我试图将一个小的RCFile(约200行数据)读入HashMap中以进行Map-Side连接,但是我很难将文件中的数据转换为可用状态。
这是我到目前为止的内容,其中大部分是从this example提取的:
public void configure(JobConf job)
{
try
{
FileSystem fs = FileSystem.get(job);
RCFile.Reader rcFileReader = new RCFile.Reader(fs, new Path("/path/to/file"), job);
int counter = 1;
while (rcFileReader.next(new LongWritable(counter)))
{
System.out.println("Fetching data for row " + counter);
BytesRefArrayWritable dataRead = new BytesRefArrayWritable();
rcFileReader.getCurrentRow(dataRead);
System.out.println("dataRead: " + dataRead + " dataRead.size(): " + dataRead.size());
for (int i = 0; i < dataRead.size(); i++)
{
BytesRefWritable bytesRefRead = dataRead.get(i);
byte b1[] = bytesRefRead.getData();
Text returnData = new Text(b1);
System.out.println("READ-DATA = " + returnData.toString());
}
counter++;
}
}
catch (IOException e)
{
throw new Error(e);
}
}
但是,我得到的输出在第一行中将每列中的所有数据连接在一起,而在其他任何行中都没有数据。
Fetching data for row 1
dataRead: org.apache.hadoop.hive.serde2.columnar.BytesRefArrayWritable@7f26d3df dataRead.size(): 5
READ-DATA = 191606656066860670
READ-DATA = United StatesAmerican SamoaGuamNorthern Mariana Islands
READ-DATA = USASGUMP
READ-DATA = USSouth PacificSouth PacificSouth Pacific
READ-DATA = 19888
Fetching data for row 2
dataRead: org.apache.hadoop.hive.serde2.columnar.BytesRefArrayWritable@1cb1a4e2 dataRead.size(): 0
Fetching data for row 3
dataRead: org.apache.hadoop.hive.serde2.columnar.BytesRefArrayWritable@52c00025 dataRead.size(): 0
Fetching data for row 4
dataRead: org.apache.hadoop.hive.serde2.columnar.BytesRefArrayWritable@3b49a794 dataRead.size(): 0
如何正确读取此数据,以便一次访问一行
(191, United States, US, US, 19)
? 最佳答案
经过更多的挖掘之后,我找到了解决方案。此处的关键是不使用RCFile.Reader
而是使用RCFileRecordReader
。
这是我最终得到的结果,它也适合于打开多个文件:
try
{
FileSystem fs = FileSystem.get(job);
FileStatus [] fileStatuses = fs.listStatus(new Path("/path/to/dir/"));
LongWritable key = new LongWritable();
BytesRefArrayWritable value = new BytesRefArrayWritable();
int counter = 1;
for (int i = 0; i < fileStatuses.length; i++)
{
FileStatus fileStatus = fileStatuses[i];
if (!fileStatus.isDir())
{
System.out.println("File: " + fileStatus);
FileSplit split = new FileSplit(fileStatus.getPath(), 0, fileStatus.getLen(), job);
RCFileRecordReader reader = new RCFileRecordReader(job, split);
while (reader.next(key, value))
{
System.out.println("Getting row " + counter);
AllCountriesRow acr = AllCountriesRow.valueOf(value);
System.out.println("ROW: " + acr);
counter++;
}
}
}
}
catch (IOException e)
{
throw new Error(e);
}
和AllCountryiesRow.valueOf:
(请注意
Column
是列的枚举,按它们在每一行中出现的顺序,而serDe
是ColumnarSerDe
的实例)public static AllCountriesRow valueOf(BytesRefArrayWritable braw) throws IOException
{
try
{
StructObjectInspector soi = (StructObjectInspector) serDe.getObjectInspector();
Object row = serDe.deserialize(braw);
List<? extends StructField> fieldRefs = soi.getAllStructFieldRefs();
Object fieldData = soi.getStructFieldData(row, fieldRefs.get(Column.ID.ordinal()));
ObjectInspector oi = fieldRefs.get(Column.ID.ordinal()).getFieldObjectInspector();
int id = ((IntObjectInspector)oi).get(fieldData);
fieldData = soi.getStructFieldData(row, fieldRefs.get(Column.NAME.ordinal()));
oi = fieldRefs.get(Column.NAME.ordinal()).getFieldObjectInspector();
String name = ((StringObjectInspector)oi).getPrimitiveJavaObject(fieldData);
fieldData = soi.getStructFieldData(row, fieldRefs.get(Column.CODE.ordinal()));
oi = fieldRefs.get(Column.CODE.ordinal()).getFieldObjectInspector();
String code = ((StringObjectInspector)oi).getPrimitiveJavaObject(fieldData);
fieldData = soi.getStructFieldData(row, fieldRefs.get(Column.REGION_NAME.ordinal()));
oi = fieldRefs.get(Column.REGION_NAME.ordinal()).getFieldObjectInspector();
String regionName = ((StringObjectInspector)oi).getPrimitiveJavaObject(fieldData);
fieldData = soi.getStructFieldData(row, fieldRefs.get(Column.CONTINENT_ID.ordinal()));
oi = fieldRefs.get(Column.CONTINENT_ID.ordinal()).getFieldObjectInspector();
int continentId = ((IntObjectInspector)oi).get(fieldData);
return new AllCountriesRow(id, name, code, regionName, continentId);
}
catch (SerDeException e)
{
throw new IOException(e);
}
}
最后以AllCountriesRow对象结束,该对象中包含相关行的所有信息。
关于java - 如何读取RCFile,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/25416114/