Chapter 52. Message Interface


This chapter describes how to implement the Message interface, which is an optional step in the implementation of a Apache Camel component.

52.1. The Message Interface


An instance of org.apache.camel.Message type can represent any kind of message (In or Out). Figure 52.1, “Message Inheritance Hierarchy” shows the inheritance hierarchy for the message type. You do not always need to implement a custom message type for a component. In many cases, the default implementation, DefaultMessage, is adequate.

Figure 52.1. Message Inheritance Hierarchy

Message inheritance hierarchy

The Message interface

Example 52.1, “Message Interface” shows the definition of the org.apache.camel.Message interface.

Example 52.1. Message Interface

package org.apache.camel;

import java.util.Map;
import java.util.Set;

import javax.activation.DataHandler;

public interface Message {

    String getMessageId();
    void setMessageId(String messageId);

    Exchange getExchange();

    boolean isFault();
    void    setFault(boolean fault);

    Object getHeader(String name);
    Object getHeader(String name, Object defaultValue);
    <T> T getHeader(String name, Class<T> type);
    <T> T getHeader(String name, Object defaultValue, Class<T> type);
    Map<String, Object> getHeaders();
    void setHeader(String name, Object value);
    void setHeaders(Map<String, Object> headers);
    Object  removeHeader(String name);
    boolean removeHeaders(String pattern);
    boolean hasHeaders();

    Object getBody();
    Object getMandatoryBody() throws InvalidPayloadException;
    <T> T  getBody(Class<T> type);
    <T> T  getMandatoryBody(Class<T> type) throws InvalidPayloadException;
    void     setBody(Object body);
    <T> void setBody(Object body, Class<T> type);

    DataHandler getAttachment(String id);
    Map<String, DataHandler> getAttachments();
    Set<String> getAttachmentNames();
    void removeAttachment(String id);
    void addAttachment(String id, DataHandler content);
    void setAttachments(Map<String, DataHandler> attachments);
    boolean hasAttachments();

    Message copy();

    void copyFrom(Message message);

    String createExchangeId();

Message methods

The Message interface defines the following methods:
  • setMessageId(), getMessageId()—Getter and setter methods for the message ID. Whether or not you need to use a message ID in your custom component is an implementation detail.
  • getExchange()—Returns a reference to the parent exchange object.
  • isFault(), setFault()—Getter and setter methods for the fault flag, which indicates whether or not this message is a fault message.
  • getHeader(), getHeaders(), setHeader(), setHeaders(), removeHeader(), hasHeaders()—Getter and setter methods for the message headers. In general, these message headers can be used either to store actual header data, or to store miscellaneous metadata.
  • getBody(), getMandatoryBody(), setBody()—Getter and setter methods for the message body. The getMandatoryBody() accessor guarantees that the returned body is non-null, otherwise the InvalidPayloadException exception is thrown.
  • getAttachment(), getAttachments(), getAttachmentNames(), removeAttachment(), addAttachment(), setAttachments(), hasAttachments()—Methods to get, set, add, and remove attachments.
  • copy()—Creates a new, identical (including the message ID) copy of the current custom message object.
  • copyFrom()—Copies the complete contents (including the message ID) of the specified generic message object, message, into the current message instance. Because this method must be able to copy from any message type, it copies the generic message properties, but not the custom properties.
  • createExchangeId()—Returns the unique ID for this exchange, if the message implementation is capable of providing an ID; otherwise, return null.