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.csdn.net/qq_44594249/article/details/97616735