Its very common when routing messages from one endpoint to another to need to convert the body payloads from one type to another such as to convert to and from the following common types
So in an endpoint you can convert a body to another type via
The default implementation, DefaultTypeConverter, uses pluggable strategies to load type converters via TypeConverterLoader. The default strategy, AnnotationTypeConverterLoader, uses a discovery mechanism to find converters.
New in Camel 1.5
The default implementation, DefaultTypeConverter, now throws a NoTypeConversionAvailableException if a suitable conversion cannot be found (CAMEL-84). The semantical ambiguity of null (both valid result and indication of no conversion found) is now resolved, but this may impact existing code in that it should now catch the exception instead of checking for null.
New in Camel 2.0
Exposed the TypeConverterRegistry from CamelContext so end users more easily will be able to add type converters at runtime. This is also usable in situations where the default discovering of type converters fails on platforms with classloading issues.
To access the registry, you get it from the CamelContext
Camel can gather utilization statistics of the runtime usage of type converters. These stats are available in JMX, and as well as from the getStatistics() method from TypeConverterRegistry.
From Camel 2.11.0/2.10.5 onwards these statistics are turned off by default as there is some performance overhead under very high concurrent load. To enable the statistics in Java, do the following:
Or in the XML DSL with:
The following sample demonstrates how to add a type converter at runtime:
And our type converter is implemented as:
And then we can convert from String to MyOrder as we are used to with the type converter:
The AnnotationTypeConverterLoader will search the classpath for a file called META-INF/services/org/apache/camel/TypeConverter. The contents are expected to be comma separated package names. These packages are then recursively searched for any objects with the @Converter annotation. Then any method marked with @Converter is assumed to be a conversion method; where the parameter is the from value and the return is the to value.
e.g. the following shows how to register a converter from File -> InputStream
Static methods are invoked; non-static methods require an instance of the converter object to be created (which is then cached). If a converter requires configuration you can plug in an Injector interface to the DefaultTypeConverter which can construct and inject converter objects via Spring or Guice.
We have most of the common converters for common Java types in the org.apache.camel.converter package and its children.
Available in Camel 2.0
Fallback type converters are used as a last resort for converting a given value to another type. Its used when the regular type converters give up.
Or you can use the non generic signature.
And the method name can be anything (convertTo is not required as a name), so it can be named convertMySpecialTypes if you like.
The purpose with this broad scope method signature is allowing you to control if you can convert the given type or not. The type parameter holds the type we want the value converted to. Its used internally in Camel for wrapper objects so we can delegate the type convertions to the body that is wrapped.
For instance in the method below we will handle all type conversions that is based on the wrapper class GenericFile and we let Camel do the type conversions on its body instead.
You are welcome to write your own converters. Remember to use the @Converter annotations on the classes and methods you wish to use. Then add the packages to a file called META-INF/services/org/apache/camel/TypeConverter in your jar. Remember to make sure that :-
The file in the JAR: META-INF/services/org/apache/camel/TypeConverter contains the following line(s)
Each line in the file is a package name. This tells Camel to go scan those packages for any classes that has been annotated with the @Converter.
Available as of Camel 2.8
The file in the JAR: META-INF/services/org/apache/camel/TypeConverter contains the following line(s) for FQN class names
As you can see each line in the file now contains a FQN class name. This is the recommended approach.
Available in Camel 1.5
Since Java provides converting the byte to String and String to byte with the charset name parameter. You can define the charset name by setting the exchange property name Exchange.CHARSET_NAME with the charset name, such as "UTF-8" or "iso-8859-1".
Available in Camel 1.5
The type converter accepts the Exchange as an optional 2nd parameter. This is usable if the type converter for instance needs information from the current exchange. For instance combined with the encoding support its possible for type converters to convert with the configured encoding. An example from camel-core for the byte -> String converter: