DBInputFormat的用法

package inputformat;import java.io.DataInput;import java.io.DataOutput;import java.io.IOException;import java.net.URI;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import mapreduce.WordCountApp;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.LongWritable;import org.apache.hadoop.io.NullWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.io.Writable;import org.apache.hadoop.mapreduce.Job;import org.apache.hadoop.mapreduce.Mapper;import org.apache.hadoop.mapreduce.lib.db.DBConfiguration;import org.apache.hadoop.mapreduce.lib.db.DBInputFormat;import org.apache.hadoop.mapreduce.lib.db.DBWritable;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;/** * 要运行本示例 * 1.把mysql的jdbc驱动放到各TaskTracker节点的lib目录下 * 2.重启集群 * */public class MyDBInputFormatApp {private static final String OUT_PATH = "hdfs://hadoop0:9000/out";public static void main(String[] args) throws Exception{Configuration conf = new Configuration();DBConfiguration.configureDB(conf, "com.mysql.jdbc.Driver", "jdbc:mysql://hadoop0:3306/test", "root", "admin");final FileSystem filesystem = FileSystem.get(new URI(OUT_PATH), conf);filesystem.delete(new Path(OUT_PATH), true);final Job job = new Job(conf , WordCountApp.class.getSimpleName());job.setJarByClass(WordCountApp.class);job.setInputFormatClass(DBInputFormat.class);DBInputFormat.setInput(job, MyUser.class, "myuser", null, null, "id", "name");job.setMapperClass(MyMapper.class);job.setMapOutputKeyClass(Text.class);job.setMapOutputValueClass(NullWritable.class);job.setNumReduceTasks(0);//指定不需要使用reduce，直接把map输出写入到HDFS中job.setOutputKeyClass(Text.class);job.setOutputValueClass(NullWritable.class);FileOutputFormat.setOutputPath(job, new Path(OUT_PATH));job.waitForCompletion(true);}public static class MyMapper extends Mapper<LongWritable, MyUser, Text, NullWritable>{protected void map(LongWritable key, MyUser value, org.apache.hadoop.mapreduce.Mapper<LongWritable,MyUser,Text,NullWritable>.Context context) throws java.io.IOException ,InterruptedException {context.write(new Text(value.toString()), NullWritable.get());};}public static class MyUser implements Writable, DBWritable{int id;String name;@Overridepublic void write(DataOutput out) throws IOException {out.writeInt(id);Text.writeString(out, name);}@Overridepublic void readFields(DataInput in) throws IOException {this.id = in.readInt();this.name = Text.readString(in);}@Overridepublic void write(PreparedStatement statement) throws SQLException {statement.setInt(1, id);statement.setString(2, name);}@Overridepublic void readFields(ResultSet resultSet) throws SQLException {this.id = resultSet.getInt(1);this.name = resultSet.getString(2);}@Overridepublic String toString() {return id + "\t" + name;}}}