Hadoop：java.lang.ClassCastException：org.apache.hadoop.io.LongWritable无法强制转换为org.apache.hadoop.io.Text

我的程序看起来像

public class TopKRecord extends Configured implements Tool { public static class MapClass extends Mapper { public void map(Text key, Text value, Context context) throws IOException, InterruptedException { // your map code goes here String[] fields = value.toString().split(","); String year = fields[1]; String claims = fields[8]; if (claims.length() > 0 && (!claims.startsWith("\""))) { context.write(new Text(year.toString()), new Text(claims.toString())); } } } public int run(String args[]) throws Exception { Job job = new Job(); job.setJarByClass(TopKRecord.class); job.setMapperClass(MapClass.class); FileInputFormat.setInputPaths(job, new Path(args[0])); FileOutputFormat.setOutputPath(job, new Path(args[1])); job.setJobName("TopKRecord"); job.setMapOutputValueClass(Text.class); job.setNumReduceTasks(0); boolean success = job.waitForCompletion(true); return success ? 0 : 1; } public static void main(String args[]) throws Exception { int ret = ToolRunner.run(new TopKRecord(), args); System.exit(ret); } } 

数据看起来像

 "PATENT","GYEAR","GDATE","APPYEAR","COUNTRY","POSTATE","ASSIGNEE","ASSCODE","CLAIMS","NCLASS","CAT","SUBCAT","CMADE","CRECEIVE","RATIOCIT","GENERAL","ORIGINAL","FWDAPLAG","BCKGTLAG","SELFCTUB","SELFCTLB","SECDUPBD","SECDLWBD" 3070801,1963,1096,,"BE","",,1,,269,6,69,,1,,0,,,,,,, 3070802,1963,1096,,"US","TX",,1,,2,6,63,,0,,,,,,,,, 3070803,1963,1096,,"US","IL",,1,,2,6,63,,9,,0.3704,,,,,,, 3070804,1963,1096,,"US","OH",,1,,2,6,63,,3,,0.6667,,,,,,, 

在运行此程序时，我在控制台上看到以下内容

 12/08/02 12:43:34 INFO mapred.JobClient: Task Id : attempt_201208021025_0007_m_000000_0, Status : FAILED java.lang.ClassCastException: org.apache.hadoop.io.LongWritable cannot be cast to org.apache.hadoop.io.Text at com.hadoop.programs.TopKRecord$MapClass.map(TopKRecord.java:26) at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:144) at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:764) at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370) at org.apache.hadoop.mapred.Child$4.run(Child.java:255) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:396) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1121) at org.apache.hadoop.mapred.Child.main(Child.java:249) 

我相信Class Types正确映射， Class Mapper ，

请让我知道我在这里做错了什么？

Answer 1

当您使用M / R程序读取文件时，映射器的输入键应该是文件中行的索引 ，而输入值将是整行。

所以这里发生的事情是你正在尝试将行索引作为Text对象，这是错误的，你需要一个LongWritable来让Hadoop不抱怨类型。

试试这个：

 public class TopKRecord extends Configured implements Tool { public static class MapClass extends Mapper { public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException { // your map code goes here String[] fields = value.toString().split(","); String year = fields[1]; String claims = fields[8]; if (claims.length() > 0 && (!claims.startsWith("\""))) { context.write(new Text(year.toString()), new Text(claims.toString())); } } } ... } 

您可能需要重新考虑代码中的一件事，即为正在处理的每条记录创建2个Text对象。 您应该只在开头创建这两个对象，然后在映射器中使用set方法设置它们的值。 如果您正在处理大量数据，这将为您节省大量时间。

Answer 2

你需要设置输入格式类

 job.setInputFormatClass(KeyValueTextInputFormat.class); job.setOutputFormatClass(TextOutputFormat.class);