[CONF] Apache Camel > Bean Binding

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Bean Binding Page edited by Reuben Garrett Comment: native english readability enhancements Changes (56) h2. 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. h3. Choosing the method to invoke The binding of a Camel [Message] to a bean method call can occur in different ways, in the following order iof 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). * if the message contains the header *CamelBeanMethodName* then that method is invoked, converting the body to the type of the method's argument. ** From *Camel 2.8* onwards you can qualify parameter types to select exactly which method to use among overloads with the same name (see 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|http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/component/bean/BeanInvocation.html] (the default payload used by the [ProxyHelper|http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/component/bean/ProxyHelper.html]) component - then that its used to invoke the method and pass the its arguments * otherwise the type of the method body is used to try find a method which matches; matching method; 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 where Camel will not be able to choose a method to invoke an {{AmbiguousMethodCallException}} is thrown. In cases where Camel cannot choose a method to invoke, an {{AmbiguousMethodCallException}} is thrown. By default the return value is set on the outbound message body. ... h3. Parameter binding When a method have has been chosen to be invoked for invokation, Camel will bind to the parameters of the method. The following Camel specific types is automatic binded: The following Camel-specific types are automatically bound: - {{org.apache.camel.Exchange}} - {{org.apache.camel.Message}} ... - {{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. So, if you declare any of these types, they will be provided by Camel. *Note that {{Exception}} will bind to the caught exception of the [Exchange]* - so it's often usable if you employ a [POJO] to handle, 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 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. 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, for instance, we declare a parameter as {{String body}}, then Camel will bind the IN body to this type. Camel will also automatically convert to the type declared in the method signature. Okay lets show some examples. 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. {code} public String doSomething(String body) {code} 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. In the following sample we got one of the automatically-bound types as well - for instance, a {{Registry}} that we can use to lookup beans. {code} public String doSomething(String body, Registry registry) {code} And we can also use [Exchange] as well: We can use [Exchange] as well: {code} public String doSomething(String body, Exchange exchange) {code} You can have multiple types as well You can also have multiple types: {code} public String doSomething(String body, Exchange exchange, TypeConverter converter) {code} And imagine you use a [POJO] to handle a given custom exception {{InvalidOrderException}} then - we can then 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). {code} public String badOrder(String body, InvalidOrderException invalid) {code} Notice that we can bind to it even if we use a sub type of {{java.lang.Exception}} as Camel still knows it's an exception and can bind the cause (if any exists). 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. h3. Binding Annotations ... h4. Examples For example, a [Bean] such as: {code} public class Bar { ... h4. @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. This has an advantage as you need not specify a method name in the Camel route, and therefore do not run into problems after renaming the method in an IDE that can't find all its references. {code:java} public class Bar { ... *Available as of Camel 2.9* Camel uses the following rules to determine if 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 eg use, e.g., body, header.foo and other [Simple] tokens. Notice the tokens must be enclosed with ${ }. Any other value is consider to be a type declaration instead, instead - see the next section about pin pointing specifying types for overloaded methods. When invoking a [Bean] you can instruct Camel to invoke a specific method by providing the method name. For example as shown below: {code} .bean(OrderService.class, "doSomething") {code} Here we tell Camel to invoke the doSomething method. How the parameters is bound is handled by Camel. Now suppose the method has 2 parameters, and the 2nd parameter is a boolean, where we want to pass in a true value, such as the method signature below: Here we tell Camel to invoke the doSomething method - Camel handles the parameters' binding. Now suppose the method has 2 parameters, and the 2nd parameter is a boolean where we want to pass in a true value: {code} public void doSomething(String payload, boolean highPriority) { ... {code} In the example above, we defined the first parameter using the wild card symbol *, which tells Camel to bind this parameter to any type, and let Camel figure this out. The 2nd parameter has a fixed value of {{true}}. Instead of the wild card symbol we can instruct Camel to use the message body as shown: {code} .bean(OrderService.class, "doSomething(${body}, true)") ... .to("bean:orderService?method=doSomething(null, true)") {code} By specifying {{null}} as a parameter value, it instructs Camel to force passing in a {{null}} value. Specifying {{null}} as a parameter value instructs Camel to force passing 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: {code} .bean(OrderService.class, "doSomethingWithHeaders(${body}, ${headers})") {code} You can also pass in other fixed values than boolean values. For example to pass in an String and integer do as follows: You can also pass in other fixed values besides booleans. For example, you can pass in a String and an integer: {code} .bean(MyBean.class, "echo('World', 5)") {code} In the example above, we invoke the echo method with two parameters. The first has the content 'World' (without quotes), and the quotes). And the 2nd has the value of 5. Camel will