Java动态替换InetAddress中DNS的做法简单分析2

2023-03-20 18:13:27

  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. }
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