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| |
| <h1 class="title">JSON Support in Axis2</h1> |
| <p>This document explains the JSON support implementation in Axis2. |
| It includes an introduction to JSON, an outline as to why JSON |
| support is useful to Axis2 and how it should be used. This document |
| also provides details on test cases and samples.</p> |
| <div class="section"><h3>What is JSON?<a name="What_is_JSON"></a></h3> |
| <p><a class="externalLink" href="http://www.json.org/">JSON</a> (Java Script Object |
| Notation) is another data exchangeable format like XML, but more |
| lightweight and easily readable. It is based on a subset of the |
| JavaScript language. Therefore, JavaScript can understand JSON, and |
| it can make JavaScript objects by using JSON strings. JSON is based |
| on key-value pairs and it uses colons to separate keys and values. |
| JSON doesn't use end tags, and it uses braces (curly brackets) to |
| enclose JSON Objects.</p> |
| <p><font size="3">e.g. <font size="2"><root><test>json |
| object</test></root> == |
| {{json object}}</font></font></p> |
| <p>When it comes to converting XML to JSON and vice versa, there |
| are two major conventions, one named "<a class="externalLink" href="http://www.sklar.com/badgerfish/">Badgerfish</a>" and the other, |
| Mapped. The main difference |
| between these two conventions exists in the way they map XML |
| namespaces into JSON.</p> |
| <p><font size="3">e.g. <font size="2"><xsl:root |
| xmlns:xsl="http://foo.com"><data>my json |
| string</data></xsl:root></font></font></p> |
| <p>This XML string can be converted into JSON as follows.</p> |
| <p><b>Using Badgerfish</b></p> |
| <p><font size="2">{"xsl:root":{"@xmlns":{"xsl":"http://foo.com"},"data":{"$":"my |
| json string"}}}</font></p> |
| <p><b>Using Mapped</b></p> |
| <p>If we use the namespace mapping as http://foo.com -> foo</p> |
| <p><font size="2">{"foo.root":{"data":"my json string"}}</font></p> |
| <p>JSON support is a new feature in <a href="../index.html">Apache Axis2/Java</a>. It will become |
| a crucial improvement in the future with applications like |
| JavaScript Web services.</p> |
| </div><div class="section"><h2>Why JSON Support for Axis2?<a name="Why_JSON_Support_for_Axis2"></a></h2> |
| <p><a href="../index.html">Apache Axis2</a> is a Web |
| services stack that delivers incoming messages into target |
| applications. In most cases, these messages are SOAP messages. In |
| addition, it is also possible to send REST messages through Axis2. |
| Both types of messages use XML as their data exchangeable format. |
| So if we can use XML as a format, why use JSON as another |
| format?</p> |
| <p>There are many advantages of implementing JSON support in Axis2. |
| Mainly, it helps the JavaScript users (services and clients written |
| in JavaScript) to deal with Axis2. When the service or the client |
| is in JavaScript, it can use the JSON string and directly build |
| JavaScript objects to retrieve information, without having to build |
| the object model (OMElement in Axis2). Also, JavaScript services |
| can return the response through Axis2, just as a JSON string can be |
| shipped in a JSONDataSource.</p> |
| <p>Other than for that, there are some extra advantages of using |
| JSON in comparison to XML. Although the conversation |
| XML or JSON? is still a hot topic, |
| many people accept the fact that JSON can be passed and built more |
| easily by machines than XML.</p> |
| <p>For more details of this implementation architecture, refer to |
| the article <a class="externalLink" href="http://wso2.org/library/768">"JSON Support for |
| Apache Axis2"</a></p> |
| <div class="section"><h2>How to use JSON in Axis2<a name="How_to_use_JSON_in_Axis2"></a></h2> |
| <p>At the moment JSON doesn't have a standard and unique content |
| type. application/json (this is |
| the content type which is approved in the <a class="externalLink" href="http://www.ietf.org/rfc/rfc4627.txt?number=4627">JSON RFC</a> ), |
| text/javascript and |
| text/json are some of the commonly |
| used content types of JSON. Due to this problem, in Axis2, the user |
| has been given the freedom of selecting the content type.</p> |
| <div class="section"><h3>Step 1<a name="Step_1"></a></h3> |
| <p>Map the appropriate MessageFormatter and OMBuilder with the |
| content type you are using in the axis2.xml file.</p> |
| <p>e.g.1: If you are using the |
| Mapped convention with the content |
| type application/json</p> |
