Java 具有ArrayWritable的Hadoop MapReduce链
我正在尝试创建一个由两个步骤组成的mapreduce链。 第一个reduce将键值对作为(key,value)发出,其中value是自定义对象的列表,第二个映射器应该读取第一个reducer的输出。 该列表是一个自定义的可写入阵列。以下是相关代码: 自定义对象:Java 具有ArrayWritable的Hadoop MapReduce链,java,hadoop,mapreduce,writable,Java,Hadoop,Mapreduce,Writable,我正在尝试创建一个由两个步骤组成的mapreduce链。 第一个reduce将键值对作为(key,value)发出,其中value是自定义对象的列表,第二个映射器应该读取第一个reducer的输出。 该列表是一个自定义的可写入阵列。以下是相关代码: 自定义对象: public class Custom implements Writable { private Text document; private IntWritable count; public Custom
public class Custom implements Writable {
private Text document;
private IntWritable count;
public Custom(){
setDocument("");
setCount(0);
}
public Custom(String document, int count) {
setDocument(document);
setCount(count);
}
@Override
public void readFields(DataInput in) throws IOException {
// TODO Auto-generated method stub
document.readFields(in);
count.readFields(in);
}
@Override
public void write(DataOutput out) throws IOException {
document.write(out);
count.write(out);
}
@Override
public String toString() {
return this.document.toString() + "\t" + this.count.toString();
}
public int getCount() {
return count.get();
}
public void setCount(int count) {
this.count = new IntWritable(count);
}
public String getDocument() {
return document.toString();
}
public void setDocument(String document) {
this.document = new Text(document);
}
}
自定义可写入阵列:
class MyArrayWritable extends ArrayWritable {
public MyArrayWritable(Writable[] values) {
super(Custom.class, values);
}
public MyArrayWritable() {
super(Custom.class);
}
@Override
public Custom[] get() {
return (Custom[]) super.get();
}
@Override
public String toString() {
return Arrays.toString(get());
}
@Override
public void write(DataOutput arg0) throws IOException {
super.write(arg0);
}
}
第一减速器:
public static class NGramReducer extends Reducer<Text, Text, Text, MyArrayWritable> {
public void reduce(Text key, Iterable<Text> values, Context context)
throws IOException, InterruptedException {
//other code
context.write(key, mArrayWritable);
}
}
当我运行它时,我得到了这个错误
错误:java.lang.ClassCastException:org.apache.hadoop.io.Text无法强制转换为检测器$MyArrayWritable
有什么问题?我必须写一个FileInputFormat吗?(job1工作正常)这似乎是因为您的Job2
InputFormat
KeyValueTextInputFormat.class
需要一个键和值,它们都是Text
对象。由于作业1输出(Text,MyArrayWritable)
,因此与值存在冲突
幸运的是,您不必编写自定义的OutputFormat
来满足您的数据需求!只需将作业1数据的输出写入序列文件,这样可以保持数据的二进制形式:
//...
job1.setOutputKeyClass(Text.class);
job1.setOutputValueClass(MyArrayWritable.class);
job1.setInputFormatClass(WholeFileInputFormat.class);
job1.setOutputFormatClass(SequenceFileOutputFormat.class);
FileInputFormat.addInputPath(job1, new Path(args[2]));
SequenceFileOutputFormat.setOutputPath(job1, TEMP_PATH);
//...
job2.setInputFormatClass(SequenceFileInputFormat.class);
SequenceFileInputFormat.addInputPath(job2, TEMP_PATH);
FileOutputFormat.setOutputPath(job2, new Path(args[3]));
我修改了输入和输出,但现在我得到了这个错误‘error:java.lang.RuntimeException:java.lang.NoSuchMethodException:Detector$MyArrayWritable。(’)似乎回答了这个问题
//...
job1.setOutputKeyClass(Text.class);
job1.setOutputValueClass(MyArrayWritable.class);
job1.setInputFormatClass(WholeFileInputFormat.class);
FileInputFormat.addInputPath(job1, new Path(args[2]));
FileOutputFormat.setOutputPath(job1, TEMP_PATH);
//...
job2.setInputFormatClass(KeyValueTextInputFormat.class);
FileInputFormat.addInputPath(job2, TEMP_PATH);
FileOutputFormat.setOutputPath(job2, new Path(args[3]));
//...
job1.setOutputKeyClass(Text.class);
job1.setOutputValueClass(MyArrayWritable.class);
job1.setInputFormatClass(WholeFileInputFormat.class);
job1.setOutputFormatClass(SequenceFileOutputFormat.class);
FileInputFormat.addInputPath(job1, new Path(args[2]));
SequenceFileOutputFormat.setOutputPath(job1, TEMP_PATH);
//...
job2.setInputFormatClass(SequenceFileInputFormat.class);
SequenceFileInputFormat.addInputPath(job2, TEMP_PATH);
FileOutputFormat.setOutputPath(job2, new Path(args[3]));