SOAP which uses only POST.
• It uses the HTTP infrastructure, whereas SOAP is transport neutral.
• The producer and consumer are aware of the content being exchanged.
• It does not support many non-functional requirements or any WS-* standards.

Installations Required

• Eclipse 4.2.0.

• Apache Wink 1.4.0.

• Apache Tomcat 8.0.9.

• JDK 1.7.0/JRE 1.7.0.

Server/Web Service

The steps to build the web service using Apache Wink are given below:

1. Create a Dynamic Web Project in Eclipse.

2. Build a Core Application that performs CRUD Operations.

3.  /**   
     *    
     */   
     package me.sumithpuri.rest.persistence;   
   
   
     import java.util.ArrayList;   
     import java.util.List;   
   
     import me.sumithpuri.rest.vo.Product;   
   
     /**   
     * @author sumith_puri   
     *   
     */   
     public class ProductPersistenceManager {   
   
       private List<Product> productDatabase = new ArrayList<Product>();   
       private static ProductPersistenceManager persistenceManager;   
       private static int id=0;   
   
       private ProductPersistenceManager() {   
   
       }   
   
       public void add(Product product) {   
   
          System.out.println("database: added one product");   
   
          // atomic id creation   
          id++;   
          product.setId(id);   
          productDatabase.add(product);   
       }   
   
       public List<Product> get() {   
          System.out.println("database: retrieved all products");   
          return productDatabase;   
       }   
   
       public void update(long productId, String productName) {   
          System.out.println("database: modified one product");   
   
          for(int i=0;i<productDatabase.size();i++) {   
   
            Product product = productDatabase.get(i);   
            if(product.getId()==productId) {   
               product.setName(productName);   
               productDatabase.remove(i);   
               productDatabase.add(i,product);   
            }   
          }   
          return;   
       }   
   
       public void delete(long productId) {   
          System.out.println("database: deleted one product");   
   
          for(int i=0;i<productDatabase.size();i++) {   
   
            Product product = productDatabase.get(i);   
            if(product.getId()==productId) productDatabase.remove(i);   
          }   
          return;   
       }   
   
       public static ProductPersistenceManager getInstance() {   
   
          if(persistenceManager==null) {   
            synchronized(ProductPersistenceManager.class) {   
               if(persistenceManager==null) {   
                 persistenceManager = new ProductPersistenceManager();   
               }   
            }   
          }   
          return persistenceManager;   
       }   
     }   
   

   
   

4. Add the Supporting JAR Files in the Build Path.

6. Create the REST Web Service using Apache Wink (GET, POST, DELETE, PUT).

7. package me.sumithpuri.rest.webservice;  
   
   
    import java.util.List;  
   
    import javax.ws.rs.DELETE;  
    import javax.ws.rs.GET;  
    import javax.ws.rs.POST;  
    import javax.ws.rs.PUT;  
    import javax.ws.rs.Path;  
    import javax.ws.rs.PathParam;  
    import javax.ws.rs.Produces;  
    import javax.ws.rs.core.MediaType;  
   
    import me.sumithpuri.rest.persistence.ProductPersistenceManager;  
    import me.sumithpuri.rest.vo.Product;  
   
    /**  
     * @author sumith_puri  
     *  
     */  
    @Path("product")  
    public class ProductWebService {  
   
        ProductPersistenceManager persistenceManager = ProductPersistenceManager.getInstance();  
   
        @GET  
        @Produces(MediaType.TEXT_PLAIN)  
        public String getProducts() {  
   
            List<Product> products = persistenceManager.get();  
            String productList = new String();  
   
            for(Product producti: products) {  
                productList+=producti.toString() + "\n";  
            }  
   
            // return as plain text - other types include xml, json  
            return productList;  
        }  
   
        @POST  
        public String addProducts(String productStr) {  
   
            Product product = new Product();  
            product.setName(productStr);  
            persistenceManager.add(product);  
   
            return productStr;  
        }  
   
        @DELETE  
        @Path("/{id}")  
        public void deleteProduct(@PathParam(value="id") long id) {  
   
            persistenceManager.delete(id);  
            return;  
        }  
   
        @PUT  
        @Path("/{id}")  
        public void modifyProduct(@PathParam(value="id") long id, String productName) {  
   
            persistenceManager.update(id, productName);  
            return;  
        }  
    }  
   

   
   

8. Configure the application for Apache Wink

9. To allow Apache Wink to locate this service as a REST web service, you can either define an additional class or configure an application file. We are using an application file to mention all our web services.

