Chapter 39. Component Interface
Chapter 39. Component Interface Abstract This chapter describes how to implement the Component interface. 39.1. The Component Interface Overview To implement a Apache Camel component, you must implement the org.apache.camel.Component interface. An instance of Component type provides the entry point into a custom component. That is, all of the other objects in a component are ultimately accessible through the Component instance. Figure 39.1, "Component Inheritance Hierarchy" shows the relevant Java interfaces and classes that make up the Component inheritance hierarchy. Figure 39.1. Component Inheritance Hierarchy The Component interface Example 39.1, "Component Interface" shows the definition of the org.apache.camel.Component interface. Example 39.1. Component Interface Component methods The Component interface defines the following methods: getCamelContext() and setCamelContext() - References the CamelContext to which this Component belongs. The setCamelContext() method is automatically called when you add the component to a CamelContext . createEndpoint() - The factory method that gets called to create Endpoint instances for this component. The uri parameter is the endpoint URI, which contains the details required to create the endpoint. 39.2. Implementing the Component Interface The DefaultComponent class You implement a new component by extending the org.apache.camel.impl.DefaultComponent class, which provides some standard functionality and default implementations for some of the methods. In particular, the DefaultComponent class provides support for URI parsing and for creating a scheduled executor (which is used for the scheduled poll pattern). URI parsing The createEndpoint(String uri) method defined in the base Component interface takes a complete, unparsed endpoint URI as its sole argument. The DefaultComponent class, on the other hand, defines a three-argument version of the createEndpoint() method with the following signature: uri is the original, unparsed URI; remaining is the part of the URI that remains after stripping off the component prefix at the start and cutting off the query options at the end; and parameters contains the parsed query options. It is this version of the createEndpoint() method that you must override when inheriting from DefaultComponent . This has the advantage that the endpoint URI is already parsed for you. The following sample endpoint URI for the file component shows how URI parsing works in practice: For this URI, the following arguments are passed to the three-argument version of createEndpoint() : Argument Sample Value uri file:///tmp/messages/foo?delete=true&moveNamePostfix=.old remaining /tmp/messages/foo parameters Two entries are set in java.util.Map : parameter delete is boolean true parameter moveNamePostfix has the string value, .old . Parameter injection By default, the parameters extracted from the URI query options are injected on the endpoint's bean properties. The DefaultComponent class automatically injects the parameters for you. For example, if you want to define a custom endpoint that supports two URI query options: delete and moveNamePostfix . All you must do is define the corresponding bean methods (getters and setters) in the endpoint class: It is also possible to inject URI query options into consumer parameters. For details, see the section called "Consumer parameter injection" . Disabling endpoint parameter injection If there are no parameters defined on your Endpoint class, you can optimize the process of endpoint creation by disabling endpoint parameter injection. To disable parameter injection on endpoints, override the useIntrospectionOnEndpoint() method and implement it to return false , as follows: Note The useIntrospectionOnEndpoint() method does not affect the parameter injection that might be performed on a Consumer class. Parameter injection at that level is controlled by the Endpoint.configureProperties() method (see Section 40.2, "Implementing the Endpoint Interface" ). Scheduled executor service The scheduled executor is used in the scheduled poll pattern, where it is responsible for driving the periodic polling of a consumer endpoint (a scheduled executor is effectively a thread pool implementation). To instantiate a scheduled executor service, use the ExecutorServiceStrategy object that is returned by the CamelContext.getExecutorServiceStrategy() method. For details of the Apache Camel threading model, see Section 2.8, "Threading Model" . Note Prior to Apache Camel 2.3, the DefaultComponent class provided a getExecutorService() method for creating thread pool instances. Since 2.3, however, the creation of thread pools is now managed centrally by the ExecutorServiceStrategy object. Validating the URI If you want to validate the URI before creating an endpoint instance, you can override the validateURI() method from the DefaultComponent class, which has the following signature: If the supplied URI does not have the required format, the implementation of validateURI() should throw the org.apache.camel.ResolveEndpointFailedException exception. Creating an endpoint Example 39.2, "Implementation of createEndpoint() " outlines how to implement the DefaultComponent.createEndpoint() method, which is responsible for creating endpoint instances on demand. Example 39.2. Implementation of createEndpoint() 1 The CustomComponent is the name of your custom component class, which is defined by extending the DefaultComponent class. 2 When extending DefaultComponent , you must implement the createEndpoint() method with three arguments (see the section called "URI parsing" ). 3 Create an instance of your custom endpoint type, CustomEndpoint , by calling its constructor. At a minimum, this constructor takes a copy of the original URI string, uri , and a reference to this component instance, this . Example Example 39.3, "FileComponent Implementation" shows a sample implementation of a FileComponent class. Example 39.3. FileComponent Implementation 1 Always define a no-argument constructor for the component class in order to facilitate automatic instantiation of the class. 2 A constructor that takes the parent CamelContext instance as an argument is convenient when creating a component instance by programming. 3 The implementation of the FileComponent.createEndpoint() method follows the pattern described in Example 39.2, "Implementation of createEndpoint() " . The implementation creates a FileEndpoint object. SynchronizationRouteAware Interface SynchronizationRouteAware interface allows you to have callbacks before and after the exchange has been routed. onBeforeRoute : Invoked before the exchange has been routed by the given route. However, this callback may not get invoked, if you add the SynchronizationRouteAware implementation to the UnitOfWork , after starting the route. onAfterRoute : Invoked after the exchange has been routed by the given route. However, if the exchange is being routed through multiple routes, it would generate call backs for each route. This invocation occurs before these callbacks: The consumer of the route writes any response back to the caller (if in InOut mode) The UnitOfWork is done by calling either Synchronization.onComplete(org.apache.camel.Exchange) or Synchronization.onFailure(org.apache.camel.Exchange)
package org.apache.camel; public interface Component { CamelContext getCamelContext(); void setCamelContext(CamelContext context); Endpoint createEndpoint(String uri) throws Exception; } protected abstract Endpoint createEndpoint( String uri, String remaining, Map parameters ) throws Exception; file:///tmp/messages/foo?delete=true&moveNamePostfix=.old public class FileEndpoint extends ScheduledPollEndpoint { public boolean isDelete() { return delete; } public void setDelete(boolean delete) { this.delete = delete; } public String getMoveNamePostfix() { return moveNamePostfix; } public void setMoveNamePostfix(String moveNamePostfix) { this.moveNamePostfix = moveNamePostfix; } } protected boolean useIntrospectionOnEndpoint() { return false; } protected void validateURI(String uri, String path, Map parameters) throws ResolveEndpointFailedException; public class CustomComponent extends DefaultComponent { 1 protected Endpoint createEndpoint(String uri, String remaining, Map parameters) throws Exception { 2 CustomEndpoint result = new CustomEndpoint (uri, this); 3 // return result; } } package org.apache.camel.component.file; import org.apache.camel.CamelContext; import org.apache.camel.Endpoint; import org.apache.camel.impl.DefaultComponent; import java.io.File; import java.util.Map; public class FileComponent extends DefaultComponent { public static final String HEADER_FILE_NAME = "org.apache.camel.file.name"; public FileComponent() { 1 } public FileComponent(CamelContext context) { 2 super(context); } protected Endpoint createEndpoint(String uri, String remaining, Map parameters) throws Exception { 3 File file = new File(remaining); FileEndpoint result = new FileEndpoint(file, uri, this); return result; } }