/**
* Convert the value into an offset into the table for this browse
*
* @return the focus value to use
* @throws BrowseException
*/
private int getOffsetForValue(String value) throws BrowseException {
// get the table name. We don't really need to care about whether we are in a
// community or collection at this point. This is only for full or second
// level browse, so there is no need to worry about distinct value browsing
String tableName = browseIndex.getTableName();
// we need to make sure that we select from the correct column. If the sort option
// is the 0th option then we use sort_value, but if it is one of the others we have
// to select from that column instead. Otherwise, we end up missing the focus value
// to do comparisons in other columns. The use of the focus value needs to be consistent
// across the browse
SortOption so = scope.getSortOption();
if (so == null || so.getNumber() == 0) {
if (browseIndex.getSortOption() != null) so = browseIndex.getSortOption();
}
String col = "sort_1";
if (so.getNumber() > 0) {
col = "sort_" + Integer.toString(so.getNumber());
}
// now get the DAO to do the query for us, returning the highest
// string value in the given column in the given table for the
// item (I think)
return dao.doOffsetQuery(col, value, scope.isAscending());
}
/**
* Get the recently submitted items for the given collection.
*
* @param collection The collection.
*/
@SuppressWarnings(
"unchecked") // The cast from getLastSubmitted is correct, it dose infact return a list of
// Items.
private java.util.List<BrowseItem> getRecientlySubmittedIems(Collection collection)
throws SQLException {
if (recentSubmissionItems != null) return recentSubmissionItems;
String source = ConfigurationManager.getProperty("recent.submissions.sort-option");
BrowserScope scope = new BrowserScope(context);
scope.setCollection(collection);
scope.setResultsPerPage(RECENT_SUBMISISONS);
// FIXME Exception Handling
try {
scope.setBrowseIndex(BrowseIndex.getItemBrowseIndex());
for (SortOption so : SortOption.getSortOptions()) {
if (so.getName().equals(source)) scope.setSortBy(so.getNumber());
}
BrowseEngine be = new BrowseEngine(context);
this.recentSubmissionItems = be.browse(scope).getResults();
} catch (BrowseException bex) {
log.error("Caught BrowseException", bex);
}
return this.recentSubmissionItems;
}
/**
* Get the position of the current start point of the browse in the field of total objects
* relevant to this browse. This is integrally related to how results are presented in pages to
* the User Interface. The argument tells us whether this is a distinct browse or not, as this has
* an impact on how results are calculated
*
* @param distinct is this a distinct browse
* @return the offset of the first result from the start of the set
* @throws SQLException
* @throws BrowseException
*/
private int getPosition(boolean distinct) throws SQLException, BrowseException {
log.debug(LogManager.getHeader(context, "get_position", "distinct=" + distinct));
// if there isn't a focus then we are at the start
if (dao.getJumpToValue() == null) {
log.debug(LogManager.getHeader(context, "get_position_return", "return=0"));
return 0;
}
// get the table name that we are going to be getting our data from
String tableName =
browseIndex.getTableName(distinct, scope.inCommunity(), scope.inCollection());
// ensure that the select is set to "*"
String[] select = {"*"};
dao.setCountValues(select);
// FIXME: it would be nice to have a good way of doing this in the DAO
// now reset all of the fields that we don't want to have constraining
// our count, storing them locally to reinstate later
boolean isAscending = dao.isAscending();
boolean useEquals = dao.useEqualsComparator();
String orderField = dao.getOrderField();
int limit = dao.getLimit();
int offset = dao.getOffset();
// reverse the direction of the query, and remove the equal comparator
// (if it exists), as well as nullifying a few other unnecessary parameters
dao.setAscending(!isAscending);
dao.setEqualsComparator(false);
dao.setOrderField(null);
dao.setLimit(-1);
dao.setOffset(-1);
// perform the query and get the result
int count = dao.doCountQuery();
// now put back the values we removed for this method
dao.setAscending(isAscending);
dao.setEqualsComparator(useEquals);
dao.setOrderField(orderField);
dao.setLimit(limit);
dao.setOffset(offset);
log.debug(LogManager.getHeader(context, "get_position_return", "return=" + count));
return count;
}
/**
* Return the focus value.
