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.

Choosing the method to invoke

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

if the message contains the header CamelBeanMethodName then that method is invoked, converting the body to whatever the argument is to the method.
- From Camel 2.8 onwards you can qualify parameter types to exact pin-point which method to use when using overloaded methods 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).
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 @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 ActiveMQ component 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) - then that its used to invoke the method and pass the arguments
otherwise the type of the method body is used to try find a 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.

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

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

Parameter binding

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

The following Camel specific types is automatic binded:

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 they will be provided by Camel. A note on the Exception is that it will bind to the caught exception of the Exchange. So its often usable if you use a Pojo to handle a given using using eg 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 declare e parameter as: String body then Camel will bind the IN body to this type. Camel will also automatic type convert to the given type declared.

Okay lets show 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)


And in this sample we got one of the automatic binded type as well, for instance the Registry that we can use to lookup beans.

public String doSomething(String body, Registry registry)



And we can also use Exchange as well:

public String doSomething(String body, Exchange exchange)



You can have multiple types as well

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



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

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

public String badOrder(String body, InvalidOrderException invalid)



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 details.

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:

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 advantage as you do not have to specify the method name in the Camel route. And thus you do not run into problems when you rename the method name using an IDE that don't find all 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
Available as of Camel 2.9

Camel uses the following rules to determine if its 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 eg 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 next section about pin pointing 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 the parameters is bound is handled by Camel. 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 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 have to use ${ } placeholders in the 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 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 values. For example to pass in an String and 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 the 2nd the value of 5.

Camel will automatic type convert the values to the parameter 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 qualifier to pin-point method to use when having overloaded methods
Available as of Camel 2.8

If you have a Bean which has 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:
MyBean

public static final class MyBean {

    public String hello(String name) {
        return "Hello " + name;
    }

    public String hello(String name, @Header("country") String country) {
        return "Hello " + name + " you are from " + country;
    }

    public String times(String name, @Header("times") int times) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < times; i++) {
            sb.append(name);
        }
        return sb.toString();
    }

    public String times(byte[] data, @Header("times") int times) {
        String s = new String(data);
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < times; i++) {
            sb.append(s);
            if (i < times - 1) {
                sb.append(",");
            }
        }
        return sb.toString();
    }

    public String times(String name, int times, char separator) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < times; i++) {
            sb.append(name);
            if (i < times - 1) {
                sb.append(separator);
            }
        }
        return sb.toString();
    }

}



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:
Invoke 2 parameter method

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



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

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



By default Camel will match the type name using the simple name, eg 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:

   .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.

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[CONF] Apache Camel > Bean Binding

Bean Binding

Page edited by Claus Ibsen

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Full Content

Bean Binding

Choosing the method to invoke

Parameter binding

Binding Annotations

Examples

@Handler

Parameter binding using method option

Using type qualifier to pin-point method to use when having overloaded methods

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