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  1. JDK
  2. JDK-8292872

MatchResult should provide values of named-capturing groups

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Details

    • CSR
    • Resolution: Approved
    • P4
    • 20
    • core-libs
    • None
    • minimal
    • Pattern.namedGroups() is currently package private. Making it public requires renaming the current implementation to something else for the current internal purposes.
    • Java API
    • SE

    Description

      Summary

      java.util.regex.MatchResult lacks the ability to use group names rather than group numbers to query the result. This proposal aims to add start(String), end(String) and group(String) for that. In addition, it adds namedGroups() to obtain a mapping from group names to group numbers, as well as hasMatch() to query whether a match was successful.

      java.util.regex.Pattern also adds a public namedGroups().

      Problem

      Interface java.util.regex.MatchResult currently offers a way to query the result details by using group numbers. But a regex pattern can specify named capturing groups as well.

      While java.util.regex.Matcher exposes methods start(String), end(String) and group(String) that accept group names, the superinterface java.util.regex.MatchResult does not.

      Solution

      Default methods start(String), end(String) and group(String) are added to java.util.regex.MatchResult. They rely on the presence of default method namedGroups(), which must be overridden to return a mapping from group names to the corresponding group number.

      In addition, the interface add a hasMatch(), which must be overridden to return whether a previous match operation was successful.

      The implementation of namedGroups() in class java.util.regex.Matcher also relies on the additional, equally named method in class java.util.regex.Pattern.

      Specification

           package java.util.regex;
      
          + * @implNote
          + * Support for named groups is implemented by the default methods
          + * {@link #start(String)}, {@link #end(String)} and {@link #group(String)}.
          + * They all make use of the map returned by {@link #namedGroups()}, whose
          + * default implementation simply throws {@link UnsupportedOperationException}.
          + * It is thus sufficient to override {@link #namedGroups()} for these methods
          + * to work. However, overriding them directly might be preferable for
          + * performance or other reasons.
          + *
            * @author  Michael McCloskey
            * @see Matcher
            * @since 1.5
            */
           public interface MatchResult
      
      
      
          +    /**
          +     * Returns the start index of the subsequence captured by the given
          +     * <a href="Pattern.html#groupname">named-capturing group</a> during the
          +     * previous match operation.
          +     *
          +     * @param  name
          +     *         The name of a named-capturing group in this matcher's pattern
          +     *
          +     * @return  The index of the first character captured by the group,
          +     *          or {@code -1} if the match was successful but the group
          +     *          itself did not match anything
          +     *
          +     * @throws  IllegalStateException
          +     *          If no match has yet been attempted,
          +     *          or if the previous match operation failed
          +     *
          +     * @throws  IllegalArgumentException
          +     *          If there is no capturing group in the pattern
          +     *          with the given name
          +     *
          +     * @implSpec
          +     * The default implementation of this method invokes {@link #namedGroups()}
          +     * to obtain the group number from the {@code name} argument, and uses it
          +     * as argument to an invocation of {@link #start(int)}.
          +     *
          +     * @since 20
          +     */
          +    default int start(String name) {
      
      
      
          +    /**
          +     * Returns the offset after the last character of the subsequence
          +     * captured by the given <a href="Pattern.html#groupname">named-capturing
          +     * group</a> during the previous match operation.
          +     *
          +     * @param  name
          +     *         The name of a named-capturing group in this matcher's pattern
          +     *
          +     * @return  The offset after the last character captured by the group,
          +     *          or {@code -1} if the match was successful
          +     *          but the group itself did not match anything
          +     *
          +     * @throws  IllegalStateException
          +     *          If no match has yet been attempted,
          +     *          or if the previous match operation failed
          +     *
          +     * @throws  IllegalArgumentException
          +     *          If there is no capturing group in the pattern
          +     *          with the given name
          +     *
          +     * @implSpec
          +     * The default implementation of this method invokes {@link #namedGroups()}
          +     * to obtain the group number from the {@code name} argument, and uses it
          +     * as argument to an invocation of {@link #end(int)}.
          +     *
          +     * @since 20
          +     */
          +    default int end(String name) {
      
      
      
          +    /**
          +     * Returns the input subsequence captured by the given
          +     * <a href="Pattern.html#groupname">named-capturing group</a> during the
          +     * previous match operation.
          +     *
          +     * <p> If the match was successful but the group specified failed to match
          +     * any part of the input sequence, then {@code null} is returned. Note
          +     * that some groups, for example {@code (a*)}, match the empty string.
          +     * This method will return the empty string when such a group successfully
          +     * matches the empty string in the input.  </p>
          +     *
          +     * @param  name
          +     *         The name of a named-capturing group in this matcher's pattern
          +     *
          +     * @return  The (possibly empty) subsequence captured by the named group
          +     *          during the previous match, or {@code null} if the group
          +     *          failed to match part of the input
          +     *
          +     * @throws  IllegalStateException
          +     *          If no match has yet been attempted,
          +     *          or if the previous match operation failed
          +     *
          +     * @throws  IllegalArgumentException
          +     *          If there is no capturing group in the pattern
          +     *          with the given name
          +     *
          +     * @implSpec
          +     * The default implementation of this method invokes {@link #namedGroups()}
          +     * to obtain the group number from the {@code name} argument, and uses it
          +     * as argument to an invocation of {@link #group(int)}.
          +     *
          +     * @since 20
          +     */
          +    default String group(String name) {
      
      
      
          +    /**
          +     * Returns an unmodifiable map from capturing group names to group numbers.
          +     * If there are no named groups, returns an empty map.
          +     *
          +     * @return an unmodifiable map from capturing group names to group numbers
          +     *
          +     * @throws UnsupportedOperationException if the implementation does not
          +     *          support named groups.
          +     *
          +     * @implSpec The default implementation of this method always throws
          +     *          {@link UnsupportedOperationException}
          +     *
          +     * @apiNote
          +     * This method must be overridden by an implementation that supports
          +     * named groups.
          +     *
          +     * @since 20
          +     */
          +    default Map<String,Integer> namedGroups() {
      
      
      
          +    /**
          +     * Returns whether {@code this} contains a valid match from
          +     * a previous match or find operation.
          +     *
          +     * @return whether {@code this} contains a valid match
          +     *
          +     * @throws UnsupportedOperationException if the implementation cannot report
          +     *          whether it has a match
          +     *
          +     * @implSpec The default implementation of this method always throws
          +     *          {@link UnsupportedOperationException}
          +     *
          +     * @since 20
          +     */
          +    default boolean hasMatch() {
          package java.util.regex;
          public final class Matcher implements MatchResult
      
      
      
          +    /**
          +     * {@inheritDoc}
          +     *
          +     * @return {@inheritDoc}
          +     *
          +     * @since {@inheritDoc}
          +     */
          +    @Override
          +    public Map<String, Integer> namedGroups() {
      
      
      
          +    /**
          +     * {@inheritDoc}
          +     *
          +     * @return {@inheritDoc}
          +     *
          +     * @since {@inheritDoc}
          +     */
          +    @Override
          +    public boolean hasMatch() {
      
          package java.util.regex;
          public final class Pattern
      
      
      
          +    /**
          +     * Returns an unmodifiable map from capturing group names to group numbers.
          +     * If there are no named groups, returns an empty map.
          +     *
          +     * @return an unmodifiable map from capturing group names to group numbers
          +     *
          +     * @since 20
          +     */
          +    public Map<String, Integer> namedGroups() {

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              rgiulietti Raffaello Giulietti
              webbuggrp Webbug Group
              Stuart Marks
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                Created:
                Updated:
                Resolved: