Spring Integration & OSGi

This is the latest addition to the spring portfolio ,and again they have made it look so simple. This is mainly meant for asynchronous messaging between modules.Here when i say modules it could be within the same JVm or outside. Spring Integration does not provide any framework for inter JVM communication instead it provides adapters for all existing frameworks like JMS,Spring Remoting,HTTP calls ,Web Services etc.

Spring Integration mainly deals with channels , which is a pipe where messages can be put , and there can be any number of subscibers listening to it.We can keep our business logic independent of the frameworks used.Here channels can be of different types direct channels,pub-sub-channel,polling channels etc .Also there are provisions to make the channel synchronous.

It also provides number of adapters like jms adapters,rmi adaptors,web service adpaters such that we always deal in terms of channels i .e we talk to channels and it publishes to the required framework.Since we keep our code independent of any framework it will be easy flip any of these using configuratiosn without affecting teh business logic.

Certain examples i came across which are very descriptive

1.Spring Integration Documentaion Examples(http://static.springsource.org/spring-integration/reference/htmlsingle/spring-integration-reference.html#samples)

2.Spring Integration Example(dist/org.springframework.integration.samples-1.0.2.SR1.jar)

3.Blog by Oleg(http://blog.springsource.com/2009/02/27/spring-integration-on-dm-server/)

Certain points to note.

1.Channels can be published as OSGi service and other bundles can import it and publish on the channel or listen to it.

Note :

When more than one pub sub channel is defined and needs to be published, filter attributes have to be used to distinguish one from teh other.

Ref : http://forum.springsource.org/showthread.php?t=75316

Two models for hiding spring integration apis from bundles

1. Have a seperate bundle(call it exchange bundle) with spring integration configurations.

2. Wrap the channel using gateway() and expose this as a service , which will be used from the publishing bundle.This makes it independent of spring integration APIs and the publishing channel needs to know only about the interface.

3a. Let all teh bundles interested in listening to teh event register with the exchange bundle using a interface.

Implement a service activator in the exchange bundle.The service activator will collect all the OSgi services interested in listening to the service and call teh method one after the other for all registered services.

3b. The service activator will have a register /unregister method ,and teh service activator will be exposed a OSgi service.The interested bundles will import this service and call the register method. On calling thr register method it will add to the list in teh activator, which will call the method when teh event is published on teh channel. (oleg's blog uses teh same model)

http://forum.springsource.org/showthread.php?t=75315

Browser Caching -Expires,Cache Control & Deflate

Expires Header – will stop the request(304 request-if modified ?) sent from browser

Disadvantage – even if the asset changes the browser will serverthe cached image without even checking if the image has changed.

The only solution is to come up with Versoning if we set Expires.


Syntax(in apache httpd.conf)

#Adding expires header

<FilesMatch "\.(jpg|jpeg|png|gif|swf)$">

Header set Expires "Wed, 31 Dec 2008 23:59:59 GMT"

</FilesMatch>

Also can set using access plus x days

Cache control will over ride expires header even if set.

Add this line for disabling cache control

Header set Cache-control: No-cache,no-store

Add this line for enabling cache control

Header set Cache-Control "private,max-age=0,must-revalidate"

The following lines can be used to remove the ETag header

Header unset ETag

FileETag None

Etag generates the tag using the ip of the hosted machine and when the assets are hosted in multiple machines , and requests may go to different machines and hence e-tags may be different and they will be downloaded again

Also while doing scp(having multiple deployment machines), to retain the original timestamps we need to use ‘scp –p’ whereas the touch command can change the access/modified time for the file after it is copied.

The above cache control works on the basis of the last modified time .And hence the modified time stamps have to be kept same in all the asset holding machines , so when copying the assets copy with same time stamps else requests will be sent again.


Adding Gzip configuration
<FilesMatch "\.(html|htm|js|css)$">
SetOutputFilter DEFLATE
</FilesMatch>


Adding Expires
ExpiresActive On
ExpiresDefault "now plus 0 seconds"

<FilesMatch "\.(jpg|jpeg|png|gif|swf|mp3)$">
ExpiresByType image/jpg "access plus 14 days"
ExpiresByType image/jpeg "access plus 14 days"
.....
.....
Header set Cache-Control "public,max-age=1209600"
Header unset Pragma
</FilesMatch>

Apache HttpClient

Although the java.net package provides basic functionality for accessing resources via HTTP, it doesn't provide the
full flexibility or functionality needed by many applications. The Jakarta Commons HttpClient component seeks to fill
this void by providing an efficient, up-to-date, and feature-rich package implementing the client side of the most
recent HTTP standards and recommendations

Feature List

http://hc.apache.org/httpclient-3.x/features.html

CGLIB-For Dynamic Proxies

The Spring Framework implements method injection by dynamically generating a subclass overriding the method, using bytecode generation via the CGLIB library.

Please be aware that in order for this dynamic subclassing to work, you will need to have the CGLIB jar(s) on your classpath. Additionally, the class that the Spring container is going to subclass cannot be final, and the method that is being overridden cannot be final either.

By default, when the Spring container is creating a proxy for a bean that is marked up with the <aop:scoped-proxy/> element, a CGLIB-based class proxy will be created. This means that you need to have the CGLIB library on the classpath of your application.

Note: CGLIB proxies will only intercept public method calls! Do not call non-public methods on such a proxy; they will not be delegated to the scoped target object.

