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

Solution 1

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.

Solution 2

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

Solution 3

It would be better to have environment specific properties in a file of its own and use Spring Profiles. For example, I have four xml files just for db configuration, local.db.xml, dev.db.xml, qa.db.xml and prod.db.xml. Inside each db.xml, I set the profile to the appropriate value.

My local.db.xml has

<beans profile="db.local" .. >

For starting Tomcat, I specify the VM options as follows

-Dspring.profiles.active=db.local 

Comments

[user2235506]

I cannot use Environment variables/JVM properties, it is a policy constraint.

[Vu Nguyen]

Mind to share your XML? I' want to do the same thing but wasn't sure of what you mentioned by changing it to Properties...