org.marc4j.MarcCombiningReader Maven / Gradle / Ivy
package org.marc4j;
import java.util.ArrayList;
import java.util.List;
import org.marc4j.marc.ControlField;
import org.marc4j.marc.DataField;
import org.marc4j.marc.Record;
import org.marc4j.marc.Subfield;
import org.marc4j.marc.VariableField;
/**
* Binary MARC records have a maximum size of 99999 bytes. In the data dumps
* from the Sirsi/Dynix Virgo system if a record with all of its holdings
* information attached would be greater that that size, the records is written
* out multiple times with each subsequent record containing a subset of the
* total holdings information. This class reads ahead to determine when the next
* record in a MaARC file is actually a continuation of the same record. When
* this occurs, the holdings information in the next record is appended
* to/merged with the in-memory MARC record representation already read.
*
* @author rh9ec
*/
public class MarcCombiningReader implements MarcReader {
Record currentRecord = null;
Record nextRecord = null;
MarcReader reader;
String idsToMerge = null;
String leftControlField = null;
String rightControlField = null;
ErrorHandler nextErrors;
ErrorHandler currentErrors;
/**
* Constructor for a "combining" Marc reader, that looks ahead at the Marc
* file to determine when the next record is a continuation of the currently
* read record.
*
* @param reader - The Lower level MarcReader that returns Marc4J Record
* objects that are read from a Marc file.
* @param idsToMerge - string representing a regular expression matching
* those fields to be merged for continuation records.
* @param leftControlField - string representing a control field in the
* current record to use for matching purposes (null to default to
* 001).
* @param rightControlField - string representing a control field in the
* next record to use for matching purposes (null to default to 001).
*/
public MarcCombiningReader(final MarcReader reader, final String idsToMerge,
final String leftControlField, final String rightControlField) {
this.reader = reader;
this.idsToMerge = idsToMerge;
this.leftControlField = leftControlField;
this.rightControlField = rightControlField;
this.nextErrors = null;
this.currentErrors = null;
}
/**
* Constructor for a "combining" Marc reader, that looks ahead at the Marc
* file to determine when the next record is a continuation of the currently
* read record. Because this reader needs to have two records in memory to
* determine when the subsequent record is a continuation, if Error Handling
* is being performed, this constructor needs to be used, so that the errors
* from the "next" record are not appended to the results for the "current"
* record. Call this constructor in the following way: ErrorHandler errors2
* = errors; errors = new ErrorHandler(); reader = new
* MarcCombiningReader(reader, errors, errors2,
* combineConsecutiveRecordsFields);
*
* @param reader - The Lower level MarcReader that returns Marc4J Record
* objects that are read from a Marc file.
* @param currentErrors - ErrorHandler Object to use for attaching errors to
* a record.
* @param nextErrors - ErrorHandler Object that was passed into the lower
* level MarcReader
* @param idsToMerge - string representing a regular expression matching
* those fields to be merged for continuation records.
* @param leftControlField - string representing a control field in the
* current record to use for matching purposes (null to default to
* 001).
* @param rightControlField - string representing a control field in the
* next record to use for matching purposes (null to default to 001).
*/
public MarcCombiningReader(final MarcReader reader, final ErrorHandler currentErrors,
final ErrorHandler nextErrors, final String idsToMerge,
final String leftControlField, final String rightControlField) {
this.reader = reader;
this.idsToMerge = idsToMerge;
this.leftControlField = leftControlField;
this.rightControlField = rightControlField;
this.nextErrors = nextErrors;
this.currentErrors = currentErrors;
}
/**
* Returns true if there is a next record; else
* false.
*/
@Override
public boolean hasNext() {
if (currentRecord == null) {
currentRecord = next();
}
return (currentRecord != null);
}
/**
* Returns the next {@link Record} record if there is one and
* null if there isn't.
