我的Map器函数如下所示：

public class preprocessMapper 
        extends Mapper<LongWritable, Text, Text, Text> {
    private String Heading = "";
    private String para ="";
    private Integer record = 0;
    private String word;

    public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {

        String fileName = ((FileSplit) context.getInputSplit()).getPath().getName();
    String date = fileName.substring(5,15);
    Text t1 = new Text(date);

        context.write(t1, value);

   }}

我的减速机函数如下所示：

public class preprocessReducer
            extends Reducer<Text, Text, Text, Text> {
     //   private IntWritable result = new IntWritable();

        public void reduce(Text key, Iterable<Text> values,Context context) throws IOException, InterruptedException {
            String para = "";
            for (Text val : values) {
                para = para + val+" ";
            }
    Text t2 = new Text(para);
            //result.set(para);
            context.write(key, t2);
        }
    }

下面是我的配置函数：

public class preprocess {

    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf, "Preprocess");
        job.setJarByClass(preprocess.class);
        job.setMapperClass(preprocessMapper.class);

        job.setReducerClass(preprocessReducer.class);
    job.setNumReduceTasks(1);
        job.setOutputKeyClass(Text.class);

        job.setOutputValueClass(Text.class);
    //job.setInputFormatClass(Text.class);

        FileInputFormat.addInputPath(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
}

`我试图处理一组文本文件使用上述，但我得到了以下有关格式的错误。有人能告诉我格式哪里不正确吗？

18/07/18 19:38:09 INFO mapreduce.Job: Task Id : 
attempt_1528077494936_5165_m_000001_2, Status : FAILED
Error: java.lang.ClassCastException: org.apache.hadoop.io.LongWritable 
cannot be cast to org.apache.hadoop.io.Text
at preprocessMapper.map(preprocessMapper.java:20)
at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:145)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:793)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:341)
at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:164)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:422)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1920)
at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:158)