MR的计算是可以嵌套使用的，比如在现实业务中有时候我们可能要求先求出总结果，在对总结果进行排序，当排序的值是number类型，当直接排序。当需要排序的是javaBean，则首先要对其进行序列化。
【1】hadoop中的序列化
Hadoop的的序列化不采用的Java的序列化，而是实现了自己的序列化机制。
Hadoop的通过Writable接口实现的序列化机制，不过没有提供比较功能，所以和Java的的中Comparable接口合并，提供一个接口WritableComparable。
1 > Writable 的使用（当不需要进行排序而只是对数据的持久化等使用）
要实现序列化的bean要实现Writable 接口并复写他的两个方法（序列化、反序列化）
public class DataBean implements Writable{
private String tel;
private long upPayLoad;
private long downPayLoad;
private long totalPayLoad;
public DataBean(){}
//一般为了方便使用，都会给一个全参的构造方法
public DataBean(String tel, long upPayLoad, long downPayLoad) {
super();
this.tel = tel;
this.upPayLoad = upPayLoad;
this.downPayLoad = downPayLoad;
this.totalPayLoad = upPayLoad + downPayLoad;
}
@Override
public String toString() {
return this.upPayLoad + "\t" + this.downPayLoad + "\t" + this.totalPayLoad;
}
//反序列化
public void write(DataOutput out) throws IOException {
out.writeUTF(tel);
out.writeLong(upPayLoad);
out.writeLong(downPayLoad);
out.writeLong(totalPayLoad);
}
//序列化
public void readFields(DataInput in) throws IOException {
this.tel = in.readUTF();
this.upPayLoad = in.readLong();
this.downPayLoad = in.readLong();
this.totalPayLoad = in.readLong();
}
//getter 和 setter方法
}
2 > WritableComparable的使用（当即需要持久化也需要排序）
当即需要对bean进行持久化又要实现某种排序，则要实现WritableComparable接口并复写三个方法（序列化、反序列化、比较）
public class InfoBean implements WritableComparable {
private String account;//key邮箱
private double income;//收入
private double expenses;//支出
private double surplus;//结余
//set方法（含参数构造方法）
public void set(String account,double income,double expenses){
this.account = account;
this.income = income;
this.expenses = expenses;
this.surplus = income - expenses;
}
//反序列化
public void write(DataOutput out) throws IOException {
out.writeUTF(account);
out.writeDouble(income);
out.writeDouble(expenses);
out.writeDouble(surplus);
}
//序列化
public void readFields(DataInput in) throws IOException {
this.account = in.readUTF();
this.income = in.readDouble();
this.expenses = in.readDouble();
this.surplus = in.readDouble();
}
//排序方法
public int compareTo(InfoBean o) {
//先比较收入，当输入相等
if(this.income == o.getIncome()){
//比支出
return this.expenses > o.getExpenses() ? 1 : -1;
}
return this.income > o.getIncome() ? 1 : -1;
}
@Override
public String toString() {
return income + "\t" + expenses + "\t" + surplus;
}
//getter 和 setter方法
}
【案例】计算出用户的总输入和总支出，并排序（如果总输入相等在按总支出排序）
【1】源数据
[email protected] 6000 0 2014-02-20
[email protected] 2000 0 2014-02-20
[email protected] 0 100 2014-02-20
[email protected] 3000 0 2014-02-20
[email protected] 9000 0 2014-02-20
[email protected] 0 200 2014-02-20
【2】结果数据
[email protected] 2000.0 100.0 1900.0
[email protected] 9000.0 0.0 9000.0
[email protected] 9000.0 200.0 8800.0
【3】实现原理：即实现一个sum的MR对数据进行sum计算，在将sum的输出结果当做源数据编写sort计算，sort的计算结果就是最终结果数据
2016-12-13_103123.png
【4】代码实现：
文件一：InfoBean.java
public class InfoBean implements WritableComparable {
private String account;//key邮箱
private double income;//收入
private double expenses;//支出
private double surplus;//结余
//set方法（含参数构造方法）
public void set(String account,double income,double expenses){
this.account = account;
this.income = income;
this.expenses = expenses;
this.surplus = income - expenses;
}
//反序列化
public void write(DataOutput out) throws IOException {
out.writeUTF(account);
out.writeDouble(income);
out.writeDouble(expenses);
out.writeDouble(surplus);
}
//序列化
public void readFields(DataInput in) throws IOException {
