[CONF] Apache CXF 2.0 Documentation: JSON Support (page edited)

Mon, 25 Dec 2006 20:21:21 -0800

Page Edited : CXF20DOC : JSON Support

JSON Support has been edited by Dan Diephouse (Dec 25, 2006).

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Content:

JSON Overview

JSON is a textual data format for data exchange. JSON stands for _javascript_ Object Notation and, as the name implies, it is itself _javascript_. Here is a small sample:

{
  "customer" : {
    "name" : "Jane Doe",
    "company" : "Acme Enterprises"
}


One of the advantages of JSON is that is very easy for _javascript_ developers to use - it simply needs to be evaluated and it becomse javscript objects. For information on this see the JSON website.



JSON is supported in CXF through Jettison. Jettison is a StAX implementation that reads and writes JSON. Jettison intercept calls to read/write XML and instead read/writes JSON. 



JSON/XML Conventions


To understand how to create a JSON service, you first need to understand how your XML structures will be converted into the JSON format. JSON does not have many concepts found in XML such as namespaces, attributes or entity references. Because of this we must adopt conventions on how to convert between the two.



Jettison supports two conventions currently. These are explained in more detail in the Jettison user's guide, but a quick summary of each follows.

1. The "mapped" convention. In this convention namespaces are mapped to json prefixes. For instance, if you have a namespace "http://acme.com" you could map it to the "acme" prefix. This means that the element <customer xmlns="http://acme.com"> would be mapped to the "acme.customer" JSON tag.

2. The BadgerFish convention. This convention provides a mapping of the full XML infoset to JSON. Attributes are represented with an @ sign - i.e. "@attributeName" : "value". Textual data is represented with the "$" as the tag. Example:




{ "customer" : { "name" : { "$" : "Jane Doe" } } }





Configuring Jettison


Jettison is configured by setting properties on your service's endpoint. Depending on which way you create your service, this can be done slightly differently.



Using ServerFactoryBeans


This example shows how to set up Jettison using a ServerFactoryBean, such as the JaxWsServerFactoryBean. First you must create a properties HashMap and set the StAX XMLInputFactory and XMLOutputFactory:




Map<String,Object> properties = new HashMap<String,Object>();

// Create a mapping between the XML namespaces and the JSON prefixes.
// The JSON prefix can be "" to specify that you don't want any prefix.
HashMap<String, String> nstojns = new HashMap<String,String>();
nstojns.put("http://customer.acme.com", "acme");

MappedXMLInputFactory xif = new MappedXMLInputFactory(nstojns);
properties.put(XMLInputFactory.class.getName(), xif);

MappedXMLOutputFactory xof = new MappedXMLOutputFactory(nstojns);
properties.put(XMLOutputFactory.class.getName(), xof);




You must also tell CXF which Content-Type you wish to serve:




// Tell CXF to use a different Content-Type for the JSON endpoint
// This should probably be application/json, but text/plain allows
// us to view easily in a web browser.
properties.put("Content-Type", "text/plain");




Last, you'll want to actually create your service:




// Build up the server factory bean
JaxWsServerFactoryBean sf = new JaxWsServerFactoryBean();
sf.setServiceClass(CustomerService.class);
// Use the HTTP Binding which understands the Java Rest Annotations
sf.setBindingFactory(new HttpBindingInfoFactoryBean());
sf.setAddress("http://localhost:8080/json");
sf.setServiceBean(new CustomerServiceImpl());

sf.setProperties(properties);

sf.create();

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