Java

Since Camel 4.3

The Java language (uses jOOR library to compile Java code) allows using Java code in your Camel expression, with some limitations.

The jOOR library integrates with the Java compiler and performs runtime compilation of Java code.

Java Options

The Java language supports 4 options, which are listed below.

Name Default Java Type Description

preCompile (advanced)

true

Boolean

Whether the expression should be pre compiled once during initialization phase. If this is turned off, then the expression is reloaded and compiled on each evaluation.

singleQuotes (advanced)

true

Boolean

Whether single quotes can be used as replacement for double quotes. This is convenient when you need to work with strings inside strings.

resultType (common)

String

Sets the class of the result type (type from output).

trim (advanced)

true

Boolean

Whether to trim the value to remove leading and trailing whitespaces and line breaks.

Usage

Variables

The Java language allows the following variables to be used in the script:

Variable Java Type Description

context

Context

The CamelContext

exchange

Exchange

The Camel Exchange

message

Message

The Camel message

body

Object

The message body

Functions

The Java language allows the following functions to be used in the script:

Function Description

bodyAs(type)

To convert the body to the given type.

headerAs(name, type)

To convert the header with the name to the given type.

headerAs(name, defaultValue, type)

To convert the header with the name to the given type. If no header exists, then use the given default value.

exchangePropertyAs(name, type)

To convert the exchange property with the name to the given type.

exchangePropertyAs(name, defaultValue, type)

To convert the exchange property with the name to the given type. If no exchange property exists, then use the given default value.

optionalBodyAs(type)

To convert the body to the given type, returned wrapped in java.util.Optional.

optionalHeaderAs(name, type)

To convert the header with the name to the given type, returned wrapped in java.util.Optional.

optionalExchangePropertyAs(name, type)

To convert the exchange property with the name to the given type, returned wrapped in java.util.Optional.

These functions are convenient for getting the message body, header or exchange properties as a specific Java type.

Here we want to get the message body as a com.foo.MyUser type we can do as follows:

var user = bodyAs(com.foo.MyUser.class);

You can omit .class to make the function a little smaller:

var user = bodyAs(com.foo.MyUser);

The type must be a fully qualified class type, but that can be inconvenient to type all the time. In such a situation, you can configure an import in the camel-joor.properties file as shown below:

import com.foo.MyUser;

And then the function can be shortened:

var user = bodyAs(MyUser);

Dependency Injection

The Camel Java language allows dependency injection by referring to beans by their id from the Camel registry. For optimization purposes, then the beans are injected once in the constructor and the scopes are singleton. This requires the injected beans to be thread safe as they will be reused for all processing.

In the Java code you declare the injected beans using the syntax #bean:beanId.

For example, suppose we have the following bean

public class MyEchoBean {

    public String echo(String str) {
        return str + str;
    }

    public String greet() {
        return "Hello ";
    }
}

And this bean is registered with the name myEcho in the Camel registry.

The Java code can then inject this bean directly in the script where the bean is in use:

from("direct:start")
    .transform().java("'Hello ' + #bean:myEcho.echo(bodyAs(String))")
    .to("mock:result");

Now this code may seem a bit magic, but what happens is that the myEcho bean is injected via a constructor, and then called directly in the script, so it is as fast as possible.

Under the hood, Camel Java generates the following source code compiled once:

public class JoorScript1 implements org.apache.camel.language.joor.JoorMethod {

    private MyEchoBean myEcho;

    public JoorScript1(CamelContext context) throws Exception {
        myEcho = context.getRegistry().lookupByNameAndType("myEcho", MyEchoBean.class);
    }

    @Override
    public Object evaluate(CamelContext context, Exchange exchange, Message message, Object body, Optional optionalBody) throws Exception {
        return "Hello " + myEcho.echo(bodyAs(exchange, String.class));
    }
}

You can also store a reference to the bean in a variable which would more resemble how you would code in Java

from("direct:start")
    .transform().java("var bean = #bean:myEcho; return 'Hello ' + bean.echo(bodyAs(String))")
    .to("mock:result");

Notice how we declare the bean as if it is a local variable via var bean = #bean:myEcho. When doing this we must use a different name as myEcho is the variable used by the dependency injection. Therefore, we use bean as name in the script.

Auto imports

The Java language will automatically import from:

import java.util.*;
import java.util.concurrent.*;
import java.util.stream.*;
import org.apache.camel.*;
import org.apache.camel.util.*;

Configuration file

You can configure the jOOR language in the camel-joor.properties file which by default is loaded from the root classpath. You can specify a different location with the configResource option on the Java language.