| <div><pre> |
| <messageFormatters> |
| <messageFormatter contentType="application/json" |
| class="org.apache.axis2.json.JSONMessageFormatter"/> |
| <!-- more message formatters --> |
| </messageFormatters> |
| |
| <messageBuilders> |
| <messageBuilder contentType="application/json" |
| class="org.apache.axis2.json.JSONOMBuilder"/> |
| <!-- more message builders --> |
| </messageBuilders> |
| </pre></div> |
| <p>e.g.2: If you are using the |
| Badgerfish convention with the |
| content type text/javascript</p> |
| <div><pre> |
| <messageFormatters> |
| <messageFormatter contentType="text/javascript" |
| class="org.apache.axis2.json.JSONBadgerfishMessageFormatter"/> |
| <!-- more message formatters --> |
| </messageFormatters> |
| |
| <messageBuilders> |
| <messageBuilder contentType="text/javascript" |
| class="org.apache.axis2.json.JSONBadgerfishOMBuilder"/> |
| <!-- more message builders --> |
| </messageBuilders> |
| </pre></div> |
| </div><div class="section"><h3>Step 2<a name="Step_2"></a></h3> |
| <p>On the client side, make the ConfigurationContext by reading the |
| axis2.xml in which the correct mappings are given.</p> |
| <p>e.g.</p> |
| <div><pre> |
| File configFile = new File("test-resources/axis2.xml"); |
| configurationContext = ConfigurationContextFactory |
| .createConfigurationContextFromFileSystem(null, configFile.getAbsolutePath()); |
| .......... |
| ServiceClient sender = new ServiceClient(configurationContext, null); |
| </pre></div> |
| </div><div class="section"><h3>Step 3<a name="Step_3"></a></h3> |
| <p>Set the <i>MESSAGE_TYPE</i> option with exactly the same content |
| type you used in the axis2.xml.</p> |
| <p>e.g. If you use the content type |
| application/json,</p> |
| <div><pre> |
| Options options = new Options(); |
| options.setProperty(Constants.Configuration.MESSAGE_TYPE, application/json); |
| //more options |
| //................... |
| |
| ServiceClient sender = new ServiceClient(configurationContext, null); |
| sender.setOptions(options); |
| </pre></div> |
| <p>If you are sending a request to a remote service, you have to |
| know the exact JSON content type that is used by that service, and |
| you have to use that content type in your client as well.</p> |
| <p>HTTP POST is used as the default method to send JSON messages |
| through Axis2, if the HTTP method is not explicitly set by the |
| user. But if you want to send JSON in HTTP GET method as a |
| parameter, you can do that by just setting an option on the client |
| side.</p> |
| <p>e.g. |
| <tt>options.setProperty(Constants.Configuration.HTTP_METHOD, |
| Constants.Configuration.HTTP_METHOD_GET);</tt></p> |
| <p>Here, the Axis2 receiving side (JSONOMBuilder) builds the |
| OMElement by reading the JSON string which is sent as a parameter. |
| The request can be made even through the browser.</p> |
| <p>e.g. Sample JSON request through HTTP GET. The JSON message is |
| encoded and sent.</p> |
| <p><tt>GET |
| /axis2/services/EchoXMLService/echoOM?query=%7B%22echoOM%22:%7B%22data%22:%5B%22my%20json%20string%22,%22my%20second%20json%20string%22%5D%7D%7D |
| HTTP/1.1</tt></p> |
| </div><div class="section"><h2>Tests and Samples<a name="Tests_and_Samples"></a></h2> |
| <div class="section"><h3>Integration Test<a name="Integration_Test"></a></h3> |
| <p>The JSON integration test is available under |
| test in the |
| json module of Axis2. It uses the |
| SimpleHTTPServer to deploy the service. A simple echo service is |
| used to return the incoming OMSourcedElementImpl object, which |
| contains the JSONDataSource. There are two test cases for two |
| different conventions and another one test case to send the request |
| in GET.</p> |
| </div><div class="section"><h3>Yahoo-JSON Sample<a name="Yahoo-JSON_Sample"></a></h3> |
| <p>This sample is available in the |
| samples module of Axis2. It is a |
| client which calls the Yahoo search API using the GET method, with |
| the parameter output=json. The |
| Yahoo search service sends the response as a |
| formatted JSON string with |
| the content type text/javascript. |
| This content type is mapped with the JSONOMBuilder in the |
| axis2.xml. All the results are shown in a GUI. To run the sample, |
| execute the ant script.</p> |
| <p>These two applications provide good examples of using JSON |
| within Axis2. By reviewing these samples, you will be able to |
| better understand Axis2's JSON support implementation.</p> |
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