44.4. The ExchangeHelper Class

Overview

The org.apache.camel.util.ExchangeHelper class is a Apache Camel utility class that provides methods that are useful when implementing a processor.

Resolve an endpoint

The static resolveEndpoint() method is one of the most useful methods in the ExchangeHelper class. You use it inside a processor to create new Endpoint instances on the fly.

Example 44.6. The resolveEndpoint() Method

public final class ExchangeHelper {
    ...
    @SuppressWarnings({"unchecked" })
    public static Endpoint
    resolveEndpoint(Exchange exchange, Object value)
        throws NoSuchEndpointException { ... }
    ...
}
The first argument to resolveEndpoint() is an exchange instance, and the second argument is usually an endpoint URI string. Example 44.7, “Creating a File Endpoint” shows how to create a new file endpoint from an exchange instance exchange

Example 44.7. Creating a File Endpoint

Endpoint file_endp = ExchangeHelper.resolveEndpoint(exchange, "file://tmp/messages/in.xml");

Wrapping the exchange accessors

The ExchangeHelper class provides several static methods of the form getMandatoryBeanProperty(), which wrap the corresponding getBeanProperty() methods on the Exchange class. The difference between them is that the original getBeanProperty() accessors return null, if the corresponding property is unavailable, and the getMandatoryBeanProperty() wrapper methods throw a Java exception. The following wrapper methods are implemented in the ExchangeHelper class: 
public final class ExchangeHelper {
    ...
    public static <T> T getMandatoryProperty(Exchange exchange, String propertyName, Class<T> type)
        throws NoSuchPropertyException { ... }

    public static <T> T getMandatoryHeader(Exchange exchange, String propertyName, Class<T> type)
        throws NoSuchHeaderException { ... }

    public static Object getMandatoryInBody(Exchange exchange)
        throws InvalidPayloadException { ... }

    public static <T> T getMandatoryInBody(Exchange exchange, Class<T> type)
        throws InvalidPayloadException { ... }

    public static Object getMandatoryOutBody(Exchange exchange)
        throws InvalidPayloadException { ... }

    public static <T> T getMandatoryOutBody(Exchange exchange, Class<T> type)
        throws InvalidPayloadException { ... }
    ...
}

Testing the exchange pattern

Several different exchange patterns are compatible with holding an In message. Several different exchange patterns are also compatible with holding an Out message. To provide a quick way of checking whether or not an exchange object is capable of holding an In message or an Out message, the ExchangeHelper class provides the following methods: 
public final class ExchangeHelper {
    ...
    public static boolean isInCapable(Exchange exchange) { ... }

    public static boolean isOutCapable(Exchange exchange) { ... }
    ...
}

Get the In message's MIME content type

If you want to find out the MIME content type of the exchange's In message, you can access it by calling the ExchangeHelper.getContentType(exchange) method. To implement this, the ExchangeHelper object looks up the value of the In message's Content-Type header—this method relies on the underlying component to populate the header value).