Java Platform, Enterprise Edition 7: Generating JSON Data

Overview

    Purpose

    This tutorial covers how to generate JavaScript Object Notation (JSON) data by using the object model and the streaming model. It also demonstrates how to consume the generated JSON using  a JavaScript client.

    Time to Complete

    Approximately 45 minutes

    Introduction

    JSON is a lightweight data-interchange format that is used in web applications and REST WebServices. With the popularity of JSON and the availability of many JSON libraries for the Java platform (for example, org.json, Jackson, and google-gson), there is a need to standardize how developers create and consume JSON.

    Java Platform, Enterprise Edition 7 (Java EE 7) introduces the JSON Processing API, which provides a standard API to parse and generate JSON so that the applications can rely upon a portable API. The JSON Processing API contains the following two packages: 

    • The javax.json package contains a reader interface, a writer interface, and a model builder interface for the object model (similar to the DOM API for XML).
    • The javax.json.stream package contains a parser interface and a generator interface for the streaming model (similar to the StAX API for XML).

    In this tutorial, you learn how to:

    • Create a Java EE 7 web application
    • Develop  two Java servlets to generate JSON data:  ServletJsonGenerateObjectModel and ServletJsonGenerateStreaming
    • Modify index.html to invoke the two servlets
    • Consuming JSON with a JavaScript client
    • Deploy the project to the GlassFish server and verify the deployment

    Hardware and Software Requirements

    The following is a list of hardware and software requirements:

    • Download and install the latest JDK from this link (Java SE 7u21 recommended).
    • Download and install NetBeans 7.3.1 with Java EE,  which includes GlassFish 4 (Java EE download bundle) from this link. During installation, be sure to select the check box to install GlassFish. JUnit is an optional installation and is not required for this tutorial.

    Prerequisites

    Before starting this tutorial, you should:

    • Have installed the required software.
    • Ensure that NetBeans is running.
    • Download and unzip the jquery-1.9.1.js.zip file.

Creating a Web Application

    In this section, you create a Java EE 7 web application in the NetBeans IDE.

    Select File > New Project.

    In the New Project dialog box, perform the following steps on the Choose Project page:

    a. Select Java Web from Categories.
    b. Select Web Application from Projects.
    c. Click Next.

    On the Name and Location page, enter JavaEE7JsonDemo as the project name and click Next.

    On the Server and Settings page, perform the following steps:

    a. Select  GlassFish Server from the Server  list.
    b. Select Java EE 7 Web  from the  Java EE Version list.
    c. Click Next.



    In the Frameworks dialog box, click Finish.


    A Java 7 web application project is created.

Developing the Servlets

    In this section, you create two servlets: ServletJsonGenerateObjectModel generates JSON data with the object model, and ServletJsonGenerateStreaming generates JSON data with the streaming model.

    In the Projects window, right-click JavaEE7JsonDemo and select New > Other.


      In the New File dialog box, perform the following steps on the Choose File Type page:

    a. Select Web from Categories.
    b. Select Servlet from File Types.
    c. Click Next.

    On the Name and Location page, perform the following steps:

    a. Enter ServletJsonGenerateObjectModel as the class name.
    b. Enter  com.example as the package name.
    c. Click Next.

    On the Configure Servlet Deployment page, accept the default values for all fields and click Finish.

    Repeat steps 1 through 4 to create the ServletJsonGenerateStreaming servlet.


 Modifying  ServletJsonGenerateObjectModel

    In this section, you modify  ServletJsonGenerateObjectModel to generate JSON data with the object model. You will build a JSON representation of an Item with the object model API.

    In the ServletJsonGenerateObjectModel class, expand all editor folds and then delete all IDE-generated code.

    Import the following packages:

    import java.io.OutputStream;
    import javax.json.Json;
    import javax.json.JsonObject;
    import javax.json.JsonWriter;

    Implement the doGet() method in the servlet.

    @Override
      protected void doGet(HttpServletRequest request, HttpServletResponse response)
              throws ServletException, IOException {

    }




    Add  the following code to the doGet() method to generate JSON objects that represent three Item objects:

    JsonObject jsonObject = Json.createObjectBuilder()
                .add("items", Json.createArrayBuilder()
                  .add(Json.createObjectBuilder()
                  .add("name", "laptop")
                  .add("quantity", 1)
                  .add("price", 1500.0))
                .add(Json.createObjectBuilder()
                  .add("name", "tablet")
                  .add("quantity", 2)
                  .add("price", 500.0))
                .add(Json.createObjectBuilder()
                  .add("name", "cellphone")
                  .add("quantity", 1)
                  .add("price", 259.99)))
                .add("Total", 2759.99).build();

     

    To generate JSON with the object model API, you must create the JSON objects by using its builders. Use the Json.createObjectBuilder() method to create JSON objects and Json.createArrayBuilder to create arrays.

    Add the following code to the doGet() method to write JSON objects to OutputStream:

    The content type is set to application/json. Writing object model JSON objects is a simple process of creating a JsonWriter with the destination output stream and then writing the objects to it. Finally, closing the jsonWriter finalizes the output and closes the underlying stream.

 Modifying ServletJsonGenerateStreaming

    In this section, you modify the ServletJsonGenerateStreaming servlet to generate JSON data with the streaming model. You will build a JSON representation of an Item with the streaming model API.

