hello  "a.txt->5 b.txt->3"
tom     "a.txt->2 b.txt->1"
kitty   "a.txt->1"

context.write("hello","a.txt->5 b.txt->3");

<"hello",{"a.txt->5","b.txt->3"}>

context.write("hello","a.txt->5");
context.write("hello","b.txt->3");

context.write("hello->a.txt",1);
context.write("hello->a.txt",1);
context.write("hello->a.txt",1);
context.write("hello->a.txt",1);
context.write("hello->a.txt",1);context.write("hello->b.txt",1);
context.write("hello->b.txt",1);
context.write("hello->b.txt",1);

<"hello->a.txt",1>
<"hello->a.txt",1>
<"hello->a.txt",1>
<"hello->a.txt",1>
<"hello->a.txt",1><"hello->b.txt",1>
<"hello->b.txt",1>
<"hello->b.txt",1>context.write("hello","a.txt->5");
context.write("hello","b.txt->3");

public class IIMapper1 extends Mapper<LongWritable, Text, Text, Text> {private Text k = new Text();//下面其实是int，不过也可以在接收端Integer.parseInt转了就好private Text v = new Text();public void map(LongWritable key, Text value, Context context)throws IOException, InterruptedException {String line = value.toString();String[] words = line.split(" ");//从context对象里找到单词属于那个文章//context.getInputSplit();找到切片 按ctrl找 发现返回时InputSplit//不过是个抽象类 ctrl + t找他的实现类//能把数据写入context，繁殖也能从context拿到很多信息//从下面inputSplit调用get的时候发现没有合适的方法，那么我们找他的实现类，调用实现类的方法//InputSplit inputSplit = context.getInputSplit();//inputSplit.get//他的子类很多    我们处理文件就用File开头的  然后有个getPathFileSplit inputSplit = (FileSplit)context.getInputSplit();//文件名是hdfs://hostname：port/a/1.txt//我们戒掉hdfs://hostname：port  不能戒掉a  应为这是文件夹否则不知道1.txt来自哪 其他文件家下可能也有同名文件//也可以不接去String path = inputSplit.getPath().toString();for(String w:words) {k.set(w+"->"+path);v.set("1");context.write(k, v);}}}

String[] wordAndPath = key.toString().split("->");String word = wordAndPath[0];String path = wordAndPath[1];// process valuesint sum = 0;for (Text val : value) {sum += Integer.parseInt(val.toString());}k.set(word);v.set(path+"->"+sum);context.write(k, v);

//不涉及多线程 用StringBuilde即可StringBuilder sb = new StringBuilder();// process valuesfor (Text val : value) {sb.append(val.toString()).append("\t");}context.write(key, new Text(sb.toString()));