src/site/xdoc/docs/json_support.xml - axis-axis2-java-core - Git at Google

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 <document xmlns="http://maven.apache.org/XDOC/2.0"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://maven.apache.org/XDOC/2.0 http://maven.apache.org/xsd/xdoc-2.0.xsd">
     <properties>
         <title>JSON Support in Axis2</title>
     </properties>
     <body>
         <h1>JSON Support in Axis2</h1>
         <section name="Introduction">
            <p>Update: This documentation represents early forms of JSON
               conventions, Badgerfish and Mapped. GSON support was added a few
 	      years later. Moshi support is now included as an alternative to
 	      GSON. For users of JSON seeking modern features, see the <a href=
 	      "json_support_gson.html">JSON Support Guide.</a>. For users of
               JSON and Spring Boot 3, see the sample application in the <a href=
 	      "json-springboot-userguide.html">JSON and Spring Boot 3 User's Guide.</a>
 	    </p>
             <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>
         </section>
         <section name="What is JSON?">
             <p><a 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">&lt;root&gt;&lt;test&gt;json
             object&lt;/test&gt;&lt;/root&gt; ==
             {{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 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">&lt;xsl:root
             xmlns:xsl="http://foo.com"&gt;&lt;data&gt;my json
             string&lt;/data&gt;&lt;/xsl:root&gt;</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 -&gt; foo</p>
             <p><font size="2">{"foo.root":{"data":"my json string"}}</font></p>
         </section>
         <section name="Why JSON Support for Axis2?">
             <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>
         </section>
         <section name="How to use JSON in Axis2">
             <p>At the moment JSON doesn't have a standard and unique content
             type. <tt>application/json</tt> (this is
             the content type which is approved in the <a href=
             "http://www.ietf.org/rfc/rfc4627.txt">JSON RFC</a>),
             <tt>text/javascript</tt> and
             <tt>text/json</tt> are some of the commonly
             used content types for JSON. Fortunately, in Axis2, the user
             has the freedom of specifying the content type to use.</p>
             <subsection name="Configuring axis2.xml">
                 <p>First of all, you need to map the appropriate message formatters and builders to the
                 content type you are using in the <tt>axis2.xml</tt> file. This applies both the to
                 client side and the server side.</p>
                 <p>E.g., if you are using the
                 Mapped convention with the content
                 type <tt>application/json</tt>, add the following declaration:</p>
 <pre><![CDATA[
     <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>
                 <p>If you are using the
                 Badgerfish convention with the
                 content type <tt>text/javascript</tt>, add:</p>
 <pre><![CDATA[
     <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>
             </subsection>
             <subsection name="Client-side configuration">
                 <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>
 <pre>
         File configFile = new File("test-resources/axis2.xml");
         configurationContext = ConfigurationContextFactory
                         .createConfigurationContextFromFileSystem(null, configFile.getAbsolutePath());
         ..........
         ServiceClient sender = new ServiceClient(configurationContext, null);
 </pre>
                 <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>
 <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>
                 <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.</p>
 <code>options.setProperty(Constants.Configuration.HTTP_METHOD,
 Constants.Configuration.HTTP_METHOD_GET);</code>
                 <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>
 <code>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</code>
             </subsection>
             <subsection name="Server-side configuration">
                 <p>Since Badgerfish defines a 1-to-1 transformation between JSON and XML, no additional configuration
                 is required on the server side if that convention is used. Any service deployed into Axis2 will work
                 out of the box.</p>
                 <p>On the other hand, if the Mapped JSON convention is used, then Axis2 needs to know the mappings
                 between XML namespaces and JSON "namespaces" in order to translate messages from JSON
                 into XML representations and vice-versa. To use the Mapped convention with a service deployed into Axis2,
                 add a <tt>xmlToJsonNamespaceMap</tt> property with these mappings to the <tt>services.xml</tt> file for that service, as
                 shown in the following example:</p>
 <pre><![CDATA[
 <service name="...">
     ...
     <parameter name="xmlToJsonNamespaceMap">
         <mappings>
             <mapping xmlNamespace="http://example.org/foo" jsonNamespace=""/>
             <mapping xmlNamespace="http://example.org/bar" jsonNamespace="bar"/>
         </mappings>
     </parameter>
     ...
 </service>
 ]]></pre>
             </subsection>
         </section>
         <section name="How the JSON implementation works - Architecture">
             <subsection name="Introduction">
                 <p>The Axis2 architecture is based on the assumption that any message flowing through
                 the Axis2 runtime is representable as a SOAP infoset, i.e. as XML wrapped in a SOAP
                 envelope. Conceptually, the two message builders <code>JSONOMBuilder</code> and
                 <code>JSONBadgerfishOMBuilder</code> convert incoming messages from JSON to XML and
                 the two message formatters <code>JSONMessageFormatter</code> and <code>JSONBadgerfishMessageFormatter</code>
                 convert outgoing messages from XML to JSON. Axis2 doesn't implement its own JSON parser and serializer, and
                 instead relies on <s><a href="http://jettison.codehaus.org/">Jettison</a></s> <em>(Codehaus hosting no longer accessible - project moved to <a href="https://github.com/jettison-json/jettison">GitHub</a>)</em> to do the JSON&lt;->XML conversions.</p>
                 <p>On the server side the XML for an incoming
                 message is typically converted to Java objects by a databinding (such as ADB or JAX-WS)
                 before the invocation of the service implementation. In the same way, the Java object returned by the
                 service implementation is converted to XML. In the case we are interested in, that XML is then converted
                 by the message formatters to JSON. The usage of an intermediate XML representation is the reason why
                 JSON can be enabled on any service deployed in Axis2.</p>
                 <p>It is important to note that the explanation given in the previous two paragraphs is only valid from
                 a conceptual point of view. The actual processing model is more complicated. In the next two sections
                 we will explain in detail how Axis2 processes incoming and outgoind JSON messages.</p>
             </subsection>
             <subsection name="Processing of incoming JSON messages">
                 <p>Axis2 relies on <a href="http://ws.apache.org/axiom/">Apache Axiom</a> as its XML object model. Although
                 Axiom has a DOM like API, it also has several advanced features that enable Axis2 to avoid
                 building a complete object model representation of the XML message. This is important for performance
                 reasons and distinguishes Axis2 from previous generation SOAP stacks. To leverage these features, the
                 JSON message builders create a SOAP envelope the body of which contains a single <code>OMSourcedElement</code>.</p>
                 <p>An <code>OMSourcedElement</code> is a special kind of <code>OMElement</code> that wraps an arbitrary
                 Java object that can be converted to XML in a well defined way. More precisely, the Java object as well as the logic
                 to convert the object to XML are encapsulated in an <code>OMDataSource</code> instance and it is that
                 <code>OMDataSource</code> instance that is used to create the <code>OMSourcedElement</code>.
                 For JSON, the <code>OMDataSource</code> implementation is <code>JSONDataSource</code> or <code>JSONBadgerfishDataSource</code>,
                 depending on the convention being used. The base class (<code>AbstractJSONDataSource</code>) of these two classes
                 actually contains the code that invokes Jettison to perform the JSON to XML conversion.</p>
                 <p>An <code>OMSourcedElement</code> still behaves like a normal <code>OMElement</code>. In particular, if the
                 element is accessed using DOM like methods, then Axiom will convert the data encapsulated by
                 the <code>OMDataSource</code> on the fly to an object model representation. This process is called <i>expansion</i> of the
                 <code>OMSourcedElement</code>. However, the <code>OMDataSource</code> API is designed such that the conversion to
                 XML is always done using a streaming API: either the <code>OMDataSource</code> produces an <code>XMLStreamReader</code>
                 instance from which the XML representation can be read (this is the case for JSON and the <code>XMLStreamReader</code> implementation
                 is actually provided by Jettison) or it serializes the XML representation to an <code>XMLStreamWriter</code>.
