我有一个map / reduce代码，它使用TwoDArrayWritable实现二维数组。当我尝试发出2d数组时，它给出了与初始化相关的异常。我搜索并发现它需要默认的构造函数，它没有提供。我如何为TwoDArrayWritable提供默认构造函数，或者还有其他一些我错了？请帮助我。
以下是映射器代码：
public class JaccardMapper extends Mapper<LongWritable, Text, IntTextPair, TwoDArrayWritable> {
Hashtable movieInfo = new Hashtable<String, String>();
String[] genres, actors, entities;
String[] attributes = new String[] {"genre", "actors", "directors", "country", "year", "ratings"};
double p,q,r,s;
double result = 0.0;
String input[] = null;
Set<String> keys;
TwoDArrayWritables array2d = new TwoDArrayWritables();
//TwoDArrayWritable array2d = new TwoDArrayWritable(IntWritable.class);
IntWritable[][] jaccard = new IntWritable[2][];
//int[][] jaccard = new int[2][];
public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException
{
p = 0;
q = 0;
r = 0;
s = 0;
/*
* dataset format
* 0 -> movieid
* 1 -> title
* 2 -> year
* 3 -> actors
* 4 -> directors
* 5 -> genre
* 6 -> country
* 7 -> ratings
* 8 -> cost
* 9 -> revenue
* */
/*
* input format
* 0 -> genre
* 1 -> actors
* 2 -> directors
* 3 -> country
* 4 -> year
* 5 -> ratings
* */
/*
* (q + r) / (p + q + r)
* p -> number of variables positive for both objects
* q -> number of variables positive for the ith objects and negative for jth objects
* r -> number of variables negative for the ith objects and positive for jth objects
* s -> number of variables negative for both objects
* */
input = value.toString().toLowerCase().split(",");
keys = movieInfo.keySet();
//the jaccards 2d array column length depends on the user input best case is 6 but the worst case depends on the sub attributes count like more than one actor/director/genre/country.
int columnlength = input[1].split("\\|").length + input[2].split("\\|").length + input[3].split("\\|").length + input[4].split("\\|").length + 2;
jaccard = new IntWritable[2][columnlength];
for (int i = 0; i < jaccard.length; i++)
{
for (int j = 0; j < jaccard[i].length; j++)
{
jaccard[i][j] = new IntWritable(0);
}
}
if (input.length > 0)
{
//iterate through the dataset in cache
for(String keyy : keys)
{
//iterate to user's input attributes
for (int attribute = 1; attribute < attributes.length; attribute++)
{
if (!input[attribute].equals("-"))
{
entities = input[attribute].toLowerCase().split("\\|");
int subattributecount = 0;
for(String entity : entities)
{
if (movieInfo.get(keyy).toString().toLowerCase().contains(entity))
{
//if user criteria match with the data set, mark 1, 1
jaccard[0][attribute + subattributecount] = new IntWritable(1);
jaccard[1][attribute + subattributecount] = new IntWritable(1);
}
else
{
//if user criteria doesn't match with the data set, mark 1, 0
jaccard[0][attribute + subattributecount] = new IntWritable(1);
jaccard[1][attribute + subattributecount] = new IntWritable(0);
}
subattributecount += 1;
}
}
}
IntTextPair pair = new IntTextPair(Integer.parseInt(input[0].toString()), movieInfo.get(keyy).toString());
array2d.set(jaccard);
//context.write(pair, array2d);
context.write(pair, array2d);
}
}
}
}
这是TwoDArrayWritables包装类： import org.apache.hadoop.io.TwoDArrayWritable;
public class TwoDArrayWritables extends TwoDArrayWritable
{
public TwoDArrayWritables() {
super(TwoDArrayWritable.class);
}
public TwoDArrayWritables(Class valueClass) {
super(valueClass);
// TODO Auto-generated constructor stub
}
}
以下是例外：
14/12/26 16:15:32 INFO mapreduce.Job: Task Id : attempt_1419259182533_0112_r_000000_0, Status : FAILED
Error: java.lang.RuntimeException: java.lang.NoSuchMethodException: org.apache.hadoop.io.TwoDArrayWritable.<init>()
at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:131)
at org.apache.hadoop.io.serializer.WritableSerialization$WritableDeserializer.deserialize(WritableSerialization.java:66)
at org.apache.hadoop.io.serializer.WritableSerialization$WritableDeserializer.deserialize(WritableSerialization.java:42)
at org.apache.hadoop.mapreduce.task.ReduceContextImpl.nextKeyValue(ReduceContextImpl.java:146)
at org.apache.hadoop.mapreduce.task.ReduceContextImpl.nextKey(ReduceContextImpl.java:121)
at org.apache.hadoop.mapreduce.lib.reduce.WrappedReducer$Context.nextKey(WrappedReducer.java:307)
at org.apache.hadoop.mapreduce.Reducer.run(Reducer.java:170)
at org.apache.hadoop.mapred.ReduceTask.runNewReducer(ReduceTask.java:627)
at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:389)
at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:167)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1554)
at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:162)
Caused by: java.lang.NoSuchMethodException: org.apache.hadoop.io.TwoDArrayWritable.<init>()
at java.lang.Class.getConstructor0(Class.java:2892)
at java.lang.Class.getDeclaredConstructor(Class.java:2058)
at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:125)
... 13 more