案例:求共同好友
需求分析
以下是qq的好友列表数据，冒号前是一个用户，冒号后是该用户的所有好友（数据中的好友关系是单向的）
~~~java
A:B,C,D,F,E,O
B:A,C,E,K
C:A,B,D,E,I
D:A,E,F,L
E:B,C,D,M,L
F:A,B,C,D,E,O,M
G:A,C,D,E,F
H:A,C,D,E,O
I:A,O
J:B,O
K:A,C,D
L:D,E,F
M:E,F,G
O:A,H,I,J
~~~
求出哪些人两两之间有共同好友，及他俩的共同好友都有谁？
### 实现步骤
#####第一步：代码实现
**Mapper类**
~~~java
public class Step1Mapper extends Mapper<LongWritable,Text,Text,Text> {
@Override
protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
//1:以冒号拆分行文本数据: 冒号左边就是V2
String[] split = value.toString().split(":");
String userStr = split[0];
//2:将冒号右边的字符串以逗号拆分,每个成员就是K2
String[] split1 = split[1].split(",");
for (String s : split1) {
//3:将K2和v2写入上下文中
context.write(new Text(s), new Text(userStr));
}
}
}
~~~
**Reducer类:**
~~~java
public class Step1Reducer extends Reducer<Text,Text,Text,Text> {
@Override
protected void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException {
//1:遍历集合,并将每一个元素拼接,得到K3
StringBuffer buffer = new StringBuffer();
for (Text value : values) {
buffer.append(value.toString()).append("-");
}
//2:K2就是V3
//3:将K3和V3写入上下文中
context.write(new Text(buffer.toString()), key);
}
}
~~~
**JobMain:**
~~~java
public class JobMain extends Configured implements Tool {
@Override
public int run(String[] args) throws Exception {
//1:获取Job对象
Job job = Job.getInstance(super.getConf(), "common_friends_step1_job");
//2:设置job任务
//第一步:设置输入类和输入路径
job.setInputFormatClass(TextInputFormat.class);
TextInputFormat.addInputPath(job, new Path("file:///D:\\input\\common_friends_step1_input"));
//第二步:设置Mapper类和数据类型
job.setMapperClass(Step1Mapper.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(Text.class);
//第三,四,五,六
//第七步:设置Reducer类和数据类型
job.setReducerClass(Step1Reducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);
//第八步:设置输出类和输出的路径
job.setOutputFormatClass(TextOutputFormat.class);
TextOutputFormat.setOutputPath(job, new Path("file:///D:\\out\\common_friends_step1_out"));
//3:等待job任务结束
boolean bl = job.waitForCompletion(true);
return bl ? 0: 1;
}
public static void main(String[] args) throws Exception {
Configuration configuration = new Configuration();
//启动job任务
int run = ToolRunner.run(configuration, new JobMain(), args);
System.exit(run);
}
}
~~~
##### 第二步：代码实现
**Mapper类**
```java
public class Step2Mapper extends Mapper<LongWritable,Text,Text,Text> {
/*
K1 V1
0 A-F-C-J-E- B
----------------------------------
K2 V2
A-C B
A-E B
A-F B
C-E B
*/
@Override
protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
//1:拆分行文本数据,结果的第二部分可以得到V2
String[] split = value.toString().split("\t");
String friendStr =split[1];
//2:继续以'-'为分隔符拆分行文本数据第一部分,得到数组
String[] userArray = split[0].split("-");
//3:对数组做一个排序
Arrays.sort(userArray);
//4:对数组中的元素进行两两组合,得到K2
/*
A-E-C -----> A C E
A C E
A C E
*/
for (int i = 0; i <userArray.length -1 ; i++) {
for (int j = i+1; j < userArray.length ; j++) {
//5:将K2和V2写入上下文中
context.write(new Text(userArray[i] +"-"+userArray[j]), new Text(friendStr));
}
}
}
}
```
**Reducer类:**
```java
public class Step2Reducer extends Reducer<Text,Text,Text,Text> {
@Override
protected void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException {
//1:原来的K2就是K3
//2:将集合进行遍历,将集合中的元素拼接,得到V3
StringBuffer buffer = new StringBuffer();
for (Text value : values) {
buffer.append(value.toString()).append("-");
}
//3:将K3和V3写入上下文中
context.write(key, new Text(buffer.toString()));
}
}
```
**JobMain:**
```java
public class JobMain extends Configured implements Tool {
@Override
public int run(String[] args) throws Exception {
//1:获取Job对象
Job job = Job.getInstance(super.getConf(), "common_friends_step2_job");
//2:设置job任务
//第一步:设置输入类和输入路径
job.setInputFormatClass(TextInputFormat.class);
TextInputFormat.addInputPath(job, new Path("file:///D:\\out\\common_friends_step1_out"));
//第二步:设置Mapper类和数据类型
job.setMapperClass(Step2Mapper.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(Text.class);
//第三,四,五,六
//第七步:设置Reducer类和数据类型
job.setReducerClass(Step2Reducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);
//第八步:设置输出类和输出的路径
job.setOutputFormatClass(TextOutputFormat.class);
TextOutputFormat.setOutputPath(job, new Path("file:///D:\\out\\common_friends_step2_out"));
//3:等待job任务结束
boolean bl = job.waitForCompletion(true);
return bl ? 0: 1;
}
public static void main(String[] args) throws Exception {
Configuration configuration = new Configuration();
//启动job任务
int run = ToolRunner.run(configuration, new JobMain(), args);
System.exit(run);
}
}
```
