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Bean Binding

The Bean Binding in Camel defines both which methods are invoked and also how the Message is converted into the parameters of the method when it is invoked.

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The binding of a Camel Message to a bean method call can occur in different ways, in the following order if of importance:

• if the message contains the header CamelBeanMethodName then that method is invoked, converting the body to whatever the argument is to type of the method's argument.
  • From Camel 2.8 onwards you can qualify parameter types to exact pin-point select exactly which method to use when using overloaded methods among overloads with the same name (see further below for more details).
  • From Camel 2.9 onwards you can specify parameter values directly in the method option (see further below for more details).
• you can explicitly specify the method name can be specified explicitly in the DSL or when using POJO Consuming or POJO Producing
• if the bean has a method that is marked with the @Handler annotation, then that method is selected
• if the bean can be converted to a Processor using the Type Converter mechanism, then this is used to process the message. This mechanism is used by the The ActiveMQ component uses this mechanism to allow any JMS MessageListener to be invoked directly by Camel without having to write any integration glue code. You can use the same mechanism to integrate Camel into any other messaging/remoting frameworks.
• if the body of the message can be converted to a BeanInvocation (the default payload used by the ProxyHelper) component - then that its is used to invoke the method and pass the its arguments
• otherwise the type of the method body is used to try find a matching method which matches; an error is thrown if a single method cannot be chosen unambiguously.
• you can also use Exchange as the parameter itself, but then the return type must be void.
• if the bean class is private (or package-private), interface methods will be preferred (from Camel 2.9 onwards) since Camel can't invoke class methods on such beans

In case cases where Camel will not be able to cannot choose a method to invoke, an AmbiguousMethodCallException is thrown.

By default the return value is set on the outbound message body. 

Asynchronous processing

From Camel 2.18 onwards you can return a CompletionStage implementation (e.g. a CompletableFuture) to implement asynchronous processing.

Please be sure to properly complete the CompletionStage with the result or exception, including any timeout handling. Exchange processing would wait for completion and would not impose any timeouts automatically. It's extremely useful to monitor Inflight repository for any hanging messages.

Note that completing with "null" won't set outbody message body to null, but would keep message intact. This is useful to support methods that don't modify exchange and return CompletableFuture<Void>. To set body to null, just add Exchange method parameter and directly modify exchange messages.

Examples:

Simple asynchronous processor, modifying message body.

public CompletableFuture<String> doSomethingAsync(String body)

Composite processor that do not modify exchange

 public CompletableFuture<Void> doSomethingAsync(String body) {
     return CompletableFuture.allOf(doA(body), doB(body), doC()); 
 }

Parameter binding

When a method have has been chosen to be invoked for invocation, Camel will bind to the parameters of the method.

The following Camel-specific types is automatic bindedare automatically bound:

• org.apache.camel.Exchange
• org.apache.camel.Message
• org.apache.camel.CamelContext
• org.apache.camel.TypeConverter
• org.apache.camel.spi.Registry
• java.lang.Exception

So, if you declare any of the given type above these types, they will be provided by Camel. A note on the Exception is that it Note that Exception will bind to the caught exception of the Exchange. So its - so it's often usable if you use employ a POJO Pojo to handle a given using using eg , e.g., an onException route.

What is most interesting is that Camel will also try to bind the body of the Exchange to the first parameter of the method signature (albeit not of any of the types above). So if we , for instance, we declare e a parameter as : String body, then Camel will bind the IN body to this type. Camel will also automatic type automatically convert to the given type declared in the method signature.

Okay lets show Let's review some examples.:

Below is just a simple method with a body binding. Camel will bind the IN body to the body parameter and convert it to a String type.

public String doSomething(String body)

In the following And in this sample we got one of the automatic binded type automatically-bound types as well , - for instance the , a Registry that we can use to lookup beans.

public String doSomething(String body, Registry registry)
 

And we We can also use Exchange as well:

public String doSomething(String body, Exchange exchange)
 

You can also have multiple types as well:

public String doSomething(String body, Exchange exchange, TypeConverter converter)
 

And imagine you use a POJO Pojo to handle a given custom exception InvalidOrderException then - we can then bind that as well:

public String badOrder(String body, InvalidOrderException invalid) 

Notice that we can bind to it even if we use a sub type of java.lang.Exception as Camel still knows its it's an exception and thus can bind the caused exception cause (if any exists).

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So what about headers and other stuff? Well now it gets a bit tricky - so we can use annotations to help us, or specify the binding in the method name option.
See the following sections for more detailsdetail.

