Merge pull request #8321 from silvafabio/master

Pre-compile the regex pattern into a Pattern object and reuse

core-java-modules/core-java-11/src/test/java/com/baeldung/patternreuse/PatternJava11UnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.patternreuse;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.function.Predicate;
+import java.util.regex.Pattern;
+import java.util.stream.Collectors;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class PatternJava11UnitTest {
+
+    @Test
+    public void givenPreCompiledPattern_whenCallAsMatchPredicate_thenReturnMatchPredicateToMatchesThePatternInTheListElements() {
+        List<String> namesToValidate = Arrays.asList("Fabio Silva", "Fabio Luis Silva");
+        Pattern firstLastNamePreCompiledPattern = Pattern.compile("[a-zA-Z]{3,} [a-zA-Z]{3,}");
+
+        Predicate<String> patternAsMatchPredicate = firstLastNamePreCompiledPattern.asMatchPredicate();
+        List<String> validatedNames = namesToValidate.stream()
+                .filter(patternAsMatchPredicate)
+                .collect(Collectors.toList());
+
+        assertTrue(validatedNames.contains("Fabio Silva"));
+        assertFalse(validatedNames.contains("Fabio Luis Silva"));
+    }
+}

core-java-modules/core-java-text/pom.xml

@@ -14,6 +14,19 @@
         <relativePath>../../parent-java</relativePath>
     </parent>
 
+    <dependencies>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-core</artifactId>
+            <version>${jmh-core.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-annprocess</artifactId>
+            <version>${jmh-core.version}</version>
+        </dependency>
+    </dependencies>
+
     <build>
         <finalName>core-java-text</finalName>
         <resources>

core-java-modules/core-java-text/src/main/java/com/baeldung/patternreuse/PatternPerformanceComparison.java

@@ -0,0 +1,92 @@
+package com.baeldung.patternreuse;
+
+import org.openjdk.jmh.annotations.*;
+import org.openjdk.jmh.infra.Blackhole;
+import org.openjdk.jmh.runner.RunnerException;
+
+import java.io.IOException;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.MILLISECONDS)
+@Fork(value = 1, warmups = 1)
+@Warmup(iterations = 5)
+@State(Scope.Benchmark)
+public class PatternPerformanceComparison {
+
+    private static final String PATTERN = "\\d*[02468]";
+    private static List<String> values;
+
+    private static Matcher matcherFromPreCompiledPattern;
+    private static Pattern preCompiledPattern;
+
+    public static void main(String[] args) throws IOException, RunnerException {
+        org.openjdk.jmh.Main.main(args);
+    }
+
+    @Benchmark
+    public void matcherFromPreCompiledPatternResetMatches(Blackhole bh) {
+        //With pre-compiled pattern and reusing the matcher
+        // 1 Pattern object created
+        // 1 Matcher objects created
+        for (String value : values) {
+            bh.consume(matcherFromPreCompiledPattern.reset(value).matches());
+        }
+    }
+
+    @Benchmark
+    public void preCompiledPatternMatcherMatches(Blackhole bh) {
+        // With pre-compiled pattern
+        // 1         Pattern object created
+        // 5_000_000 Matcher objects created
+        for (String value : values) {
+            bh.consume(preCompiledPattern.matcher(value).matches());
+        }
+    }
+
+    @Benchmark
+    public void patternCompileMatcherMatches(Blackhole bh) {
+        // Above approach "Pattern.matches(PATTERN, value)" makes this internally
+        // 5_000_000 Pattern objects created
+        // 5_000_000 Matcher objects created
+        for (String value : values) {
+            bh.consume(Pattern.compile(PATTERN).matcher(value).matches());
+        }
+    }
+
+    @Benchmark
+    public void patternMatches(Blackhole bh) {
+        // Above approach "value.matches(PATTERN)" makes this internally
+        // 5_000_000 Pattern objects created
+        // 5_000_000 Matcher objects created
+        for (String value : values) {
+            bh.consume(Pattern.matches(PATTERN, value));
+        }
+    }
+
+    @Benchmark
+    public void stringMatchs(Blackhole bh) {
+        // 5_000_000 Pattern objects created
+        // 5_000_000 Matcher objects created
+        Instant start = Instant.now();
+        for (String value : values) {
+            bh.consume(value.matches(PATTERN));
+        }
+    }
+
+    @Setup()
+    public void setUp() {
+        preCompiledPattern = Pattern.compile(PATTERN);
+        matcherFromPreCompiledPattern = preCompiledPattern.matcher("");
+
+        values = new ArrayList<>();
+        for (int x = 1; x <= 5_000_000; x++) {
+            values.add(String.valueOf(x));
+        }
+    }
+}

core-java-modules/core-java-text/src/test/java/com/baeldung/patternreuse/PatternUnitTest.java

@@ -0,0 +1,63 @@
+package com.baeldung.patternreuse;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.function.Predicate;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import static org.junit.Assert.*;
+
+public class PatternUnitTest {
+
+    private static final Pattern FIRST_LAST_NAME_PRE_COMPILED_PATTERN = Pattern.compile("[a-zA-Z]{3,} [a-zA-Z]{3,}");
+    private static final Pattern SPLIT_PRE_COMPILED_PATTERN = Pattern.compile("__");
+
+    @Test
+    public void givenPreCompiledPattern_whenCallMatcher_thenReturnAMatcherToMatches() {
+        Matcher matcherName1 = FIRST_LAST_NAME_PRE_COMPILED_PATTERN.matcher("Fabio Silva");
+        Matcher matcherName2 = FIRST_LAST_NAME_PRE_COMPILED_PATTERN.matcher("Mr. Silva");
+
+        boolean matchesName1 = matcherName1.matches();
+        boolean matchesName2 = matcherName2.matches();
+
+        assertTrue(matchesName1);
+        assertFalse(matchesName2);
+    }
+
+    @Test
+    public void givenPreCompiledPattern_whenCallAsPredicate_thenReturnPredicateToFindThePatternInTheListElements() {
+        List<String> namesToValidate = Arrays.asList("Fabio Silva", "Mr. Silva");
+        Predicate<String> patternsAsPredicate = FIRST_LAST_NAME_PRE_COMPILED_PATTERN.asPredicate();
+
+        List<String> validNames = namesToValidate.stream()
+                .filter(patternsAsPredicate)
+                .collect(Collectors.toList());
+
+        assertEquals(1, validNames.size());
+        assertTrue(validNames.contains("Fabio Silva"));
+    }
+
+    @Test
+    public void givenPreCompiledPattern_whenCallSplit_thenReturnArrayWithValuesSplitByThePattern() {
+        String[] textSplit = SPLIT_PRE_COMPILED_PATTERN.split("My_Name__is__Fabio_Silva");
+
+        assertEquals("My_Name", textSplit[0]);
+        assertEquals("is", textSplit[1]);
+        assertEquals("Fabio_Silva", textSplit[2]);
+    }
+
+    @Test
+    public void givenPreCompiledPattern_whenCallSplitAsStream_thenReturnArrayWithValuesSplitByThePattern() {
+        Stream<String> textSplitAsStream = SPLIT_PRE_COMPILED_PATTERN.splitAsStream("My_Name__is__Fabio_Silva");
+        String[] textSplit = textSplitAsStream.toArray(String[]::new);
+
+        assertEquals("My_Name", textSplit[0]);
+        assertEquals("is", textSplit[1]);
+        assertEquals("Fabio_Silva", textSplit[2]);
+    }
+}