/* * Copyright (C) 2007 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package java.util.regex; import java.io.IOException; import java.io.ObjectInputStream; import java.io.Serializable; /** * Patterns are compiled regular expressions. In many cases, convenience methods such as * {@link String#matches String.matches}, {@link String#replaceAll String.replaceAll} and * {@link String#split String.split} will be preferable, but if you need to do a lot of work * with the same regular expression, it may be more efficient to compile it once and reuse it. * The {@code Pattern} class and its companion, {@link Matcher}, also offer more functionality * than the small amount exposed by {@code String}. * * 
 * // String convenience methods:
 * boolean sawFailures = s.matches("Failures: \\d+");
 * String farewell = s.replaceAll("Hello, (\\S+)", "Goodbye, $1");
 * String[] fields = s.split(":");
 *
 * // Direct use of Pattern:
 * Pattern p = Pattern.compile("Hello, (\\S+)");
 * Matcher m = p.matcher(inputString);
 * while (m.find()) { // Find each match in turn; String can't do this.
 *     String name = m.group(1); // Access a submatch group; String can't do this.
 * }
 *
* *

Regular expression syntax

* * * *

Java supports a subset of Perl 5 regular expression syntax. An important gotcha is that Java * has no regular expression literals, and uses plain old string literals instead. This means that * you need an extra level of escaping. For example, the regular expression {@code \s+} has to * be represented as the string {@code "\\s+"}. * *

Escape sequences

*

* * * * * * * * * * * * * * *
\ Quote the following metacharacter (so {@code \.} matches a literal {@code .}).
\Q Quote all following metacharacters until {@code \E}.
\E Stop quoting metacharacters (started by {@code \Q}).
\\ A literal backslash.
\uhhhh The Unicode character U+hhhh (in hex).
\xhh The Unicode character U+00hh (in hex).
\cx The ASCII control character ^x (so {@code \cH} would be ^H, U+0008).
\a The ASCII bell character (U+0007).
\e The ASCII ESC character (U+001b).
\f The ASCII form feed character (U+000c).
\n The ASCII newline character (U+000a).
\r The ASCII carriage return character (U+000d).
\t The ASCII tab character (U+0009).
* *

Character classes

*

It's possible to construct arbitrary character classes using set operations: * * * * * * *
[abc] Any one of {@code a}, {@code b}, or {@code c}. (Enumeration.)
[a-c] Any one of {@code a}, {@code b}, or {@code c}. (Range.)
[^abc] Any character except {@code a}, {@code b}, or {@code c}. (Negation.)
[[a-f][0-9]] Any character in either range. (Union.)
[[a-z]&&[jkl]] Any character in both ranges. (Intersection.)
*

Most of the time, the built-in character classes are more useful: * * * * * * * * * *
\d Any digit character (see note below).
\D Any non-digit character (see note below).
\s Any whitespace character (see note below).
\S Any non-whitespace character (see note below).
\w Any word character (see note below).
\W Any non-word character (see note below).
\p{NAME} Any character in the class with the given NAME.
\P{NAME} Any character not in the named class.
*

Note that these built-in classes don't just cover the traditional ASCII range. For example, * \w is equivalent to the character class [\p{Ll}\p{Lu}\p{Lt}\p{Lo}\p{Nd}]. * For more details see Unicode TR-18, * and bear in mind that the set of characters in each class can vary between Unicode releases. * If you actually want to match only ASCII characters, specify the explicit characters you want; * if you mean 0-9 use [0-9] rather than \d, which would also include * Gurmukhi digits and so forth. *

There are also a variety of named classes: *

* *

Quantifiers

*

Quantifiers match some number of instances of the preceding regular expression. * * * * * * * *
* Zero or more.
? Zero or one.
+ One or more.
{n} Exactly n.
{n,} At least n.
{n,m} At least n but not more than m.
*

Quantifiers are "greedy" by default, meaning that they will match the longest possible input * sequence. There are also non-greedy quantifiers that match the shortest possible input sequence. * They're same as the greedy ones but with a trailing {@code ?}: * * * * * * * *
*? Zero or more (non-greedy).
?? Zero or one (non-greedy).
+? One or more (non-greedy).
{n}? Exactly n (non-greedy).
{n,}? At least n (non-greedy).
{n,m}? At least n but not more than m (non-greedy).
*

Quantifiers allow backtracking by default. There are also possessive quantifiers to prevent * backtracking. They're same as the greedy ones but with a trailing {@code +}: * * * * * * * *
*+ Zero or more (possessive).
?+ Zero or one (possessive).
++ One or more (possessive).
{n}+ Exactly n (possessive).
{n,}+ At least n (possessive).
{n,m}+ At least n but not more than m (possessive).
* *