                 Because of this, expansion of the <code>OMSourcedElement</code> is often not necessary, so that the overhead of
                 creating an object model representation can usually be avoided. E.g. a databinding will typically consume the message by requesting an
                 <code>XMLStreamReader</code> for the element in the SOAP body, and this doesn't require expansion of the
                 <code>OMSourcedElement</code>. In this case, the databinding pulls the XML data almost directly from the
                 underlying Jettison <code>XMLStreamReader</code> and no additional Axiom objects are created.</p>
                 <p>Actually here again, things are slightly more complicated because in order to dispatch to the right
                 operation, Axis2 needs to determine the name of the element in the body. Since the name is not known
                 in advance, that operation requires expansion of the <code>OMSourcedElement</code>. However, at this point
                 none of the children of the <code>OMSourcedElement</code> will be built. Fortunately the databindings
                 generally request the <code>XMLStreamReader</code> with caching turned off, so that the child nodes will never be
                 built. Therefore the conclusion of the previous paragraph remains valid: processing the message with a databinding
                 will not create a complete object model representation of the XML.</p>
                 <p>Usage of an <code>OMSourcedElement</code> also solves another architectural challenge posed by
                 the Mapped JSON convention: the JSON payload can only be converted to XML if the namespace mappings
                 are known. Since they are defined per service, they are only known after the incoming message has been
                 dispatched and the target service has been identified. This typically occurs
                 in <code>RequestURIBasedDispatcher</code>, which is executed after
                 the message builder. This means that <code>JSONOMBuilder</code> cannot actually perform the conversion.
                 Usage of an <code>OMSourcedElement</code> avoids this issue because the conversion is done lazily when
                 the <code>OMSourcedElement</code> is first accessed, and this occurs after <code>RequestURIBasedDispatcher</code>
                 has been executed.</p>
                 <p>Another advantage of using <code>OMSourcedElement</code> is that a JSON aware service could directly process
                 the JSON payload without going through the JSON to XML conversion. That is possible because the <code>OMDataSource</code>
                 simply keeps a reference to the JSON payload and this reference is accessible to JSON aware code.</p>
             </subsection>
             <subsection name="Processing of outgoing messages">
                 <p>For outgoing messages, the two JSON message formatters <code>JSONMessageFormatter</code> and
                 <code>JSONBadgerfishMessageFormatter</code> use Jettision to create an appropriate <code>XMLStreamWriter</code>
                 and then request Axiom to serialize the body element to that <code>XMLStreamWriter</code>. If a databinding
                 is used, then the body element will typically be an <code>OMSourcedElement</code> with an <code>OMDataSource</code>
                 implementation specific to that databinding. <code>OMSourcedElement</code> will delegate the serialization
                 request to the appropriate method defined by <code>OMDataSource</code>. This means that the databinding code
                 directly writes to the <code>XMLStreamWriter</code> instance provided by Jettision, without building an
                 intermediate XML object model.</p>
                 <p>Before doing this, the JSON message formatters actually check if the element is an <code>OMSourcedElement</code>
                 backed by a corresponding JSON <code>OMDataSource</code> implementation. If that is the case, then they will
                 extract the JSON payload and directly write it to the output stream. This allows JSON aware services to
                 bypass the XML to JSON conversion entirely.</p>
             </subsection>
         </section>
         <section name="Tests and Samples">
             <subsection name="Integration Test">
                 <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 OMSourcedElement 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>
             </subsection>
             <subsection name="Yahoo-JSON Sample">
                 <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>
             </subsection>
             <subsection name="Enabling mapped JSON on the ADB quickstart sample">
                 <p>To illustrate how JSON can be enabled on an existing service deployed in Axis2,
                 we will use the ADB stock quote service sample from the
                 <a href="quickstartguide.html#adb">Quick Start Guide</a>. The code for this sample
                 can be found in the <tt>samples/quickstartadb</tt> folder in the binary distribution.</p>
                 <p>Only a few steps are necessary to enable JSON (using the Mapped convention) on
                 that service:</p>
                 <ol>
                     <li>
                         <p>Configure the JSON message builders and formatters in <tt>conf/axis2.xml</tt>.
                         Add the following element to the <tt>messageFormatters</tt>:</p>
 <pre><![CDATA[
 <messageFormatter contentType="application/json"
                   class="org.apache.axis2.json.JSONMessageFormatter"/>
 ]]></pre>
                         <p>Also add the following element to the <tt>messageBuilders:</tt></p>
 <pre><![CDATA[
 <messageBuilder contentType="application/json"
                 class="org.apache.axis2.json.JSONOMBuilder"/>
 ]]></pre>
                     </li>
                     <li>
                         <p>Edit the <tt>services.xml</tt> for the stock quote service and add the following
                         configuration:</p>
 <pre><![CDATA[
 <parameter name="xmlToJsonNamespaceMap">
     <mappings>
         <mapping xmlNamespace="http://quickstart.samples/xsd" jsonNamespace=""/>
     </mappings>
 </parameter>
 ]]></pre>
                         <p>The <tt>services.xml</tt> file can be found under
                         <tt>samples/quickstartadb/resources/META-INF</tt>.</p>
                     </li>
                     <li>
                         <p>Build and deploy the service by executing the ant script in
                         <tt>samples/quickstartadb</tt> and then start the Axis2 server using
                         <tt>bin/axis2server.sh</tt> or <tt>bin/axis2server.bat</tt>.</p>
                     </li>
                 </ol>
                 <p>That's it; the stock quote service can now be invoked using JSON. This can be tested
                 using the well known <a href="http://curl.haxx.se/">curl</a> tool:</p>
                 <pre>curl -H 'Content-Type: application/json' -d '{"getPrice":{"symbol":"IBM"}}' http://localhost:8080/axis2/services/StockQuoteService</pre>
                 <p>This will give the following result:</p>
                 <pre>{"getPriceResponse":{"return":42}}</pre>
             </subsection>
         </section>
     </body>
 </document>
	<?xml version="1.0"?>
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	~ Licensed to the Apache Software Foundation (ASF) under one
	~ or more contributor license agreements. See the NOTICE file
	~ distributed with this work for additional information
	~ regarding copyright ownership. The ASF licenses this file
	~ to you under the Apache License, Version 2.0 (the
	~ "License"); you may not use this file except in compliance
	~ with the License. You may obtain a copy of the License at
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	~ http://www.apache.org/licenses/LICENSE-2.0
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	~ Unless required by applicable law or agreed to in writing,
	~ software distributed under the License is distributed on an
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	~ KIND, either express or implied. See the License for the
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	-->
	<document xmlns="http://maven.apache.org/XDOC/2.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/XDOC/2.0 http://maven.apache.org/xsd/xdoc-2.0.xsd">
	<properties>
	<title>JSON Support in Axis2</title>
	</properties>
	<body>
	<h1>JSON Support in Axis2</h1>
	<section name="Introduction">
	<p>Update: This documentation represents early forms of JSON
	conventions, Badgerfish and Mapped. GSON support was added a few
	years later. Moshi support is now included as an alternative to
	GSON. For users of JSON seeking modern features, see the <a href=
	"json_support_gson.html">JSON Support Guide.</a>. For users of
	JSON and Spring Boot 3, see the sample application in the <a href=
	"json-springboot-userguide.html">JSON and Spring Boot 3 User's Guide.</a>
	</p>
	<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>
	</section>
	<section name="What is JSON?">
	<p><a 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 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>
	</section>
	<section name="Why JSON Support for Axis2?">
	<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>
	</section>
	<section name="How to use JSON in Axis2">
	<p>At the moment JSON doesn't have a standard and unique content
	type. <tt>application/json</tt> (this is
	the content type which is approved in the <a href=
	"http://www.ietf.org/rfc/rfc4627.txt">JSON RFC</a>),
	<tt>text/javascript</tt> and
	<tt>text/json</tt> are some of the commonly
	used content types for JSON. Fortunately, in Axis2, the user
	has the freedom of specifying the content type to use.</p>
	<subsection name="Configuring axis2.xml">
	<p>First of all, you need to map the appropriate message formatters and builders to the
	content type you are using in the <tt>axis2.xml</tt> file. This applies both the to
	client side and the server side.</p>
	<p>E.g., if you are using the
	Mapped convention with the content
	type <tt>application/json</tt>, add the following declaration:</p>
	<pre><![CDATA[
	<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>
	<p>If you are using the
	Badgerfish convention with the
	content type <tt>text/javascript</tt>, add:</p>
	<pre><![CDATA[
	<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>
	</subsection>
	<subsection name="Client-side configuration">
	<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>
	<pre>
	File configFile = new File("test-resources/axis2.xml");
	configurationContext = ConfigurationContextFactory
	.createConfigurationContextFromFileSystem(null, configFile.getAbsolutePath());
	..........
