Chapter 44. Type Converters

This section describes the overall architecture of the type converter mechanism, which you must understand, if you want to write custom type converters. If you only need to use the built-in type converters, see Chapter 42, Understanding Message Formats.

Example 44.1, “TypeConverter Interface” shows the definition of the org.apache.camel.TypeConverter interface, which all type converters must implement.

package org.apache.camel;

public interface TypeConverter {
    <T> T convertTo(Class<T> type, Object value);
}

package org.apache.camel;

public interface TypeConverter {
    <T> T convertTo(Class<T> type, Object value);
}

The Apache Camel type converter mechanism follows a master/slave pattern. There are many slave type converters, which are each capable of performing a limited number of type conversions, and a single master type converter, which aggregates the type conversions performed by the slaves. The master type converter acts as a front-end for the slave type converters. When you request the master to perform a type conversion, it selects the appropriate slave and delegates the conversion task to that slave.

For users of the type conversion mechanism, the master type converter is the most important because it provides the entry point for accessing the conversion mechanism. During start up, Apache Camel automatically associates a master type converter instance with the CamelContext object. To obtain a reference to the master type converter, you call the CamelContext.getTypeConverter() method. For example, if you have an exchange object, exchange, you can obtain a reference to the master type converter as shown in Example 44.2, “Getting a Master Type Converter”.

org.apache.camel.TypeConverter tc = exchange.getContext().getTypeConverter();

org.apache.camel.TypeConverter tc = exchange.getContext().getTypeConverter();

The master type converter uses a type converter loader to populate the registry of slave type converters. A type converter loader is any class that implements the TypeConverterLoader interface. Apache Camel currently uses only one kind of type converter loader—the annotation type converter loader (of AnnotationTypeConverterLoader type).

Figure 44.1, “Type Conversion Process” gives an overview of the type conversion process, showing the steps involved in converting a given data value, value, to a specified type, toType.

The type conversion mechanism proceeds as follows: