Java动态替换InetAddress中DNS的做法简单分析2

1. import java.io.BufferedReader;
2. import java.io.IOException;
3. import java.io.InputStream;
4. import java.io.InputStreamReader;
5. import java.lang.reflect.Field;
6. import java.lang.reflect.Method;
7. import java.net.HttpURLConnection;
8. import java.net.InetAddress;
9. import java.net.MalformedURLException;
10. import java.net.URL;
11. import java.net.UnknownHostException;
12. import java.util.HashMap;
13. import java.util.List;
14. import java.util.Map;
15. import sun.net.spi.nameservice.NameService;
16. public class JavaDNSCacheTest {
17. /**
18. * 经测试,二种方式在Windows环境都可以, Linux环境待测
19. *
20. * @param args
21. * @throws Exception
22. */
23. public static void main(String[] args) throws Exception {
24. /* 1. 动态替换AddressCache */
25. // changeDNSWithAddressCache();
26. /* 1. 动态代理NameService */
27. changeDNSWithNameService();
28. }
29. public static void changeDNSWithNameService() throws Exception {
30. /* 1. 获取反身类 */
31. Class<?> addressClass = InetAddress.class;
32. /* 2. 获取addressCache字段 */
33. try {
34. Field nameServiceField = addressClass.getDeclaredField("nameService");// 对于Jrockit或IBM JDK
35. nameServiceField.setAccessible(true);
36. sun.net.spi.nameservice.NameService nameService = (NameService) nameServiceField.get(null);
37. nameServiceField.set(null, new NameServiceProxy(nameService));
38. nameServiceField.setAccessible(false);
39. } catch (NoSuchFieldException e) {
40. Field nameServicesField = addressClass.getDeclaredField("nameServices");// 对于OpenJDK
41. nameServicesField.setAccessible(true);
42. List<sun.net.spi.nameservice.NameService> nameServices = (List<sun.net.spi.nameservice.NameService>) nameServicesField.get(null);
43. if (nameServices != null && nameServices.size() > 0) {
44. /* 置换为代理实例 */
45. nameServices.set(0, new NameServiceProxy(nameServices.get(0)));
46. } else {
47. // 可能为空吗? 待测
48. }
49. nameServicesField.setAccessible(false);
50. }
51. getHttpConent("www.baidu.com");
52. }
53. public static void changeDNSWithCddressCache() throws Exception {
54. /* 1. 获取反身类 */
55. Class<?> addressClass = InetAddress.class;
56. /* 2. 获取addressCache字段 */
57. Field addressCacheField = addressClass.getDeclaredField("addressCache");
58. /* 3. 获取addressCache */
59. addressCacheField.setAccessible(true);
60. Object addressCache = addressCacheField.get(null);
61. addressCacheField.setAccessible(false);
62. /* 4. 获取addressCache的反射类 */
63. Class<?> addressCacheClass = addressCache.getClass();
64. /* 5. 获取addressCache的put方法 */
65. Method putMethod = addressCacheClass.getDeclaredMethod("put", String.class, InetAddress[].class);
66. /* 5. 修改addressCache将wwww.baidu.com换成指定任意IP */
67. putMethod.setAccessible(true);
68. putMethod.invoke(addressCache, "www.baidu.com", new InetAddress[] { InetAddress.getByAddress(new byte[] { 115, (byte) 239, (byte) 210, 26 }) });
69. putMethod.setAccessible(false);
70. /* 6.测试,看看是否连通 */
71. getHttpConent("www.baidu.com");
72. }
73. private static void getHttpConent(String host) throws MalformedURLException, IOException {
74. HttpURLConnection conn = (HttpURLConnection) new URL("http://" + host).openConnection();
75. try {
76. conn.setConnectTimeout(3000);// 减少连接时间,方便测试
77. conn.setDefaultUseCaches(false);
78. conn.setDoInput(true);
79. conn.setRequestMethod("GET");
80. conn.connect();
81. int code = conn.getResponseCode();
82. System.out.format("REST[%d]\n", code);
83. InputStream in = null;
84. in = conn.getErrorStream();// 如果非2xx,则由errorStream获取输出.
85. if (in == null) {
86. in = conn.getInputStream();
87. }
88. if (in != null) {
89. BufferedReader reader = new BufferedReader(new InputStreamReader(in));
90. for (String line = null; (line = reader.readLine()) != null;) {
91. System.out.println(line);
92. }
93. }
94. } finally {
95. if (conn != null) {
96. conn.disconnect();
97. }
98. }
99. }
100. @SuppressWarnings("restriction")
101. public static class NameServiceProxy implements sun.net.spi.nameservice.NameService {
102. final sun.net.spi.nameservice.NameService nameService;
103. final Map<String, InetAddress[]> mapping = new HashMap<String, InetAddress[]>();
104. {
105. try {
106. mapping.put("www.baidu.com", new InetAddress[] { InetAddress.getByAddress(new byte[] { 115, (byte) 239, (byte) 210, 26 }) });
107. } catch (UnknownHostException e) {
108. e.printStackTrace();
109. }
110. }// 实例初始化表
111. public NameServiceProxy(sun.net.spi.nameservice.NameService nameService) {
112. this.nameService = nameService;
113. }
114. @Override
115. public String getHostByAddr(byte[] addr) throws UnknownHostException {
116. return this.nameService.getHostByAddr(addr);
117. }
118. @Override
119. public InetAddress[] lookupAllHostAddr(String host) throws UnknownHostException {
120. if (mapping.containsKey(host)) {
121. return mapping.get(host);
122. } else {
123. return this.nameService.lookupAllHostAddr(host);
124. }
125. }
126. }
127. }