*
* @return the focus value to use
* @throws BrowseException
*/
private String getJumpToValue() throws BrowseException {
log.debug(LogManager.getHeader(context, "get_focus_value", ""));
// if the focus is by value, just return it
if (scope.hasJumpToValue()) {
log.debug(
LogManager.getHeader(
context, "get_focus_value_return", "return=" + scope.getJumpToValue()));
return scope.getJumpToValue();
}
// if the focus is to start with, then we need to return the value of the starts with
if (scope.hasStartsWith()) {
log.debug(
LogManager.getHeader(
context, "get_focus_value_return", "return=" + scope.getStartsWith()));
return scope.getStartsWith();
}
// since the focus is not by value, we need to obtain it
// get the id of the item to focus on
int id = scope.getJumpToItem();
// get the table name. We don't really need to care about whether we are in a
// community or collection at this point. This is only for full or second
// level browse, so there is no need to worry about distinct value browsing
String tableName = browseIndex.getTableName();
// we need to make sure that we select from the correct column. If the sort option
// is the 0th option then we use sort_value, but if it is one of the others we have
// to select from that column instead. Otherwise, we end up missing the focus value
// to do comparisons in other columns. The use of the focus value needs to be consistent
// across the browse
SortOption so = scope.getSortOption();
if (so == null || so.getNumber() == 0) {
if (browseIndex.getSortOption() != null) {
so = browseIndex.getSortOption();
}
}
String col = "sort_1";
if (so.getNumber() > 0) {
col = "sort_" + Integer.toString(so.getNumber());
}
// now get the DAO to do the query for us, returning the highest
// string value in the given column in the given table for the
// item (I think)
String max = dao.doMaxQuery(col, tableName, id);
log.debug(LogManager.getHeader(context, "get_focus_value_return", "return=" + max));
return max;
}
/*
* Creates a map of the browse options common to all pages (type / value /
* value language)
*/
Map<String, String> getCommonParameters() throws UIException {
Map<String, String> paramMap = new HashMap<String, String>();
paramMap.put(
BrowseParams.TYPE, AbstractDSpaceTransformer.URLEncode(scope.getBrowseIndex().getName()));
if (scope.getFilterValue() != null) {
paramMap.put(
BrowseParams.FILTER_VALUE, AbstractDSpaceTransformer.URLEncode(scope.getFilterValue()));
}
if (scope.getFilterValueLang() != null) {
paramMap.put(
BrowseParams.FILTER_VALUE_LANG,
AbstractDSpaceTransformer.URLEncode(scope.getFilterValueLang()));
}
return paramMap;
}
/**
* Convert the value into an offset into the table for this browse
*
* @return the focus value to use
* @throws BrowseException
*/
private int getOffsetForDistinctValue(String value) throws BrowseException {
if (!browseIndex.isMetadataIndex()) {
throw new IllegalArgumentException(
"getOffsetForDistinctValue called when not a metadata index");
}
// now get the DAO to do the query for us, returning the highest
// string value in the given column in the given table for the
// item (I think)
return dao.doDistinctOffsetQuery("sort_value", value, scope.isAscending());
}
/**
* Perform a standard browse, which will return a BrowseInfo object that represents the results
* for the current page, the total number of results, the range, and information to construct
* previous and next links on any web page
*
* @param bs the scope of the browse
* @return the results of the browse
* @throws BrowseException
*/
public BrowseInfo browse(BrowserScope bs) throws BrowseException {
log.debug(LogManager.getHeader(context, "browse", ""));
// first, load the browse scope into the object
this.scope = bs;
// since we use it so much, get the browse index out of the
// scope and store as a member
browseIndex = scope.getBrowseIndex();
// now make the decision as to how to browse
if (browseIndex.isMetadataIndex() && !scope.isSecondLevel()) {
// this is a single value browse type that has not gone to
// the second level (i.e. authors, not items by a given author)
return browseByValue(scope);
} else {
// this is the full browse type or a browse that has gone to
// the second level
return browseByItem(scope);
}
}
// returns recently changed items, checking for accessibility
private Item[] getItems(Context context, DSpaceObject dso) throws IOException, SQLException {
try {
// new method of doing the browse:
String idx = ConfigurationManager.getProperty("recent.submissions.sort-option");
if (idx == null) {
throw new IOException(
"There is no configuration supplied for: recent.submissions.sort-option");
}
BrowseIndex bix = BrowseIndex.getItemBrowseIndex();
if (bix == null) {
throw new IOException("There is no browse index with the name: " + idx);
}
BrowserScope scope = new BrowserScope(context);
scope.setBrowseIndex(bix);
if (dso != null) {
scope.setBrowseContainer(dso);
}
for (SortOption so : SortOption.getSortOptions()) {
if (so.getName().equals(idx)) {
scope.setSortBy(so.getNumber());
}
}
scope.setOrder(SortOption.DESCENDING);
scope.setResultsPerPage(itemCount);
// gather & add items to the feed.
