I have a ServiceA which has a dependency on ServiceB. The serviceB comes from a spring bean file with lazy-init=true i.e, I only want serviceB to be initialised when and if I ask for that bean.
However I do use ServiceA throughout my application and when we do a setter based injection ServiceB gets initialised.
I want ServiceA to not initialise ServiceB until any method in ServiceA is called that needs ServiceB. One way of doing this was using the Aspects but I was looking at the simplest possible solution for this particularly in the Spring XML file for serviceB or some annotation in serviceB or any proxy flag.
I think LazyInitTargetSource does what you need.
Useful when a proxy reference is needed on initialization but the actual target object should not be initialized until first use. When the target bean is defined in an ApplicationContext (or a BeanFactory that is eagerly pre-instantiating singleton beans) it must be marked as "lazy-init" too, else it will be instantiated by said ApplicationContext (or BeanFactory) on startup.
Another approach that you might want to try is discussed at http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/aop/framework/autoproxy/target/LazyInitTargetSourceCreator.html:
[LazyInitTargetSourceCreator is a] TargetSourceCreator that enforces a LazyInitTargetSource for each bean
that is defined as "lazy-init". This will lead to a proxy created for
each of those beans, allowing to fetch a reference to such a bean
without actually initialized the target bean instance.
To be registered as custom TargetSourceCreator for an auto-proxy
creator, in combination with custom interceptors for specific beans or
for the creation of lazy-init proxies only. For example, as
autodetected infrastructure bean in an XML application context
definition:
<bean class="org.springframework.aop.framework.autoproxy.BeanNameAutoProxyCreator">
<property name="customTargetSourceCreators">
<list>
<bean class="org.springframework.aop.framework.autoproxy.target.LazyInitTargetSourceCreator"/>
</list>
</property>
</bean>
<bean id="myLazyInitBean" class="mypackage.MyBeanClass" lazy-init="true">
...
</bean>
If you find yourself doing this several times in an application context, this will save on configuration.
I don't know about Spring, but in Guice you would use a Provider<ServiceB>, so that when you were ready to use the service you'd go provider.get().callMethodOnB(...).
This is, I believe, part of the JSR-330 spec, so it's possible there's an equivalent thing in Spring (I haven't used an up-to-date version of Spring for quite some time).
You can also use method injection.
As a rule it's required to obtain a new instance of a singleton bean from a context, but it can be used in your case too.
Sample:
package org.test.lazy;
public abstract class ParentBean {
public abstract LazyBean getLazy();
public void lazyDoingSomething() {
getLazy().doSomething();
}
}
package org.test.lazy;
public class LazyBean {
public void init() {
System.out.println("Initialized");
}
public void doSomething() {
System.out.println("Doing something");
}
}
package org.test.lazy;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
#ContextConfiguration
#RunWith(SpringJUnit4ClassRunner.class)
public class LazyTest {
#Autowired
private ParentBean parentBean;
#Test
public void test() {
parentBean.lazyDoingSomething();
parentBean.lazyDoingSomething();
}
}
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
">
<import resource="classpath:org/test/lazy/Lazy-context.xml"/>
<bean id="parentBean" class="org.test.lazy.ParentBean">
<lookup-method bean="lazyBean" name="getLazy"/>
</bean>
</beans>
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
"
default-lazy-init="true">
<bean id="lazyBean" class="org.test.lazy.LazyBean" init-method="init" />
</beans>
So you lazy bean will be initialized only once on demand.
Related
When the aspect is enabled, the #Autowired bean in BeanB becomes a proxy, and the name field is null. Why? What should I do if I wish the original code to work properly?
Here is the code:
public class BeanA
{
#Value("jami")
//public String name;
String name; //package visiblity
}
public class BeanB
{
#Autowired
private BeanA beanA;
public void noLongerWorks()
{
System.out.println(beanA.name);
}
}
public class Main
{
public static void main(String[] args)
{
String[] configs = {"applicationContext.xml", "applicationContext-aop.xml"};//prints null
// String[] configs = {"applicationContext.xml"};//prints jami
ApplicationContext ctx = new ClassPathXmlApplicationContext(configs);
BeanB beanB = ctx.getBean(BeanB.class);
beanB.noLongerWorks();
}
}
---------- applicationContext.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd">
<context:annotation-config />
<bean class="aop.pack1.BeanA" />
<bean class="aop.pack1.BeanB" />
</beans>
------ applicationContext-aop.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:aop="http://www.springframework.org/schema/aop"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd">
<aop:aspectj-autoproxy />
<bean class="aop.pack1.TestAspect" />
</beans>
#Aspect
public class TestAspect
{
#Pointcut("target(aop.pack1.BeanA)")
public void pointcut() {}
#Before("pointcut()")
public void advice()
{
System.err.println("___________advice__________");
}
}
EDIT:
I figured out one possible solution. But it does not seems very clean. Is there any elegant way to this? without making changes to existing code?
The solution I found:
is to make all the fields in BeanA private, and only access them via getter setters.
