Hadoop（java）更改映射器输出值的类型

Question

我正在编写一个映射函数，它将键生成为一些user_id，值也是文本类型。我是这样做的

public static class UserMapper extends Mapper<Object, Text, Text, IntWritable> {
    private final static IntWritable one = new IntWritable(1);
    private Text userid = new Text();
    private Text catid = new Text();

    /* map method */
    public void map(Object key, Text value, Context context)
                throws IOException, InterruptedException {
        StringTokenizer itr = new StringTokenizer(value.toString(), ","); /* separated by "," */
        int count = 0;

        userid.set(itr.nextToken());

        while (itr.hasMoreTokens()) {
            if (++count == 3) {
                catid.set(itr.nextToken());
                context.write(userid, catid);
            }else {
                itr.nextToken();
            }
        }
    }
}

然后，在主程序中，我将映射器的输出类设置为：

    Job job = new Job(conf, "Customer Analyzer");
    job.setJarByClass(popularCategories.class);
    job.setMapperClass(UserMapper.class);
    job.setCombinerClass(UserReducer.class);
    job.setReducerClass(UserReducer.class);

    job.setMapOutputKeyClass(Text.class);
    job.setMapOutputValueClass(Text.class);

因此，即使我将输出值的类设置为text.class，但在编译时仍然会出现以下错误：

popularCategories.java:39: write(org.apache.hadoop.io.Text,org.apache.hadoop.io.IntWritable)
 in org.apache.hadoop.mapreduce.TaskInputOutputContext<java.lang.Object,
 org.apache.hadoop.io.Text,org.apache.hadoop.io.Text,
 org.apache.hadoop.io.IntWritable> 
 cannot be applied to (org.apache.hadoop.io.Text,org.apache.hadoop.io.Text)
 context.write(userid, catid);
                           ^

 public static class UserMapper extends Mapper<Object, Text, Text, Text> {

 }

Answer 1

来自Apache文档页面

Class Mapper<KEYIN,VALUEIN,KEYOUT,VALUEOUT>

java.lang.Object
org.apache.hadoop.mapreduce.Mapper<KEYIN,VALUEIN,KEYOUT,VALUEOUT>

哪里

KEYIN = offset of the record  ( input for Mapper )
VALUEIN = value of the line in the record ( input for Mapper )
KEYOUT = Mapper output key ( Output of Mapper, input of Reducer)
VALUEOUT = Mapper output value ( Output of Mapper, input to Reducer)

在更正定义中的映射器值后，问题已经解决

public static class UserMapper extends Mapper<Object, Text, Text, IntWritable> {

public static class UserMapper extends Mapper<Object, Text, Text, Text> {