	ServiceClient sender = new ServiceClient(configurationContext, null);
	</pre>
	<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>
	<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>
	<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.</p>
	<code>options.setProperty(Constants.Configuration.HTTP_METHOD,
	Constants.Configuration.HTTP_METHOD_GET);</code>
	<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>
	<code>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</code>
	</subsection>
	<subsection name="Server-side configuration">
	<p>Since Badgerfish defines a 1-to-1 transformation between JSON and XML, no additional configuration
	is required on the server side if that convention is used. Any service deployed into Axis2 will work
	out of the box.</p>
	<p>On the other hand, if the Mapped JSON convention is used, then Axis2 needs to know the mappings
	between XML namespaces and JSON "namespaces" in order to translate messages from JSON
	into XML representations and vice-versa. To use the Mapped convention with a service deployed into Axis2,
	add a <tt>xmlToJsonNamespaceMap</tt> property with these mappings to the <tt>services.xml</tt> file for that service, as
	shown in the following example:</p>
	<pre><![CDATA[
	<service name="...">
	...
	<parameter name="xmlToJsonNamespaceMap">
	<mappings>
	<mapping xmlNamespace="http://example.org/foo" jsonNamespace=""/>
	<mapping xmlNamespace="http://example.org/bar" jsonNamespace="bar"/>
	</mappings>
	</parameter>
	...
	</service>
	]]></pre>
	</subsection>
	</section>
	<section name="How the JSON implementation works - Architecture">
	<subsection name="Introduction">
	<p>The Axis2 architecture is based on the assumption that any message flowing through
	the Axis2 runtime is representable as a SOAP infoset, i.e. as XML wrapped in a SOAP
	envelope. Conceptually, the two message builders <code>JSONOMBuilder</code> and
	<code>JSONBadgerfishOMBuilder</code> convert incoming messages from JSON to XML and
	the two message formatters <code>JSONMessageFormatter</code> and <code>JSONBadgerfishMessageFormatter</code>
	convert outgoing messages from XML to JSON. Axis2 doesn't implement its own JSON parser and serializer, and
	instead relies on <s><a href="http://jettison.codehaus.org/">Jettison</a></s> <em>(Codehaus hosting no longer accessible - project moved to <a href="https://github.com/jettison-json/jettison">GitHub</a>)</em> to do the JSON<->XML conversions.</p>
	<p>On the server side the XML for an incoming
	message is typically converted to Java objects by a databinding (such as ADB or JAX-WS)
	before the invocation of the service implementation. In the same way, the Java object returned by the
	service implementation is converted to XML. In the case we are interested in, that XML is then converted
	by the message formatters to JSON. The usage of an intermediate XML representation is the reason why
	JSON can be enabled on any service deployed in Axis2.</p>
	<p>It is important to note that the explanation given in the previous two paragraphs is only valid from
	a conceptual point of view. The actual processing model is more complicated. In the next two sections
	we will explain in detail how Axis2 processes incoming and outgoind JSON messages.</p>
	</subsection>
	<subsection name="Processing of incoming JSON messages">
	<p>Axis2 relies on <a href="http://ws.apache.org/axiom/">Apache Axiom</a> as its XML object model. Although
	Axiom has a DOM like API, it also has several advanced features that enable Axis2 to avoid
	building a complete object model representation of the XML message. This is important for performance
	reasons and distinguishes Axis2 from previous generation SOAP stacks. To leverage these features, the
	JSON message builders create a SOAP envelope the body of which contains a single <code>OMSourcedElement</code>.</p>
	<p>An <code>OMSourcedElement</code> is a special kind of <code>OMElement</code> that wraps an arbitrary
	Java object that can be converted to XML in a well defined way. More precisely, the Java object as well as the logic
	to convert the object to XML are encapsulated in an <code>OMDataSource</code> instance and it is that
	<code>OMDataSource</code> instance that is used to create the <code>OMSourcedElement</code>.
