Getting Started with RESTful Web Services

REpresentational State Transfer (REST) is an architectural style for distributed hypermedia systems, such as the World Wide Web. Central to the RESTful architecture is the concept of resources identified by universal resource identifiers (URIs). These resources can be manipulated using a standard interface, such as HTTP, and information is exchanged using representations of these resources. In this tutorial, you first learn a bit about REST and then you are shown how NetBeans IDE supports this architectural style.

Contents

• Introduction
• RESTful Web Services, Persistence, and Entity Classes
• Creating RESTful Web Services from a Database
  • Creating the Project
  • Generating Entity Classes and RESTful Services
• Testing the RESTful Web Services
• Adding a Google Map Feature
• RESTful Web Services in the Spring Framework
  • Creating a Java Web Application With the Spring Framework
  • Adding aopalliance.jar to the Project
  • Creating RESTful Services in the Spring-enabled Project
  • Compilation Errors

To follow this tutorial, you need the following software and resources.

Software or Resource	Version Required
NetBeans IDE	Java EE download bundle
Java Development Kit (JDK)	version 6 or 7
Java EE-compliant web or application server	Tomcat web server 6.x-7.x, Oracle WebLogic Server 11g-12c, or GlassFish Server Open Source Edition 3.x. Important: If you use Tomcat with this Tutorial, see the NetBeans Wiki on Tomcat with REST.
The jdbc/sample database on Java DB (Derby) database server or MySQL database server	On Java DB (Derby), The jdbc/sample database is generated by NetBeans IDE when you install the IDE with the GlassFish application server. On MySQL, the IDE populates the sample database after you create it on the MySQL server from within the IDE.

Both Tomcat and the GlassFish server can be installed with the Web and Java EE distribution of NetBeans IDE. Alternatively, you can visit the the GlassFish server downloads page or the Apache Tomcat downloads page.

Important: Java EE 6 projects require Tomcat 7.x, GlassFish Server 3.x, or Oracle WebLogic Server 12c.

Introduction

RESTful web services are services built using the RESTful architectural style. Building web services using the RESTful approach is emerging as a popular alternative to using SOAP-based technologies for deploying services on the internet, due to its lightweight nature and the ability to transmit data directly over HTTP.

The IDE supports rapid development of RESTful web services using JSR 311 - Java API for RESTful Web Services (JAX-RS) and Jersey, the reference implementation for JAX-RS.

For detailed information, refer to the following:

• JSR 311: JAX-RS: The Java API for RESTful Web Services
• Jersey, the open source JAX-RS (JSR 311) Reference Implementation for building RESTful Web services

In addition to building RESTful web services, the IDE also supports testing, building client applications that access RESTful web services, and generating code for invoking web services (both RESTful and SOAP-based.)

Here is the list of RESTful features provided by the IDE:

1. Rapid creation of RESTful web services from JPA entity classes and patterns.
2. Rapid code generation for invoking web services such as Google Map, Yahoo News Search, and StrikeIron web services by drag-and-dropping components from the Web Services manager in the Services window.
3. Generation of RESTful Java Clients for services registered in the Web Services manager.
4. Test client generation for testing RESTful web services.
5. Logical view for easy navigation of RESTful web service implementation classes in your project.
6. Fully integrated Spring framework, providing Spring transaction handling.

In this tutorial, you will be shown how the IDE supports you in generating, implementing, and testing RESTful web services.

RESTful Web Services, Persistence, and Entity Classes

RESTful web services in Java rely on the Java Persistence API to communicate with a database. Specifically, RESTful web services rely on entity classes and a persistence unit, as defined in the Persistence API. Entity classes are Java classes that map to objects in a relational database. According to The Java EE5 Tutorial, "An entity is a lightweight persistence domain object. Typically an entity represents a table in a relational database, and each entity instance corresponds to a row in that table." A persistence unit consists of the set of entity classes, the data source, the persistence provider, and the persistence unit's own name, as defined in a persistence.xml file.

You can use NetBeans IDE either to create entity classes and RESTful web services in the same process, or you can use the IDE to create RESTful web services from existing entity classes. In this tutorial, you use the RESTful Services from Database wizard to generate entity classes and RESTful web services in the same process. The wizard automatically generates the persistence unit.

Using a MySQL Database Server

If you use the MySQL database server instead of JavaDB (Derby), you need to register the database server with the IDE and add the sample database to the server.

To use a MySQL database server with this tutorial:

1. Register your MySQL server in the IDE, if the server is not registered. To register a MySQL server, go to the IDE's Services window, right-click the Databases node, and select Register MySQL server.
   

