map-reduce实现（map端join， reduce端join）

• map-reduce实现hive的join全外连接查询 (大表 +小表 ）

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假设有订单表orders， 用户表customers,   存在大表+小表的关系， 则可以使用sql的优化: 使用map端join

现在的问题是， 如何使用map-reduce 自己实现:  map端的 full outer join ? reduce端的full outer join ?

part1:  map端全外连接 （map-reduce实现）

思路： 小表在map阶段可以先加载到内存

public class App1 {
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {

        //job
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS","file:///");

        Job job = Job.getInstance();
        job.setJarByClass(App1.class);
        job.setJobName("mapjoin");

        //map,red
        job.setMapperClass(Map1.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(NullWritable.class);
        //存放：customers.txt, orders.txt
        FileInputFormat.addInputPath(job,new Path("/home/hadoop/txt/mrjoin"));

        FileSystem fs = FileSystem.get(conf);
        Path path = new Path("mapjoin");
        if (fs.exists(path)) {
            fs.delete(path, true);
        }
        FileOutputFormat.setOutputPath(job, path);

        //启动
        job.waitForCompletion(true);
    }
}

/**orders.txt
 * ------------------
 * 1,phone,7000,1
 * 2,book,34,   2
 * 3,shooe,300, 3
 * 4,cup,90,    5
 *
 * customers.txt
 * ----------------
 * 1,lisi,  23
 * 2,zs,    54
 * 3,wang,  38
 * 4,jiang, 25
 */
public class Map1  extends Mapper {
    Map map=new HashMap<>();
    static int count=0;

    @Override
    protected void setup(Context context) throws IOException, InterruptedException {
       count++;
       if (count >1)return;

        //加载 小文件件
        BufferedInputStream bfin=new BufferedInputStream(new FileInputStream("/home/hadoop/txt/mrjoin/customers.txt"));
        BufferedReader br= new BufferedReader(new InputStreamReader(bfin));

        String res=null;
        while((res=br.readLine())!=null){
            String[] splits = res.split(",");
            String id=splits[0];
            map.put(Integer.parseInt(id),res );
        }
    }

    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        //排除customers表
        InputSplit split = context.getInputSplit();
        FileSplit filesplit=(FileSplit)split;

        if ( filesplit.getPath().getName().contains("orders")){
            //取出： 订单数据
            String[] mesg = value.toString().split(",");
            int userId=Integer.parseInt(mesg[3]);
            String userInfo=map.get(userId);

            context.write(new Text(value.toString()+"--->"+ userInfo ), NullWritable.get() );
            //删除匹配完的： 用户信息
            map.remove(userId);

        }
    }

    @Override
    protected void cleanup(Context context) throws IOException, InterruptedException {
        if (count >1)return;

        //取出脏的  用户数据
        Set keys = map.keySet();
        for (Integer key : keys) {
            String val=map.get(key);
            context.write(new Text("null,--->"+val), NullWritable.get());
        }

        map.clear();
        map=null;
    }
}

part2: reduce端全外连接（map-reduce实现）

第一部分： map-reduce-app

【app类】

public class App2 {
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
        //job
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS","file:///");

        Job job = Job.getInstance();
        job.setJarByClass(App2.class);
        job.setJobName("mapjoin");

        //分区,分组 reducer个数
        job.setPartitionerClass(Partioner1.class);
        job.setGroupingComparatorClass(GroupingComparator.class);
        job.setNumReduceTasks(3);

        //map,red
        job.setMapperClass(Map2.class);
        job.setReducerClass(Red2.class);
        job.setOutputKeyClass(CompareKey.class);
        job.setOutputValueClass(NullWritable.class);

        //输入输出
        FileInputFormat.addInputPath(job,new Path("/home/hadoop/txt/mrjoin"));
        FileSystem fs = FileSystem.get(conf);
        Path path = new Path("mapjoin2");
        if (fs.exists(path)) {
            fs.delete(path, true);
        }
        FileOutputFormat.setOutputPath(job, path);

