------
 Filtering
 ------
 Franz Allan See
 ------
 2008-09-05
 ------

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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 line.

 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/classes/hello.txt>>> which contains
 exactly the same text.

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

 However, if we add a <<<\<filtering\>>>> tag to our POM and set it to <<<true>>> like this:

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

 Our <<<target/classes/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"
 option. 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/classes/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 in the <<<\<properties\>>>> element. For
 example, if we want to change the variable from "name" to "your.name", we can
 do so by adding a <<<\<your.name\>>>> element within the <<<\<properties\>>>> element.

+-----+
<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 in 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 the POM by specifying a filter file
 <<<my-filter-values.properties>>> containing:

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

 and adding that to our POM

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

  <<Warning:>> Do not filter files with binary content like images! This will most likely result in corrupt output. If
  you have both text files and binary files as resources, you need to declare two mutually exclusive resource sets. The
  first resource set defines the files to be filtered and the other resource set defines the files to copy
  unaltered as illustrated below:

+-----+
<project>
  ...
  <build>
    ...
    <resources>
      <resource>
        <directory>src/main/resources</directory>
        <filtering>true</filtering>
        <includes>
          <include>**/*.xml</include>
        </includes>
      </resource>
      <resource>
        <directory>src/main/resources</directory>
        <filtering>false</filtering>
        <excludes>
          <exclude>**/*.xml</exclude>
        </excludes>
      </resource>
      ...
    </resources>
    ...
  </build>
  ...
</project>
+-----+