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：
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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.(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。
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