Java 正则表达式之 Pattern

1. Pattern 类

public final class Pattern implements java.io.Serializable {

    public static Pattern compile(String regex) {
        return new Pattern(regex, 0);
    }

    public Matcher matcher(CharSequence input) {
        if (!compiled) {
            synchronized(this) {
                if (!compiled)
                    compile();
            }
        }
        Matcher m = new Matcher(this, input);
        return m;
    }

    public static boolean matches(String regex, CharSequence input) {
        Pattern p = Pattern.compile(regex);
        Matcher m = p.matcher(input);
        return m.matches();
    }
}

1.1 模版

public class RegexDemo {

    private static final String ENTIRE_REGEX = "(.|\\s)*";
    private static final String SUB_SEQUENCE_REGEX = "code\\d+"; // 子串
    private static final String GROUP_REGEX = "(name\\d+).*(code\\d+)";

    private static final Pattern entireCompile = Pattern.compile(ENTIRE_REGEX);
    private static final Pattern subSequenceCompile = Pattern.compile(SUB_SEQUENCE_REGEX);
    private static final Pattern groupCompile = Pattern.compile(GROUP_REGEX);

    public static void print(Object o) {
        System.out.println(o);
    }
}

1.2 matches()

matches 是匹配整个字符串

public class RegexDemo {

    private static final String REGEX = "[a-z]{3}";
    // 先编译这个模式
    private static final Pattern pattern = Pattern.compile(REGEX);

    @Test
    public void matches() {
        String input = "xyz";

        Matcher matcher = pattern.matcher(input);
        boolean matches = matcher.matches();

        print(matches);
    }

    public static void print(Object o) {
        System.out.println(o);
    }
}

链式写法

@Test
public void matchesLink() {
    String input = "xyz";

    boolean matches = Pattern.compile(REGEX)
            .matcher(input)
            .matches();
    print(matches);
}

1.3 matches(String regex, CharSequence input)

private static final String ENTIRE_REGEX = ".*match.*";
private static final Pattern entireCompile = Pattern.compile(ENTIRE_REGEX);
@Test
public void match() {
    String data = "Attempts to match the entire region against the pattern.";
    boolean matches = Pattern.matches(ENTIRE_REGEX, data);

    // 等价
    boolean matches2 = entireCompile.matcher(data).matches();
}

2. Matcher 类

public final class Matcher implements MatchResult {
    public String group() {
        return group(0);
    }

    public boolean find() {
        int nextSearchIndex = last;
        // ...
        return search(nextSearchIndex);
    }

    public boolean matches() {
        return match(from, ENDANCHOR);
    }
}

Matcher 可以理解为“某次具体匹配的结果对象”：把编译好的Pattern 对象“应用”到某个String对象上，就获得了作为“本次匹配结果”的Matcher对象

2.1 find()

每调用一次 find() 方法，如果返回 true，就表示“找到一个匹配”

@Test
public void find() {
    String str = "123-4567-00";
    Matcher matcher = digitPattern.matcher(str);

    // 找子串，找到一个子串，然后把该子串去掉
    print(matcher.find()); print(matcher.group());
    print(matcher.find());
    print(matcher.find());

    print("=====================");

    // lookingAt 每次从头开始找
    print(matcher.lookingAt());
    print(matcher.lookingAt());
    print(matcher.lookingAt());
}

2.2 find() - if/while

private static final String SUB_REGEX = "code\\d+";
private static final Pattern subSequenceCompile = Pattern.compile(SUB_REGEX);
@Test
public void subFind() {
    String data = "code001,234code222,333code111,2323";
    Matcher subMatcher = subSequenceCompile.matcher(data);

    // group() 等价 group(0)
    if (subMatcher.find()) {
        System.out.println("if: " + subMatcher.group());
    }
}

/**
 * 注意此处的 If 与 While 的区别
 *  find() 是部分匹配
 */
@Test
public void subFind2() {
    String data = "code001,234code222,333code111,2323";
    Matcher subMatcher = subSequenceCompile.matcher(data);
    while(subMatcher.find()) {
        System.out.println("while: " + subMatcher.group());
    }
}

2.3 start() / end()

@Test
public void startFind() {
    String str = "123-4567-00";
    Matcher m = pattern.matcher(str);

    print(m.find() + "; " + m.start() + "-" + m.end());
    print(m.find() + "; " + m.start() + "-" + m.end());
    print(m.find());
    // p(m.start() + "-" + m.end()); 找不到会报错
}

2.4 reset()

@Test
public void reset() {
    String str = "123-3243-564-00";
    Pattern pattern = Pattern.compile("\\d{3,5}");
    Matcher matcher = pattern.matcher(str);

    System.out.println(matcher.matches());

    // reset() 可以让 matcher.matches() 吃掉的字符吐出来
    matcher.reset();
}

2.5 替换

@Test
public void replaceAll() {
    String input = "java Java JaVA learnJAVA hellojAVA 2342342";
    String regex = "java";

    // Pattern.CASE_INSENSITIVE 不区分大小写
    Pattern pattern = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);
    Matcher matcher = pattern.matcher(input);
    while (matcher.find()) {
        // print(matcher.group());
    }

    System.out.println(matcher.replaceAll("JAVA"));
}

升级：按单双数替换

private static final String REPLACE_REGEX = "java";
private static final Pattern replacePattern = Pattern.compile(REPLACE_REGEX, Pattern.CASE_INSENSITIVE);

/**
 * 按单双数替换
 */
@Test
public void appendReplacement() {
    Matcher matcher = replacePattern.matcher("java Java JaVA learnJAVA hellojAVA 2342342");

    StringBuffer buffer = new StringBuffer();
    int i = 0;
    while (matcher.find()) {
        i++;
        if (i % 2 == 0) {
            // 替换的结果放到 buffer
            matcher.appendReplacement(buffer, "java");
        } else {
            matcher.appendReplacement(buffer, "JAVA");
        }
    }

    // 把后面的添加到buffer
    matcher.appendTail(buffer);

    print(buffer);
}