2. A dialog opens in which you type the configuration details of your MySQL server, including administrator user name and password. See "Configuring MySQL Server Properties" in Connecting to a MySQL Database.

   
3. Start the MySQL server and connect to it. See "Starting the MySQL Server" in Connecting to a MySQL Database.
4. Right-click the MySQL server node and select Create Database. The Create MySQL Database dialog opens.
   
5. Type sample as the new database name. Grant full access to your root user, or a user of your choice.
   
6. Click OK. A dialog opens informing you that sample is the name of a sample database, and asking you if you want to create the tables, objects, and data for this database.
   
7. Click Yes. The IDE creates and populates the database, and adds a connection to the database.
   

Creating RESTful Web Services from a Database

The goal of this exercise is to create a project and generate entity classes and RESTful web services from a database.

This section uses the JavaDB (Derby) database and the jdbc/sample data source. JavaDB is included with the SDK. The jdbc/sample data source is generated by NetBeans IDE automatically when you install the IDE together with GlassFish.

The IDE now generates the RESTful web services. When the IDE is finished, look in the Projects window. The generated entity classes are in the entities package. Services are in the service package. For an EE5 project, there are JPA controller classes in the controller package and a web.xml deployment descriptor under Configuration Files.

Caution: The IDE might prompt you to Resolve Reference Problems for the project. In this case, right-click the CustomerDB project node and select Resolve Reference Problems. This issue can happen when the service is the first Jersey application to run on a WebLogic installation. In this case, the IDE solves the reference problem by copying the Jersey libraries to the server.

EE6 RESTful web services from a database instantiate EntityManager in each service class. This removes the need for JPA controller classes and generates simpler code.

Testing the RESTful Web Services

The goal of this exercise is to try out your application.

1. Right-click the project node and choose Test RESTful Web Services. A dialog opens asking if you want to generate the test client inside the service project or in another Java web project. This option lets you work around security restrictions in some browsers. You can use any Web project, as long as it is configured to deploy in the same server domain as the CustomerDB project.
   
2. Select where to generate the test client and click OK. The server starts and the application is deployed. When deployment is complete, the browser displays your application, with a link for each of the web services.

   If the output window shows an error message that one or more classes fails to exist and the project does not build, add the Jersey libraries to the compile-time libraries. Right-click the project node and select Properties. In the Properties tree menu, select Libraries. Click Add Library and browse for the Jersey libraries.

   

   On the left-hand side is the set of root resources. Here they are named entities.customer and entities.discountCodes.

3. Click the entities.customer node. In the "Choose method to test" field, select either GET (application/json) or GET (application/xml). Click Test. The test client sends a request and displays the result in the Test Output section. The test client dispays the Raw View by default. The following image shows the response to an application/xml request.
   

There are 5 tabs in the Test Output section.

• The Tabular View is a flattened view that displays all the URIs in the resulting document. Currently this view only displays a warning that Container-Containee relationships are not allowed.
• The Raw View displays the actual data returned. Depending on which mime type you selected (application/xml or application/json), the data displayed will be in either XML or JSON format, respectively.
• The Sub Resource tab shows the URLs of the root resource and sub resources. When the RESTful web service is based on database entity classes, the root resource represents the database table, and the sub resources represent the columns.
• The Headers tab displays the HTTP header information.
• The HTTP Monitor tab displays the actual HTTP requests and responses sent and received.

Exit the browser and return to the IDE.

Adding a Google Map Feature

The goal of this exercise is to add Google map functionality to our RESTful web services.

1. Open the CustomerRESTFacade class (EE 5) or CustomerFacadeREST class (EE 6) in the editor.
2. Add the following method to the class:

   @GET
   @Produces("text/html")
   public String getGoogleMap() {
   // Drag and drop the getGoogleMap operation here
   
      return "";
   }

3. Sign up for a Google map key at http://www.google.com/apis/maps/signup.html. The Google map key request dialog has a field for your website's URL. Type http://localhost:8080 in that field.
4. In the IDE, open the Services tab and expand the Web Services node. Under Web Services, expand Google. Under Google, expand Map Service.
   
   
5. Drag the getGoogleMap item and drop it into the body of the getGoogleMap method you created in Step 2, just before the return = ""; line. The Customize getGoogleMap SAAS dialog opens. Accept the defaults and click OK.

   The IDE adds the following try block to the getGoogleMap method.

