Class LargeSelect<T>
- java.lang.Object
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- org.apache.torque.util.LargeSelect<T>
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- Type Parameters:
T
- the type of the objects which are returned on a query.
- All Implemented Interfaces:
Serializable
,Runnable
public class LargeSelect<T> extends Object implements Runnable, Serializable
This class can be used to retrieve a large result set from a database query. The query is started and then rows are returned a page at a time. TheLargeSelect
is meant to be placed into the Session or User.Temp, so that it can be used in response to several related requests. Note that in order to useLargeSelect
you need to be willing to accept the fact that the result set may become inconsistent with the database if updates are processed subsequent to the queries being executed. Specifying a memory page limit of 1 will give you a consistent view of the records but the totals may not be accurate and the performance will be terrible. In most cases the potential for inconsistencies data should not cause any serious problems and performance should be pretty good (but read on for further warnings).The idea here is that the full query result would consume too much memory and if displayed to a user the page would be too long to be useful. Rather than loading the full result set into memory, a window of data (the memory limit) is loaded and retrieved a page at a time. If a request occurs for data that falls outside the currently loaded window of data then a new query is executed to fetch the required data. Performance is optimized by starting a thread to execute the database query and fetch the results. This will perform best when paging forwards through the data, but a minor optimization where the window is moved backwards by two rather than one page is included for when a user pages past the beginning of the window.
As the query is performed in in steps, it is often the case that the total number of records and pages of data is unknown.
LargeSelect
provides various methods for indicating how many records and pages it is currently aware of and for presenting this information to users.LargeSelect
utilizes theCriteria
methodssetOffset()
andsetLimit()
to limit the amount of data retrieved from the database - these values are either passed through to the DBMS when supported (efficient with the caveat below) or handled by the Torque API when it is not (not so efficient).As
LargeSelect
must re-execute the query each time the user pages out of the window of loaded data, you should consider the impact of non-index sort orderings and other criteria that will require the DBMS to execute the entire query before filtering down to the offset and limit either internally or via Torque.The memory limit defaults to 5 times the page size you specify, but alternative constructors and the class method
setMemoryPageLimit()
allow you to override this for a specific instance ofLargeSelect
or future instances respectively.Typically you will create a
LargeSelect
using yourCriteria
(perhaps created from the results of a search parameter page), page size, memory page limit, return class name (for which you may have defined a business object class before hand) and peer class and place this in user.Temp thus:data.getUser().setTemp("someName", largeSelect);
In your template you will then use something along the lines of:
#set($largeSelect = $data.User.getTemp("someName")) #set($searchop = $data.Parameters.getString("searchop")) #if($searchop.equals("prev")) #set($recs = $largeSelect.PreviousResults) #else #if($searchop.equals("goto")) #set($recs = $largeSelect.getPage($data.Parameters.getInt("page", 1))) #else #set($recs = $largeSelect.NextResults) #end #end
...to move through the records.
LargeSelect
implements a number of convenience methods that make it easy to add all of the necessary bells and whistles to your template.- Version:
- $Id: LargeSelect.java 1879929 2020-07-16 07:42:57Z gk $
- Author:
- John D. McNally, Scott Eade
- See Also:
- Serialized Form
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Field Summary
Fields Modifier and Type Field Description static int
DEFAULT_MEMORY_LIMIT_PAGES
The default value for the maximum number of pages of data to be retained in memory.static String
DEFAULT_PAGE_PROGRESS_TEXT_PATTERN
default MessageFormat pattern for the page progress textstatic String
DEFAULT_RECORD_PROGRESS_TEXT_PATTERN
default MessageFormat pattern for the record progress text
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Constructor Summary
Constructors Constructor Description LargeSelect(Criteria criteria, int pageSize, int memoryPageLimit, BasePeerImpl<T> peerImpl)
Creates a LargeSelect whose results are returned as aList
containing a maximum ofpageSize
objects of the type T at a time, maintaining a maximum ofmemoryPageLimit
pages of results in memory.LargeSelect(Criteria criteria, int pageSize, BasePeerImpl<T> peerImpl)
Creates a LargeSelect whose results are returned as aList
containing a maximum ofpageSize
objects of the type defined within the class namedreturnBuilderClassName