This approach, however, requires a lot of modification of the original code (e.g. the BeanA class).
You have already figured out the issue but, I wanted to share this article I came across that lists what Spring AOP can and cannot do.
In your case
Since it uses proxy-based AOP, only method-level advising is supported; it does not support field-level interception So join-points can be at method level not at field level in a class.
Only methods with public visibility will be advised: Methods with private, protected, or default visibility will not be advised.
Just a recommendation and I think it's also a good OOP practice to create fields with private or protected visibility and provide appropriate getters and setters to access them.
These SO Q/A might be useful
Spring AOP - get old field value before calling the setter
spring singleton bean fields are not populated
Spring AOP CGLIB proxy's field is null
I have the code #Inject works in one class but not in other.
Here's my code:
context.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation=" http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd
">
<bean id="multipartResolver"
class="org.springframework.web.multipart.commons.CommonsMultipartResolver"></bean>
<context:component-scan base-package="com.myfashions.services"/>
<context:component-scan base-package="com.myfashions.dao"/>
</beans>
SellerRetriever.java
public class SellerRetriever {
#Inject
UserDAO userDAO;
...
...
}
UserDAO class is present in com.myfashions.dao package.
#Inject is not working in Seller.java. Any reason why?
Make sure that both SellerRetriever and the implementation of UserDAO are annotated for the component scan. This will ensure that the latter is injected into the former:
#Service
public class SellerRetriever {
#Inject
UserDAO userDAO;
...
}
Annotate the UserDAO implementation with #Component.
When scanning multiple paths use:
<context:component-scan base-package="com.myfashions.services, com.myfashions.dao"/>
To be eligible to scan, your class must be annotated with either a more generic #Component, or #Service or #Repositories etc.. In your case, #Service logically better fits.
You could then (if you need) define some aspects (AOP) focused specifically on services call.
Besides, you may want to use #Autowired instead of #Inject to retrieve your bean.
For more information about differences concerning these two annotations:
What is the difference between #Inject and #Autowired in Spring Framework? Which one to use under what condition?
and you can see my comment just below explaining one good reason to keep #Autowired instead of #Inject.
I found my mistake, I'm posting this because in case anyone has the same problem. I used new operator to create an SellerRetriver object. Inject won't work if new operator is used to call that particular class.
I have next situation:
Connection manager should have each time one object of ConnectionServer and new objects of DataBean
So, I have created these beans and configured out it spring xml.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
<bean id="dataBena" class="com.test.DataBean" scope="prototype"/>
<bean id="servCon" class="com.test.ServerCon"/>
<!--<bean id="test" class="com.test.Test"/>-->
<context:component-scan base-package="com.test"/>
</beans>
and added scope prototype for DataBean
After this I've created simple util/component class called Test
#Component
public class Test {
#Autowired
private DataBean bean;
#Autowired
private ServerCon server;
public DataBean getBean() {
return bean.clone();
}
public ServerCon getServer() {
return server;
}
}
BUT, Each time of calling getBean() method I am cloning this bean, and this is the problem to me.
Can I do it from spring configuration without usning clone method?
Thanks.
You are looking for lookup method functionality in Spring. The idea is that you provide an abstract method like this:
#Component
public abstract class Test {
public abstract DataBean getBean();
}
And tell Spring that it should implement it at runtime:
<bean id="test" class="com.test.Test">
<lookup-method name="getBean" bean="dataBean"/>
</bean>
Now every time you call Test.getBean you will actually call Spring-generated method. This method will ask ApplicationContext for DataBean instance. If this bean is prototype-scoped, you will get new instance each time you call it.
I wrote about this feature here.
I am using Spring 3.0.3.
I would like to use the applicationContextProvider so I declared:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:aop="http://www.springframework.org/schema/aop"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/tx
http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd
http://www.springframework.org/schema/aop
http://www.springframework.org/schema/aop/spring-aop-3.0.xsd">
<bean id="applicationContextProvider" class="com.mycompany.util.ApplicationContextProvider"></bean>
<context:annotation-config/>
<tx:annotation-driven/>
</beans>
and my ApplicationContextProvider:
public class ApplicationContextProvider implements ApplicationContextAware {
private static ApplicationContext applicationContext = null;
public static ApplicationContext getApplicationContext() {
return applicationContext;
}
public void setApplicationContext(ApplicationContext _applicationContext) throws BeansException {
applicationContext = _applicationContext;
}
}
But the set is never being called!
and whenever I am using ApplicationContextProvider.getApplicationContext() returns null.
why is it?
Part of the problem may be that your getter is static. So its possible for you to call it before Spring has created an instance of ApplicationContextProvider.
