public void login(Configuration conf) throws IOException {       
  System.setProperty("java.security.krb5.conf", "krb5配置文件路径");
  UserGroupInformation.setConfiguration(conf);
  UserGroupInformation.loginUserFromKeytab(PRNCIPAL_NAME, PATH_TO_KEYTAB);        
}

/*
* 通过java.security.krb5.conf       获取 krb.conf
* 通过hadoop.security.auth_to_local 设置 principal 映射规则
*/
public static void setConfiguration(Configuration conf) {
  initialize(conf, true);
}
private static synchronized void initialize(Configuration conf,
                                              boolean overrideNameRules) {
  // 根据 hadoop.security.authentication 判断 hadoop 的认证方法
  authenticationMethod = SecurityUtil.getAuthenticationMethod(conf);
  if (overrideNameRules || !HadoopKerberosName.hasRulesBeenSet()) {
    try {
// (以非IBM jdk为例)
// 1. 通过反射实例化 sun.security.krb5.Config: 在本例中Config的实例化信息 来自 java.security.krb5.conf 指定的krb5.conf配置文件
// 2. 读取 hadoop.security.auth_to_local，并设置principal映射规则
      HadoopKerberosName.setConfiguration(conf);
    } catch (IOException ioe) {
      throw new RuntimeException(
        "Problem with Kerberos auth_to_local name configuration", ioe);
    }
  }
  // metrics 和 groups 
  if (!(groups instanceof TestingGroups)) {
    groups = Groups.getUserToGroupsMappingService(conf);
  }
  UserGroupInformation.conf = conf;
  if (metrics.getGroupsQuantiles == null) {
    int[] intervals = conf.getInts(HADOOP_USER_GROUP_METRICS_PERCENTILES_INTERVALS);
    if (intervals != null && intervals.length > 0) {
      final int length = intervals.length;
      MutableQuantiles[] getGroupsQuantiles = new MutableQuantiles[length];
      for (int i = 0; i < length; i++) {
        getGroupsQuantiles[i] = metrics.registry.newQuantiles(
          "getGroups" + intervals[i] + "s",
          "Get groups", "ops", "latency", intervals[i]);
      }
      metrics.getGroupsQuantiles = getGroupsQuantiles;
    }
  }
}

public synchronized
  static void loginUserFromKeytab(String user,
                                  String path
                                  ) throws IOException {
    if (!isSecurityEnabled())
      return;

    keytabFile = path;
    keytabPrincipal = user;
    Subject subject = new Subject();
    LoginContext login; 
    long start = 0;
    try {
      // 
      login = newLoginContext(HadoopConfiguration.KEYTAB_KERBEROS_CONFIG_NAME,
            subject, new HadoopConfiguration());
      start = Time.now();
      // Krb5LoginModule
      // HadoopLoginModule
      login.login();
      metrics.loginSuccess.add(Time.now() - start);
      loginUser = new UserGroupInformation(subject);
      loginUser.setLogin(login);
      loginUser.setAuthenticationMethod(AuthenticationMethod.KERBEROS);
    } catch (LoginException le) {
      if (start > 0) {
        metrics.loginFailure.add(Time.now() - start);
      }
      throw new IOException("Login failure for " + user + " from keytab " + 
                            path+ ": " + le, le);
    }
    LOG.info("Login successful for user " + keytabPrincipal
        + " using keytab file " + keytabFile);
  }

import java.util.ArrayList;
import java.util.List;
import java.util.Set;
import java.util.concurrent.CopyOnWriteArraySet;
import java.util.concurrent.CountDownLatch;

public class TestTwo {

    public static void main(String[] args) throws Exception {
        System.out.println("Hello World!");
        // 构造一个10000个元素的集合
        List<Integer> list = new ArrayList<>();
        for (int i = 0; i < 10000; i++) {
            list.add(i);
        }
        // 统计并行执行list的线程
        Set<Thread> threadSet = new CopyOnWriteArraySet<>();
        // 并行执行
        list.parallelStream().forEach(integer -> {
            Thread thread = Thread.currentThread();
            // System.out.println(thread);
            // 统计并行执行list的线程
            threadSet.add(thread);
        });
        System.out.println("threadSet一共有" + threadSet.size() + "个线程");
        System.out.println("系统一个有" + Runtime.getRuntime().availableProcessors() + "个cpu");


        List<Integer> list1 = new ArrayList<>();
        List<Integer> list2 = new ArrayList<>();
        for (int i = 0; i < 100000; i++) {
            list1.add(i);
            list2.add(i);
        }
        Set<Thread> threadSetTwo1 = new CopyOnWriteArraySet<>();
        CountDownLatch countDownLatch = new CountDownLatch(2);
        Thread threadA = new Thread(() -> {
            list1.parallelStream().forEach(integer -> {
                Thread thread = Thread.currentThread();
                threadSetTwo1.add(thread);
            });
            countDownLatch.countDown();
        });
        Set<Thread> threadSetTwo2 = new CopyOnWriteArraySet<>();
        Thread threadB = new Thread(() -> {
            list2.parallelStream().forEach(integer -> {
                Thread thread = Thread.currentThread();
                threadSetTwo2.add(thread);
            });
            countDownLatch.countDown();
        });

        threadA.start();
        threadB.start();
        countDownLatch.await();
        System.out.println("threadSetTwo1一共有" + threadSetTwo1.size() + "个线程");
        System.out.println("threadSetTwo2一共有" + threadSetTwo2.size() + "个线程");

        System.out.println("---------------------------");
        System.out.println("threadSet:"+threadSet);
        System.out.println("threadSet1:"+threadSetTwo1);
        System.out.println("threadSet2:"+threadSetTwo2);
        System.out.println("---------------------------");
        //threadSetTwo.addAll(threadSet);
        //System.out.println(threadSetTwo);
        //System.out.println("threadSetTwo一共有" + threadSetTwo.size() + "个线程");
        //System.out.println("系统一个有" + Runtime.getRuntime().availableProcessors() + "个cpu");
    }
}

class Tse{
    public static void main(String[] args){
      ForkJoinPool forkJoinPool = new ForkJoinPool(2);
      forkJoinPool.submit(() ->
          IntStream.range(1, 1_000_000).parallel().filter(PrimesPrint::isPrime).collect(toList())
      ).get();
    }
}