this.account = in.readUTF();
this.income = in.readDouble();
this.expenses = in.readDouble();
this.surplus = in.readDouble();
}
@Override
public int compareTo(InfoBean o) {
//先比较收入，当输入相等
if(this.income == o.getIncome()){
//比支出
return this.expenses > o.getExpenses() ? 1 : -1;
}
return this.income > o.getIncome() ? 1 : -1;
}
@Override
public String toString() {
return income + "\t" + expenses + "\t" + surplus;
}
//getter setter方法
}
文件二：求和SumStep.java
public class SumStep {
public static class SumMapper extends Mapper {
private Text k = new Text();
private InfoBean v = new InfoBean();
protected void map(LongWritable key, Text value, Context context)
throws java.io.IOException ,InterruptedException {
String line = value.toString();
String[] fields = line.split("\t");
String account = fields[0];
double in = Double.parseDouble(fields[1]);
double out = Double.parseDouble(fields[2]);
k.set(account);
v.set(account, in, out);
context.write(k, v);
//context.write(new Text(), new InfoBean());//这里为了避免多次new对象占用资源改为上方提前new好
};
}
public static class SumReduce extends Reducer {
private InfoBean v = new InfoBean();
protected void reduce(Text key, Iterable values, Context context)
throws java.io.IOException ,InterruptedException {
double in_sum = 0 ;
double out_sum = 0 ;
for(InfoBean bean : values){
in_sum += bean.getIncome();
out_sum += bean.getExpenses();
}
v.set("", in_sum, out_sum);
context.write(key, v);
};
}
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
Job job = Job.getInstance(conf);
job.setJarByClass(SumStep.class);
job.setMapperClass(SumMapper.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(InfoBean.class);
FileInputFormat.setInputPaths(job, new Path("/mrDemo/input/sum_sort"));
job.setReducerClass(SumReduce.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(InfoBean.class);
FileOutputFormat.setOutputPath(job, new Path("/mrDemo/output/sum_sort"));
job.waitForCompletion(true);
}
}
//打jar包执行：hadoop jar /root/Desktop/mr_JAR/sumAndSort.jar
文件三：排序 SortStep.java
public class SortStep {
public static class SortMapper extends Mapper {
private InfoBean k = new InfoBean();
protected void map(LongWritable key, Text value, Context context)
throws java.io.IOException ,InterruptedException {
String line = value.toString();
String[] fields = line.split("\t");
String account = fields[0];
double in = Double.parseDouble(fields[1]);
double out = Double.parseDouble(fields[2]);
k.set(account, in, out);
context.write(k, NullWritable.get());
};
}
public static class SortReduce extends Reducer {
private Text k = new Text();
protected void reduce(InfoBean bean, Iterable values, Context context)
throws java.io.IOException ,InterruptedException {
String account = bean.getAccount();
k.set(account);
context.write(k, bean);
};
}
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
Job job = Job.getInstance(conf);
job.setJarByClass(SortStep.class);
job.setMapperClass(SortMapper.class);
job.setMapOutputKeyClass(InfoBean.class);
job.setMapOutputValueClass(NullWritable.class);
FileInputFormat.setInputPaths(job, new Path("/mrDemo/output/sum_sort/part-r-00000"));
job.setReducerClass(SortReduce.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(InfoBean.class);
FileOutputFormat.setOutputPath(job, new Path("/mrDemo/output/sumAndSort"));
job.waitForCompletion(true);
}
}
//打jar包执行 hadoop jar /root/Desktop/mr_JAR/sumAndSort1.jar
注意：MR自身会使用快速排序将key排序，key必须可序列化
input.png
output.png