Package com.puppycrawl.tools.checkstyle.checks.coding

Class MatchXpathCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable
    public class MatchXpathCheck
extends AbstractCheck

    Evaluates Xpath query and report violation on all matching AST nodes. This check allows user to implement custom checks using Xpath. If Xpath query is not specified explicitly, then the check does nothing.

    It is recommended to define custom message for violation to explain what is not allowed and what to use instead, default message might be too abstract. To customize a message you need to add message element with matchxpath.match as key attribute and desired message as value attribute.

    Please read more about Xpath syntax at Xpath Syntax. Information regarding Xpath functions can be found at XSLT/XPath Reference. Note, that @text attribute can be used only with token types that are listed in XpathUtil.

    • Property query - Specify Xpath query. Type is java.lang.String. Default value is "".

    Checkstyle provides command line tool and GUI application with options to show AST and to ease usage of Xpath queries.

    -T option prints AST tree of the checked file.

     $ java -jar checkstyle-X.XX-all.jar -T Main.java
 CLASS_DEF -> CLASS_DEF [1:0]
 |--MODIFIERS -> MODIFIERS [1:0]
 |   `--LITERAL_PUBLIC -> public [1:0]
 |--LITERAL_CLASS -> class [1:7]
 |--IDENT -> Main [1:13]
 `--OBJBLOCK -> OBJBLOCK [1:18]
 |--LCURLY -> { [1:18]
 |--METHOD_DEF -> METHOD_DEF [2:4]
 |   |--MODIFIERS -> MODIFIERS [2:4]
 |   |   `--LITERAL_PUBLIC -> public [2:4]
 |   |--TYPE -> TYPE [2:11]
 |   |   `--IDENT -> String [2:11]
 |   |--IDENT -> sayHello [2:18]
 |   |--LPAREN -> ( [2:26]
 |   |--PARAMETERS -> PARAMETERS [2:27]
 |   |   `--PARAMETER_DEF -> PARAMETER_DEF [2:27]
 |   |       |--MODIFIERS -> MODIFIERS [2:27]
 |   |       |--TYPE -> TYPE [2:27]
 |   |       |   `--IDENT -> String [2:27]
 |   |       `--IDENT -> name [2:34]
 |   |--RPAREN -> ) [2:38]
 |   `--SLIST -> { [2:40]
 |       |--LITERAL_RETURN -> return [3:8]
 |       |   |--EXPR -> EXPR [3:25]
 |       |   |   `--PLUS -> + [3:25]
 |       |   |       |--STRING_LITERAL -> "Hello, " [3:15]
 |       |   |       `--IDENT -> name [3:27]
 |       |   `--SEMI -> ; [3:31]
 |       `--RCURLY -> } [4:4]
 `--RCURLY -> } [5:0]

    -b option shows AST nodes that match given Xpath query. This command can be used to validate accuracy of Xpath query against given file.

     $ java -jar checkstyle-X.XX-all.jar Main.java -b "//METHOD_DEF[./IDENT[@text='sayHello']]"
 CLASS_DEF -> CLASS_DEF [1:0]
 `--OBJBLOCK -> OBJBLOCK [1:18]
 |--METHOD_DEF -> METHOD_DEF [2:4]

    The following example demonstrates validation of methods order, so that public methods should come before the private ones: 

     <module name="MatchXpath">
  <property name="query" value="//METHOD_DEF[.//LITERAL_PRIVATE and
  following-sibling::METHOD_DEF[.//LITERAL_PUBLIC]]"/>
  <message key="matchxpath.match"
  value="Private methods must appear after public methods"/>
 </module>

    Example: 

     public class Test {
  public void method1() { }
  private void method2() { } // violation
  public void method3() { }
  private void method4() { } // violation
  public void method5() { }
  private void method6() { } // ok
 }

    To violate if there are any parametrized constructors 

     <module name="MatchXpath">
  <property name="query" value="//CTOR_DEF[count(./PARAMETERS/*) > 0]"/>
  <message key="matchxpath.match"
  value="Parameterized constructors are not allowed, there should be only default
  ctor"/>
 </module>

    Example: 

     public class Test {
  public Test(Object c) { } // violation
  public Test(int a, HashMap<String, Integer> b) { } // violation
  public Test() { } // ok
 }

    To violate if method name is 'test' or 'foo' 

     <module name="MatchXpath">
  <property name="query" value="//METHOD_DEF[./IDENT[@text='test' or @text='foo']]"/>
  <message key="matchxpath.match"
  value="Method name should not be 'test' or 'foo'"/>
 </module>

    Example: 

     public class Test {
  public void test() {} // violation
  public void getName() {} // ok
  public void foo() {} // violation
  public void sayHello() {} // ok
 }

    To violate if new instance creation was done without var type 

     <module name="MatchXpath">
  <property name="query" value="//VARIABLE_DEF[./ASSIGN/EXPR/LITERAL_NEW
  and not(./TYPE/IDENT[@text='var'])]"/>
  <message key="matchxpath.match"
  value="New instances should be created via 'var' keyword to avoid duplication of type
  reference in statement"/>
 </module>

    Example: 

     public class Test {
   public void foo() {
     SomeObject a = new SomeObject(); // violation
     var b = new SomeObject(); // OK
   }
 }

    Parent is com.puppycrawl.tools.checkstyle.TreeWalker

    Violation Message Keys:

    • matchxpath.match
    Since:
    8.39

    • Field Detail

      • MSG_KEY

        public static final java.lang.String MSG_KEY
        A key is pointing to the warning message text provided by user.
        See Also:
        Constant Field Values

      • query

        private java.lang.String query
        Specify Xpath query.

      • xpathExpression

        private net.sf.saxon.sxpath.XPathExpression xpathExpression
        Xpath expression.

    • Method Detail

      • setQuery

        public void setQuery​(java.lang.String query)
        Setter to specify Xpath query.
        Parameters:
        query - Xpath query.
        Throws:
        java.lang.IllegalStateException - if creation of xpath expression fails

      • 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

      • beginTree

        public void beginTree​(DetailAST rootAST)
        Description copied from class: AbstractCheck
        Called before the starting to process a tree. Ideal place to initialize information that is to be collected whilst processing a tree.
        Overrides:
        beginTree in class AbstractCheck
        Parameters:
        rootAST - the root of the tree

      • findMatchingNodesByXpathQuery

        private java.util.List<DetailAST> findMatchingNodesByXpathQuery​(DetailAST rootAST)
        Find nodes that match query.
        Parameters:
        rootAST - root node
        Returns:
        list of matching nodes
        Throws:
        java.lang.IllegalStateException - if evaluation of xpath query fails