BrowseEngine be = new BrowseEngine(context);
BrowseInfo bi = be.browseMini(scope);
Item[] results = bi.getItemResults(context);
if (includeAll) {
return results;
} else {
// Check to see if we can include this item
// Group[] authorizedGroups = AuthorizeManager.getAuthorizedGroups(context, results[i],
// Constants.READ);
// boolean added = false;
List<Item> items = new ArrayList<Item>();
for (Item result : results) {
checkAccess:
for (Group group :
AuthorizeManager.getAuthorizedGroups(context, result, Constants.READ)) {
if ((group.getID() == Group.ANONYMOUS_ID)) {
items.add(result);
break checkAccess;
}
}
}
return items.toArray(new Item[items.size()]);
}
} catch (SortException se) {
log.error("caught exception: ", se);
throw new IOException(se.getMessage(), se);
} catch (BrowseException e) {
log.error("caught exception: ", e);
throw new IOException(e.getMessage(), e);
}
}
/**
* Convert the value into an offset into the table for this browse
*
* @return the focus value to use
* @throws BrowseException
*/
private int getOffsetForValue(String value) throws BrowseException {
// we need to make sure that we select from the correct column. If the sort option
// is the 0th option then we use sort_value, but if it is one of the others we have
// to select from that column instead. Otherwise, we end up missing the focus value
// to do comparisons in other columns. The use of the focus value needs to be consistent
// across the browse
SortOption so = scope.getSortOption();
if (so == null || so.getNumber() == 0) {
if (browseIndex.getSortOption() != null) {
so = browseIndex.getSortOption();
}
}
String col = "sort_1";
if (so.getNumber() > 0) {
col = "sort_" + Integer.toString(so.getNumber());
}
// now get the DAO to do the query for us, returning the highest
// string value in the given column in the given table for the
// item (I think)
return dao.doOffsetQuery(col, value, scope.isAscending());
}
/**
* Convert the value into an offset into the table for this browse
*
* @return the focus value to use
* @throws BrowseException
*/
private int getOffsetForDistinctValue(String value) throws BrowseException {
if (!browseIndex.isMetadataIndex())
throw new IllegalArgumentException(
"getOffsetForDistinctValue called when not a metadata index");
// get the table name. We don't really need to care about whether we are in a
// community or collection at this point. This is only for full or second
// level browse, so there is no need to worry about distinct value browsing
String tableName = browseIndex.getTableName();
// now get the DAO to do the query for us, returning the highest
// string value in the given column in the given table for the
// item (I think)
return dao.doDistinctOffsetQuery("sort_value", value, scope.isAscending());
}
/**
* Return a normalized focus value. If there is no normalization that can be performed, return the
* focus value that is passed in.
*
* @param value a focus value to normalize
* @return the normalized focus value
* @throws BrowseException
*/
private String normalizeJumpToValue(String value) throws BrowseException {
// If the scope has a focus value (focus by value)
if (scope.hasJumpToValue()) {
// Normalize it based on the specified language as appropriate for this index
return OrderFormat.makeSortString(
scope.getJumpToValue(), scope.getJumpToValueLang(), scope.getBrowseIndex().getDataType());
} else if (scope.hasStartsWith()) {
// Scope has a starts with, so normalize that instead
return OrderFormat.makeSortString(
scope.getStartsWith(), null, scope.getBrowseIndex().getDataType());
}
// No focus value on the scope (ie. focus by id), so just return the passed focus value
// This is useful in cases where we have pulled a focus value from the index
// which will already be normalized, and avoids another DB lookup
return value;
}
String getKey() {
try {
String key = "";
key += "-" + scope.getBrowseIndex().getName();
key += "-" + scope.getBrowseLevel();
key += "-" + scope.getStartsWith();
key += "-" + scope.getResultsPerPage();
key += "-" + scope.getSortBy();
key += "-" + scope.getSortOption().getNumber();
key += "-" + scope.getOrder();
key += "-" + scope.getJumpToItem();
key += "-" + scope.getFilterValue();
key += "-" + scope.getFilterValueLang();
key += "-" + scope.getJumpToValue();
key += "-" + scope.setJumpToValueLang();
key += "-" + etAl;
return key;
} catch (Exception e) {
return null; // ignore exception and return no key
}
}
/**
* Browse the archive by single values (such as the name of an author). This produces a BrowseInfo
* object that contains Strings as the results of the browse
*
* @param bs the scope of the browse
* @return the results of the browse
* @throws BrowseException
*/
private BrowseInfo browseByValue(BrowserScope bs) throws BrowseException {
log.info(LogManager.getHeader(context, "browse_by_value", "focus=" + bs.getJumpToValue()));
try {
// get the table name that we are going to be getting our data from
// this is the distinct table constrained to either community or collection
dao.setTable(browseIndex.getDistinctTableName());
// remind the DAO that this is a distinct value browse, so it knows what sort
// of query to build
dao.setDistinct(true);
// tell the browse query whether we are ascending or descending on the value
dao.setAscending(scope.isAscending());
// set our constraints on community or collection
if (scope.inCollection() || scope.inCommunity()) {
// Scoped browsing of distinct metadata requires the mapping
// table to be specified.
dao.setFilterMappingTables(null, browseIndex.getMapTableName());
if (scope.inCollection()) {
Collection col = (Collection) scope.getBrowseContainer();
dao.setContainerTable("collection2item");
dao.setContainerIDField("collection_id");
dao.setContainerID(col.getID());
} else if (scope.inCommunity()) {
Community com = (Community) scope.getBrowseContainer();
dao.setContainerTable("communities2item");
dao.setContainerIDField("community_id");
dao.setContainerID(com.getID());
}
}
// this is the total number of results in answer to the query
int total = getTotalResults(true);
// set the ordering field (there is only one option)
dao.setOrderField("sort_value");
// assemble the focus clause if we are to have one
// it will look like one of the following
// - sort_value < myvalue
// = sort_1 > myvalue
dao.setJumpToField("sort_value");
int offset = scope.getOffset();
String rawFocusValue = null;
if (offset < 1 && scope.hasJumpToValue() || scope.hasStartsWith()) {
String focusValue = getJumpToValue();
// store the value to tell the Browse Info object which value we are browsing on
rawFocusValue = focusValue;
// make sure the incoming value is normalised
focusValue = normalizeJumpToValue(focusValue);
offset = getOffsetForDistinctValue(focusValue);
}
// assemble the offset and limit
dao.setOffset(offset);
dao.setLimit(scope.getResultsPerPage());
// Holder for the results
List<String[]> results = null;
// Does this browse have any contents?
if (total > 0) {
// now run the query
results = dao.doValueQuery();
// now, if we don't have any results, we are at the end of the browse. This will
// be because a starts_with value has been supplied for which we don't have
// any items.
if (results.size() == 0) {
// In this case, we will calculate a new offset for the last page of results
offset = total - scope.getResultsPerPage();
if (offset < 0) {
offset = 0;
}
// And rerun the query
dao.setOffset(offset);
results = dao.doValueQuery();
}
} else {
// No records, so make an empty list
results = new ArrayList<String[]>();
}
// construct the BrowseInfo object to pass back
BrowseInfo browseInfo = new BrowseInfo(results, offset, total, offset);
if (offset + scope.getResultsPerPage() < total) {
browseInfo.setNextOffset(offset + scope.getResultsPerPage());
}
if (offset - scope.getResultsPerPage() > -1) {
browseInfo.setPrevOffset(offset - scope.getResultsPerPage());
}
// add the browse index to the Browse Info
browseInfo.setBrowseIndex(browseIndex);
// set the sort option for the Browse Info
browseInfo.setSortOption(scope.getSortOption());
// tell the Browse Info which way we are sorting
browseInfo.setAscending(scope.isAscending());
// tell the Browse Info which level of browse we are at
browseInfo.setBrowseLevel(scope.getBrowseLevel());
// set the browse value if there is one
browseInfo.setFocus(rawFocusValue);
// tell the browse info if it is working from a starts with parameter
browseInfo.setStartsWith(scope.hasStartsWith());
// tell the browse info what the container for the browse was
if (scope.inCollection() || scope.inCommunity()) {
browseInfo.setBrowseContainer(scope.getBrowseContainer());
}
browseInfo.setResultsPerPage(scope.getResultsPerPage());
return browseInfo;
} catch (SQLException e) {
log.error("caught exception: ", e);
throw new BrowseException(e);
}
}
/**
* Browse the archive by the full item browse mechanism. This produces a BrowseInfo object which
* contains full BrowseItem objects as its result set.
*
* @param bs the scope of the browse
* @return the results of the browse
* @throws BrowseException
*/
private BrowseInfo browseByItem(BrowserScope bs) throws BrowseException {
log.info(LogManager.getHeader(context, "browse_by_item", ""));
try {
// get the table name that we are going to be getting our data from
dao.setTable(browseIndex.getTableName());
// tell the browse query whether we are ascending or descending on the value
dao.setAscending(scope.isAscending());
// assemble the value clause
String rawValue = null;
if (scope.hasFilterValue() && scope.isSecondLevel()) {
String value = scope.getFilterValue();
rawValue = value;
// make sure the incoming value is normalised
value =
OrderFormat.makeSortString(
value, scope.getFilterValueLang(), scope.getBrowseIndex().getDataType());
dao.setAuthorityValue(scope.getAuthorityValue());
// set the values in the Browse Query
if (scope.isSecondLevel()) {
dao.setFilterValueField("value");
dao.setFilterValue(rawValue);
} else {
dao.setFilterValueField("sort_value");
dao.setFilterValue(value);
}
dao.setFilterValuePartial(scope.getFilterValuePartial());
// to apply the filtering, we need the distinct and map tables for the index
dao.setFilterMappingTables(
browseIndex.getDistinctTableName(), browseIndex.getMapTableName());
}
// define a clause for the WHERE clause which will allow us to constrain
// our browse to a specified community or collection
if (scope.inCollection() || scope.inCommunity()) {
if (scope.inCollection()) {
Collection col = (Collection) scope.getBrowseContainer();
dao.setContainerTable("collection2item");
dao.setContainerIDField("collection_id");
dao.setContainerID(col.getID());
} else if (scope.inCommunity()) {
Community com = (Community) scope.getBrowseContainer();
dao.setContainerTable("communities2item");
dao.setContainerIDField("community_id");
dao.setContainerID(com.getID());
}
}
// this is the total number of results in answer to the query
int total = getTotalResults();
// assemble the ORDER BY clause
String orderBy = browseIndex.getSortField(scope.isSecondLevel());
if (scope.getSortBy() > 0) {
orderBy = "sort_" + Integer.toString(scope.getSortBy());
}
dao.setOrderField(orderBy);
int offset = scope.getOffset();
String rawFocusValue = null;
if (offset < 1
&& (scope.hasJumpToItem() || scope.hasJumpToValue() || scope.hasStartsWith())) {
// We need to convert these to an offset for the actual browse query.