        //启动
        job.waitForCompletion(true);
    }
}

【map类】

public class Map2 extends Mapper  {

    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        //排除customers表
        InputSplit split = context.getInputSplit();
        FileSplit filesplit=(FileSplit)split;
        String fileName = filesplit.getPath().getName();

        if (fileName .contains("orders")){
            //取出： 订单数据
            String[] mesg = value.toString().split(",");
            int userId=Integer.parseInt(mesg[3]);
            int orderId=Integer.parseInt(mesg[0]);
            /**
             * orders.txt
             *  * ------------------
             *  * 1,phone,7000,1
             *  * 2,book,34,   2
             *  * 3,shooe,300, 3
             *  * 4,cup,90,    5
             *  *
             */
            CompareKey compkey = new CompareKey();
            compkey.setFlag(2);
            compkey.setUserId(userId);
            compkey.setOrderId(orderId);
            compkey.setInfo(value.toString());

            context.write(compkey, NullWritable.get() );
        }else {
            //取出： 用户数据
            String[] mesg = value.toString().split(",");
            int userId=Integer.parseInt(mesg[0]);
            /**
             * customers.txt
             *  * ----------------
             *  * 1,lisi,  23
             *  * 2,zs,    54
             *  * 3,wang,  38
             *  * 4,jiang, 25
             *  *
             */
            CompareKey compkey = new CompareKey();
            compkey.setFlag(1);
            compkey.setUserId(userId);
            compkey.setInfo(value.toString());

            context.write(compkey, NullWritable.get() );
        }
    }
}

【reduce类】

public class Red2 extends Reducer {
    @Override
    protected void reduce(CompareKey key, Iterable values, Context context) throws IOException, InterruptedException {

        /**
         * 取出： order---customer数据， 拼接字符串
         */
        String userInfo=null;
        Iterator it = values.iterator();
        StringBuilder sb = new StringBuilder();

        it.next();
        //第一条数据： user数据
        if (key.getFlag()==1){
            userInfo=key.getInfo();

            //剩余数据
            if (it.hasNext()){
                while (it.hasNext()) {
                    it.next();
                    //order数据
                    sb.append(key.getInfo()).append(", ");
                    System.out.print(sb.toString());
                }

            }else {
                sb.append("null");
            }

        }else {//第一条数据: order
            sb.append(key.getInfo()).append(", ");

            //剩余数据
                while (it.hasNext()) {
                    it.next();
                    //order数据
                    sb.append(key.getInfo()).append(", ");
                    System.out.print(sb.toString());
                }
        }

        context.write(new Text(userInfo+"   --->"+ sb.toString()), NullWritable.get());
       System.out.println(userInfo+ ", orders-->"+sb.toString()+"===============");
    }
}

第二部分： 自定义（组合键-排序，分区函数， 分组比较）

【组合键】

public class CompareKey implements WritableComparable {
    //属性
    private int userId;
    private int orderId;
    int flag=0;
    private String info;

    @Override
    public int compareTo(CompareKey o) {
        int ouserId = o.getUserId();
        int oorderId = o.getOrderId();
        int oflag = o.getFlag();

        //先用户信息--------->订单信息
        /**
         * user-->order
         * order-->user
         *
         * order--->order
         */
        if (this.flag ==1 | oflag==1){
            return orderId-oorderId;
        }

        if (this.flag==2 && oflag==2){
            return userId-ouserId;
        }
        return 0;
    }

    @Override
    public void write(DataOutput dataOutput) throws IOException {
        dataOutput.writeInt(userId);
        dataOutput.writeInt(orderId);
        dataOutput.writeInt(flag);
        dataOutput.writeUTF(info);
    }

    @Override
    public void readFields(DataInput dataInput) throws IOException {
        this.userId=dataInput.readInt();
        this.orderId=dataInput.readInt();
        this.flag=dataInput.readInt();
        this.info=dataInput.readUTF();
    }

    //get, set,toString()...
 }

【map端： 分区函数】

public class Partioner1 extends Partitioner {

    @Override
    public int getPartition(CompareKey compareKey, NullWritable nullWritable, int numPartitions) {
        return compareKey.getUserId() % numPartitions;
    }
}

【reduce端： 分组比较】

public class GroupingComparator extends WritableComparator {

    //由父类创建： 组合键对象,防止null空指针
    public GroupingComparator() {
        super(CompareKey.class, true);
    }

    @Override
    public int compare(WritableComparable a, WritableComparable b) {
        CompareKey a1= (CompareKey) a;
        CompareKey b1= (CompareKey) b;

        return a1.getUserId()-b1.getUserId();
    }
}

日志打印结果如下