Allow font cache to be cleared

DEVSIX-3216

Author: yulian-gaponenko

io/src/main/java/com/itextpdf/io/font/FontCache.java

@@ -54,7 +54,6 @@ This file is part of the iText (R) project.
 import com.itextpdf.io.font.constants.FontResources;
 import com.itextpdf.io.util.IntHashtable;
 import com.itextpdf.io.util.ResourceUtil;
-
 import java.io.InputStream;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -148,6 +147,16 @@ public static CMapCidByte getCid2Byte(String cmap) {
         return parseCmap(cmap, cidByte);
     }
 
+    /**
+     * Clears the cache by removing fonts that were added via {@link #saveFont(FontProgram, String)}.
+     * <p>
+     * Be aware that in multithreading environment this method call will affect the result of {@link #getFont(String)}.
+     * This in its turn affects creation of fonts via factories when {@code cached} argument is set to true (which is by default).
+     */
+    public static void clearSavedFonts() {
+        fontCache.clear();
+    }
+
     public static FontProgram getFont(String fontName) {
         return fontCache.get(FontCacheKey.create(fontName));
     }

io/src/test/java/com/itextpdf/io/font/FontCacheTest.java

@@ -0,0 +1,38 @@
+package com.itextpdf.io.font;
+
+import com.itextpdf.io.font.otf.Glyph;
+import com.itextpdf.test.ExtendedITextTest;
+import com.itextpdf.test.annotations.type.UnitTest;
+import org.junit.Assert;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+
+@Category(UnitTest.class)
+public class FontCacheTest extends ExtendedITextTest {
+
+    @Test
+    public void clearFontCacheTest() {
+        String fontName = "FreeSans.ttf";
+        Assert.assertNull(FontCache.getFont(fontName));
+
+        FontProgram fontProgram = new FontProgramMock();
+        FontCache.saveFont(fontProgram, fontName);
+        Assert.assertEquals(fontProgram, FontCache.getFont(fontName));
+
+        FontCache.clearSavedFonts();
+        Assert.assertNull(FontCache.getFont(fontName));
+    }
+
+    private static class FontProgramMock extends FontProgram {
+
+        @Override
+        public int getPdfFontFlags() {
+            return 0;
+        }
+
+        @Override
+        public int getKerning(Glyph first, Glyph second) {
+            return 0;
+        }
+    }
+}