Need help in running a custom check in checkstyle

Question

I want to run a simple custom check implemented in checkstyle on a java program samples/Test.java. And I came across the below error.

com.puppycrawl.tools.checkstyle.api.CheckstyleException: cannot initialize module TreeWalker - Unable to instantiate 'com.checkstyle.checks.IllegalExceptionThrowsCheck' class, it is also not possible to instantiate it as null.

Pardon me, even though the error makes sense, I couldn't make any progress on fixing it. I have posted the complete error at the end of the post. Below is the implementation of the custom check. IllegalExceptionThrowsCheck.java

package com.checkstyle.checks;

import java.util.Arrays;
import java.util.List;

import com.puppycrawl.tools.checkstyle.api.Check;
import com.puppycrawl.tools.checkstyle.api.DetailAST;
import com.puppycrawl.tools.checkstyle.api.TokenTypes;

public final class IllegalExceptionThrowsCheck extends Check {

    List<String> illegalExceptionThrows;

    /** {@inheritDoc} */
    public int[] getDefaultTokens() {
       return new int[] { TokenTypes.LITERAL_THROWS };
    }

    /** {@inheritDoc} */
    public int[] getRequiredTokens() {
       return getDefaultTokens();
    }

    /** {@inheritDoc} */
   public void visitToken(DetailAST aDetailAST) {
      DetailAST identDetailAST = aDetailAST.findFirstToken(TokenTypes.IDENT);
      if (identDetailAST == null) {
         return;
      }
      if (illegalExceptionThrows.contains(identDetailAST.getText())) {
           log(aDetailAST, "Illegal Throws Clause  -> "
                + identDetailAST.getText());
      }
  }

  public void setIllegalExceptionThrows(String illegalExceptionThrowsStr) {
      this.illegalExceptionThrows =   Arrays.asList(illegalExceptionThrowsStr
            .split(","));
   }
}

And the checkstyle configuration is custom-checkstyle.xml

   <?xml version="1.0" encoding="UTF-8"?>
   <!DOCTYPE module PUBLIC "-//Puppy Crawl//DTD Check Configuration 1.2//EN" "http://www.puppycrawl.com/dtds/configuration_1_2.dtd">
   <module name="Checker">
       <property name="severity" value="error" />
       <module name="TreeWalker">
        <property name="severity" value="error" />
        <module name="com.checkstyle.checks.IllegalExceptionThrowsCheck">
            <property name="severity" value="error" />
            <property name="illegalExceptionThrows" value="Exception" />
        </module>
       </module>
   </module>

The package structure is

Project
 |
 |->src
 |   |
 |   |->com
 |      |
 |      |->checkstyle
 |            |
 |            |-> checks
 |                  |
 |                  |-> IllegalExceptionThrowsCheck.java
 |
 |
 |-> lib
 |   |
 |   |->checkstyle-8.10.1-all.jar
 |
 |
 |-> Samples
       |
       | -> Test.java

The command I ran to execute the check on java program was

java -jar lib/checkstyle-8.10.1-all.jar com.puppycrawl.tools.checkstyle.Main -c custom_check.xml samples/Test.java

Any comments would be greatly helpful.

APPENDIX

Complete error log

com.puppycrawl.tools.checkstyle.api.CheckstyleException: cannot initialize module TreeWalker - Unable to instantiate 'com.checkstyle.checks.IllegalExceptionThrowsCheck' class, it is also not possible to instantiate it as null. Please recheck that class name is specified as canonical name or read how to configure short name usage http://checkstyle.sourceforge.net/config.html#Packages. Please also recheck that provided ClassLoader to Checker is configured correctly. at com.puppycrawl.tools.checkstyle.Checker.setupChild(Checker.java:460) at com.puppycrawl.tools.checkstyle.api.AutomaticBean.configure(AutomaticBean.java:198) at com.puppycrawl.tools.checkstyle.Main.runCheckstyle(Main.java:550) at com.puppycrawl.tools.checkstyle.Main.runCli(Main.java:465) at com.puppycrawl.tools.checkstyle.Main.main(Main.java:219) Caused by: com.puppycrawl.tools.checkstyle.api.CheckstyleException: Unable to instantiate 'com.checkstyle.checks.IllegalExceptionThrowsCheck' class, it is also not possible to instantiate it as null. Please recheck that class name is specified as canonical name or read how to configure short name usage http://checkstyle.sourceforge.net/config.html#Packages. Please also recheck that provided ClassLoader to Checker is configured correctly. at com.puppycrawl.tools.checkstyle.PackageObjectFactory.createModule(PackageObjectFactory.java:208) at com.puppycrawl.tools.checkstyle.TreeWalker.setupChild(TreeWalker.java:151) at com.puppycrawl.tools.checkstyle.api.AutomaticBean.configure(AutomaticBean.java:198) at com.puppycrawl.tools.checkstyle.Checker.setupChild(Checker.java:455) ... 4 more Checkstyle ends with 1 errors.

rveach · Accepted Answer · 2018-06-04 04:03:31Z

class IllegalExceptionThrowsCheck extends Check {

First, the base class is no longer Check. It is AbstractCheck. Check was removed a while ago, and you CLI command says you are using 8.10.1, so I don't know how you got this to check to compile with a non-existent base class Check.

java -jar lib/checkstyle-8.10.1-all.jar com.puppycrawl.tools.checkstyle.Main -c custom_check.xml samples/Test.java

Second, since your not mentioning your project/jar in this command line, checkstyle will never find your class. You are telling the JVM only about checkstyle-8.10.1-all.jar and not about your project and it's class files.

I recommend packaging your project into a jar and then include that in your command line. Example: java -classpath MyCustom.jar;checkstyle-8.10.1-all.jar com.puppycrawl.tools.checkstyle.Main -c config.xml Check.java
http://checkstyle.sourceforge.net/cmdline.html#Usage_by_Classpath_update

Third, you can change your setter to:

public void setIllegalExceptionThrows(String... illegalExceptionThrowsStr) {
    this.illegalExceptionThrows = Arrays.asList(illegalExceptionThrowsStr);
}

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