[CONFIGURATION-181] [configuration] Conditional directives in property files

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Won't Fix
• Fix Version/s: 1.4

Environment

Operating System: other
Platform: Other

• Bugzilla Id: 36397
• Assignee: Unassigned
• Reporter: Bogdan Calmac
• Created: 28/Aug/05 11:21
• Updated: 22/Aug/09 19:36
• Resolved: 02/Feb/07 19:44

Description

This patch adds conditional directives to property files similar to C macros:
%if, %elseif, %else, %end.

To illustrate the necessity and the syntax I will take as example a section of
my hibernate configuration file. Switching between databases normally requires
to comment/uncomment a lot of properties, and more importantly, cannot be done
automatically at runtime.

1. 1. JNDI Datasource
      #hibernate.connection.datasource = jdbc/test
      #hibernate.connection.username = db2
      #hibernate.connection.password = db2

1. 1. HypersonicSQL
      hibernate.dialect = net.sf.hibernate.dialect.HSQLDialect
      hibernate.connection.driver_class = org.hsqldb.jdbcDriver
      hibernate.connection.username = sa
      hibernate.connection.url = jdbc:hsqldb:hsql://localhost

1. 1. PostgreSQL
      #hibernate.dialect = net.sf.hibernate.dialect.PostgreSQLDialect
      #hibernate.connection.driver_class = org.postgresql.Driver
      #hibernate.connection.url = jdbc:postgresql:template1
      #hibernate.connection.username = pg
      #hibernate.connection.password

1. 1. JTA transactions
      #hibernate.transaction.factory_class =
      net.sf.hibernate.transaction.JTATransactionFactory
      #jta.UserTransaction = jta/usertransaction
      #jta.UserTransaction = javax.transaction.UserTransaction
      #jta.UserTransaction = UserTransaction

1. 1. JDBC transactions
      hibernate.transaction.factory_class =
      net.sf.hibernate.transaction.JDBCTransactionFactory

Here is now how it would look like with conditional directives. The only thing
to change now is the property at the top of the file (which could be defined as
a system property if you don't want to touch the file at all). Note that it uses
nested directives.

db = jndi

%if db = jndi

1. 1. JNDI Datasource
      hibernate.connection.datasource = jdbc/test
      hibernate.connection.username = db2
      hibernate.connection.password = db2

1. 1. JTA transactions
      hibernate.transaction.factory_class =
      net.sf.hibernate.transaction.JTATransactionFactory
      jta.UserTransaction = jta/usertransaction
      jta.UserTransaction = javax.transaction.UserTransaction
      jta.UserTransaction = UserTransaction

%else

1. 1. JDBC transactions
      hibernate.transaction.factory_class =
      net.sf.hibernate.transaction.JDBCTransactionFactory

%if db = hypersonic

1. 1. HypersonicSQL
      hibernate.dialect = net.sf.hibernate.dialect.HSQLDialect
      hibernate.connection.driver_class = org.hsqldb.jdbcDriver
      hibernate.connection.username = sa
      hibernate.connection.url = jdbc:hsqldb:hsql://localhost

%elseif db = postgres

1. 1. PostgreSQL
      hibernate.dialect = net.sf.hibernate.dialect.PostgreSQLDialect
      hibernate.connection.driver_class = org.postgresql.Driver
      hibernate.connection.url = jdbc:postgresql:template1
      hibernate.connection.username = pg
      hibernate.connection.password

%end
%end

The directives used are:

%if condition
%elseif condition
%else
%end

The condition can be:

property (true if the property is defined)
property = value (values are interpolated)
property != value

For the implementation, I've replaced in PropertiesConfiguration.java the call
to read a line from the file with a new getNextLine() method which processes
the conditional directives and returns the next property line. The method is
noop unless the line starts with '%', so it should work just fine with files
that do not use the directives.

I've also added the TestPropertiesConfiguration.testConditionalDirectives() unit
test which uses properties added at the end of test.properties.