Eclipse – Checkstyle – Exclude folder

The quick and dirty way:

Right click on a folder, go to properties, and mark a folder as derived. Derived entities are excluded from searching by default. The problem with this approach is that Eclipse "forgets" that the folder is derived if you delete it (either from within Eclipse or externally, followed by refreshing the project tree). Like so often with Eclipse, this is a long-standing bug (10 years in this case) which still applies to the current version (4.6 Neon at the time of writing).

The safe way:

Create a working set including only those entities you want searched and search only within that working set. See Dave Ray's answer for details on this procedure.

Check out the use of the supressionCommentFilter at http://checkstyle.sourceforge.net/config_filters.html#SuppressionCommentFilter. You'll need to add the module to your checkstyle.xml

<module name="SuppressionCommentFilter"/>

and it's configurable. Thus you can add comments to your code to turn off checkstyle (at various levels) and then back on again through the use of comments in your code. E.g.

//CHECKSTYLE:OFF
public void someMethod(String arg1, String arg2, String arg3, String arg4) {
//CHECKSTYLE:ON

Or even better, use this more tweaked version:

<module name="SuppressionCommentFilter">
    <property name="offCommentFormat" value="CHECKSTYLE.OFF\: ([\w\|]+)"/>
    <property name="onCommentFormat" value="CHECKSTYLE.ON\: ([\w\|]+)"/>
    <property name="checkFormat" value="$1"/>
</module>

which allows you to turn off specific checks for specific lines of code:

//CHECKSTYLE.OFF: IllegalCatch - Much more readable than catching 7 exceptions
catch (Exception e)
//CHECKSTYLE.ON: IllegalCatch

*Note: you'll also have to add the FileContentsHolder:

<module name="FileContentsHolder"/>

See also

<module name="SuppressionFilter">
    <property name="file" value="docs/suppressions.xml"/>
</module>

under the SuppressionFilter section on that same page, which allows you to turn off individual checks for pattern matched resources.

So, if you have in your checkstyle.xml:

<module name="ParameterNumber">
   <property name="id" value="maxParameterNumber"/>
   <property name="max" value="3"/>
   <property name="tokens" value="METHOD_DEF"/>
</module>

You can turn it off in your suppression xml file with:

<suppress id="maxParameterNumber" files="YourCode.java"/>

Another method, now available in Checkstyle 5.7 is to suppress violations via the @SuppressWarnings java annotation. To do this, you will need to add two new modules (SuppressWarningsFilter and SuppressWarningsHolder) in your configuration file:

<module name="Checker">
   ...
   <module name="SuppressWarningsFilter" />
   <module name="TreeWalker">
       ...
       <module name="SuppressWarningsHolder" />
   </module>
</module> 

Then, within your code you can do the following:

@SuppressWarnings("checkstyle:methodlength")
public void someLongMethod() throws Exception {

or, for multiple suppressions:

@SuppressWarnings({"checkstyle:executablestatementcount", "checkstyle:methodlength"})
public void someLongMethod() throws Exception {

NB: The "checkstyle:" prefix is optional (but recommended). According to the docs the parameter name have to be in all lowercase, but practice indicates any case works.