checkstyle

checkstyle documentation

Version in MegaLinter: 10.3
Visit Official Web Site
See How to configure checkstyle rules
- If custom sun_checks.xml config file is not found, sun_checks.xml will be used
See How to disable checkstyle rules in files
See Index of problems detected by checkstyle

Configuration in MegaLinter

Enable checkstyle by adding JAVA_CHECKSTYLE in ENABLE_LINTERS variable
Disable checkstyle by adding JAVA_CHECKSTYLE in DISABLE_LINTERS variable

Variable	Description	Default value
JAVA_CHECKSTYLE_ARGUMENTS	User custom arguments to add in linter CLI call Ex: `-s --foo "bar"`
JAVA_CHECKSTYLE_FILTER_REGEX_INCLUDE	Custom regex including filter Ex: `(src\\|lib)`	Include every file
JAVA_CHECKSTYLE_FILTER_REGEX_EXCLUDE	Custom regex excluding filter Ex: `(test\\|examples)`	Exclude no file
JAVA_CHECKSTYLE_CLI_LINT_MODE	Override default CLI lint mode - `file`: Calls the linter for each file - `list_of_files`: Call the linter with the list of files as argument - `project`: Call the linter from the root of the project	`file`
JAVA_CHECKSTYLE_FILE_EXTENSIONS	Allowed file extensions. `"*"` matches any extension, `""` matches empty extension. Empty list excludes all files Ex: `[".py", ""]`	`[".java"]`
JAVA_CHECKSTYLE_FILE_NAMES_REGEX	File name regex filters. Regular expression list for filtering files by their base names using regex full match. Empty list includes all files Ex: `["Dockerfile(-.+)?", "Jenkinsfile"]`	Include every file
JAVA_CHECKSTYLE_PRE_COMMANDS	List of bash commands to run before the linter	None
JAVA_CHECKSTYLE_POST_COMMANDS	List of bash commands to run after the linter	None
JAVA_CHECKSTYLE_CONFIG_FILE	checkstyle configuration file name Use `LINTER_DEFAULT` to let the linter find it	`sun_checks.xml`
JAVA_CHECKSTYLE_RULES_PATH	Path where to find linter configuration file	Workspace folder, then MegaLinter default rules
JAVA_CHECKSTYLE_DISABLE_ERRORS	Run linter but consider errors as warnings	`false`
JAVA_CHECKSTYLE_DISABLE_ERRORS_IF_LESS_THAN	Maximum number of errors allowed	`0`

IDE Integration

Use checkstyle in your favorite IDE to catch errors before MegaLinter !

IDE	Extension Name	Install
Eclipse	eclipse-cs	Visit Web Site
IDEA	checkstyle-idea
Visual Studio Code	vscode-checkstyle

MegaLinter Flavours

This linter is available in the following flavours

	Flavor	Description	Embedded linters	Info
	all	Default MegaLinter Flavor	97
	java	Optimized for JAVA based projects	43

Behind the scenes

How are identified applicable files

File extensions: .java

How the linting is performed

checkstyle is called one time by identified file

Example calls

java -jar /usr/bin/checkstyle myfile.java

java -jar /usr/bin/checkstyle -c sun_checks.xml myfile.java

Help content

Usage: java [options] <mainclass> [args...]
           (to execute a class)
   or  java [options] -jar <jarfile> [args...]
           (to execute a jar file)
   or  java [options] -m <module>[/<mainclass>] [args...]
       java [options] --module <module>[/<mainclass>] [args...]
           (to execute the main class in a module)
   or  java [options] <sourcefile> [args]
           (to execute a single source-file program)

 Arguments following the main class, source file, -jar <jarfile>,
 -m or --module <module>/<mainclass> are passed as the arguments to
 main class.

 where options include:

