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XML JSON Data Format (camel-xmljson)

Available as of Camel 2.10

Camel already supports a number of data formats to perform XML and JSON-related conversions, but all of them require a POJO either as an input (for marshalling) or produce a POJO as output (for un-marshaling). This data format provides the capability to convert from XML to JSON and viceversa directly, without stepping through intermediate POJOs.

This data format leverages the Json-lib library to achieve direct conversion. In this context, XML is considered the high-level format, while JSON is the low-level format. Hence, the marshal/unmarshal semantics are assigned as follows:

  • marshalling => converting from XML to JSON
  • un-marshaling => converting from JSON to XML.

Options

This data format supports the following options. You can set them via all DSLs. The defaults marked with (*) are determined by json-lib, rather than the code of the data format itself. They are reproduced here for convenience to avoid having to consult the json-lib documentation directly.

Basic Usage With the Java DSL

Explicitly Instantiating the DataFormat

Just instantiate the XmlJsonDataFormat from package org.apache.camel.dataformat.xmljson. Make sure you have installed the camel-xmljson feature (if running on OSGi) or that you've included camel-xmljson-{version}.jar and its transitive dependencies in your classpath.

Example, initialization with a default configuration:

XmlJsonDataFormat xmlJsonFormat = new XmlJsonDataFormat();

To tune the behavior of the data format as per the options above, use the appropriate setters:

XmlJsonDataFormat xmlJsonFormat = new XmlJsonDataFormat();
xmlJsonFormat.setEncoding("UTF-8");
xmlJsonFormat.setForceTopLevelObject(true);
xmlJsonFormat.setTrimSpaces(true);
xmlJsonFormat.setRootName("newRoot");
xmlJsonFormat.setSkipNamespaces(true);
xmlJsonFormat.setRemoveNamespacePrefixes(true);
xmlJsonFormat.setExpandableProperties(Arrays.asList("d", "e"));

Once the DataFormat is instantiated, the next step is to use it as a parameter to either of the marshal()/unmarshal() DSL elements:

// From XML to JSON
from("direct:marshal")
  .marshal(xmlJsonFormat)
  .to("mock:json");

// From JSON to XML
from("direct:unmarshal")
  .unmarshal(xmlJsonFormat)
  .to("mock:xml");

Defining the DataFormat in-line

Alternatively, you can define the data format inline by using the xmljson() DSL element.

// From XML to JSON - inline dataformat
from("direct:marshalInline")
  .marshal()
  .xmljson()
  .to("mock:jsonInline");

// From JSON to XML - inline dataformat
from("direct:unmarshalInline")
  .unmarshal()
  .xmljson()
  .to("mock:xmlInline");

If you wish, you can even pass in a Map<String, String> to the inline methods to provide custom options:

Map<String, String> xmlJsonOptions = new HashMap<String, String>();

xmlJsonOptions.put(org.apache.camel.model.dataformat.XmlJsonDataFormat.ENCODING, "UTF-8");
xmlJsonOptions.put(org.apache.camel.model.dataformat.XmlJsonDataFormat.ROOT_NAME, "newRoot");
xmlJsonOptions.put(org.apache.camel.model.dataformat.XmlJsonDataFormat.SKIP_NAMESPACES, "true");
xmlJsonOptions.put(org.apache.camel.model.dataformat.XmlJsonDataFormat.REMOVE_NAMESPACE_PREFIXES, "true");
xmlJsonOptions.put(org.apache.camel.model.dataformat.XmlJsonDataFormat.EXPANDABLE_PROPERTIES, "d e");

// From XML to JSON - inline dataformat w/options
from("direct:marshalInlineOptions")
  .marshal()
  .xmljson(xmlJsonOptions)
  .to("mock:jsonInlineOptions");

// From JSON to XML - inline dataformat w/options
from("direct:unmarshalInlineOptions")
  .unmarshal()
  .xmljson(xmlJsonOptions)
  .to("mock:xmlInlineOptions");

Basic Usage with Spring or Blueprint DSL

Within the <dataFormats> block, simply configure an xmljson element with unique IDs:

<dataFormats>
    <xmljson id="xmljson"/>
    <xmljson id="xmljsonWithOptions" 
             forceTopLevelObject="true" 
             trimSpaces="true" 
             rootName="newRoot" 
             skipNamespaces="true" 
             removeNamespacePrefixes="true" 
             expandableProperties="d e"/>
</dataFormats>