You can choose to have the Spring container create 'standard' JDK interface-based proxies for such scoped beans by specifying 'false' for the value of the 'proxy-target-class' attribute of the <aop:scoped-proxy/> element. Using JDK interface-based proxies does mean that you don't need any additional libraries on your application's classpath to effect such proxying, but it does mean that the class of the scoped bean must implement at least one interface, and all of the collaborators into which the scoped bean is injected must be referencing the bean via one of its interfaces.

Spring AOP can also use CGLIB proxies. This is necessary to proxy classes, rather than interfaces. CGLIB is used by default if a business object does not implement an interface. As it is good practice to program to interfaces rather than classes, business classes normally will implement one or more business interfaces. It is possible to force the use of CGLIB, in those (hopefully rare) cases where you need to advise a method that is not declared on an interface, or where you need to pass a proxied object to a method as a concrete type.

Hibernate Mapping with parent child relation mapping into same tables

Consider cases when you have parent child relations in the same tables, this becomes very difficult to handle.

In most cases we seperate out mapping of maintaining this parent child relation into another table.

Lets consider an example

we have category which can have subcategories and both these persist on the same table.

Example : Electronics can have subcategory camera, and further camera can have its subcategories.


@Entity
@Table(name = "t_product_category")
public class ProductCategory {

@Id
@GeneratedValue
@Column(name = "f_category_id")
private int categoryId;

@Column(name = "f_category_name")
private String categoryName;

/* The following onetomany relations says that one ProductCategory can have many childrens of teh same type(ProductCategory) identified by
a collection(Set) children.
The initialisation is set to EAGER meaning when you fetch the parent product category all its childeren are automatically
loaded */

@OneToMany(mappedBy = "parent" ,fetch =FetchType.EAGER)
private Set<ProductCategory> children;

/* The following many to one relation means that many(children) of ProductCategory can have a parent of the same kind identified by
parent */


@ManyToOne
@JoinColumn(name="f_parent")
private ProductCategory parent;

public Set<ProductCategory> getChildren() {
return children;
}

public void setChildren(Set<ProductCategory> children) {
this.children = children;
}

public ProductCategory getParent() {
return parent;
}

public void setParent(ProductCategory parent) {
this.parent = parent;
}


Just by mentioning the two mapping and the corresponding getters & setters our relationship is ready.

Database table looks like this

CREATE TABLE `t_product_category` (
`F_CATEGORY_ID` int(11) NOT NULL auto_increment,
`F_CATEGORY_NAME` varchar(150) NOT NULL,
`F_PARENT` int(11) default NULL,
PRIMARY KEY (`CATEGORY_ID`), .......}

Getting jar name & location from loaded class

The following method with the classname passed as parameter will return the location of the jar from which the class is loaded.

import java.net.URL;
import java.security.CodeSource;
import java.security.ProtectionDomain;

public static String getJarLocation(String className) {
try {
Class cls = Class.forName(className);
ProtectionDomain pDomain = cls.getProtectionDomain();
CodeSource cSource = pDomain.getCodeSource();
URL loc = cSource.getLocation();
return loc.toString();
} catch (Exception e) {
e.printStackTrace();
}

return null;

}

Alternatively we can also add the following to the startup JVM paramteres , which will print all the classes loaded along with the jar names and its path.

-verbose:class

Scheduling simple Quartz job Using Spring

Currently, Spring supports the Timer, part of the JDK since 1.3, and the Quartz Scheduler (http://www.quartzscheduler.org).
Both schedulers are set up using a FactoryBean with optional references to Timers or Triggers, respectively

Quartx job can be written in several ways

1. Wiring up jobs using triggers and the SchedulerFactoryBean


<bean id="sampleJob" class="com.xyx.SampleJob" />


<bean id="sampleJobTrigger" class="org.springframework.scheduling.quartz.SimpleTriggerBean">
<property name="jobDetail" ref="sampleJob" />
<property name="startDelay" value="10000" />
<property name="repeatInterval" value="50000" />
</bean>

OR

<bean id="sampleJobTrigger" class="org.springframework.scheduling.quartz.CronTriggerBean">
<property name="jobDetail" ref="exampleJob"/>
<!-- run every morning at 6 AM -->
<property name="cronExpression" value="0 0 6 * * ?"/>
</bean>


<bean class="org.springframework.scheduling.quartz.SchedulerFactoryBean">
<property name="triggers">
<list>
<ref bean="sampleJobTrigger" />
</list>
</property>
</bean>



2. Using the JobDetailBean

<bean name="exampleJob" class="org.springframework.scheduling.quartz.JobDetailBean">
<property name="jobClass" value="com.xyx.SampleJob"/>
<property name="jobDataAsMap">
<map>
<entry key="timeout" value="5"/>
</map>
</property>
</bean>


In this case com.xyx.SampleJob has to extend QuartzJobBean.


3. Using the MethodInvokingJobDetailFactoryBean

Often you just need to invoke a method on a specific object. Using the MethodInvokingJobDetailFactoryBean you can do as follows

<bean id="jobDetail" class="org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean">
<property name="targetObject" ref="sampleJob"/>
<property name="targetMethod" value="sampleMethod"/>
</bean>

The above example will result in the sampleMethod() being called on the sampleJob object.

Ref:
http://www.opensymphony.com/quartz.
http://static.springframework.org/spring/docs/1.2.9/reference/scheduling.html