You need to refer to the bean 'applicationContextProvider' that Spring has created for you when Spring is "ready" for you to use it. See Bean lifecycle
E.g. via a Junit test with your bean in 'app-context.xml' in src/test/resources
package com.mycompany.util;
import static org.junit.Assert.*;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
#ContextConfiguration(locations="classpath:app-context.xml")
#RunWith(SpringJUnit4ClassRunner.class)
public class ApplicationContextProviderTest {
#Autowired // Injected by Spring when bean is "ready"
ApplicationContextProvider contextProvider;
#Test
public void testContext() {
assertNotNull(contextProvider);
ApplicationContext context = ApplicationContextProvider.getApplicationContext();
assertNotNull(context);
System.out.println("My context has " + context.getBeanDefinitionCount() + " beans");
}
}
Then this gets a green bar for applicationContext being set.
Example output (don't leave System.out in the test btw).
INFO : org.springframework.test.context.TestContextManager - #TestExecutionListeners is not present for class [class com.mycompany.util.ApplicationContextProviderTest]: using defaults.
INFO : org.springframework.beans.factory.xml.XmlBeanDefinitionReader - Loading XML bean definitions from class path resource [app-context.xml]
INFO : org.springframework.context.support.GenericApplicationContext - Refreshing org.springframework.context.support.GenericApplicationContext#4c331059: startup date [Sun Feb 27 13:38:13 GMT 2011]; root of context hierarchy
INFO : org.springframework.beans.factory.support.DefaultListableBeanFactory - Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory#4b1c2b67: defining beans [applicationContextProvider,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor]; root of factory hierarchy
My context has 5 beans
INFO : org.springframework.context.support.GenericApplicationContext - Closing org.springframework.context.support.GenericApplicationContext#4c331059: startup date [Sun Feb 27 13:38:13 GMT 2011]; root of context hierarchy
INFO : org.springframework.beans.factory.support.DefaultListableBeanFactory - Destroying singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory#4b1c2b67: defining beans [applicationContextProvider,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor]; root of factory hierarchy
app-context.xml:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="applicationContextProvider" class="com.mycompany.util.ApplicationContextProvider"></bean>
</beans>
Seems like you are doing something the wrong way here... Do you want to get access to Spring beans from object not managed by Spring? How about WebApplicationContextUtils:
WebApplicationContextUtils.getRequiredWebApplicationContext(servletContext);
But WebApplicationContextUtils should always be treated as a last resort because this is not a Spring way. Are you sure you cannot integrate web services with Spring somehow? For instance with Apache CXF one can simply implement WS endpoint as a Spring bean or inject client proxy to other beans...
Using static fields is always asking yourself for trouble. I am sure you can achieve your goals in a more elegant fashion.
This is an old question with already accepted answer, but for me it wasn't really clear why the setApplicationContext() method wasn't being called on the applicationContextProvider. The answer provided how but really not the why.
Spring creates beans using lazy strategy: a bean will only be created the first time it is needed. That is why example in the accepted answer works: the bean is needed by ApplicationContextProviderTest and so it is created at that point, and not before, and setApplicationContext() method is being called at that point in time and everything works as intended.
However, if your bean is not auto-wired anywhere none of this will happen. In this case the solution is to tell Spring to not use lazy instantiation, i.e.:
<bean id="applicationContextProvider" lazy-init="false" class="com.mycompany.util.ApplicationContextProvider" />
This way, the bean will be created on application startup and method setApplicationContext() will be called at that time. You can then use the bean afterwords, provided that the usage happens after application startup is done.
Of course, much better way is to auto-wire the bean wherever you need it, but sometime it is not possible (read: legacy apps).
I'm looking for a way to have spring beans registering themselves to a job processor bean who in turn will execute the registered beans on a schedule.
I'm hoping that the bean would just have to implement an interface and by some spring mechanism get registered to the job processor bean. Or alternatively inject the job processor bean into the beans and then somehow the job processor bean can keep track of where it's been injected.
Any suggestions appreciated, it might be that spring is not the tool for this sort of thing?
Use a spring context something like this:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
<!--Scans the classpath for annotated
components #Component, #Repository,
#Service, and #Controller -->
<context:component-scan base-package="org.foo.bar"/>
<!--Activates #Required, #Autowired,
#PostConstruct, #PreDestroy
and #Resource-->
<context:annotation-config/>
</beans>
And define a pojo like this:
#Component
public class FooBar {}
And inject like this:
#Component
public class Baz {
#Autowired private FooBar fooBar;
}
Spring has a powerful abstraction layer for Task Execution and Scheduling.
In Spring 3, there are also some annotations that you can use to mark bean methods as scheduled (see Annotation Support for Scheduling and Asynchronous Execution)
You can let a method execute in a fixed interval:
#Scheduled(fixedRate=5000)
public void doSomething() {
// something that should execute periodically
}
Or you can add a CRON-style expression:
#Scheduled(cron="*/5 * * * * MON-FRI")
public void doSomething() {
// something that should execute on weekdays only
}
Here's the XML code you'll need to add (or something similar):
<task:annotation-driven executor="myExecutor" scheduler="myScheduler"/>
<task:executor id="myExecutor" pool-size="5"/>
<task:scheduler id="myScheduler" pool-size="10"/>
Used together with
<context:component-scan base-package="org.foo.bar"/>
<context:annotation-config/>
as described by PaulMcKenzie, that should get you where you want to go.