// First, get a value that we can look up in the ordering field
rawFocusValue = getJumpToValue();
// make sure the incoming value is normalised
String focusValue = normalizeJumpToValue(rawFocusValue);
log.debug("browsing using focus: " + focusValue);
// Convert the focus value into an offset
offset = getOffsetForValue(focusValue);
}
dao.setOffset(offset);
// assemble the LIMIT clause
dao.setLimit(scope.getResultsPerPage());
// Holder for the results
List<BrowseItem> results = null;
// Does this browse have any contents?
if (total > 0) {
// now run the query
results = dao.doQuery();
// now, if we don't have any results, we are at the end of the browse. This will
// be because a starts_with value has been supplied for which we don't have
// any items.
if (results.size() == 0) {
// In this case, we will calculate a new offset for the last page of results
offset = total - scope.getResultsPerPage();
if (offset < 0) {
offset = 0;
}
// And rerun the query
dao.setOffset(offset);
results = dao.doQuery();
}
} else {
// No records, so make an empty list
results = new ArrayList<BrowseItem>();
}
// construct the BrowseInfo object to pass back
// BrowseInfo browseInfo = new BrowseInfo(results, position, total, offset);
BrowseInfo browseInfo = new BrowseInfo(results, offset, total, offset);
if (offset + scope.getResultsPerPage() < total) {
browseInfo.setNextOffset(offset + scope.getResultsPerPage());
}
if (offset - scope.getResultsPerPage() > -1) {
browseInfo.setPrevOffset(offset - scope.getResultsPerPage());
}
// add the browse index to the Browse Info
browseInfo.setBrowseIndex(browseIndex);
// set the sort option for the Browse Info
browseInfo.setSortOption(scope.getSortOption());
// tell the Browse Info which way we are sorting
browseInfo.setAscending(scope.isAscending());
// tell the Browse Info which level of browse we are at
browseInfo.setBrowseLevel(scope.getBrowseLevel());
// set the browse value if there is one
browseInfo.setValue(rawValue);
// set the browse authority key if there is one
browseInfo.setAuthority(scope.getAuthorityValue());
// set the focus value if there is one
browseInfo.setFocus(rawFocusValue);
if (scope.hasJumpToItem()) {
browseInfo.setFocusItem(scope.getJumpToItem());
}
// tell the browse info if it is working from a starts with parameter
browseInfo.setStartsWith(scope.hasStartsWith());
// tell the browse info what the container for the browse was
if (scope.inCollection() || scope.inCommunity()) {
browseInfo.setBrowseContainer(scope.getBrowseContainer());
}
browseInfo.setResultsPerPage(scope.getResultsPerPage());
browseInfo.setEtAl(scope.getEtAl());
return browseInfo;
} catch (SQLException e) {
log.error("caught exception: ", e);
throw new BrowseException(e);
}
}
/**
* Perform a limited browse, which only returns the results requested, without any extraneous
* information. To perform a full browse, use BrowseEngine.browse() above. This supports Item
* browse only, and does not currently support focus or values. This method is used, for example,
* to generate the Recently Submitted Items results.
