PDFBOX-5902: cache CMap-string-mappings to avoid multiple instances of the very same string

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/trunk@1922530 13f79535-47bb-0310-9956-ffa450edef68

Author: lehmi

fontbox/src/main/java/org/apache/fontbox/cmap/CMapParser.java

@@ -814,7 +814,11 @@ private static boolean increment(byte[] data, int position, boolean useStrictMod
 
     private static String createStringFromBytes(byte[] bytes)
     {
-        return new String(bytes, bytes.length == 1 ? StandardCharsets.ISO_8859_1 : StandardCharsets.UTF_16BE);
+        if (bytes.length <= 2)
+        {
+            return CMapStrings.getMapping(bytes);
+        }
+        return new String(bytes, StandardCharsets.UTF_16BE);
     }
 
     /**

fontbox/src/main/java/org/apache/fontbox/cmap/CMapStrings.java

@@ -0,0 +1,77 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.fontbox.cmap;
+
+import java.nio.charset.StandardCharsets;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Many CMaps are using the same values for the mapped strings. This class provides all common one- and two-byte
+ * mappings to avoid duplicate strings.
+ */
+public class CMapStrings
+{
+    private static final Map<Integer, String> twoByteMappings = new HashMap<>();
+    private static final Map<Integer, String> oneByteMappings = new HashMap<>();
+
+    static
+    {
+        // create all mappings when loading the class to avoid concurrency issues
+        fillMappings();
+    }
+
+    private CMapStrings()
+    {
+    }
+
+    private static void fillMappings()
+    {
+        for (int i = 0; i < 256; i++)
+        {
+            for (int j = 0; j < 256; j++)
+            {
+                byte[] bytes = { (byte) i, (byte) j };
+                twoByteMappings.put(CMap.toInt(bytes),
+                        new String(bytes, StandardCharsets.UTF_16BE));
+            }
+        }
+        for (int i = 0; i < 256; i++)
+        {
+            byte[] bytes = { (byte) i };
+            oneByteMappings.put(i, new String(bytes, StandardCharsets.ISO_8859_1));
+        }
+    }
+
+    /**
+     * Get the mapped string value for the given combination of bytes. The mapping is limited to one and two-byte
+     * mappings. Any longer byte sequence produces null as return value.
+     * 
+     * @param bytes the given combination of bytes
+     * @return the string representation for the given combination of bytes
+     */
+    public static String getMapping(byte[] bytes)
+    {
+        if (bytes.length > 2)
+        {
+            return null;
+        }
+        return bytes.length == 1 ? oneByteMappings.get(CMap.toInt(bytes))
+                : twoByteMappings.get(CMap.toInt(bytes));
+    }
+}