at a time, maintaining a maximum ofLargeSelect.memoryPageLimit
pages of results in memory.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description int
getCurrentPageNumber()
Retrieve the number of the current page.List<T>
getCurrentPageResults()
Provide access to the results from the current page.int
getCurrentPageSize()
Provides a count of the number of rows to be displayed on the current page - for the last page this may be less than the configured page size.int
getFirstRecordNoForPage()
Provide the record number of the first row included on the current page.int
getLastRecordNoForPage()
Provide the record number of the last row included on the current page.int
getMemoryPageLimit()
Retrieves the multiplier that will be used to compute the memory limit when a constructor with no memory page limit is used - the memory limit will be this number multiplied by the page size.List<T>
getNextResults()
Gets the next page of rows.boolean
getNextResultsAvailable()
Indicates if further result pages are available.List<T>
getPage(int pageNumber)
Retrieve a specific page, if it exists.String
getPageProgressText()
A convenience method that provides text showing progress through the selected rows on a page basis.String
getPageProgressTextPattern()
Retrieve the MessageFormat pattern for the page progress The default isint
getPageSize()
Retrieve the page size.boolean
getPaginated()
Provide an indication of whether or not paging of results will be required.List<T>
getPreviousResults()
Gets the previous page of rows.boolean
getPreviousResultsAvailable()
Indicates if previous results pages are available.String
getRecordProgressText()
A convenience method that provides text showing progress through the selected rows on a record basis.String
getRecordProgressTextPattern()
Retrieve the MessageFormat pattern for the record progress The default isString
getSearchParam(String name)
Retrieve a search parameter.String
getSearchParam(String name, String defaultValue)
Retrieve a search parameter.int
getTotalPages()
Retrieve the total number of pages of search results that are known to exist (this will be the actual value when the query has completeted (seegetQyeryCompleted()
).int
getTotalRecords()
Retrieve the total number of search result records that are known to exist (this will be the actual value when the query has completed (seegetTotalsFinalized()
).boolean
getTotalsFinalized()
Provide access to indicator that the total values for the number of records and pages are now accurate as opposed to known upper limits.boolean
hasResultsAvailable()
Indicates if any results are available.void
invalidateResult()
Clear the query result so that the query is re-executed when the next page is retrieved.void
removeSearchParam(String name)
Remove a value from the search parameters.void
run()
A background thread that retrieves the rows.void
setMemoryPageLimit(int memoryPageLimit)
Sets the multiplier that will be used to compute the memory limit when a constructor with no memory page limit is used - the memory limit will be this number multiplied by the page size.void
setPageProgressTextPattern(String pageProgressTextPattern)
Set the MessageFormat pattern for the page progress.void
setRecordProgressTextPattern(String recordProgressTextPattern)
Set the MessageFormat pattern for the record progress.void
setSearchParam(String name, String value)
Set a search parameter.String
toString()
Provide something useful for debugging purposes.
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Field Detail
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DEFAULT_PAGE_PROGRESS_TEXT_PATTERN
public static final String DEFAULT_PAGE_PROGRESS_TEXT_PATTERN
default MessageFormat pattern for the page progress text- See Also:
- Constant Field Values
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DEFAULT_RECORD_PROGRESS_TEXT_PATTERN
public static final String DEFAULT_RECORD_PROGRESS_TEXT_PATTERN
default MessageFormat pattern for the record progress text- See Also:
- Constant Field Values
-
DEFAULT_MEMORY_LIMIT_PAGES
public static final int DEFAULT_MEMORY_LIMIT_PAGES
The default value for the maximum number of pages of data to be retained in memory.- See Also:
- Constant Field Values
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Constructor Detail
-
LargeSelect
public LargeSelect(Criteria criteria, int pageSize, BasePeerImpl<T> peerImpl)
Creates a LargeSelect whose results are returned as aList
containing a maximum ofpageSize
objects of the type defined within the class namedreturnBuilderClassName
at a time, maintaining a maximum ofLargeSelect.memoryPageLimit
pages of results in memory.- Parameters:
criteria
- object used by BasePeer to build the query. In order to allow this class to utilize database server implemented offsets and limits (when available), the provided criteria must not have any limit or offset defined.pageSize
- number of rows to return in one block.peerImpl
- the peer that will be used to do the select operations- Throws:
IllegalArgumentException
- ifcriteria
uses one or both of offset and limit, ifpageSize
is less than 1 or the Criteria object does not contain SELECT columns.