*
* @param bs the scope of the browse
* @return the results of the browse
*/
public BrowseInfo browseMini(BrowserScope bs) throws BrowseException {
log.info(LogManager.getHeader(context, "browse_mini", ""));
// load the scope into the object
this.scope = bs;
// since we use it so much, get the browse index out of the
// scope and store as a member
browseIndex = scope.getBrowseIndex();
// get the table name that we are going to be getting our data from
dao.setTable(browseIndex.getTableName());
// tell the browse query whether we are ascending or descending on the value
dao.setAscending(scope.isAscending());
// define a clause for the WHERE clause which will allow us to constrain
// our browse to a specified community or collection
if (scope.inCollection() || scope.inCommunity()) {
if (scope.inCollection()) {
Collection col = (Collection) scope.getBrowseContainer();
dao.setContainerTable("collection2item");
dao.setContainerIDField("collection_id");
dao.setContainerID(col.getID());
} else if (scope.inCommunity()) {
Community com = (Community) scope.getBrowseContainer();
dao.setContainerTable("communities2item");
dao.setContainerIDField("community_id");
dao.setContainerID(com.getID());
}
}
dao.setOffset(scope.getOffset());
dao.setLimit(scope.getResultsPerPage());
// assemble the ORDER BY clause
String orderBy = browseIndex.getSortField(scope.isSecondLevel());
if (scope.getSortBy() > 0) {
orderBy = "sort_" + Integer.toString(scope.getSortBy());
}
dao.setOrderField(orderBy);
// now run the query
List<BrowseItem> results = dao.doQuery();
// construct the mostly empty BrowseInfo object to pass back
BrowseInfo browseInfo = new BrowseInfo(results, 0, scope.getResultsPerPage(), 0);
// add the browse index to the Browse Info
browseInfo.setBrowseIndex(browseIndex);
// set the sort option for the Browse Info
browseInfo.setSortOption(scope.getSortOption());
// tell the Browse Info which way we are sorting
browseInfo.setAscending(scope.isAscending());
// tell the browse info what the container for the browse was
if (scope.inCollection() || scope.inCommunity()) {
browseInfo.setBrowseContainer(scope.getBrowseContainer());
}
browseInfo.setResultsPerPage(scope.getResultsPerPage());
browseInfo.setEtAl(scope.getEtAl());
return browseInfo;
}
/**
* Get the value (for single value browses) for the result that appears at the top of the previous
* page, for when the User Interface is performing result set paging. The callback argument allows
* for this method to populate the List with the results obtained from the query, which can be
* useful when, for example, reaching the final browse page and needing additional results to pad
* up to the number of results per page
*
* @param callback A List object for holding String objects indexed numerically in the correct
* order
* @return the value of the top of the previous page
* @throws SQLException
* @throws BrowseException
*/
private String getPreviousPageValue(List callback) throws SQLException, BrowseException {
// do we want to capture the results?
boolean capture = false;
if (callback != null) {
capture = true;
}
log.debug(
LogManager.getHeader(context, "get_previous_page_value", "capture_results=" + capture));
// the only thing we need to do is reverse the direction
// of the query, and set it to not use the "=" part of the
// comparator (i.e. < and > not <= and >=).
boolean isAscending = dao.isAscending();
dao.setAscending(!isAscending);
boolean useEquals = dao.useEqualsComparator();
dao.setEqualsComparator(false);
// store in local scope the things that we are going to change
// during this method
int resultLimit = dao.getLimit();
// if the database supports it (postgres does), we use limit
// and offset to minimise the work it has to do.
// the limit will be the size of a page, or double the size of the
// page if we are capturing the result set (because the first page's worth
// will be the results, so the previous link will need to come from the
// page *before* that)
int limit = scope.getResultsPerPage();
if (capture) {
limit *= 2;
}
dao.setLimit(limit);
// now we have a query which is exactly the opposite of the
// original query. So lets execute it:
List results = dao.doValueQuery();
// before we continue, put back the variables we messed with
dao.setAscending(isAscending);
dao.setEqualsComparator(useEquals);
dao.setLimit(resultLimit);
Iterator itr = results.iterator();
// work our way through the list, capturing if necessary, and finally
// having the last result, which will be the top of the previous page
int i = 0;
String prev = null;
while (itr.hasNext()) {
String value = (String) itr.next();
// we need to copy this, because of the scoping vs by-reference issue
prev = value;
// if we need to capture the results in the call back, do it here.
// Note that since the results will come in backwards, we place
// each one at the start of the array so that it displaces the others
// in the right direction. By the end, they should be sorted correctly
// we use the index i to be sure that we only grab one page's worth
// of results (see note above about limit)
if (capture && i < scope.getResultsPerPage()) {
callback.add(0, value);
i++;
}
}
log.debug(LogManager.getHeader(context, "get_previous_page_value_return", "return=" + prev));
return prev;
}