    -cp <class search path of directories and zip/jar files>
    -classpath <class search path of directories and zip/jar files>
    --class-path <class search path of directories and zip/jar files>
                  A : separated list of directories, JAR archives,
                  and ZIP archives to search for class files.
    -p <module path>
    --module-path <module path>...
                  A : separated list of directories, each directory
                  is a directory of modules.
    --upgrade-module-path <module path>...
                  A : separated list of directories, each directory
                  is a directory of modules that replace upgradeable
                  modules in the runtime image
    --add-modules <module name>[,<module name>...]
                  root modules to resolve in addition to the initial module.
                  <module name> can also be ALL-DEFAULT, ALL-SYSTEM,
                  ALL-MODULE-PATH.
    --list-modules
                  list observable modules and exit
    -d <module name>
    --describe-module <module name>
                  describe a module and exit
    --dry-run     create VM and load main class but do not execute main method.
                  The --dry-run option may be useful for validating the
                  command-line options such as the module system configuration.
    --validate-modules
                  validate all modules and exit
                  The --validate-modules option may be useful for finding
                  conflicts and other errors with modules on the module path.
    -D<name>=<value>
                  set a system property
    -verbose:[class|module|gc|jni]
                  enable verbose output
    -version      print product version to the error stream and exit
    --version     print product version to the output stream and exit
    -showversion  print product version to the error stream and continue
    --show-version
                  print product version to the output stream and continue
    --show-module-resolution
                  show module resolution output during startup
    -? -h -help
                  print this help message to the error stream
    --help        print this help message to the output stream
    -X            print help on extra options to the error stream
    --help-extra  print help on extra options to the output stream
    -ea[:<packagename>...|:<classname>]
    -enableassertions[:<packagename>...|:<classname>]
                  enable assertions with specified granularity
    -da[:<packagename>...|:<classname>]
    -disableassertions[:<packagename>...|:<classname>]
                  disable assertions with specified granularity
    -esa | -enablesystemassertions
                  enable system assertions
    -dsa | -disablesystemassertions
                  disable system assertions
    -agentlib:<libname>[=<options>]
                  load native agent library <libname>, e.g. -agentlib:jdwp
                  see also -agentlib:jdwp=help
    -agentpath:<pathname>[=<options>]
                  load native agent library by full pathname
    -javaagent:<jarpath>[=<options>]
                  load Java programming language agent, see java.lang.instrument
    -splash:<imagepath>
                  show splash screen with specified image
                  HiDPI scaled images are automatically supported and used
                  if available. The unscaled image filename, e.g. image.ext,
                  should always be passed as the argument to the -splash option.
                  The most appropriate scaled image provided will be picked up
                  automatically.
                  See the SplashScreen API documentation for more information
    @argument files
                  one or more argument files containing options
    -disable-@files
                  prevent further argument file expansion
    --enable-preview
                  allow classes to depend on preview features of this release
To specify an argument for a long option, you can use --<name>=<value> or
--<name> <value>.

Installation on mega-linter Docker image

Dockerfile commands :

# Parent descriptor install
ENV JAVA_HOME=/usr/lib/jvm/java-11-openjdk
ENV PATH="$JAVA_HOME/bin:${PATH}"
# Linter install
RUN CHECKSTYLE_LATEST=$(curl -s https://api.github.com/repos/checkstyle/checkstyle/releases/latest \
        | grep browser_download_url \
        | grep ".jar" \
        | cut -d '"' -f 4) \
    && curl --retry 5 --retry-delay 5 -sSL $CHECKSTYLE_LATEST \
        --output /usr/bin/checkstyle

Example success log

Results of checkstyle linter (version 8.38)
See documentation on https://megalinter.github.io/descriptors/java_checkstyle/
-----------------------------------------------

[SUCCESS] .automation/test/java/java_good_1.java
    Starting audit...
    Audit done.

Example error log

Results of checkstyle linter (version 8.38)
See documentation on https://megalinter.github.io/descriptors/java_checkstyle/
-----------------------------------------------

[ERROR] .automation/test/java/java_bad_1.java
    Starting audit...
    [ERROR] .automation/test/java/java_bad_1.java:1:1: Utility classes should not have a public or default constructor. [HideUtilityClassConstructor]
    [ERROR] .automation/test/java/java_bad_1.java:1:7: Name 'java_bad_1' must match pattern '^[A-Z][a-zA-Z0-9]*$'. [TypeName]
    [ERROR] .automation/test/java/java_bad_1.java:2:1: '{' at column 1 should be on the previous line. [LeftCurly]
    [ERROR] .automation/test/java/java_bad_1.java:4:29: Parameter args should be final. [FinalParameters]
    [ERROR] .automation/test/java/java_bad_1.java:4:40: Array brackets at illegal position. [ArrayTypeStyle]
    [ERROR] .automation/test/java/java_bad_1.java:5:5: '{' at column 5 should be on the previous line. [LeftCurly]
    Audit done.
    Checkstyle ends with 6 errors.