For example, you can add additional imports in the camel-joor.properties file by adding:

import com.foo.MyUser;
import com.bar.*;
import static com.foo.MyHelper.*;

You can also add aliases (key=value) where an alias will be used as a shorthand replacement in the code.

echo()=bodyAs(String) + bodyAs(String)

Which allows using echo() in the jOOR language script such as:

from("direct:hello")
    .transform(java("'Hello ' + echo()"))
    .log("You said ${body}");

The echo() alias will be replaced with its value resulting in a script as:

.transform(java("'Hello ' + bodyAs(String) + bodyAs(String)"))

You can configure a custom configuration location for the camel-joor.properties file or reference to a bean in the registry:

JavaLanguage joor = (JavaLanguage) context.resolveLanguage("java");
java.setConfigResource("ref:MyJoorConfig");

And then register a bean in the registry with id MyJoorConfig that is a String value with the content.

String config = "....";
camelContext.getRegistry().put("MyJoorConfig", config);

Example

For example, to transform the message using jOOR language to the upper case

from("seda:orders")
  .transform().java("message.getBody(String.class).toUpperCase()")
  .to("seda:upper");

And in XML DSL:

<route>
   <from uri="seda:orders"/>
   <transform>
     <java>message.getBody(String.class).toUpperCase()</joor>
   </transform>
   <to uri="seda:upper"/>
</route>

Multi statements

It is possible to include multiple statements. The code below shows an example where the user header is retrieved in a first statement. And then, in a second statement we return a value whether the user is null or not.

from("seda:orders")
  .transform().java("var user = message.getHeader(\"user\"); return user != null ? \"User: \" + user : \"No user exists\";")
  .to("seda:user");

Notice how we have to quote strings in strings, and that is annoying, so instead we can use single quotes:

from("seda:orders")
  .transform().java("var user = message.getHeader('user'); return user != null ? 'User: ' + user : 'No user exists';")
  .to("seda:user");

Hot re-load

You can turn off pre-compilation for the Java language and then Camel will recompile the script for each message. You can externalize the code into a resource file, which will be reloaded on each message as shown:

JavaLanguage java = (JavaLanguage) context.resolveLanguage("java");
java.setPreCompile(false);

from("jms:incoming")
    .transform().java("resource:file:src/main/resources/orders.java")
    .to("jms:orders");

Here the Java code is externalized into the file src/main/resources/orders.java which allows you to edit this source file while running the Camel application and try the changes with hot-reloading.

In XML DSL it’s easier because you can turn off pre-compilation in the <java> XML element:

<route>
    <from uri="jms:incoming"/>
    <transform>
      <java preCompile="false">resource:file:src/main/resources/orders.java</java>
    </transform>
    <to uri="jms:orders"/>
</route>

Lambda-based AggregationStrategy

The Java language has special support for defining an org.apache.camel.AggregationStrategy as a lambda expression. This is useful when using EIP patterns that use aggregation such as the Aggregator, Splitter, Recipient List, Enrich, and others.

To use this, then the Java language script must be in the following syntax:

(e1, e2) -> { }

Where e1 and e2 are the old Exchange and new Exchange from the aggregate method in the AggregationStrategy. The returned value is used as the aggregated message body, or use null to skip this.

The lambda syntax is representing a Java util BiFunction<Exchange, Exchange, Object> type.

For example, to aggregate message bodies together, we can do this as shown:

(e1, e2) -> {
  String b1 = e1.getMessage().getBody(String.class);
  String b2 = e2.getMessage().getBody(String.class);
  return b1 + ',' + b2;
}

Limitations

The Java Camel language is only supported as a block of Java code that gets compiled into a Java class with a single method. The code that you can write is therefore limited to a number of Java statements.

The supported runtime is intended for Java standalone, Spring Boot, Camel Quarkus and other microservices runtimes. It is not supported on any kind of Java Application Server runtime.

Java does not support runtime compilation with Spring Boot using fat jar packaging (https://github.com/jOOQ/jOOR/issues/69), it works with exploded classpath.

Dependencies

To use scripting languages in your camel routes, you need to add a dependency on camel-joor.

If you use Maven you could add the following to your pom.xml, substituting the version number for the latest and greatest release.

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-joor</artifactId>
  <version>x.x.x</version>
</dependency>

Unresolved include directive in modules/languages/pages/java-language.adoc - include::spring-boot:partial$starter.adoc[]