Binding Annotations

You can use the Parameter Binding Annotations to customize how parameter values are created from the Message

Examples

For example, a Bean such as:

public class Bar {

    public String doSomething(String body) {
      // process the in body and return whatever you want 
      return "Bye World"; 
   }
 

Or the Exchange example. Notice that the return type must be void when there is only a single parameter of the type org.apache.camel.Exchange:

 public
public class Bar {

     public void doSomething(Exchange exchange) {
         // process the exchange 
         exchange.getIn().setBody("Bye World"); 
   }

@Handler

You can mark a method in your bean with the @Handler annotation to indicate that this method should be used for Bean Binding.
This has the an advantage as you do need not have to specify the a method name in the Camel route. And thus you , and therefore do not run into problems when you rename after renaming the method name using in an IDE that doncan't find all its references.

public class Bar {

    @Handler 
    public String doSomething(String body) {
        // process the in body and return whatever you want 
        return "Bye World"; 
    }
} 

Parameter binding using method option

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Camel uses the following rules to determine if its it's a parameter value in the method option

• The value is either true or false which denotes a boolean value
• The value is a numeric value such as 123 or 7
• The value is a String enclosed with either single or double quotes
• The value is null which denotes a null value
• It can be evaluated using the Simple language, which means you can use

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• , e.g., body, header.foo and other Simple tokens. Notice the tokens must be enclosed with ${ }.

Any other value is consider to be a type declaration instead , - see the next section about pin pointing specifying types for overloaded methods.

When invoking a Bean you can instruct Camel to invoke a specific method by providing the method name. For example as shown below:

   .bean(OrderService.class, "doSomething")

Here we tell Camel to invoke the doSomething method . How - Camel handles the parameters is bound is handled by Camel' binding. Now suppose the method has 2 parameters, and the 2nd parameter is a boolean , where we want to pass in a true value, such as the method signature below:

public void doSomething(String payload, boolean highPriority) {
    ... 
}

This is now possible in Camel 2.9 onwards:

   .bean(OrderService.class, "doSomething(*, true)")
 

In the example above, we defined the first parameter using the wild card symbol *, which tells Camel to bind this parameter to any type, and let Camel figure this out. The 2nd parameter has a fixed value of true. Instead of the wild card wildcard symbol we can instruct Camel to use the message body as shown:

   .bean(OrderService.class, "doSomething(${body}, true)")
 

The syntax of the parameters is using the Simple expression language so we can use ${ } placeholders to make this more expressive:

   .bean(OrderService.class, "doSomething(${body}, true)")

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have to use ${ } placeholders in the

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body to refer to the message body.

If you want to pass in a null value, then you can explicit define this in the method option as shown below:

   .to("bean:orderService?method=doSomething(null, true)")

By specifying Specifying null as a parameter value , it instructs Camel to force passing in a null value.

Besides the message body, you can pass in the message headers as a java.util.Map type, and declare it as follows:

   .bean(OrderService.class, "doSomethingWithHeaders(${body}, ${headers})")
 

You can also pass in other fixed values than boolean valuesbesides booleans. For example to , you can pass in an a String and an integer do as follows:

   .bean(MyBean.class, "echo('World', 5)")
 

In the example above, we invoke the echo method with two parameters. The first has the content 'World' (without the quotes). And , and the 2nd has the value of 5.
Camel will automatic type automatically convert the these values to the parameter parameters' types.

Having the power of the Simple language allows us to bind to message headers and other values such as:

   .bean(OrderService.class, "doSomething(${body}, ${header.high})")
 

You can also use the OGNL support of the Simple expression language. Now suppose the message body is an object which has a method named asXml. To invoke the asXml method we can do as follows:

   .bean(OrderService.class, "doSomething(${body.asXml}, ${header.high})")
 

Instead of using .bean as shown in the examples above, you may want to use .to instead as shown:

   .to("bean:orderService?method=doSomething(${body.asXml}, ${header.high})")
 

Using type

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qualifiers to select among overloaded methods

Available as of Camel 2.8

If you have a Bean which has with overloaded methods, you can now specify the parameter types in the method name , so Camel can match the method you intend to use.
Given the following bean:

 from("direct:start")
    .bean(MyBean.class, "hello(String)")
    .to("mock:result");

{snippet:id=e1|lang=java|title=MyBean|url=camel/trunk/camel-core/src/test/java/org/apache/camel/component/bean/BeanOverloadedMethodTest.java}

Then the MyBean has 2 overloaded methods with the names hello and times. So if we want to use the method which has 2 parameters we can do as follows in the Camel route:

from("direct:start")
    .bean(MyBean.class, "hello(String,String)")
    .to("mock:result"); 

{snippet:id=e2|lang=java|title=Invoke 2 parameter method|url=camel/trunk/camel-core/src/test/java/org/apache/camel/component/bean/BeanOverloadedMethodTest.java}

We can also use a * as wildcard so we can just say we want to execute the method with 2 parameters we do

 from("direct:start")
    .bean(MyBean.class, "hello(*,*)")
    .to("mock:result");

{snippet:id=e3|lang=java|title=Invoke 2 parameter method using wildcard|url=camel/trunk/camel-core/src/test/java/org/apache/camel/component/bean/BeanOverloadedMethodTest.java}

By default Camel will match the type name using the simple name, eg e.g. any leading package name will be disregarded. However if you want to match using the FQN, then specify the FQN type and Camel will leverage that. So if you have a com.foo.MyOrder and you want to match against the FQN, and not the simple name "MyOrder" then do as follows, then follow this example:

   .bean(OrderService.class, "doSomething(com.foo.MyOrder)")

Camel currently only supports either specifying parameter binding or type per parameter in the method name option. You cannot specify both at the same time, such as

 doSomething

(com.foo.MyOrder ${body}, boolean ${header.high})

This may change in the future.