Load environment-specific properties for use with PropertyPlaceholderConfigurer?

Question

This seems like a pretty common problem, but I haven't found any sort of consensus on the best method, so I'm posing the question here.

I'm working on a command-line Java application using Spring Batch and Spring. I'm using a properties file along with a PropertyPlaceholderConfigurer, but I'm a little unsure of the best way of handling the properties files for multiple environments (dev, test, etc.). My Googling is only turning up programmatic ways of loading the properties (i.e., in the Java code itself), which doesn't work for what I'm doing.

One approach I've considered is simply placing each environment's properties file on the server and adding the file's directory to the classpath via a command-line argument, but I've been having trouble loading the file using that method.

The other method I'm considering is to just include all the properties files in the jar and use a system property or command line argument to fill in the name of the properties file at runtime, like this:

<bean id="propertyConfigurer"     class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">     <property name="locations">         <list>             <value>classpath:job.properties.${env}</value>         </list>     </property> </bean> 

I lean towards the latter solution, but I'm also looking to see if there's a better method I'm overlooking.

I should also mention that I have to make the substitution at runtime rather than in the build. The process I'm constrained to use requires a single build which will be promoted through the environments to production, so I'm unable to use substitution ala Maven or Ant.

Answer 1

Essentially you have a finished JAR which you want to drop into another environment, and without any modification have it pick up the appropriate properties at runtime. If that is correct, then the following approaches are valid:

1) Rely on the presence of a properties file in the user home directory.

Configure the PropertyPlaceholderConfigurer to reference a properties file external to the JAR like this:

<bean id="applicationProperties" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">     <property name="ignoreUnresolvablePlaceholders" value="false"/>     <property name="order" value="1"/>     <property name="locations">       <list>         <!-- User home holds secured information -->         <value>file:${user.home}/MyApp/application.properties</value>       </list>     </property>   </bean> 

The operating system will secure the contents of the application.properties file so that only the right people can have access to it. Since this file does not exist when you first run up the application, create a simple script that will interrogate the user for the critical values (e.g. username, password, Hibernate dialect etc) at start up. Provide extensive help and sensible default values for the command line interface.

2) If your application is in a controlled environment so that a database can be seen then the problem can be reduced to one of creating the basic credentials using technique 1) above to connect to the database during context startup and then performing substitution using values read via JDBC. You will need a 2-phase approach to application start up: phase 1 invokes a parent context with the application.properties file populating a JdbcTemplate and associated DataSource; phase 2 invokes the main context which references the parent so that the JdbcTemplate can be used as configured in the JdbcPropertyPlaceholderConfigurer.

An example of this kind of code would be this:

public class JdbcPropertyPlaceholderConfigurer extends PropertyPlaceholderConfigurer {    private Logger log = Logger.getLogger(JdbcPropertyPlaceholderConfigurer.class);   private JdbcTemplate jdbcTemplate;   private String nameColumn;   private String valueColumn;   private String propertiesTable;    /**    * Provide a different prefix    */   public JdbcPropertyPlaceholderConfigurer() {     super();     setPlaceholderPrefix("#{");   }    @Override   protected void loadProperties(final Properties props) throws IOException {     if (null == props) {       throw new IOException("No properties passed by Spring framework - cannot proceed");     }     String sql = String.format("select %s, %s from %s", nameColumn, valueColumn, propertiesTable);     log.info("Reading configuration properties from database");     try {       jdbcTemplate.query(sql, new RowCallbackHandler() {          public void processRow(ResultSet rs) throws SQLException {           String name = rs.getString(nameColumn);           String value = rs.getString(valueColumn);           if (null == name || null == value) {             throw new SQLException("Configuration database contains empty data. Name='" + name + "' Value='" + value + "'");           }           props.setProperty(name, value);         }        });     } catch (Exception e) {       log.fatal("There is an error in either 'application.properties' or the configuration database.");       throw new IOException(e);     }     if (props.size() == 0) {       log.fatal("The configuration database could not be reached or does not contain any properties in '" + propertiesTable + "'");     }   }    public void setJdbcTemplate(JdbcTemplate jdbcTemplate) {     this.jdbcTemplate = jdbcTemplate;   }    public void setNameColumn(String nameColumn) {     this.nameColumn = nameColumn;   }    public void setValueColumn(String valueColumn) {     this.valueColumn = valueColumn;   }    public void setPropertiesTable(String propertiesTable) {     this.propertiesTable = propertiesTable;   }  } 

The above would then be configured in Spring like this (note the order property comes after the usual $ prefixed placeholders):

  <!-- Enable configuration through the JDBC configuration with fall-through to framework.properties -->   <bean id="jdbcProperties" class="org.example.JdbcPropertyPlaceholderConfigurer">     <property name="ignoreUnresolvablePlaceholders" value="false"/>     <property name="order" value="2"/>     <property name="nameColumn" value="name"/>     <property name="valueColumn" value="value"/>     <property name="propertiesTable" value="my_properties_table"/>     <property name="jdbcTemplate" ref="configurationJdbcTemplate"/> <!-- Supplied in a parent context -->   </bean> 

This would allow the follow to occur in the Spring configuration

<!-- Read from application.properties --> <property name="username">${username}</property>   ... <!-- Read in from JDBC as part of second pass after all $'s have been fulfilled --> <property name="central-thing">#{name.key.in.db}</property>  

3) Of course, if you're in a web application container then you just use JNDI. But you're not so you can't.

Hope this helps!

Answer 2

You could use <context:property-placeholder location="classpath:${target_env}configuration.properties" /> in your Spring XML and configure ${target_env} using a command-line argument (-Dtarget_env=test.).

Starting in Spring 3.1 you could use <context:property-placeholder location="classpath:${target_env:prod.}configuration.properties" /> and specify a default value, thereby eliminating the need to set the value on the command-line.

In case Maven IS an option, the Spring variable could be set during plugin execution, e.g. during test or integration test execution.

<plugin>     <groupId>org.apache.maven.plugins</groupId>     <artifactId>maven-surefire-plugin</artifactId>     <version>2.12</version>     <configuration>         <systemPropertyVariables>             <target_env>test.</target_env>         </systemPropertyVariables>     </configuration> </plugin> 

I assume different Maven profiles would also work.