email 도메인이 호스팅 중인지 체크하는 간단한 java 프로그램

필요 라이브러리

<!-- https://mvnrepository.com/artifact/commons-validator/commons-validator -->
        <dependency>
            <groupId>commons-validator</groupId>
            <artifactId>commons-validator</artifactId>
            <version>1.8.0</version>
        </dependency>

코드(java ver)

import java.io.File;
import java.io.IOException;
import java.util.Arrays;
import java.util.Hashtable;
import java.util.List;
import java.util.Set;
import javax.naming.NamingEnumeration;
import javax.naming.NamingException;
import javax.naming.directory.Attribute;
import javax.naming.directory.Attributes;
import javax.naming.directory.DirContext;
import javax.naming.directory.InitialDirContext;
import org.apache.commons.io.FileUtils;
import org.apache.commons.lang3.StringUtils;
import org.apache.commons.validator.routines.EmailValidator;

public class CheckEmailDomainSample {

  /** 알고있는 유효한 이메일 호스트명  */
  private static final Set<String> CACHED_VALID_HOSTNAME = Sets.newLinkedHashSet(Arrays.asList("gmail.com", "naver.com"));
  private static final String targetFilePath = "검사할 도메인이 저장된 파일 경로(개행 구분)";

  private static final EmailValidator emailValid = EmailValidator.getInstance();

  public static void main(String[] args) throws IOException {

 
    List<String> emailDomainList = FileUtils.readLines(new File(targetFilePath));

    for (String hostname : emailDomainList) {
      System.out.println(String.format("%s : %s'", hostname, isValidHostname(hostname)));
    }
  }


  public static boolean isValidHostname(String hostname) {

    try {

      if (CACHED_VALID_HOSTNAME.contains(StringUtils.lowerCase(hostname))) {
        return true;
      }

      final String mxStr = "MX";
      Hashtable<String, String> hashtable = new Hashtable<>();

      hashtable.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory");
      hashtable.put("com.sun.jndi.dns.timeout.initial", "5000"); /* quite short... too short? */
      hashtable.put("com.sun.jndi.dns.timeout.retries", "1");

      DirContext ictx = new InitialDirContext(hashtable);

      Attributes attrs = ictx.getAttributes(hostname, new String[]{mxStr});
      Attribute attr = attrs.get(mxStr);

      if (attr == null || attr.size() == 0) {
        return false; //없음
      }

      NamingEnumeration e = attr.getAll();

      while (e.hasMore()) {
        String mxs = String.valueOf(e.next());
        String[] mx = mxs.split("\\s+");

        for (String mxString : mx) {
          if (StringUtils.endsWith(mxString, ".")) {
            return true;
          }
        }
      }

    } catch (NamingException ne) {
      return false;
    }

    return false;
  }

}