*/
@Override
public Record next() {
if (currentRecord != null) {
final Record tmp = currentRecord;
currentRecord = null;
return (tmp);
} else if (currentRecord == null) {
if (nextRecord != null) {
currentRecord = nextRecord;
copyErrors(currentErrors, nextErrors);
nextRecord = null;
}
if (!reader.hasNext()) {
return ((currentRecord != null) ? next() : null);
}
try {
nextRecord = reader.next();
} catch (final Exception e) {
if (currentRecord != null) {
final String recCntlNum = currentRecord.getControlNumber();
throw new MarcException("Couldn't get next record after " +
(recCntlNum != null ? recCntlNum : "") + " -- " +
e.toString());
} else {
throw new MarcException("Marc record couldn't be read -- " +
e.toString());
}
}
while (recordsMatch(currentRecord, nextRecord)) {
currentRecord =
combineRecords(currentRecord, nextRecord, idsToMerge);
mergeErrors(currentErrors, nextErrors);
if (reader.hasNext()) {
try {
nextRecord = reader.next();
} catch (final Exception e) {
final String recCntlNum = currentRecord.getControlNumber();
throw new MarcException(
"Couldn't get next record after " +
(recCntlNum != null ? recCntlNum : "") +
" -- " + e.toString());
}
} else {
nextRecord = null;
}
}
return (next());
}
return null;
}
/**
* Support method to find a specific control field within a record and
* return its contents as a string.
*
* @param record - record to search
* @param tag - tag number to search for
*/
private String findControlField(final Record record, final String tag) {
final String tagstart = tag.substring(0, 3);
final List fields = record.getVariableFields(tagstart);
for (final VariableField field : fields) {
if (field instanceof ControlField) {
final ControlField cf = (ControlField) field;
if (cf.getTag().matches(tagstart)) {
return (cf.getData());
}
} else if (field instanceof DataField) {
final DataField df = (DataField) field;
if (df.getTag().matches(tagstart)) {
char subfieldtag = 'a';
if (tag.length() > 3) {
subfieldtag = tag.charAt(4);
}
final Subfield sf = df.getSubfield(subfieldtag);
if (sf != null) {
return (sf.getData());
}
}
}
}
return null;
}
/**
* Support method to detect if two records match.
*
* @param left - left side of the comparison (current record)
* @param right - right side of the comparison (next record)
*/
private boolean recordsMatch(final Record left, final Record right) {
// Records can't match if they don't exist!
if (left == null || right == null) {
return false;
}
// Initialize match strings extracted from records:
String leftStr = null;
String rightStr = null;
// For both sides of the match (left and right), check to see if the
// user provided a control field setting. If no preference was provided,
// we'll match using the record ID. If a preference exists, we need to
// look up the specified control field in the record.
if (leftControlField == null) {
leftStr = left.getControlNumber();
} else {
leftStr = findControlField(left, leftControlField);
}
if (rightControlField == null) {
rightStr = right.getControlNumber();
} else {
rightStr = findControlField(right, rightControlField);
}
// Check for a match and return an appropriate status:
if (leftStr != null && rightStr != null && leftStr.equals(rightStr)) {
return true;
}
return false;
}
private void copyErrors(final ErrorHandler currentErr, final ErrorHandler nextErr) {
if (currentErr != null && nextErr != null) {
currentErr.reset();
mergeErrors(currentErr, nextErr);
}
}
private void mergeErrors(final ErrorHandler currentErr, final ErrorHandler nextErr) {
if (currentErr != null && nextErr != null) {
currentErr.addErrors(nextErr.getErrors());
}
}
/**
* Combines fields (identified by the idsToMerge) from the
* second {@link Record} into the first.
*
* @param currentRecord
* @param nextRecord
* @param idsToMerge
* @return
*/
static public Record combineRecords(final Record currentRecord,
final Record nextRecord, final String idsToMerge) {
final List fields = nextRecord.getVariableFields();
for (final VariableField field : fields) {
if (field.getTag().matches(idsToMerge)) {
currentRecord.addVariableField(field);
}
}
return (currentRecord);
}
/**
* Combines fields (identified by the idsToMerge from the
* second {@link Record} into the first (before the supplied field).
*
* @param currentRecord
* @param nextRecord
* @param idsToMerge
* @param fieldInsertBefore
* @return
*/
static public Record combineRecords(final Record currentRecord,
final Record nextRecord, final String idsToMerge, final String fieldInsertBefore) {
final List existingFields = currentRecord.getVariableFields();
final List fieldsToMove = new ArrayList();
// temporarily remove some existing fields
for (final VariableField field : existingFields) {
if (field.getTag().matches(fieldInsertBefore)) {
fieldsToMove.add(field);
currentRecord.removeVariableField(field);
}
}
final List fields = nextRecord.getVariableFields();
for (final VariableField field : fields) {
if (field.getTag().matches(idsToMerge)) {
currentRecord.addVariableField(field);
}
}
// now add back the temporarily removed fields
for (final VariableField field : fieldsToMove) {
currentRecord.addVariableField(field);
}
return (currentRecord);
}
}
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