Ant -propertyfile resolve from cmd - ant

Question

I am trying to create property file for a project.
the project can use different DB (Oracle or Mssql , but not both)
Beacuse of that i have made 3 property files:
common.properties
mssql.properties
oracle.properties
i want to use the ant properties hierarchy feature in order to set some of this properties.
for example,i can define at,common.properties :
db.hostname= localhost
db.port= 1433
then on mssql\oracle.proprties file i can build
db.connectionString= jdbc:sqlserver://${db.hostname}:${db.port}
on my build.xml
I have wrote :
<property file="common.properties"/>
In order to set concrete DB i have wrote on CMD :
Ant-1.8.4\bin\ant -propertyfile mssql.properties
The problem is that ant doesn't use the references i have defined at the common.properties
int order to resolve:
db.connectionString
How can i solve this issue using cmd?

Answer 1

The problem is the order in which the properties are created. The file "mssql.properties" gets loaded first before executing the ANT script. This explains why the property "db.connectionString" is assigned the strings "${db.hostname}" and "${db.port}" because these properties have no value. Their value gets set when the script runs and loads the second property file.
Alternative approach is to use a property to indicate the db type.
Example
├── build.xml
├── common.properties
└── mssql.properties
Run as follows
$ ant -Ddb=mssql
Buildfile: /home/mark/tmp/build.xml
echo:
[echo] db.connectionString=jdbc:sqlserver://localhost:1433
build.xml
<project name="demo" default="echo">
<property file="common.properties"/>
<property file="${db}.properties"/>
<target name="echo">
<echo message="db.connectionString=${db.connectionString}"/>
</target>
</project>
For extra credit
This approach also enables error checking, in case the correct db type is not specified:
<project name="demo" default="echo">
<property file="common.properties"/>
<property file="${db}.properties"/>
<available property="db.prop.file" file="${db.properties}"/>
<target name="echo">
<fail message="Missing a property file for a ${db} database" unless="db.prop.file"/>
<echo message="db.connectionString=${db.connectionString}"/>
</target>
</project>