update doc, add multi ip demo code; add multi ip test case.

Author: oldratlee

library/README.md

@@ -55,13 +55,25 @@ Java Dns Cache Manipulator(DCM) Library
 DnsCacheManipulator.setDnsCache("www.hello.com", "192.168.1.1");
 DnsCacheManipulator.setDnsCache("www.world.com", "1234:5678:0:0:0:0:0:200e"); // 支持IPv6地址
 
-// 之后Java代码中使用到域名都会解析成上面指定的IP。
-// 下面是一个简单获取域名对应的IP，演示一下：
+// 之后Java代码中的域名解析都会是上面设定的IP。
+// 下面用一个简单获取域名对应的IP，来演示一下：
 
 String ip = InetAddress.getByName("www.hello.com").getHostAddress();
 // ip = "192.168.1.1"
 String ipv6 = InetAddress.getByName("www.world.com").getHostAddress();
 // ipv6 = "1234:5678:0:0:0:0:0:200e"
+
+
+// 可以设置多个IP
+DnsCacheManipulator.setDnsCache("www.hello-world.com", "192.168.2.1", "192.168.2.2");
+
+String ipHw = InetAddress.getByName("www.hello-world.com").getHostAddress();
+// ipHw = 192.168.2.1 ，读到第一个IP
+InetAddress[] allIps = InetAddress.getAllByName("www.hello-world.com");
+// 上面读到设置的多个IP
+
+// 设置过期时间，单元毫秒
+DnsCacheManipulator.setDnsCache(3600 * 1000, "www.hello-hell.com", "192.168.1.1", "192.168.1.2");
 ```
 
 通过`dns-cache.properties`文件批量配置

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

@@ -1,5 +1,6 @@
 package com.alibaba.dcm;
 
+import org.junit.Assert;
 import org.junit.Before;
 import org.junit.Test;
 
@@ -13,11 +14,7 @@
 
 import static java.lang.System.currentTimeMillis;
 import static java.lang.Thread.sleep;
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNotSame;
-import static org.junit.Assert.assertNull;
-import static org.junit.Assert.assertTrue;
-import static org.junit.Assert.fail;
+import static org.junit.Assert.*;
 
 /**
  * @author Jerry Lee (oldratlee at gmail dot com)
@@ -52,6 +49,18 @@ public void test_loadDnsCacheConfig_fromMyConfig() throws Exception {
         assertEquals(IP2, ip);
     }
 
+    @Test
+    public void test_setMultiIp() throws Exception {
+        DnsCacheManipulator.setDnsCache("multi.ip.com", "1.1.1.1", "2.2.2.2");
+        String ip = InetAddress.getByName("multi.ip.com").getHostAddress();
+        assertEquals("1.1.1.1", ip);
+
+        InetAddress[] all = InetAddress.getAllByName("multi.ip.com");
+        assertEquals(2, all.length);
+        String[] ips = {all[0].getHostAddress(), all[1].getHostAddress()};
+        assertArrayEquals(new String[]{"1.1.1.1", "2.2.2.2"}, ips);
+    }
+
     @Test
     public void test_configNotFound() throws Exception {
         try {