faster replace for large feeds (#881)

pom.xml

@@ -116,7 +116,7 @@
 						</goals>
 						<configuration>
 							<transformers>
-								<transformer implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer"/>
+								<transformer implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer" />
 								<transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
 									<mainClass>com.commafeed.CommaFeedApplication</mainClass>
 								</transformer>
@@ -279,11 +279,11 @@
 				</exclusion>
 			</exclusions>
 		</dependency>
-                <dependency>
+		<dependency>
-                        <groupId>io.dropwizard.metrics</groupId>
+			<groupId>io.dropwizard.metrics</groupId>
-                        <artifactId>metrics-graphite</artifactId>
+			<artifactId>metrics-graphite</artifactId>
-                        <version>3.1.2</version>
+			<version>3.1.2</version>
-                </dependency>
+		</dependency>
 
 		<dependency>
 			<groupId>org.apache.httpcomponents</groupId>
@@ -386,7 +386,11 @@
 			<artifactId>jdom2</artifactId>
 			<version>2.0.6</version>
 		</dependency>
-
+		<dependency>
+			<groupId>org.ahocorasick</groupId>
+			<artifactId>ahocorasick</artifactId>
+			<version>0.4.0</version>
+		</dependency>
 		<dependency>
 			<groupId>org.jsoup</groupId>
 			<artifactId>jsoup</artifactId>

src/main/java/com/commafeed/backend/feed/FeedUtils.java

@@ -6,6 +6,7 @@ import java.net.URL;
 import java.nio.charset.Charset;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.Date;
 import java.util.Iterator;
@@ -13,6 +14,9 @@ import java.util.List;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
 
+import org.ahocorasick.trie.Emit;
+import org.ahocorasick.trie.Trie;
+import org.ahocorasick.trie.Trie.TrieBuilder;
 import org.apache.commons.codec.binary.Base64;
 import org.apache.commons.lang3.ArrayUtils;
 import org.apache.commons.lang3.StringUtils;
@@ -132,7 +136,32 @@ public class FeedUtils {
 	}
 
 	public static String replaceHtmlEntitiesWithNumericEntities(String source) {
-		return StringUtils.replaceEach(source, HtmlEntities.HTML_ENTITIES, HtmlEntities.NUMERIC_ENTITIES);
+		// Create a buffer sufficiently large that re-allocations are minimized.
+		StringBuilder sb = new StringBuilder(source.length() << 1);
+
+		TrieBuilder builder = Trie.builder();
+		builder.ignoreOverlaps();
+
+		for (String key : HtmlEntities.HTML_ENTITIES) {
+			builder.addKeyword(key);
+		}
+
+		Trie trie = builder.build();
+		Collection<Emit> emits = trie.parseText(source);
+
+		int prevIndex = 0;
+		for (Emit emit : emits) {
+			int matchIndex = emit.getStart();
+
+			sb.append(source.substring(prevIndex, matchIndex));
+			sb.append(HtmlEntities.HTML_TO_NUMERIC_MAP.get(emit.getKeyword()));
+			prevIndex = emit.getEnd() + 1;
+		}
+
+		// Add the remainder of the string (contains no more matches).
+		sb.append(source.substring(prevIndex));
+
+		return sb.toString();
 	}
 
 	/**

src/main/java/com/commafeed/backend/feed/HtmlEntities.java

@@ -1,9 +1,11 @@
 package com.commafeed.backend.feed;
 
+import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.Map;
 
 public class HtmlEntities {
+	public static final Map<String, String> HTML_TO_NUMERIC_MAP;
 	public static final String[] HTML_ENTITIES;
 	public static final String[] NUMERIC_ENTITIES;
 
@@ -260,6 +262,7 @@ public class HtmlEntities {
 		map.put("&zwj;", "&#8205;");
 		map.put("&zwnj;", "&#8204;");
 
+		HTML_TO_NUMERIC_MAP = Collections.unmodifiableMap(map);
 		HTML_ENTITIES = map.keySet().toArray(new String[map.size()]);
 		NUMERIC_ENTITIES = map.values().toArray(new String[map.size()]);
 	}