Red Hat Summit Red Hat SummitApoyoConsolaDesarrolladoresIniciar una pruebaContacto

Este contenido no está disponible en el idioma seleccionado.

30.4. Expressions

Overview
Copiar enlace

The simple language provides various elementary expressions that return different parts of a message exchange. For example, the expression, simple("${header.timeOfDay}"), would return the contents of a header called timeOfDay from the incoming message.
Note
Since Apache Camel 2.9, you must always use the placeholder syntax, ${Expression}, to return a variable value. It is never permissible to omit the enclosing tokens (${ and }).

Contents of a single variable
Copiar enlace

You can use the simple language to define string expressions, based on the variables provided. For example, you can use a variable of the form, in.header.HeaderName, to obtain the value of the HeaderName header, as follows: 
simple("${in.header.foo}")
Copy to Clipboard Toggle word wrap

Variables embedded in a string
Copiar enlace

You can embed simple variables in a string expression—for example: 
simple("Received a message from ${in.header.user} on ${date:in.header.date:yyyyMMdd}.")
Copy to Clipboard Toggle word wrap

date and bean variables
Copiar enlace

As well as providing variables that access all of the different parts of an exchange (see Table 30.1, “Variables for the Simple Language”), the simple language also provides special variables for formatting dates, date:command:pattern, and for calling bean methods, bean:beanRef. For example, you can use the date and the bean variables as follows: 
simple("Todays date is ${date:now:yyyyMMdd}")
simple("The order type is ${bean:orderService?method=getOrderType}")
Copy to Clipboard Toggle word wrap

Specifying the result type
Copiar enlace

You can specify the result type of an expression explicitly. This is mainly useful for converting the result type to a boolean or numerical type.
In the Java DSL, specify the result type as an extra argument to simple(). For example, to return an integer result, you could evaluate a simple expression as follows: 
...
.setHeader("five", simple("5", Integer.class))
Copy to Clipboard Toggle word wrap
In the XML DSL, specify the result type using the resultType attribute. For example: 
<setHeader headerName="five">
  <!-- use resultType to indicate that the type should be a java.lang.Integer --> 
  <simple resultType="java.lang.Integer">5</simple>
</setHeader>
Copy to Clipboard Toggle word wrap

Nested expressions
Copiar enlace

Simple expressions can be nested—for example: 
simple("${header.${bean:headerChooser?method=whichHeader}}")
Copy to Clipboard Toggle word wrap

Accessing constants or enums
Copiar enlace

You can access a bean's constant or enum fields using the following syntax: 
type:ClassName.Field
Copy to Clipboard Toggle word wrap
For example, consider the following Java enum type: 
package org.apache.camel.processor;
...
public enum Customer {
    GOLD, SILVER, BRONZE
}
Copy to Clipboard Toggle word wrap
You can access the Customer enum fields, as follows: 
 from("direct:start")
    .choice()
        .when().simple("${header.customer} ==
          ${type:org.apache.camel.processor.Customer.GOLD}")
            .to("mock:gold")
        .when().simple("${header.customer} ==
          ${type:org.apache.camel.processor.Customer.SILVER}")
            .to("mock:silver")
        .otherwise()
            .to("mock:other");
Copy to Clipboard Toggle word wrap

OGNL expressions
Copiar enlace

The Object Graph Navigation Language (OGNL) is a notation for invoking bean methods in a chain-like fashion. If a message body contains a Java bean, you can easily access its bean properties using OGNL notation. For example, if the message body is a Java object with a getAddress() accessor, you can access the Address object and the Address object's properties as follows: 
simple("${body.address}")
simple("${body.address.street}")
simple("${body.address.zip}")
simple("${body.address.city}")
Copy to Clipboard Toggle word wrap
Where the notation, ${body.address.street}, is shorthand for ${body.getAddress.getStreet}.

OGNL null-safe operator
Copiar enlace

You can use the null-safe operator, ?., to avoid encountering null-pointer exceptions, in case the body does not have an address. For example: 
simple("${body?.address?.street}")
Copy to Clipboard Toggle word wrap
If the body is a java.util.Map type, you can look up a value in the map with the key, foo, using the following notation: 
simple("${body[foo]?.name}")
Copy to Clipboard Toggle word wrap

OGNL list element access
Copiar enlace

You can also use square brackets notation, [k], to access the elements of a list. For example: 
simple("${body.address.lines[0]}")
simple("${body.address.lines[1]}")
simple("${body.address.lines[2]}")
Copy to Clipboard Toggle word wrap
The last keyword returns the index of the last element of a list. For example, you can access the second last element of a list, as follows: 
simple("${body.address.lines[last-1]}")
Copy to Clipboard Toggle word wrap
You can use the size method to query the size of a list, as follows: 
simple("${body.address.lines.size}")
Copy to Clipboard Toggle word wrap

OGNL array length access
Copiar enlace

You can access the length of a Java array through the length method, as follows: 
String[] lines = new String[]{"foo", "bar", "cat"};
exchange.getIn().setBody(lines);

simple("There are ${body.length} lines")
Copy to Clipboard Toggle word wrap
Volver arriba
Red Hat logoGithubredditYoutubeTwitter

Aprender

Pruebe, compre y venda

Comunidades

Acerca de la documentación de Red Hat

Ayudamos a los usuarios de Red Hat a innovar y alcanzar sus objetivos con nuestros productos y servicios con contenido en el que pueden confiar. Explore nuestras recientes actualizaciones.

Hacer que el código abierto sea más inclusivo

Red Hat se compromete a reemplazar el lenguaje problemático en nuestro código, documentación y propiedades web. Para más detalles, consulte el Blog de Red Hat.

Acerca de Red Hat

Ofrecemos soluciones reforzadas que facilitan a las empresas trabajar en plataformas y entornos, desde el centro de datos central hasta el perímetro de la red.

Theme

© 2025 Red Hat