2.6. Transforming Message Content
Abstract
2.6.1. Simple Message Transformations
Overview
World!
, to the end of the incoming message body.
Example 2.1. Simple Transformation of Incoming Messages
from("SourceURL").setBody(body().append(" World!")).to("TargetURL");
setBody()
command replaces the content of the incoming message's body.
API for simple transformations
org.apache.camel.model.ProcessorDefinition
org.apache.camel.builder.Builder
org.apache.camel.builder.ValueBuilder
ProcessorDefinition class
org.apache.camel.model.ProcessorDefinition
class defines the DSL commands you can insert directly into a router rule—for example, the setBody()
command in Example 2.1, “Simple Transformation of Incoming Messages”. Table 2.5, “Transformation Methods from the ProcessorDefinition Class” shows the ProcessorDefinition
methods that are relevant to transforming message content:
Table 2.5. Transformation Methods from the ProcessorDefinition Class
Method | Description |
---|---|
Type convertBodyTo(Class type) | Converts the IN message body to the specified type. |
Type removeFaultHeader(String name) | Adds a processor which removes the header on the FAULT message. |
Type removeHeader(String name) | Adds a processor which removes the header on the IN message. |
Type removeProperty(String name) | Adds a processor which removes the exchange property. |
ExpressionClause<ProcessorDefinition<Type>> setBody() | Adds a processor which sets the body on the IN message. |
Type setFaultBody(Expression expression) | Adds a processor which sets the body on the FAULT message. |
Type setFaultHeader(String name, Expression expression) | Adds a processor which sets the header on the FAULT message. |
ExpressionClause<ProcessorDefinition<Type>> setHeader(String name) | Adds a processor which sets the header on the IN message. |
Type setHeader(String name, Expression expression) | Adds a processor which sets the header on the IN message. |
ExpressionClause<ProcessorDefinition<Type>> setOutHeader(String name) | Adds a processor which sets the header on the OUT message. |
Type setOutHeader(String name, Expression expression) | Adds a processor which sets the header on the OUT message. |
ExpressionClause<ProcessorDefinition<Type>> setProperty(String name) | Adds a processor which sets the exchange property. |
Type setProperty(String name, Expression expression) | Adds a processor which sets the exchange property. |
ExpressionClause<ProcessorDefinition<Type>> transform() | Adds a processor which sets the body on the OUT message. |
Type transform(Expression expression) | Adds a processor which sets the body on the OUT message. |
Builder class
org.apache.camel.builder.Builder
class provides access to message content in contexts where expressions or predicates are expected. In other words, Builder
methods are typically invoked in the arguments of DSL commands—for example, the body()
command in Example 2.1, “Simple Transformation of Incoming Messages”. Table 2.6, “Methods from the Builder Class” summarizes the static methods available in the Builder
class.
Table 2.6. Methods from the Builder Class
Method | Description |
---|---|
static <E extends Exchange> ValueBuilder<E> body() | Returns a predicate and value builder for the inbound body on an exchange. |
static <E extends Exchange,T> ValueBuilder<E> bodyAs(Class<T> type) | Returns a predicate and value builder for the inbound message body as a specific type. |
static <E extends Exchange> ValueBuilder<E> constant(Object value) | Returns a constant expression. |
static <E extends Exchange> ValueBuilder<E> faultBody() | Returns a predicate and value builder for the fault body on an exchange. |
static <E extends Exchange,T> ValueBuilder<E> faultBodyAs(Class<T> type) | Returns a predicate and value builder for the fault message body as a specific type. |
static <E extends Exchange> ValueBuilder<E> header(String name) | Returns a predicate and value builder for headers on an exchange. |
static <E extends Exchange> ValueBuilder<E> outBody() | Returns a predicate and value builder for the outbound body on an exchange. |
static <E extends Exchange> ValueBuilder<E> outBodyAs(Class<T> type) | Returns a predicate and value builder for the outbound message body as a specific type. |
static ValueBuilder property(String name) | Returns a predicate and value builder for properties on an exchange. |
static ValueBuilder regexReplaceAll(Expression content, String regex, Expression replacement) | Returns an expression that replaces all occurrences of the regular expression with the given replacement. |
static ValueBuilder regexReplaceAll(Expression content, String regex, String replacement) | Returns an expression that replaces all occurrences of the regular expression with the given replacement. |
static ValueBuilder sendTo(String uri) | Returns an expression processing the exchange to the given endpoint uri. |
static <E extends Exchange> ValueBuilder<E> systemProperty(String name) | Returns an expression for the given system property. |
static <E extends Exchange> ValueBuilder<E> systemProperty(String name, String defaultValue) | Returns an expression for the given system property. |
ValueBuilder class
org.apache.camel.builder.ValueBuilder
class enables you to modify values returned by the Builder
methods. In other words, the methods in ValueBuilder
provide a simple way of modifying message content. Table 2.7, “Modifier Methods from the ValueBuilder Class” summarizes the methods available in the ValueBuilder
class. That is, the table shows only the methods that are used to modify the value they are invoked on (for full details, see the API Reference documentation).
