------
 Filtering
 ------
 Franz Allan See
 ------
 July 2006
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Filtering

 Variables can be included in your resources. These variables, denoted by the
 $\{...\} delimiters, can come from the System properties, your project
 properties, from your filter resources and from the command lines.

 For example, if we have a resource src/main/resources/hello.txt containing

+-----+
Hello ${name}
+-----+

 And a pom like this

+-----+
<project>
  [...]
  <name>My Resources Plugin Practice Project</name>
  [...]
  <build>
    [...]
    <resources>
      [...]
      <resource>
        <directory>src/main/resources</directory>
      </resource>
      [...]
    </resources>
  [...]
  </build>
  [...]
</project>
+-----+

 Upon calling

+-----+
mvn resources:resources
+-----+

 This will create a resource output in target/class/hello.txt which contains
 exactly the same.

+-----+
Hello ${name}
+-----+

 However, if we add a filtering tag to our pom and set it to true such as this

+-----+
      [...]
      <resource>
        <directory>src/main/resources</directory>
        <filtering>true</filtering>
      </resource>
      [...]
+-----+

 Our target/class/hello.txt after calling

+-----+
mvn resources:resources
+-----+

 would be

+-----+
Hello My Resources Plugin Practice Project
+-----+

 That's because the name variable was replaced by the value of the project's
 name (which was specified
 in the pom).

 Moreover, we can also assign values through the command line using the "-D"
 tag. For example, to change the value for the variable name to "world", we can
 simply invoke this command

+-----+
mvn resources:resources -Dname="world"
+-----+

 And the output in target/class/hello.txt would be

+-----+
Hello world
+-----+

 Furthermore, we are not limited to use pre-defined project variables. We can
 specify our own variables and their values under the properties tag. For
 example, if we want to change the variable from "name" to "your.name", we can
 do so by adding a "your.name" tag under the "properties" tag.

+-----+
<project>
  [...]
  <properties>
    <your.name>world</your.name>
  </properties>
  [...]
</project>
+-----+

 But to organize your project, you may want to put all your variables and their
 values on a separate file so that you will not have to rewrite your pom, or set
 their values all the time with every build. This can be done by adding a
 filter.

+-----+
<project>
  [...]
  <name>My Resources Plugin Practice Project</name>
  [...]
  <build>
    [...]
    <filters>
      <filter> [a filter property] </filter>
    </filters>
    [...]
  [...]
  </build>
  [...]
</project>
+-----+

 For example, we can separate "your.name" from pom by specifying a filter, "my
 filter values.properties" containing

+-----+
your.name = world
+-----+

 and adding that to our pom

+-----+
    [...]
    <filters>
      <filter>my filter values.properties</filter>
    </filters>
    [...]
+-----+