通过JDBC连接hive

hive是大数据技术簇中进行数据仓库应用的基础组件，是其它类似数据仓库应用的对比基准。基础的数据操作我们可以通过脚本方式以hive-client进行处理。若需要开发应用程序，则需要使用hive的jdbc驱动进行连接。本文以hive wiki上示例为基础，详细讲解了如何使用jdbc连接hive数据库。hive wiki原文地址：

https://cwiki.apache.org/confluence/display/Hive/HiveClient

https://cwiki.apache.org/confluence/display/Hive/HiveServer2+Clients#HiveServer2Clients-JDBC

首先hive必须以服务方式启动，我们平台选用hdp平台，hdp2.2平台默认启动时hive server2 模式。hiveserver2是比hiveserver更高级的服务模式，提供了hiveserver不能提供的并发控制、安全机制等高级功能。服务器启动以不同模式启动，客户端代码的编码方式也略有不同，具体见代码。

服务启动完成之后，在eclipse环境中编辑代码。代码如下：

import java.sql.SQLException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.DriverManager; 

public class HiveJdbcClient {

  /*hiverserver 版本使用此驱动*/
  //private static String driverName = "org.apache.hadoop.hive.jdbc.HiveDriver";
  /*hiverserver2 版本使用此驱动*/
  private static String driverName = "org.apache.hive.jdbc.HiveDriver";

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

    try {
      Class.forName(driverName);
    } catch (ClassNotFoundException e) {
      e.printStackTrace();
      System.exit(1);
    }

    /*hiverserver 版本jdbc url格式*/
    //Connection con = DriverManager.getConnection("jdbc:hive://hostip:10000/default", "", "");

    /*hiverserver2 版本jdbc url格式*/
    Connection con = DriverManager.getConnection("jdbc:hive2://hostip:10000/default", "hive", "hive");
    Statement stmt = con.createStatement();
    //参数设置测试
    //boolean resHivePropertyTest = stmt
    //        .execute("SET tez.runtime.io.sort.mb = 128");

    boolean resHivePropertyTest = stmt
            .execute("set hive.execution.engine=tez");
    System.out.println(resHivePropertyTest);

    String tableName = "testHiveDriverTable";
    stmt.executeQuery("drop table " + tableName);
    ResultSet res = stmt.executeQuery("create table " + tableName + " (key int, value string)");

    //show tables
    String sql = "show tables ‘" + tableName + "‘";
    System.out.println("Running: " + sql);
    res = stmt.executeQuery(sql);
    if (res.next()) {
      System.out.println(res.getString(1));
    }

    //describe table
    sql = "describe " + tableName;
    System.out.println("Running: " + sql);
    res = stmt.executeQuery(sql);
    while (res.next()) {
      System.out.println(res.getString(1) + "\t" + res.getString(2));
    } 

    // load data into table
    // NOTE: filepath has to be local to the hive server
    // NOTE: /tmp/a.txt is a ctrl-A separated file with two fields per line
    String filepath = "/tmp/a.txt";
    sql = "load data local inpath ‘" + filepath + "‘ into table " + tableName;
    System.out.println("Running: " + sql);
    res = stmt.executeQuery(sql); 

    // select * query
    sql = "select * from " + tableName;
    System.out.println("Running: " + sql);
    res = stmt.executeQuery(sql);
    while (res.next()) {
      System.out.println(String.valueOf(res.getInt(1)) + "\t" + res.getString(2));
    }

    // regular hive query
    sql = "select count(1) from " + tableName;
    System.out.println("Running: " + sql);
    res = stmt.executeQuery(sql);
    while (res.next()) {
      System.out.println(res.getString(1));
    }

  }

}

可以将如下jar包放在eclipse buildpath，可以在启动时放在classpath路径。

其中jdbcdriver可用hive-jdbc.jar,这样的话，其他的jar也必须包含，或者用jdbc-standalone jar包，用此jar包其他jar包就可以不用包含。其中hadoop-common包一定要包含。

