Red Hat Summit Red Hat SummitSupportoConsoleSviluppatoriInizia una provaContatti

Questo contenuto non è disponibile nella lingua selezionata.

31.8. Using Variables and Functions

Evaluating variables in a route
Copia collegamento

When evaluating XPath expressions inside a route, you can use XPath variables to access the contents of the current exchange, as well as O/S environment variables and Java system properties. The syntax to access a variable value is $VarName or $Prefix:VarName, if the variable is accessed through an XML namespace.
For example, you can access the In message's body as $in:body and the In message's header value as $in:HeaderName. O/S environment variables can be accessed as $env:EnvVar and Java system properties can be accessed as $system:SysVar.
In the following example, the first route extracts the value of the /person/city element and inserts it into the city header. The second route filters exchanges using the XPath expression, $in:city = 'London', where the $in:city variable is replaced by the value of the city header. 
from("file:src/data?noop=true")
    .setHeader("city").xpath("/person/city/text()")
    .to("direct:tie");
        
from("direct:tie")
    .filter().xpath("$in:city = 'London'").to("file:target/messages/uk");
Copy to Clipboard Toggle word wrap

Evaluating functions in a route
Copia collegamento

In addition to the standard XPath functions, the XPath language defines additional functions. These additional functions (which are listed in Table 31.4, “XPath Custom Functions”) can be used to access the underlying exchange, to evaluate a simple expression or to look up a property in the Apache Camel property placeholder component.
For example, the following example uses the in:header() function and the in:body() function to access a head and the body from the underlying exchange: 
from("direct:start").choice()
  .when().xpath("in:header('foo') = 'bar'").to("mock:x")
  .when().xpath("in:body() = '<two/>'").to("mock:y")
  .otherwise().to("mock:z");
Copy to Clipboard Toggle word wrap
Notice the similarity between theses functions and the corresponding in:HeaderName or in:body variables. The functions have a slightly different syntax however: in:header('HeaderName') instead of in:HeaderName; and in:body() instead of in:body.

Evaluating variables in XPathBuilder
Copia collegamento

You can also use variables in expressions that are evaluated using the XPathBuilder class. In this case, you cannot use variables such as $in:body or $in:HeaderName, because there is no exchange object to evaluate against. But you can use variables that are defined inline using the variable(Name, Value) fluent builder method.
For example, the following XPathBuilder construction evaluates the $test variable, which is defined to have the value, London: 
String var = XPathBuilder.xpath("$test")
               .variable("test", "London")
               .evaluate(getContext(), "<name>foo</name>");
Copy to Clipboard Toggle word wrap
Note that variables defined in this way are automatically entered into the global namespace (for example, the variable, $test, uses no prefix).
Torna in cima
Red Hat logoGithubredditYoutubeTwitter

Formazione

Prova, acquista e vendi

Community

Informazioni sulla documentazione di Red Hat

Aiutiamo gli utenti Red Hat a innovarsi e raggiungere i propri obiettivi con i nostri prodotti e servizi grazie a contenuti di cui possono fidarsi. Esplora i nostri ultimi aggiornamenti.

Rendiamo l’open source più inclusivo

Red Hat si impegna a sostituire il linguaggio problematico nel codice, nella documentazione e nelle proprietà web. Per maggiori dettagli, visita il Blog di Red Hat.

Informazioni su Red Hat

Forniamo soluzioni consolidate che rendono più semplice per le aziende lavorare su piattaforme e ambienti diversi, dal datacenter centrale all'edge della rete.

Theme

© 2025 Red Hat