uk.ac.starlink.feather.StarColumnWriter Maven / Gradle / Ivy
package uk.ac.starlink.feather;
import java.io.IOException;
import java.io.OutputStream;
import org.json.JSONObject;
import uk.ac.bristol.star.feather.BufUtils;
import uk.ac.bristol.star.feather.ColStat;
import uk.ac.bristol.star.feather.FeatherColumnWriter;
import uk.ac.bristol.star.feather.FeatherType;
import uk.ac.starlink.table.ColumnInfo;
import uk.ac.starlink.table.DefaultValueInfo;
import uk.ac.starlink.table.RowSequence;
import uk.ac.starlink.table.StarTable;
import uk.ac.starlink.table.StoragePolicy;
/**
* FeatherColumnWriter for use with StarTables.
*
* @author Mark Taylor
* @since 26 Feb 2020
*/
public abstract class StarColumnWriter implements FeatherColumnWriter {
private final StarTable table_;
private final int icol_;
private final FeatherType featherType_;
private final boolean isNullable_;
/**
* Constructor.
*
* The isNullable parameter only needs to be given true
* if the writeData method cannot represent null values in its
* byte representation.
*
* @param table inupt table
* @param icol column index in input table
* @param featherType data type for output column
* @param isNullable true iff writeData cannot write in-band null values
*/
protected StarColumnWriter( StarTable table, int icol,
FeatherType featherType, boolean isNullable ) {
table_ = table;
icol_ = icol;
featherType_ = featherType;
isNullable_ = isNullable;
}
/**
* Writes the bytes consituting the data stream for this column,
* excluding any optional validity mask.
* Note the output does not need to be aligned on an 8-byte boundary.
*
* @param out destination stream
* @return information about what was actually written
*/
public abstract DataStat writeDataBytes( OutputStream out )
throws IOException;
/**
* Returns the table on which this writer is operating.
*
* @return input table
*/
public StarTable getTable() {
return table_;
}
/**
* Returns the index of the input table column which is being written.
*
* @return input column index
*/
public int getColumnIndex() {
return icol_;
}
/**
* Returns the output data type code.
*
* @return feather output type
*/
public FeatherType getFeatherType() {
return featherType_;
}
/**
* Indicates whether this writer may write a validity mask.
*
* @return true iff output type supports masked null values
*/
public boolean isNullable() {
return isNullable_;
}
public String getName() {
return table_.getColumnInfo( icol_ ).getName();
}
public String getUserMetadata() {
ColumnInfo info = table_.getColumnInfo( icol_ );
JSONObject json = new JSONObject();
addJsonEntry( json, FeatherStarTable.UNIT_KEY, info.getUnitString() );
addJsonEntry( json, FeatherStarTable.UCD_KEY, info.getUCD() );
addJsonEntry( json, FeatherStarTable.UTYPE_KEY, info.getUtype() );
addJsonEntry( json, FeatherStarTable.DESCRIPTION_KEY,
info.getDescription() );
addJsonEntry( json, FeatherStarTable.SHAPE_KEY,
DefaultValueInfo.formatShape( info.getShape() ) );
return json.length() > 0
? json.toString( 0 ).replaceAll( "\n", " " )
: null;
}
public ColStat writeColumnBytes( OutputStream out ) throws IOException {
/* Write mask, if applicable. */
long nNull = 0;
final long maskBytes;
if ( isNullable_ && table_.getColumnInfo( icol_ ).isNullable() ) {
int mask = 0;
int ibit = 0;
long nrow = 0;
RowSequence rseq = table_.getRowSequence();
try {
while ( rseq.next() ) {
nrow++;
if ( rseq.getCell( icol_ ) == null ) {
nNull++;
}
else {
mask |= 1 << ibit;
}
if ( ++ibit == 8 ) {
out.write( mask );
ibit = 0;
mask = 0;
}
}
if ( ibit > 0 ) {
out.write( mask );
}
}
finally {
rseq.close();
}
long mb = ( nrow + 7 ) / 8;
maskBytes = mb + BufUtils.align8( out, mb );
}
else {
maskBytes = 0;
}
/* Write data. */
DataStat dataStat = writeDataBytes( out );
/* Package and return statistics. */
long db = dataStat.getByteCount();
final long rowCount = dataStat.getRowCount();
long dataBytes = db + BufUtils.align8( out, db );
boolean hasNull = nNull > 0;
final long byteCount = maskBytes + dataBytes;
final long dataOffset = maskBytes;
final long nullCount = nNull;
return new ColStat() {
public long getRowCount() {
return rowCount;
}
public long getByteCount() {
return byteCount;
}
public long getDataOffset() {
return dataOffset;
}
public long getNullCount() {
return nullCount;
}
};
}
public abstract ItemAccumulator
createItemAccumulator( StoragePolicy storage );
/**
* Adds a key-value entry to a supplied JSON object.
*
* @param json json object (map), altered on exit
* @param key key to add
* @param value value to add
*/
private static void addJsonEntry( JSONObject json,
String key, String value ) {
if ( value != null && value.trim().length() > 0 ) {
json.put( key, value );
}
}
/**
* Aggregates information about column output.
*/
public static class DataStat {
private final long byteCount_;
private final long rowCount_;
/**
* Constructor.
*
* @param byteCount number of bytes written
* @param rowCount number of rows written
*/
public DataStat( long byteCount, long rowCount ) {
byteCount_ = byteCount;
rowCount_ = rowCount;
}
/**
* Returns the number of bytes written.
*
* @return byte count
*/
public long getByteCount() {
return byteCount_;
}
/**
* Returns the number of rows written.
*
* @return row count
*/
public long getRowCount() {
return rowCount_;
}
}
}