Zero-width assertions

*

* * * * * * * * *
^ At beginning of line.
$ At end of line.
\A At beginning of input.
\b At word boundary.
\B At non-word boundary.
\G At end of previous match.
\z At end of input.
\Z At end of input, or before newline at end.
* *

Look-around assertions

*

Look-around assertions assert that the subpattern does (positive) or doesn't (negative) match * after (look-ahead) or before (look-behind) the current position, without including the matched * text in the containing match. The maximum length of possible matches for look-behind patterns * must not be unbounded. *

* * * * *
(?=a) Zero-width positive look-ahead.
(?!a) Zero-width negative look-ahead.
(?<=a) Zero-width positive look-behind.
(?<!a) Zero-width negative look-behind.
* *

Groups

* *

* * * * *
(a) A capturing group.
(?:a) A non-capturing group.
(?>a) An independent non-capturing group. (The first match of the subgroup is the only match tried.)
\n The text already matched by capturing group n.
*

See {@link Matcher#group} for details of how capturing groups are numbered and accessed. * *

Operators

*

* * *
ab Expression a followed by expression b.
a|b Either expression a or expression b.
* *

Flags

*

* * *
(?dimsux-dimsux:a) Evaluates the expression a with the given flags enabled/disabled.
(?dimsux-dimsux) Evaluates the rest of the pattern with the given flags enabled/disabled.
* *

The flags are: * * * * * * * *
{@code i} {@link #CASE_INSENSITIVE} case insensitive matching
{@code d} {@link #UNIX_LINES} only accept {@code '\n'} as a line terminator
{@code m} {@link #MULTILINE} allow {@code ^} and {@code $} to match beginning/end of any line
{@code s} {@link #DOTALL} allow {@code .} to match {@code '\n'} ("s" for "single line")
{@code u} {@link #UNICODE_CASE} enable Unicode case folding
{@code x} {@link #COMMENTS} allow whitespace and comments
*

Either set of flags may be empty. For example, {@code (?i-m)} would turn on case-insensitivity * and turn off multiline mode, {@code (?i)} would just turn on case-insensitivity, * and {@code (?-m)} would just turn off multiline mode. *

Note that on Android, {@code UNICODE_CASE} is always on: case-insensitive matching will * always be Unicode-aware. *

There are two other flags not settable via this mechanism: {@link #CANON_EQ} and * {@link #LITERAL}. Attempts to use {@link #CANON_EQ} on Android will throw an exception. * * *

Implementation notes

* *

The regular expression implementation used in Android is provided by * ICU. The notation for the regular * expressions is mostly a superset of those used in other Java language * implementations. This means that existing applications will normally work as * expected, but in rare cases Android may accept a regular expression that is * not accepted by other implementations. * *

In some cases, Android will recognize that a regular expression is a simple * special case that can be handled more efficiently. This is true of both the convenience methods * in {@code String} and the methods in {@code Pattern}. * * @see Matcher */ public final class Pattern implements Serializable { private static final long serialVersionUID = 5073258162644648461L; /** * This constant specifies that a pattern matches Unix line endings ('\n') * only against the '.', '^', and '$' meta characters. Corresponds to {@code (?d)}. */ public static final int UNIX_LINES = 0x01; /** * This constant specifies that a {@code Pattern} is matched * case-insensitively. That is, the patterns "a+" and "A+" would both match * the string "aAaAaA". See {@link #UNICODE_CASE}. Corresponds to {@code (?i)}. */ public static final int CASE_INSENSITIVE = 0x02; /** * This constant specifies that a {@code Pattern} may contain whitespace or * comments. Otherwise comments and whitespace are taken as literal * characters. Corresponds to {@code (?x)}. */ public static final int COMMENTS = 0x04; /** * This constant specifies that the meta characters '^' and '$' match only * the beginning and end of an input line, respectively. Normally, they * match the beginning and the end of the complete input. Corresponds to {@code (?m)}. */ public static final int MULTILINE = 0x08; /** * This constant specifies that the whole {@code Pattern} is to be taken * literally, that is, all meta characters lose their meanings. */ public static final int LITERAL = 0x10; /** * This constant specifies that the '.' meta character matches arbitrary * characters, including line endings, which is normally not the case. * Corresponds to {@code (?s)}. */ public static final int DOTALL = 0x20; /** * This constant specifies that a {@code Pattern} that uses case-insensitive matching * will use Unicode case folding. On Android, {@code UNICODE_CASE} is always on: * case-insensitive matching will always be Unicode-aware. If your code is intended to * be portable and uses case-insensitive matching on non-ASCII characters, you should * use this flag. Corresponds to {@code (?u)}. */ public static final int UNICODE_CASE = 0x40; /** * This constant specifies that a character in a {@code Pattern} and a * character in the input string only match if they are canonically * equivalent. It is (currently) not supported in Android. */ public static final int CANON_EQ = 0x80; private final String pattern; private final int flags; transient long address; /** * Returns a {@link Matcher} for this pattern applied to the given {@code input}. * The {@code Matcher} can be used to match the {@code Pattern} against the * whole input, find occurrences of the {@code Pattern} in the input, or * replace parts of the input. */ public Matcher matcher(CharSequence input) { return new Matcher(this, input); } /** * Splits the given {@code input} at occurrences of this pattern. * *

