add getDnsCachePolicy/getDnsNegativeCachePolicy methods; add synchronized when set cache policy. #25

Author: oldratlee

src/main/java/com/alibaba/dcm/DnsCacheManipulator.java

@@ -208,6 +208,24 @@ public static void clearDnsCache() {
         }
     }
 
+    /**
+     * Get JVM DNS cache policy.
+     *
+     * @return cache seconds.
+     * <p/>
+     * <ul>
+     * <li> {@code -1} means never expired.(In effect, all negative value)</li>
+     * <li> {@code 0} never cached.</li>
+     * </ul>
+     */
+    public static int getDnsCachePolicy() {
+        try {
+            return InetAddressCacheUtil.getDnsCachePolicy();
+        } catch (Exception e) {
+            throw new DnsCacheManipulatorException("Fail to getDnsCachePolicy, cause: " + e.toString(), e);
+        }
+    }
+
     /**
      * Set JVM DNS cache policy
      *
@@ -226,6 +244,24 @@ public static void setDnsCachePolicy(int cacheSeconds) {
         }
     }
 
+    /**
+     * JVM DNS negative cache policy
+     *
+     * @return negative cache seconds.
+     * <p/>
+     * <ul>
+     * <li> {@code -1} means never expired.(In effect, all negative value)</li>
+     * <li> {@code 0} never cached.</li>
+     * </ul>
+     */
+    public static int getDnsNegativeCachePolicy() {
+        try {
+            return InetAddressCacheUtil.getDnsNegativeCachePolicy();
+        } catch (Exception e) {
+            throw new DnsCacheManipulatorException("Fail to getDnsNegativeCachePolicy, cause: " + e.toString(), e);
+        }
+    }
+
     /**
      * Set JVM DNS negative cache policy
      *

src/main/java/com/alibaba/dcm/internal/InetAddressCacheUtil.java

@@ -297,6 +297,11 @@ public static void setDnsCachePolicy(int cacheSeconds)
         setCachePolicy0(false, cacheSeconds);
     }
 
+    public static int getDnsCachePolicy()
+            throws NoSuchFieldException, IllegalAccessException {
+        return InetAddressCachePolicy.get();
+    }
+
     /**
      * Set JVM DNS negative cache policy
      *
@@ -313,16 +318,25 @@ public static void setDnsNegativeCachePolicy(int negativeCacheSeconds)
         setCachePolicy0(true, negativeCacheSeconds);
     }
 
+    public static int getDnsNegativeCachePolicy()
+            throws NoSuchFieldException, IllegalAccessException {
+        return InetAddressCachePolicy.getNegative();
+    }
+
     static void setCachePolicy0(boolean isNegative, int seconds)
             throws NoSuchFieldException, IllegalAccessException {
         if (seconds < 0) {
             seconds = -1;
         }
-        Class<?> clazz = sun.net.InetAddressCachePolicy.class;
+
+        Class<?> clazz = InetAddressCachePolicy.class;
         Field cachePolicyFiled = clazz.getDeclaredField(
                 isNegative ? "negativeCachePolicy" : "cachePolicy");
         cachePolicyFiled.setAccessible(true);
-        cachePolicyFiled.set(null, seconds);
+
+        synchronized (InetAddressCachePolicy.class) { // static synchronized method! 
+            cachePolicyFiled.set(null, seconds);
+        }
     }
 
     private InetAddressCacheUtil() {

src/test/java/com/alibaba/dcm/DnsCacheManipulatorTest.java

@@ -186,6 +186,7 @@ public void test_nullSafeForGetDnsCache() throws Exception {
     public void test_setDnsCachePolicy() throws Exception {
         final String host = "baidu.com";
         DnsCacheManipulator.setDnsCachePolicy(2);
+        assertEquals(2, DnsCacheManipulator.getDnsCachePolicy());
 
         InetAddress.getByName(host).getHostAddress();
         final long tick = currentTimeMillis();
@@ -217,6 +218,7 @@ public void test_setDnsCachePolicy() throws Exception {
     @Test
     public void test_setNegativeDnsCachePolicy() throws Exception {
         DnsCacheManipulator.setDnsNegativeCachePolicy(2);
+        assertEquals(2, DnsCacheManipulator.getDnsNegativeCachePolicy());
 
         try {
             InetAddress.getByName(DOMAIN_NOT_EXISTED).getHostAddress();