Class EmptyCatchBlockCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable

    public class EmptyCatchBlockCheck
    extends AbstractCheck

    Checks for empty catch blocks. By default check allows empty catch block with any comment inside.

    There are two options to make validation more precise: exceptionVariableName and commentFormat. If both options are specified - they are applied by any of them is matching.

    • Property exceptionVariableName - Specify the RegExp for the name of the variable associated with exception. If check meets variable name matching specified value - empty block is suppressed. Type is java.util.regex.Pattern. Default value is "^$".
    • Property commentFormat - Specify the RegExp for the first comment inside empty catch block. If check meets comment inside empty catch block matching specified format - empty block is suppressed. If it is multi-line comment - only its first line is analyzed. Type is java.util.regex.Pattern. Default value is ".*".

    To configure the check:

     <module name="EmptyCatchBlock"/>
     

    Example:

     try {
       throw new RuntimeException();
     } catch (RuntimeException expected) {
     } // violation
    
     try {
       throw new RuntimeException();
     } catch (RuntimeException ignore) {
       // no handling
     } // ok, catch block has comment
    
     try {
       throw new RuntimeException();
     } catch (RuntimeException o) {
     } // violation
    
     try {
       throw new RuntimeException();
     } catch (RuntimeException ex) {
       // This is expected
     } // ok
     

    To configure the check to suppress empty catch block if exception's variable name is expected or ignore or there's any comment inside:

     <module name="EmptyCatchBlock">
       <property name="exceptionVariableName" value="expected|ignore"/>
     </module>
     

    Such empty blocks would be both suppressed:

     try {
       throw new RuntimeException();
     } catch (RuntimeException expected) {
     } // ok
    
     try {
       throw new RuntimeException();
     } catch (RuntimeException ignore) {
       // no handling
     } // ok
    
     try {
       throw new RuntimeException();
     } catch (RuntimeException o) {
     } // violation
    
     try {
       throw new RuntimeException();
     } catch (RuntimeException ex) {
       // This is expected
     } // ok
     

    To configure the check to suppress empty catch block if single-line comment inside is "//This is expected":

     <module name="EmptyCatchBlock">
       <property name="commentFormat" value="This is expected"/>
     </module>
     

    Such empty block would be suppressed:

     try {
       throw new RuntimeException();
     } catch (RuntimeException expected) {
     } // violation
    
     try {
       throw new RuntimeException();
     } catch (RuntimeException ignore) {
       // no handling
     } // violation
    
     try {
       throw new RuntimeException();
     } catch (RuntimeException o) {
     } // violation
    
     try {
       throw new RuntimeException();
     } catch (RuntimeException ex) {
       // This is expected
     } // ok
     

    To configure the check to suppress empty catch block if single-line comment inside is "//This is expected" or exception's variable name is "myException" (any option is matching):

     <module name="EmptyCatchBlock">
       <property name="commentFormat" value="This is expected"/>
       <property name="exceptionVariableName" value="myException"/>
     </module>
     

    Such empty blocks would be suppressed:

     try {
       throw new RuntimeException();
     } catch (RuntimeException e) {
       //This is expected
     }
     ...
     try {
       throw new RuntimeException();
     } catch (RuntimeException e) {
       //   This is expected
     }
     ...
     try {
       throw new RuntimeException();
     } catch (RuntimeException e) {
       // This is expected
       // some another comment
     }
     ...
     try {
       throw new RuntimeException();
     } catch (RuntimeException e) {
       /* This is expected */
     }
     ...
     try {
       throw new RuntimeException();
     } catch (RuntimeException e) {
       /*
       *
       * This is expected
       * some another comment
       */
     }
     ...
     try {
       throw new RuntimeException();
     } catch (RuntimeException myException) {
    
     }
     

    Parent is com.puppycrawl.tools.checkstyle.TreeWalker

    Violation Message Keys:

    • catch.block.empty
    Since:
    6.4
    • Field Detail

      • exceptionVariableName

        private Pattern exceptionVariableName
        Specify the RegExp for the name of the variable associated with exception. If check meets variable name matching specified value - empty block is suppressed.
      • commentFormat

        private Pattern commentFormat
        Specify the RegExp for the first comment inside empty catch block. If check meets comment inside empty catch block matching specified format - empty block is suppressed. If it is multi-line comment - only its first line is analyzed.
    • Method Detail

      • setExceptionVariableName

        public void setExceptionVariableName​(Pattern exceptionVariablePattern)
        Setter to specify the RegExp for the name of the variable associated with exception. If check meets variable name matching specified value - empty block is suppressed.
        Parameters:
        exceptionVariablePattern - pattern of exception's variable name.
      • setCommentFormat

        public void setCommentFormat​(Pattern commentPattern)
        Setter to specify the RegExp for the first comment inside empty catch block. If check meets comment inside empty catch block matching specified format - empty block is suppressed. If it is multi-line comment - only its first line is analyzed.
        Parameters:
        commentPattern - pattern of comment.
      • getAcceptableTokens

        public int[] getAcceptableTokens()
        Description copied from class: AbstractCheck
        The configurable token set. Used to protect Checks against malicious users who specify an unacceptable token set in the configuration file. The default implementation returns the check's default tokens.
        Specified by:
        getAcceptableTokens in class AbstractCheck
        Returns:
        the token set this check is designed for.
        See Also:
        TokenTypes
      • visitCatchBlock

        private void visitCatchBlock​(DetailAST catchAst)
        Visits catch ast node, if it is empty catch block - checks it according to Check's options. If exception's variable name or comment inside block are matching specified regexp - skips from consideration, else - puts violation.
        Parameters:
        catchAst - LITERAL_CATCH
      • getCommentFirstLine

        private static String getCommentFirstLine​(DetailAST catchAst)
        Gets the first line of comment in catch block. If comment is single-line - returns it fully, else if comment is multi-line - returns the first line.
        Parameters:
        catchAst - LITERAL_CATCH
        Returns:
        the first line of comment in catch block, "" if no comment was found.
      • isVerifiable

        private boolean isVerifiable​(DetailAST emptyCatchAst,
                                     String commentContent)
        Checks if current empty catch block is verifiable according to Check's options (exception's variable name and comment format are both in consideration).
        Parameters:
        emptyCatchAst - empty catch LITERAL_CATCH block.
        commentContent - text of comment.
        Returns:
        true if empty catch block is verifiable by Check.
      • isEmptyCatchBlock

        private static boolean isEmptyCatchBlock​(DetailAST catchAst)
        Checks if catch block is empty or contains only comments.
        Parameters:
        catchAst - LITERAL_CATCH
        Returns:
        true if catch block is empty.