✨ Fix #12383

pom.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <!--
     Description: Solo POM.
-    Version: 3.17.2.50, Nov 9, 2017
+    Version: 3.18.2.50, Dec 16, 2017
     Author: <a href="http://88250.b3log.org">Liang Ding</a>
     Author: <a href="http://www.annpeter.cn">Ann Peter</a>
     Author: <a href="http://vanessa.b3log.org">Vanessa</a>
@@ -85,6 +85,7 @@
         <qiniu.version>7.0.4.1</qiniu.version>
         <jetty.version>9.2.9.v20150224</jetty.version>
         <commons-cli.version>1.3.1</commons-cli.version>
+        <commons-codec.version>1.10</commons-codec.version>
         <emoji-java.version>3.2.0</emoji-java.version>
         <jodd.version>3.6.6</jodd.version>
         <snakeyaml.version>1.18</snakeyaml.version>
@@ -215,6 +216,12 @@
             <version>${snakeyaml.version}</version>
         </dependency>
 
+        <dependency>
+            <groupId>commons-codec</groupId>
+            <artifactId>commons-codec</artifactId>
+            <version>${commons-codec.version}</version>
+        </dependency>
+
         <dependency>
             <groupId>org.mockito</groupId>
             <artifactId>mockito-all</artifactId>

src/main/java/org/b3log/solo/util/Markdowns.java

@@ -19,9 +19,12 @@ import com.vladsch.flexmark.html.HtmlRenderer;
 import com.vladsch.flexmark.profiles.pegdown.Extensions;
 import com.vladsch.flexmark.profiles.pegdown.PegdownOptionsAdapter;
 import com.vladsch.flexmark.util.options.DataHolder;
+import org.apache.commons.codec.digest.DigestUtils;
 import org.apache.commons.io.IOUtils;
 import org.apache.commons.lang.StringUtils;
 import org.b3log.latke.Latkes;
+import org.b3log.latke.cache.Cache;
+import org.b3log.latke.cache.CacheFactory;
 import org.b3log.latke.ioc.LatkeBeanManagerImpl;
 import org.b3log.latke.logging.Level;
 import org.b3log.latke.logging.Logger;
@@ -30,6 +33,7 @@ import org.b3log.latke.service.LangPropsServiceImpl;
 import org.b3log.latke.util.Callstacks;
 import org.b3log.latke.util.Stopwatchs;
 import org.b3log.latke.util.Strings;
+import org.json.JSONObject;
 import org.jsoup.Jsoup;
 import org.jsoup.nodes.Document;
 
@@ -48,7 +52,7 @@ import java.util.concurrent.*;
  * </p>
  *
  * @author <a href="http://88250.b3log.org">Liang Ding</a>
- * @version 2.2.0.6, Dec 16, 2017
+ * @version 2.3.0.6, Dec 16, 2017
  * @since 0.4.5
  */
 public final class Markdowns {
@@ -63,6 +67,11 @@ public final class Markdowns {
      */
     private static final LangPropsService LANG_PROPS_SERVICE = LatkeBeanManagerImpl.getInstance().getReference(LangPropsServiceImpl.class);
 
+    /**
+     * Markdown cache.
+     */
+    private static final Cache MD_CACHE = CacheFactory.getCache("markdown");
+
     /**
      * Markdown to HTML timeout.
      */
@@ -98,6 +107,8 @@ public final class Markdowns {
     public static boolean MARKED_AVAILABLE;
 
     static {
+        MD_CACHE.setMaxCount(1024 * 10 * 4);
+
         try {
             final URL url = new URL(MARKED_ENGINE_URL);
             final HttpURLConnection conn = (HttpURLConnection) url.openConnection();
@@ -144,6 +155,11 @@ public final class Markdowns {
             return "";
         }
 
+        final String cachedHTML = getHTML(markdownText);
+        if (null != cachedHTML) {
+            return cachedHTML;
+        }
+
         final ExecutorService pool = Executors.newSingleThreadExecutor();
         final long[] threadId = new long[1];
 
@@ -177,6 +193,9 @@ public final class Markdowns {
             String ret = doc.select("body").html();
             ret = StringUtils.trim(ret);
 
+            // cache it
+            putHTML(markdownText, ret);
+
             return ret;
         };
 
@@ -225,4 +244,33 @@ public final class Markdowns {
 
         return html;
     }
+
+    /**
+     * Gets HTML for the specified markdown text.
+     *
+     * @param markdownText the specified markdown text
+     * @return HTML
+     */
+    private static String getHTML(final String markdownText) {
+        final String hash = DigestUtils.md5Hex(markdownText);
+        final JSONObject value = MD_CACHE.get(hash);
+        if (null == value) {
+            return null;
+        }
+
+        return value.optString("data");
+    }
+
+    /**
+     * Puts the specified HTML into cache.
+     *
+     * @param markdownText the specified markdown text
+     * @param html         the specified HTML
+     */
+    private static void putHTML(final String markdownText, final String html) {
+        final String hash = DigestUtils.md5Hex(markdownText);
+        final JSONObject value = new JSONObject();
+        value.put("data", html);
+        MD_CACHE.put(hash, value);
+    }
 }