automatic type convert the values to the parameter types. Camel will automatically convert these values to the parameters' types. Having the power of the [Simple] language allows us to bind to message headers and other values such as: ... h3. Using type qualifier to pin-point method to use when having overloaded methods h3. Using type qualifiers to select among 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. If you have a [Bean] with overloaded methods, you can now specify parameter types in the method name so Camel can match the method you intend to use. Given the following bean: {snippet:id=e1|lang=java|title=MyBean|url="" ... {snippet:id=e3|lang=java|title=Invoke 2 parameter method using wildcard|url="" By default Camel will match the type name using the simple name, 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: follow this example: {code} .bean(OrderService.class, "doSomething(com.foo.MyOrder)") ... Full Content Bean Binding 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, in the following order of importance: if the message contains the header CamelBeanMethodName then that method is invoked, converting the body to the type of the method's argument. From Camel 2.8 onwards you can qualify parameter types to select exactly which method to use among overloads with the same name (see below for more details). From Camel 2.9 onwards you can specify parameter values directly in the method option (see below for more details). you can explicitly specify the method name in the DSL or when using POJO Consuming or POJO Producing if the bean has a method 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. 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 is used to invoke the method and pass its arguments otherwise the type of the body is used to find a matching method; 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 cases where Camel cannot 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 has been chosen for invokation, Camel will bind to the parameters of the method. The following Camel-specific types are 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 these types, they will be provided by Camel. Note that Exception will bind to the caught exception of the Exchange - so it's often usable if you employ a Pojo to handle, 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, for instance, we declare a parameter as String body, then Camel will bind the IN body to this type. Camel will also automatically convert to the type declared in the method signature. Let's review some examples: Below is a simple method with a body binding. Camel will bind the IN body to the body parameter and convert it to a String. public String doSomething(String body) In the following sample we got one of the automatically-bound types as well - for instance, a Registry that we can use to lookup beans. public String doSomething(String body, Registry registry) We can use Exchange as well: public String doSomething(String body, Exchange exchange) You can also have multiple types: public String doSomething(String body, Exchange exchange, TypeConverter converter) And imagine you use a Pojo to handle a given custom exception InvalidOrderException - 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 it's an exception and can bind the cause (if any exists). 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 detail. 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 an advantage as you need not specify a method name in the Camel route, and therefore do not run into problems after renaming the method in an IDE that can'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 Available as of Camel 2.9 Camel uses the following rules to determine if 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, e.g., body, header.foo and other Simple tokens. Notice the tokens must be enclosed with ${ }. Any other value is consider to be a type declaration instead - see the next section about specifying types for overloaded methods. When invoking a Bean you can instruct Camel to invoke a specific method by providing the method name: .bean(OrderService.class, "doSomething") Here we tell Camel to invoke the doSomething method - Camel handles the parameters' binding. Now suppose the method has 2 parameters, and the 2nd parameter is a boolean where we want to pass in a true value: public void doSomething(String payload, boolean highPriority) { ... } This is now possible in Camel 2.9 onwards: .bean(OrderService.class, "doSomething(*, true)") In the example above, we defined the first parameter using the wild card symbol *, which tells Camel to bind this parameter to any type, and let Camel figure this out. The 2nd parameter has a fixed value of true. Instead of the wildcard symbol we can instruct Camel to use the message body as shown: .bean(OrderService.class, "doSomething(${body}, true)") The syntax of the parameters is using the Simple _expression_ language so we have to use ${ } placeholders in the body to refer to the message body. If you want to pass in a null value, then you can explicit define this in the method option as shown below: .to("bean:orderService?method=doSomething(null, true)") Specifying null as a parameter value instructs Camel to force passing a null value. Besides the message body, you can pass in the message headers as a java.util.Map: .bean(OrderService.class, "doSomethingWithHeaders(${body}, ${headers})") You can also pass in other fixed values besides booleans. For example, you can pass in a String and an integer: .bean(MyBean.class, "echo('World', 5)") In the example above, we invoke the echo method with two parameters. The first has the content 'World' (without quotes), and the 2nd has the value of 5. Camel will automatically convert these values to the parameters' types. Having the power of the Simple language allows us to bind to message headers and other values such as: .bean(OrderService.class, "doSomething(${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 qualifiers to select among overloaded methods Available as of Camel 2.8 If you have a Bean with overloaded methods, you can now specify 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, 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 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. Change Notification Preferences View Online | View Changes | Add Comment