	For JSON, the <code>OMDataSource</code> implementation is <code>JSONDataSource</code> or <code>JSONBadgerfishDataSource</code>,
	depending on the convention being used. The base class (<code>AbstractJSONDataSource</code>) of these two classes
	actually contains the code that invokes Jettison to perform the JSON to XML conversion.</p>
	<p>An <code>OMSourcedElement</code> still behaves like a normal <code>OMElement</code>. In particular, if the
	element is accessed using DOM like methods, then Axiom will convert the data encapsulated by
	the <code>OMDataSource</code> on the fly to an object model representation. This process is called <i>expansion</i> of the
	<code>OMSourcedElement</code>. However, the <code>OMDataSource</code> API is designed such that the conversion to
	XML is always done using a streaming API: either the <code>OMDataSource</code> produces an <code>XMLStreamReader</code>
	instance from which the XML representation can be read (this is the case for JSON and the <code>XMLStreamReader</code> implementation
	is actually provided by Jettison) or it serializes the XML representation to an <code>XMLStreamWriter</code>.
	Because of this, expansion of the <code>OMSourcedElement</code> is often not necessary, so that the overhead of
	creating an object model representation can usually be avoided. E.g. a databinding will typically consume the message by requesting an
	<code>XMLStreamReader</code> for the element in the SOAP body, and this doesn't require expansion of the
	<code>OMSourcedElement</code>. In this case, the databinding pulls the XML data almost directly from the
	underlying Jettison <code>XMLStreamReader</code> and no additional Axiom objects are created.</p>
	<p>Actually here again, things are slightly more complicated because in order to dispatch to the right
	operation, Axis2 needs to determine the name of the element in the body. Since the name is not known
	in advance, that operation requires expansion of the <code>OMSourcedElement</code>. However, at this point
	none of the children of the <code>OMSourcedElement</code> will be built. Fortunately the databindings
	generally request the <code>XMLStreamReader</code> with caching turned off, so that the child nodes will never be
	built. Therefore the conclusion of the previous paragraph remains valid: processing the message with a databinding
	will not create a complete object model representation of the XML.</p>
	<p>Usage of an <code>OMSourcedElement</code> also solves another architectural challenge posed by
	the Mapped JSON convention: the JSON payload can only be converted to XML if the namespace mappings
	are known. Since they are defined per service, they are only known after the incoming message has been
	dispatched and the target service has been identified. This typically occurs
	in <code>RequestURIBasedDispatcher</code>, which is executed after
	the message builder. This means that <code>JSONOMBuilder</code> cannot actually perform the conversion.
