通过剖析源码单步调试详解MapReduce分组group遍历

通过剖析源码单步调试详解MapReduce分组group遍历：
马克-to-win @ 马克java社区：mapreduce的group知识点是最难理解的，本小节将通过仔细剖析源码，单步调试，来详解之。
另外注意：数据文件写时一定注意：结尾不能有回车和空格，通过在map里面加断点，F8（resume），一轮一轮，调试一行一行的数据，才发现最后一行数据出毛病了，只有是多了一个换行符的毛病。

package com;
import org.apache.hadoop.io.WritableComparable;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

public class OrderBean implements WritableComparable<OrderBean>{
    private String orderId;
    private Double amount;

    public OrderBean() {
    }

    public OrderBean(String orderId, Double amount) {
        this.orderId = orderId;
        this.amount = amount;
    }
    public void set(String orderId, Double amount) {
        this.orderId = orderId;
        this.amount = amount;
    }
    public String getOrderId() {
        return orderId;
    }

    public void setOrderId(String orderId) {
        this.orderId = orderId;
    }

    public Double getAmount() {
        return amount;
    }

    public void setAmount(Double amount) {
        this.amount = amount;
    }

    @Override
    public int compareTo(OrderBean o) {
        /*马克-to-win: 如orderId相等，则比较amount，否则比较id即可，这样id相同的连在一起了。因为id先比，amount后比*/
        int cmp = this.getOrderId().compareTo(o.getOrderId());
 
更多请见：https://blog.youkuaiyun.com/qq_44594249/article/details/97616735