本篇文章给大家分享的是有关mr如何使用hcatalog读写hive表，小编觉得挺实用的，因此分享给大家学习，希望大家阅读完这篇文章后可以有所收获，话不多说，跟着小编一起来看看吧。
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public class onTimeMapper extends Mapper {@Overrideprotected void map(WritableComparable key, HCatRecord value,org.apache.hadoop.mapreduce.Mapper.Context context)throws IOException, InterruptedException {// Get table schemaHCatSchema schema = HCatBaseInputFormat.getTableSchema(context);Integer year = new Integer(value.getString("year", schema));Integer month = new Integer(value.getString("month", schema));Integer DayofMonth = value.getInteger("dayofmonth", schema);context.write(new IntPair(year, month), new IntWritable(DayofMonth));}}
public class onTimeReducer extends Reducer {public void reduce (IntPair key, Iterable value, Context context) throws IOException, InterruptedException{ int count = 0; // records counter for particular year-month for (IntWritable s:value) { count++; } // define output record schema List columns = new ArrayList(3); columns.add(new HCatFieldSchema("year", HCatFieldSchema.Type.INT, "")); columns.add(new HCatFieldSchema("month", HCatFieldSchema.Type.INT, "")); columns.add(new HCatFieldSchema("flightCount", HCatFieldSchema.Type.INT,"")); HCatSchema schema = new HCatSchema(columns); HCatRecord record = new DefaultHCatRecord(3); record.setInteger("year", schema, key.getFirstInt()); record.set("month", schema, key.getSecondInt()); record.set("flightCount", schema, count); context.write(null, record);}} public class onTimeDriver extends Configured implements Tool{private static final Log log = LogFactory.getLog( onTimeDriver.class );public int run( String[] args ) throws Exception{Configuration conf = new Configuration();Job job = new Job(conf, "OnTimeCount");job.setJarByClass(onTimeDriver.class);job.setMapperClass(onTimeMapper.class);job.setReducerClass(onTimeReducer.class);HCatInputFormat.setInput(job, "airline", "ontimeperf");job.setInputFormatClass(HCatInputFormat.class);job.setMapOutputKeyClass(IntPair.class);job.setMapOutputValueClass(IntWritable.class);job.setOutputKeyClass(Text.class);job.setOutputValueClass(DefaultHCatRecord.class);job.setOutputFormatClass(HCatOutputFormat.class);HCatOutputFormat.setOutput(job, OutputJobInfo.create("airline", "flight_count", null));HCatSchema s = HCatOutputFormat.getTableSchema(job);HCatOutputFormat.setSchema(job, s);return (job.waitForCompletion(true)? 0:1);}public static void main(String[] args) throws Exception{int exitCode = ToolRunner.run(new onTimeDriver(), args);System.exit(exitCode);}}
create table airline.flight_count(Year INT ,Month INT ,flightCount INT)ROW FORMAT DELIMITED FIELDS TERMINATED BY ','STORED AS TEXTFILE;
以上就是mr如何使用hcatalog读写hive表，小编相信有部分知识点可能是我们日常工作会见到或用到的。希望你能通过这篇文章学到更多知识。更多详情敬请关注创新互联行业资讯频道。