null-safe for method DnsCacheManipulator.getDnsCache #21

Author: oldratlee

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

@@ -9,6 +9,8 @@
 import java.util.Properties;
 import java.util.regex.Pattern;
 
+import javax.annotation.Nullable;
+
 /**
  * Setting dns (in fact dns cache).
  * <p/>
@@ -119,9 +121,10 @@ public static void loadDnsCacheConfig(String propertiesFileName) {
     /**
      * Get dns cache.
      *
-     * @return dns cache
+     * @return dns cache. return {@code null} if no entry for host or dns cache is expired.
      * @throws DnsCacheManipulatorException Operation fail
      */
+    @Nullable
     public static DnsCacheEntry getDnsCache(String host) {
         try {
             return InetAddressCacheUtil.getInetAddressCache(host);

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

@@ -181,11 +181,21 @@ public static DnsCacheEntry getInetAddressCache(String host)
             throws NoSuchFieldException, IllegalAccessException {
         host = host.toLowerCase();
 
-        Object cacheEntry;
+        final Object cacheEntry;
         synchronized (getAddressCacheFieldOfInetAddress()) {
             cacheEntry = getCacheFiledOfAddressCacheFiledOfInetAddress().get(host);
         }
-        return inetAddress$CacheEntry2DnsCacheEntry(host, cacheEntry);
+
+        if (null == cacheEntry) return null;
+
+        final DnsCacheEntry dnsCacheEntry = inetAddress$CacheEntry2DnsCacheEntry(host, cacheEntry);
+        if (isDnsCacheEntryExpired(dnsCacheEntry.getHost())) return null;
+
+        return dnsCacheEntry;
+    }
+
+    static boolean isDnsCacheEntryExpired(String host) {
+        return null == host || "0.0.0.0".equals(host);
     }
 
     public static DnsCache listInetAddressCache()
@@ -202,7 +212,7 @@ public static DnsCache listInetAddressCache()
         for (Map.Entry<String, Object> entry : cache.entrySet()) {
             final String host = entry.getKey();
 
-            if ("0.0.0.0".equals(host) || host == null) { // exclude expired entries!
+            if (isDnsCacheEntryExpired(host)) { // exclude expired entries!
                 continue;
             }
             retCache.add(inetAddress$CacheEntry2DnsCacheEntry(host, entry.getValue()));

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

@@ -1,7 +1,6 @@
 package com.alibaba.dcm;
 
 import org.junit.Before;
-import org.junit.BeforeClass;
 import org.junit.Test;
 
 import java.net.InetAddress;
@@ -11,6 +10,7 @@
 import java.util.List;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
@@ -150,4 +150,10 @@ public void test_multi_ips_in_config_file() throws Exception {
                 new String[]{"42.42.41.1", "42.42.41.2", "42.42.41.3", "42.42.41.4"}, new Date(Long.MAX_VALUE));
         assertEquals(entryLoose, DnsCacheManipulator.getDnsCache(hostLoose));
     }
+
+    @Test
+    public void test_nullSafeForGetDnsCache() throws Exception {
+        final DnsCacheEntry dnsCache = DnsCacheManipulator.getDnsCache(DOMAIN_NOT_EXISTED);
+        assertNull(dnsCache);
+    }
 }