如何使用Pooled Spring bean而不是Singleton？

Question

For efficiency reasons, I am interested in limiting the number of threads that simultaneously uses the beans of the Spring application context (I don't want an unlimited number of threads proccessing in my limited memory).

I have found here (spring documentation) a way to achieve this by pooling the beans in a EJB style, by doing the following:

• Declare the target bean as scope "prototype".
• Declare a Pool provider that will deliver a limited number of pooled "target" instances.
• Declare a "ProxyFactoryBean" which function is not clear to me.

Here is the declaration of this beans:

<bean id="businessObjectTarget" class="com.mycompany.MyBusinessObject" 
    scope="prototype">
  ... properties omitted
</bean>

<bean id="poolTargetSource" class="org.springframework.aop.target.CommonsPoolTargetSource">
  <property name="targetBeanName" value="businessObjectTarget"/>
  <property name="maxSize" value="25"/>
</bean>

<bean id="businessObject" class="org.springframework.aop.framework.ProxyFactoryBean">
  <property name="targetSource" ref="poolTargetSource"/>
  <property name="interceptorNames" value="myInterceptor"/>
</bean>

My problem is that when I will declare another bean to use pooled instances of the "businessObjectTarget", how should I do it? I mean, when i try to do something like this:

<bean id="clientBean" class="com.mycompany.ClientOfTheBusinessObject">
  <property name="businessObject" ref="WHAT TO PUT HERE???"/>
</bean>

What should be the value of the "ref" ??

Answer 1

You cannot use properties to get instances of prototypes.
One option is to use the lookup methods (see chapter 3.3.7.1 )
Another option to get your bean in code: make your com.mycompany.ClientOfTheBusinessObject to implement the ApplicationContextAware interface and then call context.getBean("clientBean")

Answer 2

我使用Java配置在接口上构造了一个代理，该接口使用apache commons-pool处理池以实现调用级池。

Answer 3

Please note the name of the third bean in the spring example:-"businessObject"

It means this the bean from where you are supposed to access the common pool.

For your case if you need your own client bean you may have it as follows. But in such a case businessObject is not required.:-

<bean id="businessObjectTarget" class="com.mycompany.MyBusinessObject" 
    scope="prototype">

  ... properties omitted
</bean>

<bean id="poolTargetSource" class="org.springframework.aop.target.CommonsPoolTargetSource">
  <property name="targetBeanName" value="businessObjectTarget"/>
  <property name="maxSize" value="25"/>
</bean>

<bean id="clientBean" class="com.mycompany.ClientOfTheBusinessObject">
 <property name="poolTargetSource" ref="poolTargetSource"/>
</bean>


Java classes:-
public class ClientOfTheBusinessObject{
     CommonsPoolTargetSource poolTargetSource;
//<getter and setter for poolTargeTSource>
  public void methodToAccessCommonPool(){
     //The following line gets the object from the pool.If there is nothing left in the pool then the thread will be blocked.(The blocking can be replaced with an exception by changing the properties of the CommonsPoolTargetSource bean)
     MyBusinessObject mbo = (MyBusinessObject)poolTargetSource.getTarget();
     //Do whatever you want to do with mbo
     //the following line puts the object back to the pool
     poolTargetSource.releaseTarget(mbo);
  }
}

Answer 4

I'm pretty sure you can limit the number of simultaneous threads in a less convoluted way. Did you look at the Java Concurrency API, specifically at the Executors.newFixedThreadPool() ?