Type Converter

Type Converter

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

• File
• String
• byte[] and yteBuffer
• InputStream and OutputStream
• Reader and Writer
• Document and Source

The Message interface defines a helper method to allow conversions to be done via the getBody(Class) method.

So in an endpoint you can convert a body to another type via

Message message = exchange.getIn();
Document document = message.getBody(Document.class);

How Type Conversion works

The type conversion strategy is defined by the TypeConverter interface which can be customized on a CamelContext.

The default implementation, DefaultTypeConverter uses pluggable strategies to load type converters via TypeConverterLoader. The default strategy, AnnotationTypeConverterLoader uses a discovery mechanism to find converters.

Discovering Type Converters

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

@Converter
public class IOConverter {

    @Converter
    public static InputStream toInputStream(File file) throws FileNotFoundException {
        return new BufferedInputStream(new FileInputStream(file));
    }
}

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.