Apache Karaf is a small OSGi based runtime which provides a lightweight container onto which various components and applications can be deployed
Defination
What is it in details?
- Karaf is a platform that allow you to deploy your application
- You can install/uninstall/start/stop your application in several easy way
- You can replace/update it and you can change it on the fly
What is an application?
- An application is a composition of modules
- Each module can depend from other modules of application or form other modules of the container
What is a module?
- A module is a bundle
- Bundle is a jar with a Manifest than that one
How a bundle interact?
- Each bundle can register one or more service
- Each service can be retrieved by other bundle
- Each service can obtain the reference of other services
What is a service?
- A service is a self-contained unit of functionality
OSGI service example
// file CustomerService.java
package com.www.customer.service;
public interface CustomerService {
Customer lookupCustomer(String customerId);
}
// file CustomerServiceImpl.java
package com.www.customer.service.impl;
public class CustomerServiceImpl implements CustomerService {
public CustomerServiceImpl() {
// constructor
}
public void init() {
// define some init steps here
}
public void destroy() {
// define some destroy steps here
}
public Customer lookupCustomer(String customerId) {
Customer customer = new Customer();
customer.setFirstName("Loc");
customer.setLastName("Nguyen");
customer.setPhoneNumber("+84978909371");
customer.setId(customerId);
return customer;
}
}
<?xml version="1.0" encoding="UTF-8"?>
<blueprint
xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0">
<bean id="customerServiceImpl" class="com.www.customer.service.impl.CustomerServiceImpl" init-method="init" destroy-method="destroy"></bean>
<service ref="customerServiceImpl" interface="com.www.customer.service.CustomerService"></service>
</blueprint>
What is a karaf feature?
- A group of relatived bundles
How to start a Karaf server
- Download karaf from http://karaf.apache.org/download.html
- Extract the downloaded file
- Add or update KARAF_HOME env
- Run command bin\karaf.bat (for windows) or bin/karaf (for Linux)
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/ ,< / __ `/ ___/ __ `/ /_
/ /| |/ /_/ / / / /_/ / __/
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Apache Karaf (4.2.0)
Hit '<tab>' for a list of available commands
and '[cmd] --help' for help on a specific command.
Hit '<ctrl-d>' or type 'system:shutdown' or 'logout' to shutdown Karaf.
karaf@root()>
Directory structure
-
/bin: control scripts to start, stop, login, …
-
/examples: contains several examples to start with Apache Karaf
-
/etc: configuration files
-
/data: working directory
-
/data/cache: OSGi framework bundle cache
-
/data/generated-bundles: temporary folder used by the deployers
-
/data/log: log files
-
-
/deploy: hot deploy directory
-
/instances: directory containing
[instances|instances] -
/lib: contains libraries
-
/lib/boot: contains the system libraries used at Karaf bootstrap
-
/lib/endorsed: directory for endorsed libraries
-
/lib/ext: directory for JRE extensions
-
-
/system: OSGi bundles repository, laid out as a Maven 2 repository
Stop karaf server (3 ways)
- Enter ^D in the console
- Enter system:shutdown in the console
- Enter halt in the console (this is system:shutdown’s alias)
Cleaning the Karaf state
- Just delete the data directory when Karaf is not running
- Start karaf with argument clean (e.g bin/karaf clean)
How to deploy an application in Karaf
Karaf commands
https://cwiki.apache.org/confluence/display/KARAF/4.1.+Console+and+Commands
Karaf and Web
Karaf examples
- Karaf bundle example
- Karaf cfx example
- [Dockerizing an Apache Karaf image] (https://nqloc.github.io)