1． 需求
在得出統計每一個用戶（手機號）所耗費的總上行流量、下行流量，總流量結果的基礎之上再加一個需求：將統計結果按照總流量倒序排序。
2． 分析
基本思路：
實現自定義的bean來封裝流量信息，並將bean作爲map輸出的key來傳輸
MR程序在處理數據的過程中會對數據排序(map輸出的kv對傳輸到reduce之前，會排序)，排序的依據是map輸出的key。所以，我們如果要實現自己需要的排序規則，則可以考慮將排序因素放到key中，讓key實現接口：WritableComparable，然後重寫key的compareTo方法。
3． 實現
自定義的bean
public class FlowBean implements WritableComparable<FlowBean>{
private long upFlow;
private long downFlow;
private long sumFlow;
//這裏反序列的時候會用到
public FlowBean() {
}
public FlowBean(long upFlow, long downFlow, long sumFlow) {
this.upFlow = upFlow;
this.downFlow = downFlow;
this.sumFlow = sumFlow;
}
public FlowBean(long upFlow, long downFlow) {
this.upFlow = upFlow;
this.downFlow = downFlow;
this.sumFlow = upFlow+downFlow;
}
public void set(long upFlow, long downFlow) {
this.upFlow = upFlow;
this.downFlow = downFlow;
this.sumFlow = upFlow+downFlow;
}
@Override
public String toString() {
return upFlow+"\t"+downFlow+"\t"+sumFlow;
}
/這裏是序列化方法
@Override
public void write(DataOutput out) throws IOException {
out.writeLong(upFlow);
out.writeLong(downFlow);
out.writeLong(sumFlow);
}
/這裏是反序列化方法
@Override
public void readFields(DataInput in) throws IOException {
//注意反序列化的順序跟序列化的順序一致
this.upFlow = in.readLong();
this.downFlow = in.readLong();
this.sumFlow = in.readLong();
}
//這裏進行bean的自定義比較大小
@Override
public int compareTo(FlowBean o) {
//實現按照 sumflow 的大小倒序排序
return this.sumFlow>o.getSumFlow()?-1:1;
}
}public class FlowSumMapper extends Mapper<LongWritable, Text, Text, FlowBean>{
Text k = new Text();
FlowBean v = new FlowBean();
@Override
protected void map(LongWritable key, Text value,Context context)
throws IOException, InterruptedException {
String line = value.toString();
String[] fields = line.split("\t");
String phoneNum = fields[1];
long upFlow = Long.parseLong(fields[fields.length-3]);
long downFlow = Long.parseLong(fields[fields.length-2]);
k.set(phoneNum);
v.set(upFlow, downFlow);
context.write(k, v);
}
}
public class FlowSumReducer extends Reducer<Text, FlowBean, Text, FlowBean> {
FlowBean v = new FlowBean();
@Override
protected void reduce(Text key, Iterable<FlowBean> values, Context context)
throws IOException, InterruptedException {
long upFlowCount = 0;
long downFlowCount = 0;
for (FlowBean bean : values) {
upFlowCount += bean.getUpFlow();
downFlowCount += bean.getDownFlow();
}
v.set(upFlowCount, downFlowCount);
context.write(key, v);
}
}