   @GET
   @Produces("text/html")
   public String getGoogleMap() {
   // Drag and drop the getGoogleMap operation here
           
       try {
                
            String address = "16 Network Circle, Menlo Park";
            java.lang.Integer zoom = 15;
            String iframe = "false";
            RestResponse result = GoogleMapService.getGoogleMap(address, zoom, iframe);
            //TODO - Uncomment the print Statement below to print result.
            //System.out.println("The SaasService returned: "+result.getDataAsString());
       } catch (Exception ex) {
            ex.printStackTrace();
       }
   
       return "";
   
   }
                   

   The IDE also creates the packages org.netbeans.saas and org.netbeans.saas.google, which contain the following classes and resources:

   • RestConnection - A wrapper around HttpUrlConnection
   • RestResponse - A wrapper for the HTTP response
   • googlemapservice.properties - A properties file that stores the API key
   • GoogleMapService - A service wrapper containing the wrapper methods that uses RestConnection to make calls to the Google Map service.
   
6. In the try block of getGoogleMap(), replace the commented-out print statement with the line return result.getDataAsString();. The method now looks like this:

   @GET
   @Produces("text/html")
   public String getGoogleMap() {
   // Drag and drop the getGoogleMap operation here
           
       try {
                
            String address = "16 Network Circle, Menlo Park";
            java.lang.Integer zoom = 15;
            String iframe = "false";
            RestResponse result = GoogleMapService.getGoogleMap(address, zoom, iframe);
            return result.getDataAsString();
       } catch (Exception ex) {
            ex.printStackTrace();
       }
   
       return "";
   }

7. Open googlemapservice.properties. Paste in the API key you got from Google in Step 3. Save your changes. The IDE automatically redeploys your project.
8. Refresh your browser window with the test client.
9. Click entities.customer in the left sidebar. The GET (text/html) method appears in the "Choose method to test" field. Click Test. The GoogleMap of 16 Network Circle, Menlo Park opens in the Raw View.
   

10. The Google map of the Menlo Park address appears for all customers in the database. To display the Google maps of the actual addresses of the customers, create an instance of Customer and set the address equal to a concatenation of address variables for that instance of Customer.

    Find an instance of Customer by calling the entity manager's find() method. In an EE5 service, the customer facade uses its own find method to call CustomerJpaController, which instantiates the entity manager. In an EE6 service, the customer facade uses the abstract facade to access the entity manager. The generic find() method requires explicit argument type casting to Object and an explicit entity id. The following code displays the map location of the customer with id number 1 (changes in bold):

    EE5 service:

    @GET
    @Produces("text/html")
    public String getGoogleMap() {
        try {
             Customer c = find(1);
             String address = c.getAddressline1() + " " + c.getAddressline2() + " " +
                     c.getCity() + " " + c.getState() + " " + c.getZip();
             java.lang.Integer zoom = 15;
             String iframe = "false";
     
             RestResponse result = GoogleMapService.getGoogleMap(address, zoom, iframe);
             return result.getDataAsString();
         
         } catch (Exception ex) {
             ex.printStackTrace();
         } 
    
         
         return "";
     }

    EE6 service:

    @GET
    @Produces("text/html")
    public String getGoogleMap() {
        try {
             Customer c = getEntityManager().find(Customer.class, 1);
             String address = c.getAddressline1() + " " + c.getAddressline2() + " " +
                     c.getCity() + " " + c.getState() + " " + c.getZip();
             java.lang.Integer zoom = 15;
             String iframe = "false";
     
             RestResponse result = GoogleMapService.getGoogleMap(address, zoom, iframe);
             return result.getDataAsString();
         
         } catch (Exception ex) {
             ex.printStackTrace();
         } 
    
         
         return "";
     }

11. Test the RESTful web services again. The customer id is specified as an argument for the find() method and the tester displays the raw view by default. For customer 1, the following map displays:

    Tip: Try to change the id number passed as an argument to getEntityManager().find(Customer.class, id). A real world client would get the value of this argument from a UI form.

    
    

    Note: If GoogleMaps cannot find an address, it shows a zoomed in view of the ocean.

RESTful Web Services in the Spring Framework

Jersey is integrated into the Spring Framework. When you create a Java Web application with the Spring framework, a REST-aware servlet is automatically created. However, Spring 3 doesn't contain aopalliance.jar, which the RESTful web service requires to inject an EntityManager object.

See Also

For more information about using NetBeans IDE to develop Java EE applications, see the following resources:

• NetBeans to Generate Simpler RESTful Web Services
• Creating RESTful Service Clients in NetBeans Modules
• Web Services Learning Trail
• YouTube: RESTful Web Services, Building and Deploying (Part 1)
• YouTube: NetBeans RESTful Testing and Invoking RESTful Resources (Part 2)

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