jLuger.de - Replace connection properties in persistence.xml with ant

When developing a JPA based application you may want to have different database settings for unit testing and production. The easy way is to have two persistence.xml files and let the ant task select which one to copy to your build artifacts. This approach gets very painful in the long run. You always have to remember to make changes in both files. And when you require a third connection you need to maintain three files. Wouldn't it be better when there is one persistence.xml and the different parts are in templates? Well I think so and the good news is that you can do this completely with ant.

It's pretty easy. You just load the template file in a property and then use a replace task to replace the connection settings. See the following code:
<loadfile property="test_connection_properties" srcFile="${template_dir}/test_connection.template"/>
<replaceregexp file="${build_dir}/META_INF/persistence.xml"
    match="&lt;properties&gt;.*&lt;/properties&gt;"
    replace="${test_connection_properties}"
    byline="false"
    flags="gs"
/>

The code in detail:

• loadfile reads the file with the new connection settings into a property. That's needed because I haven't found a way to tell replaceregexp to use a whole file as replace token.
• replaceregexp is an optional task. Since jdk 1.4 there is no need to install additional libraries as the jdk has a regexp library.
• The file which is operated on is in the build dir. Don't take the file from the source directory.
• < and > need to be masked as &lt; and &gt; because as an ant file is xml and xml doesn't allow this characters out of CDDATA in attributes. But despite this it will recognize <properties> and </properties>
• .* is java regexp and means any character zero or more times.
• The value of flags are from the net. I have to admit that I don't know what they are triggering but without them it won't work. From the tool sed I know that g is for globally and s for substitution but I doubt that they have the same meaning here.