Question

我对一个小的测试脚本有疑问：

import java.util.regex.Pattern;
import java.util.regex.Matcher;

cfgText = "PATTERN1 = 9\nPATTERN2 = 136.225.73.44\nPATTERN3 = 136.225.236.12"

cfgLine = cfgText.split('\n');
def p = /.*PATTERN2.*/;
def PATTERN2_found = false;
for (i=0; PATTERN2_found==false && i < cfgLine.length; i++)
{
    println("cfgLine" +i+ ": " + cfgLine[i]);
    def m = cfgLine[i] =~ p;
    println("m: " + m)
    println("m.asBoolean(): " + m.asBoolean());
    println("m: " + m)
    println("m.asBoolean(): " + m.asBoolean());
    if(m.asBoolean()){
        println("Heeeyyyy");
    }
    println("--------------------------------");
}

这是它的输出：

cfgLine0: PATTERN1 = 9
m: java.util.regex.Matcher[pattern=.*PATTERN2.* region=0,12 lastmatch=]
m.asBoolean(): false
m: java.util.regex.Matcher[pattern=.*PATTERN2.* region=0,12 lastmatch=]
m.asBoolean(): false
--------------------------------
cfgLine1: PATTERN2 = 136.225.73.44
m: java.util.regex.Matcher[pattern=.*PATTERN2.* region=0,24 lastmatch=]
m.asBoolean(): true
m: java.util.regex.Matcher[pattern=.*PATTERN2.* region=0,24 lastmatch=PATTERN2 = 136.225.73.44]
m.asBoolean(): false
--------------------------------
cfgLine2: PATTERN3 = 136.225.236.12
m: java.util.regex.Matcher[pattern=.*PATTERN2.* region=0,25 lastmatch=]
m.asBoolean(): false
m: java.util.regex.Matcher[pattern=.*PATTERN2.* region=0,25 lastmatch=]
m.asBoolean(): false
--------------------------------

WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.codehaus.groovy.reflection.CachedConstructor$1 (file:/usr/share/groovy/lib/groovy-2.4.15.jar) to constructor java.util.regex.Matcher()
WARNING: Please consider reporting this to the maintainers of org.codehaus.groovy.reflection.CachedConstructor$1
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

如您所见，正则表达式在第二个循环中匹配，但是行为对我来说很奇怪。我真的不知道为什么我对同一个Matcher对象使用两次asBoolean会导致结果不同。它具有内部迭代器还是类似的东西？

PS：我已经使用==~运算符解决了这个问题，但是我想知道为什么asBoolean可以这样工作。

Answer 1

发生这种情况是因为StringGroovyMethods.asBoolean(Matcher matcher)调用matcher.find()会修改匹配器的内部状态。

/**
 * Coerce a Matcher instance to a boolean value.
 *
 * @param matcher the matcher
 * @return the boolean value
 * @since 1.7.0
 */
public static boolean asBoolean(Matcher matcher) {
    if (null == matcher) {
        return false;
    }

    RegexSupport.setLastMatcher(matcher);
    return matcher.find();
}

来源：src/main/org/codehaus/groovy/runtime/StringGroovyMethods.java

这就是为什么当您第一次调用m.asBoolean()时会返回true的原因，因为它在此调用之前的状态为（未找到匹配项）：

m: java.util.regex.Matcher[pattern=.*PATTERN2.* region=0,24 lastmatch=]

现在，当您第二次调用m.asBoolean()时，匹配对象将由上一次调用修改，并由以下内容表示：

m: java.util.regex.Matcher[pattern=.*PATTERN2.* region=0,24 lastmatch=PATTERN2 = 136.225.73.44]

它返回false，因为没有其他部分满足匹配器。

对Matcher类的asBoolean方法的误解

1 个答案: