CODEWITHSUNDEEP
javaspring
Niche
Niche

Reputation: 142

Conditional initialization of classes in spring

I have a service which refers to a single source.

<bean id="XYZService" class="com.services.impl.DataService1">
    <constructor-arg ref="DataSource1" />
</bean>

<bean id="DataSource1" class="com.source.impl.DataSource1">
        <constructor-arg ref="DBDataSource"/>
        <constructor-arg value="xyz"/>      
</bean>

<bean id="DataSource2" class="com.source.impl.DataSource2">
        <constructor-arg ref="MsgDataSource"/>
        <constructor-arg value="xyz"/>      
</bean>

Now if i want to perform a conditional check and my service should be able listen to particular source based on a input variable something like below.

<bean id="XYZService" class="com.services.impl.DataService1">
    <constructor-arg ref=" $VARIABLE == true ? DataSource1 : DataSource2" />
</bean>

I did tried SPEL however no luck. I am beginner in spring. Any help will be appreciated. Thanks.

Upvotes: 2

Views: 3931

Answers (3)

PaoloV
PaoloV

Reputation: 126

Assuming you are using Spring 3.1 or later, Spring Profiles may be the best solution.

Using the example of Production and Dev/QA environments, common bean declarations go in a shared file

<beans>
  <bean id="XYZService" class="com.services.impl.DataService1">
    <constructor-arg ref="DataSource" />
  </bean>
</beans>

A separate configuration contains production references

<beans profiles="prod">
  <bean id="DataSource" class="com.source.impl.DataSource1">
    <constructor-arg ref="DBDataSource"/>
    <constructor-arg value="xyz"/>      
  </bean>
</beans>

Another contains dev references

<beans profile="dev">
  <bean id="DataSource" class="com.source.impl.DataSource2">
    <constructor-arg ref="MsgDataSource"/>
    <constructor-arg value="xyz"/>      
  </bean>
</beans>

To activate the given profile add -Dspring.profiles.active=prod to your JVM arguments

You can find more info here

Another approach uses factory methods. 

<bean id="DataSource" class="com.source.impl.DataSourceFactory" factory-method="getInstance">
    <constructor-arg value="#{VARIABLE}" />
</bean>

The above fragment assumes that you want your factory method to explcitly invoke the constructor of each of your services. If you dead set on using Spring to create the instances you can pass each datasource implementation as constructor arguments and use the constructor method as a simple dispatcher.

Upvotes: 2

Andrei Stefan
Andrei Stefan

Reputation: 52368

You need something like this:

<constructor-arg 
     ref="#{systemProperties.variable == 'true' ? 'DataSource1' : 'DataSource2'}" />

where "variable" is set like -Dvariable=true.

Upvotes: 1

Aaron Digulla
Aaron Digulla

Reputation: 328624

There are many solutions. Here are two: You can use profiles for this. Define two profiles, define the DataSource beans with the same name but different profiles. (docs)

Alternatively, you can use a single bean and a static factory method (docs). 

<bean id="DataSource" class="com.source.impl.DataSourceFactory"
    factory-method="createInstance"/>

Inside of DataSourceFactory.createInstance(), you can check the flag and then create the correct data source in plain Java.

The latter is a bit easier to understand, IMO. Using profiles allows you to keep everything in XML (but you should really consider switching to the Java Configuration). The drawback with profiles is that you must not forget to activate at least one of the bean won't be defined.

A third option is to use three XML files and then modify the list of XML files that should be parsed when you pass it to the ApplicationContext. But that only works if you have control over this part of the code.

Upvotes: 2

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