关于hadoop中的DBInputFormat试验

1、注意，需要声明为静态内部类，否则会报java.lang.NoSuchMethodException...<init>的错误
public static class MySqlWritable implements Writable, DBWritable {

2、如果输出目录存在，需要先删除

3、由于需要从mysql数据取值，则需要有mysql数据库驱动包，hadoop classpath查看hadoop类加载路径，将驱动包拷贝到其中一个目录下即可；

4、解决mysql"Access denied for user'root'@'IP地址'"问题
a、登录mysql
mysql -u username -p passwd

b、然后执行如下命令：
b-1、 GRANT ALL PRIVILEGES ON *.* TO 'myuser'@'%' IDENTIFIED BY 'mypassword' WITH GRANT OPTION;
b-2、FLUSH   PRIVILEGES;

Java代码：

package cn.sniper.hadoop.inputformat;

import java.io.DataInput;
import java.io.DataOutput;
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.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
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;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;

import cn.sniper.hadoop.util.HdfsUtil;

public class MyDBInputFormat {

    public static String IN_PATH = "hdfs://192.168.1.231:9000/README.txt";
    public static String OUT_PATH = "hdfs://192.168.1.231:9000/out";
    
    public static class MyMap extends Mapper<LongWritable, MySqlWritable, Text, IntWritable> {
        protected void map(LongWritable key, MySqlWritable value, org.apache.hadoop.mapreduce.Mapper<LongWritable,MySqlWritable,Text,IntWritable>.Context context) throws java.io.IOException ,InterruptedException {
            System.out.println(value);
            context.write(new Text(value.toString()), new IntWritable(1));
        };
    }
    
    /**
     * 注意，需要声明为静态内部类，否则会报java.lang.NoSuchMethodException...<init>的错误
     * @author sniper
     *
     */
    public static class MySqlWritable implements Writable, DBWritable {
        
        private String id;
        
        private String name;
        
        private String nickName;
        
        @Override
        public void readFields(ResultSet resultSet) throws SQLException {
            id = resultSet.getString(1);
            name = resultSet.getString(2);
            nickName = resultSet.getString(3);
        }

        @Override
        public void write(PreparedStatement statement) throws SQLException {
            statement.setString(1, id);
            statement.setString(2, name);
            statement.setString(3, nickName);
        }

        @Override
        public void readFields(DataInput dataInput) throws IOException {
            id = dataInput.readUTF();
            name = dataInput.readUTF();
            nickName = dataInput.readUTF();
        }

        @Override
        public void write(DataOutput dataOutput) throws IOException {
            dataOutput.writeUTF(id);
            dataOutput.writeUTF(name);
            dataOutput.writeUTF(nickName);
        }

        @Override
        public String toString() {
            return "MySqlWritable [id=" + id + ", name=" + name + ", nickName="
                    + nickName + "]";
        }
    }
    
    public static void main(String[] args) throws Exception {        
        Configuration conf = new Configuration();
        
        String driverClass = "com.mysql.jdbc.Driver";
        String dbUrl = "jdbc:mysql://192.168.1.105:3306/my";
        String userName = "root";
        String passwd = "123456";
        DBConfiguration.configureDB(conf, driverClass, dbUrl, userName, passwd);
        
        Job job = Job.getInstance(conf, MyDBInputFormat.class.getName());
        job.setJarByClass(MyDBInputFormat.class);
        
        //默认是TextInputFormat
        job.setInputFormatClass(DBInputFormat.class);
        String inputQuery = "select c_id, c_name, c_nickName from t_test";
        String inputCountQuery = "select count(*) from t_test";
        
        DBInputFormat.setInput(job, MySqlWritable.class, inputQuery, inputCountQuery);
        
        /*String tableName = "t_test";
        String conditions = "";
        String orderBy = "";
        String[] fieldNames = new String[]{"c_id", "c_name", "c_nickName"};
        DBInputFormat.setInput(job, MySqlWritable.class, tableName, conditions, orderBy, fieldNames);*/
        
        job.setOutputFormatClass(TextOutputFormat.class);
        FileOutputFormat.setOutputPath(job, new Path(OUT_PATH));
        
        job.setMapperClass(MyMap.class);
        
        //map输出的key如果不做设置，默认和reduce的key、value一致
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(IntWritable.class);
        
        job.waitForCompletion(true);
    }
}