Chapter 350. XStream DataFormat

Available as of Camel version 1.3

XStream is a Data Format which uses the XStream library to marshal and unmarshal Java objects to and from XML.

To use XStream in your camel routes you need to add the a dependency on camel-xstream which implements this data format.

Maven users will need to add the following dependency to their pom.xml for this component:

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-xstream</artifactId>
  <version>x.x.x</version>
  <!-- use the same version as your Camel core version -->
</dependency>

350.1. Options

The XStream dataformat supports 10 options which are listed below.

NameDefaultJava TypeDescription

permissions

 

String

Adds permissions that controls which Java packages and classes XStream is allowed to use during unmarshal from xml/json to Java beans. A permission must be configured either here or globally using a JVM system property. The permission can be specified in a syntax where a plus sign is allow, and minus sign is deny. Wildcards is supported by using . as prefix. For example to allow com.foo and all subpackages then specfy com.foo.. Multiple permissions can be configured separated by comma, such as com.foo.,-com.foo.bar.MySecretBean. The following default permission is always included: -,java.lang.,java.util. unless its overridden by specifying a JVM system property with they key org.apache.camel.xstream.permissions.

encoding

 

String

Sets the encoding to use

driver

 

String

To use a custom XStream driver. The instance must be of type com.thoughtworks.xstream.io.HierarchicalStreamDriver

driverRef

 

String

To refer to a custom XStream driver to lookup in the registry. The instance must be of type com.thoughtworks.xstream.io.HierarchicalStreamDriver

mode

 

String

Mode for dealing with duplicate references The possible values are: NO_REFERENCES ID_REFERENCES XPATH_RELATIVE_REFERENCES XPATH_ABSOLUTE_REFERENCES SINGLE_NODE_XPATH_RELATIVE_REFERENCES SINGLE_NODE_XPATH_ABSOLUTE_REFERENCES

converters

 

List

List of class names for using custom XStream converters. The classes must be of type com.thoughtworks.xstream.converters.Converter

aliases

 

Map

Alias a Class to a shorter name to be used in XML elements.

omitFields

 

Map

Prevents a field from being serialized. To omit a field you must always provide the declaring type and not necessarily the type that is converted.

implicitCollections

 

Map

Adds a default implicit collection which is used for any unmapped XML tag.

contentTypeHeader

false

Boolean

Whether the data format should set the Content-Type header with the type from the data format if the data format is capable of doing so. For example application/xml for data formats marshalling to XML, or application/json for data formats marshalling to JSon etc.

350.2. Using the Java DSL

// lets turn Object messages into XML then send to MQSeries
from("activemq:My.Queue").
  marshal().xstream().
  to("mqseries:Another.Queue");

If you would like to configure the XStream instance used by the Camel for the message transformation, you can simply pass a reference to that instance on the DSL level.

XStream xStream = new XStream();
xStream.aliasField("money", PurchaseOrder.class, "cash");
// new Added setModel option since Camel 2.14
xStream.setModel("NO_REFERENCES");
...

from("direct:marshal").
  marshal(new XStreamDataFormat(xStream)).
  to("mock:marshaled");

350.3. XMLInputFactory and XMLOutputFactory

The XStream library uses the javax.xml.stream.XMLInputFactory and javax.xml.stream.XMLOutputFactory, you can control which implementation of this factory should be used.

The Factory is discovered using this algorithm: 1. Use the javax.xml.stream.XMLInputFactory , javax.xml.stream.XMLOutputFactory system property. 2. Use the lib/xml.stream.properties file in the JRE_HOME directory. 3. Use the Services API, if available, to determine the classname by looking in the META-INF/services/javax.xml.stream.XMLInputFactory, META-INF/services/javax.xml.stream.XMLOutputFactory files in jars available to the JRE. 4. Use the platform default XMLInputFactory,XMLOutputFactory instance.

350.4. How to set the XML encoding in Xstream DataFormat?

From Camel 2.2.0, you can set the encoding of XML in Xstream DataFormat by setting the Exchange’s property with the key Exchange.CHARSET_NAME, or setting the encoding property on Xstream from DSL or Spring config.

from("activemq:My.Queue").
  marshal().xstream("UTF-8").
  to("mqseries:Another.Queue");

350.5. Setting the type permissions of Xstream DataFormat

In Camel, one can always use its own processing step in the route to filter and block certain XML documents to be routed to the XStream’s unmarhall step. From Camel 2.16.1, 2.15.5, you can set XStream’s type permissions to automatically allow or deny the instantiation of certain types.

The default type permissions setting used by Camel denies all types except for those from java.lang and java.util packages. This setting can be changed by setting System property org.apache.camel.xstream.permissions. Its value is a string of comma-separated permission terms, each representing a type being allowed or denied, depending on whether the term is prefixed with '' (note '' may be omitted) or with '-', respectively.

Each term may contain a wildcard character ''. For example, value "-,java.lang.,java.util." indicates denying all types except for java.lang.* and java.util.* classes. Setting this value to an empty string "" reverts to the default XStream’s type permissions handling which denies certain blacklisted classes and allow others.

The type permissions setting can be extended at an individual XStream DataFormat instance by setting its type permissions property.

    <dataFormats>
        <xstream id="xstream-default"
                 permissions="org.apache.camel.samples.xstream.*"/>
        ...