📅  最后修改于: 2023-12-03 15:31:06.892000             🧑  作者: Mango
HCatalog是Hadoop生态系统的一部分。它是一个表和存储管理服务,提供了对Apache Hive和Apache Pig等数据处理工具的元数据访问。HCatalog的主要目的是为Hadoop生态系统中的数据提供一个元数据管理系统,因此可以方便地将不同类型和格式的数据存储在Hadoop分布式文件系统(HDFS)和Apache HBase中。
在HCatalog中,输入输出格式用于指定数据的存储格式。Hadoop平台支持多种文件格式,例如文本格式、序列文件格式等。以下是Hadoop平台支持的一些常见文件格式:
HCatalog支持所有这些格式,并提供了多个自定义输入输出格式,方便用户实现自己的输入输出格式。
以下是使用HCatalog自定义输入输出格式的示例:
以下是一个简单的Java类,演示如何使用HCatalog's来编写自定义输入输出格式的数据。我们将使用自定义的TripletTextOutputFormatter将数据以xyzn文本格式写入HDFS中。
import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hive.conf.HiveConf;
import org.apache.hadoop.hive.serde2.io.DoubleWritable;
import org.apache.hadoop.hive.serde2.io.ShortWritable;
import org.apache.hadoop.io.DefaultStringifier;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hive.hcatalog.mapreduce.OutputJobInfo;
import org.apache.hive.hcatalog.mapreduce.TextOutputFormat;
import org.apache.hive.hcatalog.data.DefaultHCatRecord;
import org.apache.hadoop.mapreduce.Job;
public class WriteXYZNData {
public static void main(String[] args)
throws IOException, InterruptedException, ClassNotFoundException {
Configuration conf = new HiveConf();
Job job = new Job(conf, "write-xyzndata");
job.setJarByClass(WriteXYZNData.class);
job.setMapperClass(MyMapper.class);
job.setNumReduceTasks(0);
job.setOutputFormatClass(TextOutputFormat.class);
job.setOutputKeyClass(NullWritable.class);
job.setOutputValueClass(DefaultHCatRecord.class);
String inputDir = args[0];
String outputDir = args[1];
Path inPath = new Path(inputDir);
Path outPath = new Path(outputDir);
TextOutputFormat.setOutputPath(job, outPath);
OutputJobInfo outputJobInfo = OutputJobInfo.create(null, null, outPath.toString());
TextOutputFormat.setOutputPath(job, new Path(outPath + "/temp"));
outputJobInfo.setOutputSchema(JobInfo.getOutputSchema("XYZNSchema"));
TextOutputFormat.setOutputPath(job, outPath);
TextOutputFormat.setHiveOutputJobInfo(job, outputJobInfo);
FileSystem fs = FileSystem.get(outPath.toUri(), conf);
if (fs.exists(outPath)) {
fs.delete(outPath, true);
}
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
public static class MyMapper extends {
@Override
protected void map(LongWritable key, GenericRecord value, Context context)
throws IOException, InterruptedException {
// TODO: Write mapper output
}
private HCatRecord mapXYZNToRecord(String xyzn) {
// TODO: Parse XYZN values and map to HCatRecord
}
}
}
以下是一个简单的Java类,演示如何使用HCatalog来读取以xyzn文本格式存储的数据。我们将使用自定义的TripletTextInputFormatter读取HDFS中的数据。
import java.io.IOException;
import java.util.Properties;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hive.conf.HiveConf;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hive.hcatalog.common.HCatException;
import org.apache.hive.hcatalog.common.HCatUtil;
import org.apache.hive.hcatalog.data.schema.HCatSchema;
import org.apache.hive.hcatalog.mapreduce.HCatInputFormat;
import org.apache.hive.hcatalog.mapreduce.InputJobInfo;
public class ReadXYZNData {
public static void main(String[] args)
throws IOException, InterruptedException, ClassNotFoundException, HCatException {
String inputDir = args[0];
String outputDir = args[1];
Configuration conf = new HiveConf();
Job job = new Job(conf, "read-xyzndata");
job.setJarByClass(ReadXYZNData.class);
job.setMapOutputKeyClass(NullWritable.class);
job.setMapOutputValueClass(Text.class);
FileInputFormat.setInputPaths(job, new Path(inputDir));
Properties props = HCatUtil.getInputJobProperties(new HCatSchema("XYZNSchema"), null, null);
InputJobInfo inputJobInfo = InputJobInfo.create(null, null, props);
HCatInputFormat.setInput(job, inputJobInfo);
job.setMapperClass(MyMapper.class);
// TODO: Define reducer class here
Path outPath = new Path(outputDir);
FileSystem fs = FileSystem.get(outPath.toUri(), conf);
if (fs.exists(outPath)) {
fs.delete(outPath, true);
}
FileOutputFormat.setOutputPath(job, outPath);
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
public static class MyMapper extends Mapper<WritableComparable, HCatRecord, NullWritable, Text> {
private Text textValue = new Text();
private DecimalFormat df = new DecimalFormat("#.##");
@Override
protected void map(WritableComparable key, HCatRecord value, Context context)
throws IOException, InterruptedException {
// TODO: Write mapper output
}
}
}
本文介绍了HCatalog输入输出格式的概念和用法。我们还提供了实现自定义输入输出格式的Java示例,以方便用户参考。自定义输入输出格式的引入可以帮助用户根据自身需求来选择合适的存储格式,以便更好地处理数据。