	Usage of an <code>OMSourcedElement</code> avoids this issue because the conversion is done lazily when
	the <code>OMSourcedElement</code> is first accessed, and this occurs after <code>RequestURIBasedDispatcher</code>
	has been executed.</p>
	<p>Another advantage of using <code>OMSourcedElement</code> is that a JSON aware service could directly process
	the JSON payload without going through the JSON to XML conversion. That is possible because the <code>OMDataSource</code>
	simply keeps a reference to the JSON payload and this reference is accessible to JSON aware code.</p>
	</subsection>
	<subsection name="Processing of outgoing messages">
	<p>For outgoing messages, the two JSON message formatters <code>JSONMessageFormatter</code> and
	<code>JSONBadgerfishMessageFormatter</code> use Jettision to create an appropriate <code>XMLStreamWriter</code>
	and then request Axiom to serialize the body element to that <code>XMLStreamWriter</code>. If a databinding
	is used, then the body element will typically be an <code>OMSourcedElement</code> with an <code>OMDataSource</code>
	implementation specific to that databinding. <code>OMSourcedElement</code> will delegate the serialization
	request to the appropriate method defined by <code>OMDataSource</code>. This means that the databinding code
	directly writes to the <code>XMLStreamWriter</code> instance provided by Jettision, without building an
	intermediate XML object model.</p>
	<p>Before doing this, the JSON message formatters actually check if the element is an <code>OMSourcedElement</code>
	backed by a corresponding JSON <code>OMDataSource</code> implementation. If that is the case, then they will
	extract the JSON payload and directly write it to the output stream. This allows JSON aware services to
	bypass the XML to JSON conversion entirely.</p>
	</subsection>
	</section>
	<section name="Tests and Samples">
	<subsection name="Integration Test">
	<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 OMSourcedElement 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>
	</subsection>
	<subsection name="Yahoo-JSON Sample">
	<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>
	</subsection>
	<subsection name="Enabling mapped JSON on the ADB quickstart sample">
	<p>To illustrate how JSON can be enabled on an existing service deployed in Axis2,
	we will use the ADB stock quote service sample from the
	<a href="quickstartguide.html#adb">Quick Start Guide</a>. The code for this sample
	can be found in the <tt>samples/quickstartadb</tt> folder in the binary distribution.</p>
	<p>Only a few steps are necessary to enable JSON (using the Mapped convention) on
	that service:</p>
	<ol>
	<li>
	<p>Configure the JSON message builders and formatters in <tt>conf/axis2.xml</tt>.
	Add the following element to the <tt>messageFormatters</tt>:</p>
	<pre><![CDATA[
	<messageFormatter contentType="application/json"
	class="org.apache.axis2.json.JSONMessageFormatter"/>
	]]></pre>
	<p>Also add the following element to the <tt>messageBuilders:</tt></p>
	<pre><![CDATA[
	<messageBuilder contentType="application/json"
	class="org.apache.axis2.json.JSONOMBuilder"/>
	]]></pre>
	</li>
	<li>
	<p>Edit the <tt>services.xml</tt> for the stock quote service and add the following
	configuration:</p>
	<pre><![CDATA[
	<parameter name="xmlToJsonNamespaceMap">
	<mappings>
	<mapping xmlNamespace="http://quickstart.samples/xsd" jsonNamespace=""/>
	</mappings>
	</parameter>
	]]></pre>
	<p>The <tt>services.xml</tt> file can be found under
	<tt>samples/quickstartadb/resources/META-INF</tt>.</p>
	</li>
	<li>
	<p>Build and deploy the service by executing the ant script in
	<tt>samples/quickstartadb</tt> and then start the Axis2 server using
	<tt>bin/axis2server.sh</tt> or <tt>bin/axis2server.bat</tt>.</p>
	</li>
	</ol>
	<p>That's it; the stock quote service can now be invoked using JSON. This can be tested
	using the well known <a href="http://curl.haxx.se/">curl</a> tool:</p>
	<pre>curl -H 'Content-Type: application/json' -d '{"getPrice":{"symbol":"IBM"}}' http://localhost:8080/axis2/services/StockQuoteService</pre>
	<p>This will give the following result:</p>
	<pre>{"getPriceResponse":{"return":42}}</pre>
	</subsection>
	</section>
	</body>
	</document>