   You can place this under WEB-INF/and name the file simply ‘application’ (without any extension).

    me.sumithpuri.rest.webservice.ProductWebService  

   
   Next, you need to specify the servlet-related configuration for allowing Apache Wink REST Servlet to locate this application configuration. You do that by specifying the location of ‘application’ as the parameter ‘applicationConfigLocation’ in WEB-INF/web.xml

   <?xml version="1.0" encoding="UTF-8"?>  
    <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">  
     <display-name>products</display-name>  
     <servlet>  
      <servlet-name>restService</servlet-name>  
      <servlet-class>org.apache.wink.server.internal.servlet.RestServlet</servlet-class>  
      <init-param>  
       <param-name>applicationConfigLocation</param-name>  
       <param-value>/WEB-INF/application</param-value>  
      </init-param>  
     </servlet>  
     <servlet-mapping>  
      <servlet-name>restService</servlet-name>  
      <url-pattern>/rest/*</url-pattern>  
     </servlet-mapping>  
    </web-app>  

   
   

10. Deploy as an Apache Tomcat Web App, Directly:

Client/Web Service Client

The steps to test the web service or write a REST client are as follows:

1. Create a Java project in Eclipse.

2. Include the Support Client JAR files in the Classpath.

3. Build the Client to Test or Access the GET method.

4. Build the Client to Test or Access the POST method.

5. Build the Client to Test or Access the DELETE method.

6. Build the Client to Test or Access the PUT method.

   package me.sumithpuri.rest.client;  
   
    import javax.ws.rs.core.MediaType;  
   
    import org.apache.wink.client.ClientConfig;  
    import org.apache.wink.client.Resource;  
    import org.apache.wink.client.RestClient;  
   
   
    /**  
     * @author sumith_puri  
     *  
     */  
    class ProductRESTClient {  
   
        static String REST_WEB_SERVICE="http://localhost:8080/products/rest/product";  
        static ClientConfig clientConfig = new ClientConfig();  
   
        /**  
         * @param args  
         */  
        public static void main(String[] args) throws Exception {  
   
            try {  
   
                ProductRESTClient restClient = new ProductRESTClient();              
                System.out.println("Apache Wink Based REST Client");  
                System.out.println("Sumith Kumar Puri (c) 2015");  
                System.out.println("=============================");  
   
                restClient.configureClient();  
                System.out.println();  
   
                restClient.invokeGET();  
                System.out.println();  
   
                String product="Sumith Puri" + (int) (Math.random()*9999);  
                restClient.invokePOST(product);  
   
                System.out.println();  
                product="Sumith Puri" + (int) (Math.random()*9999);  
                restClient.invokePOST(product);  
   
                System.out.println();  
                product="Sumith Puri" + (int) (Math.random()*9999);  
                restClient.invokePOST(product);  
   
                System.out.println();  
                product="Sumith Puri" + (int) (Math.random()*9999);  
                restClient.invokePOST(product);  
   
                System.out.println();  
                restClient.invokeGET();  
   
                System.out.println();  
                restClient.invokeDELETE(2L);  
   
                System.out.println();  
                restClient.invokeGET();  
   
                System.out.println();  
                product="Sumith Puri" + (int) (Math.random()*9999);  
                restClient.invokePOST(product);  
   
                System.out.println();  
                product="Sumith Puri" + (int) (Math.random()*9999);  
                restClient.invokePOST(product);  
   
                System.out.println();  
                restClient.invokeDELETE(4L);  
   
                System.out.println();  
                restClient.invokeGET();  
   
                System.out.println();  
                restClient.invokePUT(3L,"Sumith Puri");  
   
                System.out.println();  
                restClient.invokeGET();  
            } catch (Exception e) {  
   
                e.printStackTrace();  
            }  
        }  
   
   
        public void configureClient() {  
   
        }  
   
        public void invokeGET() {  
   
            System.out.println("Testing GET command....");      
            RestClient restClient = new RestClient(clientConfig);  
            Resource resource = restClient.resource(REST_WEB_SERVICE);  
            String response = resource.accept("text/plain").get(String.class);  
            System.out.printf(response);  
            System.out.println("...GET command is successful");  
        }  
   
        public void invokePOST(String product) {  
   
            System.out.println("Testing POST command...");  
            RestClient restClient = new RestClient(clientConfig);  
            Resource resource = restClient.resource(REST_WEB_SERVICE);  
            resource.contentType(MediaType.TEXT_PLAIN).accept(MediaType.TEXT_PLAIN).post(String.class,product);  
            System.out.println("...POST command is successful");  
        }  
   
   
        public void invokePUT(Long id, String productName) {  
   
            System.out.println("Testing PUT command...");  
            RestClient restClient = new RestClient(clientConfig);  
            Resource resource = restClient.resource(REST_WEB_SERVICE+"/"+id);  
            resource.contentType(MediaType.TEXT_PLAIN).accept(MediaType.TEXT_PLAIN).put(String.class, productName);  
            System.out.println("...PUT command is successful");  
        }  
   
        public void invokeDELETE(Long id) {  
   
            System.out.println("Testing DELETE command...");  
            RestClient restClient = new RestClient(clientConfig);  
            Resource resource = restClient.resource(REST_WEB_SERVICE+"/"+id);  
            resource.contentType(MediaType.TEXT_PLAIN).accept(MediaType.TEXT_PLAIN).delete();  
            System.out.println("...DELETE command is successful");  
        }  
    }  

Output (First Access)

Downloads

You may download the products.war (including source) web service as well as the products-client.jar (including source).

Conclusion

In this blog, you have seen how to build REST web services using Apache Wink for basic data types. Next, I will blog on how to include Jackson or Jettison as the stream reader or stream writer JSON libraries so that we can read and write complex or application object types. It will be titled  "JAX-RS (REST Web Services) using Apache Wink - 02" [REST Using Apache Wink and Jackson/Jettison].