Apache Camel routing API call to message queue - rest

Question

I have two applications that talk to each other using a REST API.
I would like to know if I can use Apache Camel as a proxy that could "persist" the API calls, for example storing them as messages in ActiveMQ, and then later route the requests to the actual API endpoint.
Practically, I would like to use Apache Camel to "enhance" the API endpoints adding persistence, throttling of requests, etc...
What component do you suggest to use?

Answer 1

You can always try to bridge your HTTP request into a queue, but making the thread wait by forcing the exchangePattern to InOut.
See this example :
import org.apache.activemq.broker.BrokerService;
import org.apache.camel.LoggingLevel;
import org.apache.camel.builder.RouteBuilder;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class Main {
private static final Logger logger = LoggerFactory.getLogger(SimpleRouteBuilder.class);
public static void main(String[] args) throws Exception {
org.apache.camel.main.Main main = new org.apache.camel.main.Main();
main.addRouteBuilder(new SimpleRouteBuilder());
logger.info("Next call is blocking, ctrl-c to exit\n");
main.run();
}
}
class SimpleRouteBuilder extends RouteBuilder {
private static final Logger logger = LoggerFactory.getLogger(SimpleRouteBuilder.class);
public void configure() throws Exception {
// launching an activemq in background
final BrokerService broker = new BrokerService();
broker.setBrokerName("activemq");
broker.addConnector("tcp://localhost:61616");
Runnable runnable = () -> {
try {
broker.start();
} catch (Exception e) {
e.printStackTrace();
}
};
runnable.run();
// receiving http request but queuing them
from("jetty:http://127.0.0.1:10000/input")
.log(LoggingLevel.INFO, logger, "received request")
.to("activemq:queue:persist?exchangePattern=InOut"); // InOut has to be forced with JMS
// dequeuing and calling backend
from("activemq:queue:persist")
.log(LoggingLevel.INFO, logger,"requesting to destination")
.removeHeaders("CamelHttp*")
.setHeader("Cache-Control",constant("private, max-age=0,no-store"))
.to("jetty:http://perdu.com?httpMethod=GET");
}
}
If you are using maven, here is the pom.xml :
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>be.jschoreels.camel</groupId>
<artifactId>camel-simple</artifactId>
<version>1.0-SNAPSHOT</version>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
<dependencies>
<dependency>
<groupId>org.apache.camel</groupId>
<artifactId>camel-core</artifactId>
<version>2.19.2</version>
</dependency>
<dependency>
<groupId>org.apache.camel</groupId>
<artifactId>camel-jms</artifactId>
<version>2.19.2</version>
</dependency>
<dependency>
<groupId>org.apache.camel</groupId>
<artifactId>camel-jetty</artifactId>
<version>2.19.2</version>
</dependency>
<dependency>
<groupId>org.apache.activemq</groupId>
<artifactId>activemq-camel</artifactId>
<version>5.15.3</version>
</dependency>
<dependency>
<groupId>org.apache.activemq</groupId>
<artifactId>activemq-all</artifactId>
<version>5.15.3</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.apache.activemq/activemq-kahadb-store -->
<dependency>
<groupId>org.apache.activemq</groupId>
<artifactId>activemq-kahadb-store</artifactId>
<version>5.15.3</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.25</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-simple</artifactId>
<version>1.7.25</version>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
</dependencies>
</project>