    Delete all IDE-generated code inside the ServletJsonGenerateStreaming class. 

    Import the following packages:

    import java.io.OutputStream;
    import javax.json.Json;
    import javax.json.stream.JsonGenerator;

      Perform the following steps to modify the doGet()method:

      a. Add the following code to the doGet() method:

    response.setContentType("application/json");
    OutputStream out = response.getOutputStream();

    This code sets the ContentType to application/json and creates an instance of OutputStream to write JSON objects to the stream.

    b. Add the following code to generate the JSON representation of  three Item objects by using the streaming model:

    JsonGenerator generator = Json.createGenerator(out);
            generator.writeStartObject();
            generator.writeStartArray("items");
            generator.writeStartObject();
            generator.write("name", "laptop");
            generator.write("quantity", 1);
            generator.write("price", 1500.0);
            generator.writeEnd();
            generator.writeStartObject();
            generator.write("name", "tablet");
            generator.write("quantity", 2);
            generator.write("price", 500.0);
            generator.writeEnd();
            generator.writeStartObject();
            generator.write("name", "cellphone");
            generator.write("quantity", 1);
            generator.write("price", 259.99);
            generator.writeEnd();
            generator.writeEnd();
            generator.write("total", 2759.99);
            generator.writeEnd();
            generator.close();

    To generate JSON by using the streaming API, you must create JsonGenerator with the desired outputStream. You must sequentially write the JSON string by using JsonGenerator. Closing the generator finalizes the writing and closes the underlying stream.

Modifying index.html

    In this section, you invoke the two servlets by changing index.html.

     Enter JSON Processing for the title of the page. 

    Delete IDE-generated code in the <body> section and add  a <table> section with a heading.


    Add  two <a> elements to the <table> section to create hyperlinks to the servlets.

    <tr>
       <td><a href="http://localhost:8080/JavaEE7JsonDemo/ServletJsonGenerateStreaming">Generate using Streaming API</a></td>
      </tr>

      <tr>

       <td><a href="http://localhost:8080/JavaEE7JsonDemo/ServletJsonGenerateObjectModel">Generate using Object Model API</a></td>
      </tr>


     

Testing the JSON Generation in the Servlets

    In this section, you verify the JSON generation in the two servlets by deploying and running the project .

    In the Projects window, right-click JavaEE7JsonDemo and select Deploy.


    In the Projects window, right-click JavaEE7JsonDemo and select Run.



    The application appears in the browser.


    Perform the following steps:

    a. Click Generate using Streaming API. ServletJsonGenerateStreaming is invoked, and the JSON data generated with the streaming API is displayed.



    b. Click Generate using Object Model API. ServletJsonGenerateObjectModel is invoked, and the JSON data generated with the object model API is displayed.


Consuming JSON with a JavaScript Client

    In this section, you develop a JavaScript client that contacts the ServletJsonGenerateObjectModel servlet, retrieves data via an AJAX call, and displays it on the HTML page by using jQuery, JavaScript library.

    Add the jQuery library to the project.

    a. Browse to the location where you saved the jquery-1.9.1.js file specified in the Prerequisites section.

    b. Copy jquery-1.9.1.js.

    c. In the Projects window, under JavaEE7JsonDemo, right-click Web Pages, and select Paste. The jquery-1.9.1.js file is copied to the Web Pages folder.

    Perform the following steps to edit index.html:

    a. In the <head> section, add the <script> tags to generate an AJAX request.

      <script src="jquery-1.9.1.js"></script>
            <script>
                $(document).ready(function() {
                    $.ajax({
                        type: 'GET',
                        contentType: 'application/json',
                        processData: false,
                        url: 'ServletJsonGenerateObjectModel',
                        success: function(data, textStatus, jqXHR) {
                            $('#status').text("SUCCESS");
                            for(var i = 0; i < data.items.length; i++) {
                                $('#results').append("Name: " + data.items[i].name + " " +
                                        "Quantity: " + data.items[i].quantity + " " +
                                        "Price: " + data.items[i].price + "<br/>");
                            }
                            $('#results').append("Total: " + data.Total);
                        },
                        error: function(jqXHR, textStatus, errorThrown) {
                            $('#status').text('POST error: ' + textStatus + ',' + errorThrown);
                        }
                    });
                });
            </script>


    b. Add the following code to the <body> section to render the response and the status:

          
          <b>Status:</b>   <div id="status"></div>
          <b>Response: </b><div id="results"></div>

     

Testing the JavaScript Client

     In this section, you verify the response from the JSON client. You do that by deploying and running the project .

    In the Projects window, right-click JavaEE7JsonDemo and select Deploy.


    In the Projects window, right-click JavaEE7JsonDemo and select Run.



    The application appears in the browser.



    The status of the AJAX request and the Item details is displayed.

Summary

    In this tutorial, you learned how to:

    • Create a Java EE 7 web application
    • Generate JSON data by using the Java API for JSON processing
    • Develop a JSON JavaScript client

    Resources

    Credits

    • Lead  Curriculum Developer: Anjana Shenoy
    • Other Contributors: Eduardo Moranchel, Matt Heimer
    • Editor: Susan Moxley
    • QA: Diganta Choudhury

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