Then you simply refer to the data format object within your <marshal/> and <unmarshal/> DSLs:

<route>
    <from uri="direct:marshal"/>
    <marshal ref="xmljson"/>
    <to uri="mock:json"/>
</route>

<route>
    <from uri="direct:unmarshalWithOptions"/>
    <unmarshal ref="xmljsonWithOptions"/>
    <to uri="mock:xmlWithOptions"/>
</route>

Enabling XML DSL autocompletion for this component is easy: just refer to the appropriate Schema locations, depending on whether you're using Spring or Blueprint DSL. Remember that this data format is available from Camel 2.10. Therefore only schemas from that version or later will include these new XML elements and attributes.

The syntax with Blueprint is identical to that of the Spring DSL. Just ensure the correct namespaces and schemaLocations are in use.

Namespace Mappings

XML has namespaces to fully qualify elements and attributes; JSON doesn't. You need to take this into account when performing XML-JSON conversions.

To bridge the gap, Json-lib has an option to bind namespace declarations in the form of prefixes and namespace URIs to XML output elements while un-marshaling, e.g., converting from JSON to XML.

For example, provided the following JSON string:

{ "pref1:a": "value1", "pref2:b": "value2" }

you can ask json-lib to output namespace declarations on elements pref1:a and pref2:b to bind the prefixes pref1 and pref2 to specific namespace URIs.

To use this feature, simply create XmlJsonDataFormat.NamespacesPerElementMapping objects and add them to the namespaceMappings option (which is a List).

The XmlJsonDataFormat.NamespacesPerElementMapping holds an element name and a Map of [prefix => namespace URI]. To facilitate mapping multiple prefixes and namespace URIs, the NamespacesPerElementMapping(String element, String pipeSeparatedMappings) constructor takes a String-based pipe-separated sequence of [prefix, namespaceURI] pairs in the following way: |ns2|http://camel.apache.org/personalData|ns3|http://camel.apache.org/personalData2|.

In order to define a default namespace, just leave the corresponding key field empty: |ns1|http://camel.apache.org/test1||http://camel.apache.org/default|.

Binding namespace declarations to an element name = empty string will attach those namespaces to the root element.

The code for this is:

XmlJsonDataFormat namespacesFormat = new XmlJsonDataFormat();
List<XmlJsonDataFormat.NamespacesPerElementMapping> namespaces = new ArrayList<XmlJsonDataFormat.NamespacesPerElementMapping>();

namespaces.add(new XmlJsonDataFormat.NamespacesPerElementMapping("", "|ns1|http://camel.apache.org/test1||http://camel.apache.org/default|"));
namespaces.add(new XmlJsonDataFormat.NamespacesPerElementMapping("surname", "|ns2|http://camel.apache.org/personalData|ns3|http://camel.apache.org/personalData2|"));
namespacesFormat.setNamespaceMappings(namespaces);
namespacesFormat.setRootElement("person");

And you can achieve the same in Spring DSL.

Example

Using the namespace bindings in the Java snippet above on the following JSON string:

{ "name": "Raul", "surname": "Kripalani", "f": true, "g": null}

 

Would yield the following XML:

<person xmlns="http://camel.apache.org/default" xmlns:ns1="http://camel.apache.org/test1">
    <f>true</f>
    <g null="true"/>
    <name>Raul</name>
    <surname xmlns:ns2="http://camel.apache.org/personalData" xmlns:ns3="http://camel.apache.org/personalData2">Kripalani</surname>
</person>

Remember that the JSON spec defines a JSON object as follows:

An object is an unordered set of name/value pairs. [...].

That's why the elements are in a different order in the output XML.

Dependencies

To use the XmlJson dataformat in your camel routes you need to add the following dependency to your pom.

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-xmljson</artifactId>
  <version>x.x.x</version>
  <!-- Use the same version as camel-core, but remember that this component is only available from Camel 2.10 -->
</dependency>

<!-- And also XOM must be included. XOM cannot be included by default due to an incompatible
license with ASF; so add this manually -->
<dependency>
  <groupId>xom</groupId>
  <artifactId>xom</artifactId>
  <version>1.2.5</version>
</dependency>

See Also

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