Content

Localization Support

Checkstyle supports localization of the output messages. If your language is not supported, please consider translating the messages in the messages.properties file. Please let us know if you translate the file.

Enable External DTD load

The property checkstyle.enableExternalDtdLoad defines ability use custom DTD files in config and load them from some location. The property type is boolean and defaults to false. Disabled by default due to security concerns.

Examples

The following is an example of include xml files content in xml by ENTITY feature to let keep common part of configs in single file and composite main config by few smaller parts.
Imagine we want to define for test sources a bit different requirements than for main code.

Common part checkstyle-common.xml: 

<module name="FileLength">
  <property name="max" value="1"/>
</module>

Main config checkstyle.xml: 

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
          "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
          "https://checkstyle.org/dtds/configuration_1_3.dtd" [
    <!ENTITY common SYSTEM "checkstyle-common.xml">
]>
<module name="Checker">

    &common;

    <module name="TreeWalker">
        <module name="MemberName">
            <property name="format" value="^[a-z][a-zA-Z]+$"/>
        </module>
    </module>

</module>

Test config checkstyle-test.xml: 

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
          "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
          "https://checkstyle.org/dtds/configuration_1_3.dtd" [
    <!ENTITY common SYSTEM "checkstyle-common.xml">
]>
<module name="Checker">

    &common;

    <module name="TreeWalker">
        <module name="MemberName">
            <property name="format" value="_[a-z]"/>
        </module>
    </module>

</module>

Target file for validation Test.java: 

class Test {
  int i = 0;
}

Example of execution for checkstyle.xml. Violation from Check of common.xml is expected, validation of field name is done by main code rules: 

$ java -Dcheckstyle.enableExternalDtdLoad=true -classpath checkstyle-XX.X-all.jar \
        com.puppycrawl.tools.checkstyle.Main -c checkstyle.xml Test.java
Starting audit...
[ERROR] Test.java:1: File length is 3 lines (max allowed is 1). [FileLength]
[ERROR] Test.java:2:7: 'i' must match pattern '^[a-z][a-zA-Z]+$'. [MemberName]
Audit done.
Checkstyle ends with 2 errors.

Example of execution for checkstyle-test.xml. Violation from Check of common.xml is expected, validation of field name is done by test code rules: 

$ java -Dcheckstyle.enableExternalDtdLoad=true -classpath checkstyle-XX.X-all.jar \
          com.puppycrawl.tools.checkstyle.Main -c checkstyle-test.xml Test.java
Starting audit...
[ERROR] Test.java:1: File length is 3 lines (max allowed is 1). [FileLength]
[ERROR] Test.java:2:7: 'i' must match pattern '_[a-z]'. [MemberName]
Audit done.
Checkstyle ends with 2 errors.

Property chaining support

Checkstyle supports property expansion within property definitions, also known as property chaining. This feature allows you to define properties using other properties. For example: 

checkstyle.dir=/home/user/checkstyle
config.dir=configs
checkstyle.suppressions.file=${checkstyle.dir}/${config.dir}/suppressions.xml
You can then use ${checkstyle.suppressions.file} in your checkstyle configuration, which will resolve to /home/user/checkstyle/configs/suppressions.xml.

Notes

Note that property variable expression must be of the form ${expression}.

It is not necessary to define chained properties sequentially.