Spring Property Placeholders with String Concatenation

Question

My problem looks simple but I'm not able to resolve it. I have a properties file which contains configuration details of all environments (dev, qa, prod).

Example config.properties:

dev.maxLength=2000  
qa.maxLength=4000

We have a parent Properties file which holds the host name, environment mappings.

Example hosts.properties:

host1=dev
host2=qa

The property name host1 is stored in a bean hostname.

<bean id="hostname"
  factory-bean="localhostInetAddress"
  factory-method="getHostName"/> 

To resolve the config properties name I have to join the strings as follows, ${${**hostname**}.maxLength} which should be resolved as ${dev.maxLength}

I tried using SpEL with no success. I am getting Could not resolve placeholder Exception. How can I concatenate a bean value in property place holder? How are dynamic property names constructed?

Spring version 3.2

Answer 1

To concatenate the values parsed from Spring property placeholders, you need to escape their values using single quoutes ('') and wrap the placeholder expressions by a SpEL expression using #{}.

<bean id="myService" class=""com.services.MyService">
  ...
  <property name="endpointAddress" value="#{'${server}' + ':' + '${port}' + '${endpoint}'}" />
</bean>

where:

server = http://domain.host.com

port = 7777

endpoint = /services/myservice

The result would be:

http://domain.host.com:7777/services/myservice

Answer 2

I solved the issue by changing PropertyPlaceholderConfigurer beans to Properties. <util:properties/> are accessible in SpEL.

Example: "#{prop[host+'.'+'maxLength']}"

where host is a string bean.