执行后等待结果正确运行。若出现异常，则根据提示进行解决。提示不明确的几个异常的解决方案如下：

1. 假如classpath或者buildpath中不包含hadoop-common-0.23.9.jar，出现如下错误

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/hadoop/conf/Configuration
    at org.apache.hive.jdbc.HiveConnection.createBinaryTransport(HiveConnection.java:393)
    at org.apache.hive.jdbc.HiveConnection.openTransport(HiveConnection.java:187)
    at org.apache.hive.jdbc.HiveConnection.<init>(HiveConnection.java:163)
    at org.apache.hive.jdbc.HiveDriver.connect(HiveDriver.java:105)
    at java.sql.DriverManager.getConnection(DriverManager.java:664)
    at java.sql.DriverManager.getConnection(DriverManager.java:247)
    at HiveJdbcClient.main(HiveJdbcClient.java:28)
Caused by: java.lang.ClassNotFoundException: org.apache.hadoop.conf.Configuration
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 7 more

2. HIVE JDBC连接服务器卡死:

假如使用hiveserver    版本JDBCdriver 连接hiverserver2,将可能出现此问题，具体在JDBCDriver连接上之后根据协议要求请求hiveserver2返回数据时，hiveserver2不返回任何数据，因此JDBC driver将卡死不返回。

3. TezTask出错，返回错误号1.

Exception in thread "main" java.sql.SQLException: Error while processing statement: FAILED: Execution Error, return code 1 from org.apache.hadoop.hive.ql.exec.tez.TezTask
    at org.apache.hive.jdbc.HiveStatement.execute(HiveStatement.java:296)
    at org.apache.hive.jdbc.HiveStatement.executeQuery(HiveStatement.java:392)
    at HiveJdbcClient.main(HiveJdbcClient.java:40)

错误号1代表用户认证失败，在连接时必须指定用户名密码，有可能通过服务器设置可以不需要用户认证就可以执行，hdp默认安装配置用户名密码是hive,hive

3. TezTask出错，返回错误号2.

TaskAttempt 3 failed, info=[Error: Failure while running task:java.lang.IllegalArgumentException: tez.runtime.io.sort.mb 256 should be larger than 0 and should be less than the available task memory (MB):133
    at com.google.common.base.Preconditions.checkArgument(Preconditions.java:88)
    at org.apache.tez.runtime.library.common.sort.impl.ExternalSorter.getInitialMemoryRequirement(ExternalSorter.java:291)
    at org.apache.tez.runtime.library.output.OrderedPartitionedKVOutput.initialize(OrderedPartitionedKVOutput.java:95)
    at org.apache.tez.runtime.LogicalIOProcessorRuntimeTask$InitializeOutputCallable.call(LogicalIOProcessorRuntimeTask.java:430)
    at org.apache.tez.runtime.LogicalIOProcessorRuntimeTask$InitializeOutputCallable.call(LogicalIOProcessorRuntimeTask.java:409)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
]], Vertex failed as one or more tasks failed. failedTasks:1, Vertex vertex_1441168955561_1508_2_00 [Map 1] killed/failed due to:null]
Vertex killed, vertexName=Reducer 2, vertexId=vertex_1441168955561_1508_2_01, diagnostics=[Vertex received Kill while in RUNNING state., Vertex killed as other vertex failed. failedTasks:0, Vertex vertex_1441168955561_1508_2_01 [Reducer 2] killed/failed due to:null]
DAG failed due to vertex failure. failedVertices:1 killedVertices:1
FAILED: Execution Error, return code 2 from org.apache.hadoop.hive.ql.exec.tez.TezTask

code 2，代表错误是参数错误，一般是指对应的值不合适，以上堆栈指示tez.runtime.io.sort.mb参数256比可用内存大，因此修改配置文件或者执行查询之前先设置其大小即可。

通过以上设置以及参数修正之后，应用程序就能正确的使用jdbc连接hive数据库。

另可以用squirrel-sql GUI客户端管理hivedb，驱动设置方式与代码中对应jar包、驱动类、url等使用同样方式设置，测试成功建立好alias就可以开始连接hive，可以比较方便的管理和操作hive数据库。