Table 2.7. Modifier Methods from the ValueBuilder Class
Method | Description |
---|---|
ValueBuilder<E> append(Object value) | Appends the string evaluation of this expression with the given value. |
Predicate contains(Object value) | Create a predicate that the left hand expression contains the value of the right hand expression. |
ValueBuilder<E> convertTo(Class type) | Converts the current value to the given type using the registered type converters. |
ValueBuilder<E> convertToString() | Converts the current value a String using the registered type converters. |
Predicate endsWith(Object value) | |
<T> T evaluate(Exchange exchange, Class<T> type) | |
Predicate in(Object... values) | |
Predicate in(Predicate... predicates) | |
Predicate isEqualTo(Object value) | Returns true, if the current value is equal to the given value argument. |
Predicate isGreaterThan(Object value) | Returns true, if the current value is greater than the given value argument. |
Predicate isGreaterThanOrEqualTo(Object value) | Returns true, if the current value is greater than or equal to the given value argument. |
Predicate isInstanceOf(Class type) | Returns true, if the current value is an instance of the given type. |
Predicate isLessThan(Object value) | Returns true, if the current value is less than the given value argument. |
Predicate isLessThanOrEqualTo(Object value) | Returns true, if the current value is less than or equal to the given value argument. |
Predicate isNotEqualTo(Object value) | Returns true, if the current value is not equal to the given value argument. |
Predicate isNotNull() | Returns true, if the current value is not null . |
Predicate isNull() | Returns true, if the current value is null . |
Predicate matches(Expression expression) | |
Predicate not(Predicate predicate) | Negates the predicate argument. |
ValueBuilder prepend(Object value) | Prepends the string evaluation of this expression to the given value. |
Predicate regex(String regex) | |
ValueBuilder<E> regexReplaceAll(String regex, Expression<E> replacement) | Replaces all occurrencies of the regular expression with the given replacement. |
ValueBuilder<E> regexReplaceAll(String regex, String replacement) | Replaces all occurrencies of the regular expression with the given replacement. |
ValueBuilder<E> regexTokenize(String regex) | Tokenizes the string conversion of this expression using the given regular expression. |
ValueBuilder sort(Comparator comparator) | Sorts the current value using the given comparator. |
Predicate startsWith(Object value) | Returns true, if the current value matches the string value of the value argument. |
ValueBuilder<E> tokenize() | Tokenizes the string conversion of this expression using the comma token separator. |
ValueBuilder<E> tokenize(String token) | Tokenizes the string conversion of this expression using the given token separator. |
2.6.2. Marshalling and Unmarshalling
Java DSL commands
marshal()
— Converts a high-level data format to a low-level data format.unmarshal
() — Converts a low-level data format to a high-level data format.
Data formats
- Java serialization
- JAXB
- XMLBeans
- XStream
Java serialization
from("SourceURL").unmarshal().serialization() .<FurtherProcessing>.to("TargetURL");
<camelContext id="serialization" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="SourceURL"/> <unmarshal> <serialization/> </unmarshal> <to uri="TargetURL"/> </route> </camelContext>
JAXB
org.apache.camel.spi.DataFormat jaxb = new org.apache.camel.model.dataformat.JaxbDataFormat("GeneratedPackageName"); from("SourceURL").unmarshal(jaxb) .<FurtherProcessing>.to("TargetURL");
<camelContext id="jaxb" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="SourceURL"/> <unmarshal> <jaxb prettyPrint="true" contextPath="GeneratedPackageName"/> </unmarshal> <to uri="TargetURL"/> </route> </camelContext>
XMLBeans
from("SourceURL").unmarshal().xmlBeans() .<FurtherProcessing>.to("TargetURL");
<camelContext id="xmlBeans" xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="SourceURL"/> <unmarshal> <xmlBeans prettyPrint="true"/> </unmarshal> <to uri="TargetURL"/> </route> </camelContext>
XStream
from("SourceURL").unmarshal().xstream() .<FurtherProcessing>.to("TargetURL");
2.6.3. Endpoint Bindings
What is a binding?
