DBWritable的使用

首先导入mysql连接驱动jar包

或者maven模式下在pom.xml文件中追加：

<dependency>

<groupId>mysql</groupId>

<artifactId>mysql-connector-java</artifactId>

<version>5.1.38</version>

</dependency>

代码：

package com.neworigin.db;

import java.io.IOException;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

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.mapreduce.Job;

import org.apache.hadoop.mapreduce.Mapper;

import org.apache.hadoop.mapreduce.Reducer;

import org.apache.hadoop.mapreduce.lib.db.DBConfiguration;

import org.apache.hadoop.mapreduce.lib.db.DBInputFormat;

import org.apache.hadoop.mapreduce.lib.db.DBOutputFormat;

import org.apache.hadoop.mapreduce.lib.db.DBWritable;

import org.apache.hadoop.mapreduce.lib.input.FileSplit;

import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class DBJob {

public static class TableUers implements DBWritable{//表的映射

int id;

String name;

int age;

public int getId() {

return id;

}

public void setId(int id) {

this.id = id;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public int getAge() {

return age;

}

public void setAge(int age) {

this.age = age;

}

public TableUers(int id, String name, int age) {

this.id = id;

this.name = name;

this.age = age;

}

public TableUers() {

}

//将表的映射对象中的属性设置进（写入数据库）

public void write(PreparedStatement statement) throws SQLException {

statement.setInt(1, id);

statement.setString(2, name);

statement.setInt(3, age);

}

//从结果集通过与字段匹配的赋值给表的映射对象（读取数据库）

public void readFields(ResultSet resultSet) throws SQLException {//获取表中的属性

this.id=resultSet.getInt("id");

this.name=resultSet.getString("name");

this.age=resultSet.getInt("age");

}

@Override

public String toString() {

return  id + "  " + name + " " + age;

}

}

public static class MyMapper extends Mapper<Object ,TableUers,TableUers,NullWritable>{

protected void map(Object key, TableUers value, Mapper<Object, TableUers, TableUers, NullWritable>.Context context)

throws IOException, InterruptedException {

String s = value.toString();

System.out.println(s);

context.write(value,NullWritable.get());

}

}

public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {

Path out=new Path("file:///F:/安装/java工程/MR/data/db/out");

Job job = Job.getInstance();

Configuration conf = job.getConfiguration();

/* FileSystem fs =FileSystem.get(conf);

if(fs.exists(out))

{

fs.delete(out);

}*/

job.setInputFormatClass(DBInputFormat.class);

DBConfiguration.configureDB(conf, "com.mysql.jdbc.Driver", "jdbc:mysql://127.0.0.1/mydb","root","123456");

DBInputFormat.setInput(job, TableUers.class, "select id,name,age from user", "select count(*) from user");

job.setOutputFormatClass(DBOutputFormat.class);

DBOutputFormat.setOutput(job, "aaa", "id","name","age");

job.setMapperClass(MyMapper.class);

job.setMapOutputKeyClass(TableUers.class);

job.setMapOutputValueClass(NullWritable.class);

job.setOutputKeyClass(TableUers.class);

job.setOutputValueClass(NullWritable.class);

job.setNumReduceTasks(0);

//FileOutputFormat.setOutputPath(job, out);

job.waitForCompletion(true);

}

}