If this pattern does not occur in the input, the result is an * array containing the input (converted from a {@code CharSequence} to * a {@code String}). * *

Otherwise, the {@code limit} parameter controls the contents of the * returned array as described below. * * @param limit * Determines the maximum number of entries in the resulting * array, and the treatment of trailing empty strings. *

*/ public String[] split(CharSequence input, int limit) { return Splitter.split(this, pattern, input.toString(), limit); } /** * Equivalent to {@code split(input, 0)}. */ public String[] split(CharSequence input) { return split(input, 0); } /** * Returns the regular expression supplied to {@code compile}. */ public String pattern() { return pattern; } @Override public String toString() { return pattern; } /** * Returns the flags supplied to {@code compile}. */ public int flags() { return flags; } /** * Returns a compiled form of the given {@code regularExpression}, as modified by the * given {@code flags}. See the flags overview for more on flags. * * @throws PatternSyntaxException if the regular expression is syntactically incorrect. * * @see #CANON_EQ * @see #CASE_INSENSITIVE * @see #COMMENTS * @see #DOTALL * @see #LITERAL * @see #MULTILINE * @see #UNICODE_CASE * @see #UNIX_LINES */ public static Pattern compile(String regularExpression, int flags) throws PatternSyntaxException { return new Pattern(regularExpression, flags); } /** * Equivalent to {@code Pattern.compile(pattern, 0)}. */ public static Pattern compile(String pattern) { return new Pattern(pattern, 0); } private Pattern(String pattern, int flags) throws PatternSyntaxException { if ((flags & CANON_EQ) != 0) { throw new UnsupportedOperationException("CANON_EQ flag not supported"); } int supportedFlags = CASE_INSENSITIVE | COMMENTS | DOTALL | LITERAL | MULTILINE | UNICODE_CASE | UNIX_LINES; if ((flags & ~supportedFlags) != 0) { throw new IllegalArgumentException("Unsupported flags: " + (flags & ~supportedFlags)); } this.pattern = pattern; this.flags = flags; compile(); } private void compile() throws PatternSyntaxException { if (pattern == null) { throw new NullPointerException("pattern == null"); } String icuPattern = pattern; if ((flags & LITERAL) != 0) { icuPattern = quote(pattern); } // These are the flags natively supported by ICU. // They even have the same value in native code. int icuFlags = flags & (CASE_INSENSITIVE | COMMENTS | MULTILINE | DOTALL | UNIX_LINES); address = compileImpl(icuPattern, icuFlags); } /** * Tests whether the given {@code regularExpression} matches the given {@code input}. * Equivalent to {@code Pattern.compile(regularExpression).matcher(input).matches()}. * If the same regular expression is to be used for multiple operations, it may be more * efficient to reuse a compiled {@code Pattern}. * * @see Pattern#compile(java.lang.String, int) * @see Matcher#matches() */ public static boolean matches(String regularExpression, CharSequence input) { return new Matcher(new Pattern(regularExpression, 0), input).matches(); } /** * Quotes the given {@code string} using "\Q" and "\E", so that all * meta-characters lose their special meaning. This method correctly * escapes embedded instances of "\Q" or "\E". If the entire result * is to be passed verbatim to {@link #compile}, it's usually clearer * to use the {@link #LITERAL} flag instead. */ public static String quote(String string) { StringBuilder sb = new StringBuilder(); sb.append("\\Q"); int apos = 0; int k; while ((k = string.indexOf("\\E", apos)) >= 0) { sb.append(string.substring(apos, k + 2)).append("\\\\E\\Q"); apos = k + 2; } return sb.append(string.substring(apos)).append("\\E").toString(); } @Override protected void finalize() throws Throwable { try { closeImpl(address); } finally { super.finalize(); } } private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException { s.defaultReadObject(); compile(); } private static native void closeImpl(long addr); private static native long compileImpl(String regex, int flags); }