DataFormatBinding
DataFormatBinding
class is useful for the specific case where you want to define a binding that marshals and unmarshals a particular data format (see Section 2.6.2, “Marshalling and Unmarshalling”). In this case, all that you need to do to create a binding is to create a DataFormatBinding
instance, passing a reference to the relevant data format in the constructor.
jaxb
) that is capable of marshalling and unmarshalling the JAXB data format when it is associated with an Apache Camel endpoint:
Example 2.2. JAXB Binding
<beans ... >
...
<bean id="jaxb" class="org.apache.camel.processor.binding.DataFormatBinding">
<constructor-arg ref="jaxbformat"/>
</bean>
<bean id="jaxbformat" class="org.apache.camel.model.dataformat.JaxbDataFormat">
<property name="prettyPrint" value="true"/>
<property name="contextPath" value="org.apache.camel.example"/>
</bean>
</beans>
Associating a binding with an endpoint
Binding URI
binding:NameOfBinding
, where NameOfBinding
is the bean ID of the binding (for example, the ID of a binding bean created in Spring XML).
<beans ...> ... <camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="binding:jaxb:activemq:orderQueue"/> <to uri="binding:jaxb:activemq:otherQueue"/> </route> </camelContext> ... </beans>
BindingComponent
BindingComponent
class.
jaxb
binding with activemq
endpoints, you could define a new BindingComponent
instance as follows:
<beans ... >
...
<bean id="jaxbmq" class="org.apache.camel.component.binding.BindingComponent">
<constructor-arg ref="jaxb"/>
<constructor-arg value="activemq:foo."/>
</bean>
<bean id="jaxb" class="org.apache.camel.processor.binding.DataFormatBinding">
<constructor-arg ref="jaxbformat"/>
</bean>
<bean id="jaxbformat" class="org.apache.camel.model.dataformat.JaxbDataFormat">
<property name="prettyPrint" value="true"/>
<property name="contextPath" value="org.apache.camel.example"/>
</bean>
</beans>
jaxbmq
defines a URI prefix. You can now use the jaxbmq
ID as the scheme for an endpoint URI. For example, you can define the following route using this binding component:
<beans ...> ... <camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="jaxbmq:firstQueue"/> <to uri="jaxbmq:otherQueue"/> </route> </camelContext> ... </beans>
<beans ...> ... <camelContext xmlns="http://camel.apache.org/schema/spring"> <route> <from uri="binding:jaxb:activemq:foo.firstQueue"/> <to uri="binding:jaxb:activemq:foo.otherQueue"/> </route> </camelContext> ... </beans>
org.apache.camel.spi.HasBinding
interface.
BindingComponent constructors
BindingComponent
class supports the following constructors:
public BindingComponent()
- No arguments form. Use property injection to configure the binding component instance.
public BindingComponent(Binding binding)
- Associate this binding component with the specified
Binding
object,binding
. public BindingComponent(Binding binding, String uriPrefix)
- Associate this binding component with the specified
Binding
object,binding
, and URI prefix,uriPrefix
. This is the most commonly used constructor. public BindingComponent(Binding binding, String uriPrefix, String uriPostfix)
- This constructor supports the additional URI post-fix,
uriPostfix
, argument, which is automatically appended to any URIs defined using this binding component.
Implementing a custom binding
DataFormatBinding
, which is used for marshalling and unmarshalling data formats, you can implement your own custom bindings. Define a custom binding as follows:
- Implement an
org.apache.camel.Processor
class to perform a transformation on messages incoming to a consumer endpoint (appearing in afrom
element). - Implement a complementary
org.apache.camel.Processor
class to perform the reverse transformation on messages outgoing from a producer endpoint (appearing in ato
element). - Implement the
org.apache.camel.spi.Binding
interface, which acts as a factory for the processor instances.
Binding interface
org.apache.camel.spi.Binding
interface, which you must implement to define a custom binding.
Example 2.3. The org.apache.camel.spi.Binding Interface
// Java package org.apache.camel.spi; import org.apache.camel.Processor; /** * Represents a <a href="http://camel.apache.org/binding.html">Binding</a> or contract * which can be applied to an Endpoint; such as ensuring that a particular * <a href="http://camel.apache.org/data-format.html">Data Format</a> is used on messages in and out of an endpoint. */ public interface Binding { /** * Returns a new {@link Processor} which is used by a producer on an endpoint to implement * the producer side binding before the message is sent to the underlying endpoint. */ Processor createProduceProcessor(); /** * Returns a new {@link Processor} which is used by a consumer on an endpoint to process the * message with the binding before its passed to the endpoint consumer producer. */ Processor createConsumeProcessor(); }