Attempt to fix thread-safety of CharacterProtector

* Add simple unit tests for class.

Fixes Issue # 20.

Signed-off-by: Alex Coles <alex@alexbcoles.com>

core/src/main/java/org/markdownj/CharacterProtector.java

@@ -36,13 +36,14 @@ liability, whether in contract, strict liability, or tort (including
 package org.markdownj;
 
 import java.util.Collection;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Random;
 
-class CharacterProtector {
-    private Map<String, String> protectMap = new HashMap<String, String>();
-    private Map<String, String> unprotectMap = new HashMap<String, String>();
+public class CharacterProtector {
+    private final Map<String, String> protectMap = new HashMap<String, String>();
+    private final Map<String, String> unprotectMap = new HashMap<String, String>();
     private static final String GOOD_CHARS = "0123456789qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM";
     private Random rnd = new Random();
 
@@ -59,17 +60,20 @@ public String decode(String coded) {
     }
 
     public Collection<String> getAllEncodedTokens() {
-        return unprotectMap.keySet();
+        return Collections.unmodifiableSet(unprotectMap.keySet());
     }
 
     private void addToken(String literal) {
         String encoded = longRandomString();
-        protectMap.put(literal, encoded);
-        unprotectMap.put(encoded, literal);
+
+        synchronized (this) {
+          protectMap.put(literal, encoded);
+          unprotectMap.put(encoded, literal);
+        }
     }
 
     private String longRandomString() {
-        StringBuffer sb = new StringBuffer();
+        StringBuilder sb = new StringBuilder();
         final int CHAR_MAX = GOOD_CHARS.length();
         for (int i = 0; i < 20; i++) {
             sb.append(GOOD_CHARS.charAt(rnd.nextInt(CHAR_MAX)));

core/src/test/java/org/markdownj/test/CharacterProtectorTest.java

@@ -0,0 +1,52 @@
+package org.markdownj.test;
+
+import java.util.Collection;
+import static org.junit.Assert.*;
+import org.junit.Before;
+import org.junit.Test;
+import org.markdownj.CharacterProtector;
+
+/**
+ *
+ * @author alexbcoles
+ */
+public class CharacterProtectorTest {
+
+    private CharacterProtector characterProtector;
+
+    @Before
+    public void createCharacterProtector() {
+        characterProtector = new CharacterProtector();
+    }
+
+    @Test
+    public void testEncodeAndDecodeRoundtrip() {
+        String encoded = characterProtector.encode("<h4>Warnemünde</h4>");
+        assertEquals("<h4>Warnemünde</h4>", characterProtector.decode(encoded));
+    }
+
+    @Test
+    public void testGetAllEncodedTokens() {
+        Collection tokens = characterProtector.getAllEncodedTokens();
+        assertEquals(0, tokens.size());
+
+        characterProtector.encode("<nav><div></div></nav>");
+        characterProtector.encode("<h1 id='heading'>Schifffahrt nach Warnemünde</h1>");
+        characterProtector.encode("<br/>");
+        assertEquals(3, tokens.size());
+    }
+
+    @Test(expected=UnsupportedOperationException.class)
+    public void testGetAllEncodedTokensCanNotModified1() {
+        Collection tokens = characterProtector.getAllEncodedTokens();
+        tokens.clear();
+    }
+
+    @Test(expected=UnsupportedOperationException.class)
+    public void testGetAllEncodedTokensCanNotModified2() {
+        Collection tokens = characterProtector.getAllEncodedTokens();
+        tokens.add("another_token");
+        tokens.remove("another_token");
+    }
+
+}