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LargeSelect
public LargeSelect(Criteria criteria, int pageSize, int memoryPageLimit, BasePeerImpl<T> peerImpl)
Creates a LargeSelect whose results are returned as aList
containing a maximum ofpageSize
objects of the type T at a time, maintaining a maximum ofmemoryPageLimit
pages of results in memory.- Parameters:
criteria
- object used by BasePeerImpl to build the query. In order to allow this class to utilize database server implemented offsets and limits (when available), the provided criteria must not have any limit or offset defined.pageSize
- number of rows to return in one block.memoryPageLimit
- maximum number of pages worth of rows to be held in memory at one time.peerImpl
- the peer that will be used to do the select operations- Throws:
IllegalArgumentException
- ifcriteria
uses one or both of offset and limit, ifpageSize
ormemoryLimitPages
are less than 1 or the Criteria object does not contain SELECT columns..
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Method Detail
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getPage
public List<T> getPage(int pageNumber) throws TorqueException
Retrieve a specific page, if it exists.- Parameters:
pageNumber
- the number of the page to be retrieved - must be greater than zero. An emptyList
will be returned ifpageNumber
exceeds the total number of pages that exist.- Returns:
- a
List
of query results containing a maximum ofpageSize
results. - Throws:
IllegalArgumentException
- whenpageNo
is not greater than zero.TorqueException
- if a sleep is unexpectedly interrupted.
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getNextResults
public List<T> getNextResults() throws TorqueException
Gets the next page of rows.- Returns:
- a
List
of query results containing a maximum ofpageSize
results. - Throws:
TorqueException
- if a sleep is unexpectedly interrupted.
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getCurrentPageResults
public List<T> getCurrentPageResults() throws TorqueException
Provide access to the results from the current page.- Returns:
- a
List
of query results containing a maximum ofpageSize
results. - Throws:
TorqueException
- if a sleep is unexpectedly interrupted.
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getPreviousResults
public List<T> getPreviousResults() throws TorqueException
Gets the previous page of rows.- Returns:
- a
List
of query results containing a maximum ofpageSize
results. - Throws:
TorqueException
- if a sleep is unexpectedly interrupted.
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run
public void run()
A background thread that retrieves the rows.
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getCurrentPageNumber
public int getCurrentPageNumber()
Retrieve the number of the current page.- Returns:
- the current page number.
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getTotalRecords
public int getTotalRecords()
Retrieve the total number of search result records that are known to exist (this will be the actual value when the query has completed (seegetTotalsFinalized()
). The convenience methodgetRecordProgressText()
may be more useful for presenting to users.- Returns:
- the number of result records known to exist (not accurate until
getTotalsFinalized()
returnstrue
).
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getPaginated
public boolean getPaginated()
Provide an indication of whether or not paging of results will be required.- Returns:
true
when multiple pages of results exist.
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getTotalPages
public int getTotalPages()
Retrieve the total number of pages of search results that are known to exist (this will be the actual value when the query has completeted (seegetQyeryCompleted()
). The convenience methodgetPageProgressText()
may be more useful for presenting to users.- Returns:
- the number of pages of results known to exist (not accurate until
getTotalsFinalized()
returnstrue
).
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getPageSize
public int getPageSize()
Retrieve the page size.- Returns:
- the number of records returned on each invocation of
getNextResults()
/getPreviousResults()
.
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getTotalsFinalized
public boolean getTotalsFinalized()
Provide access to indicator that the total values for the number of records and pages are now accurate as opposed to known upper limits.- Returns:
true
when the totals are known to have been fully computed.
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getPageProgressTextPattern
public String getPageProgressTextPattern()
Retrieve the MessageFormat pattern for the page progress The default is{0} of {1,choice,0#> |1#}{2}
- Returns:
- the pattern as a string
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setPageProgressTextPattern
public void setPageProgressTextPattern(String pageProgressTextPattern)
Set the MessageFormat pattern for the page progress. The default is{0} of {1,choice,0#> |1#}{2}
The pattern contains three placeholders
- {0} - the current page
- {1} - 0 if the total number of pages is not yet known, 1 otherwise
- {2} - the total number of pages
Localized example in German:
Seite {0} von {1,choice,0#mehr als |1#}{2}
- Parameters:
pageProgressTextPattern
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getRecordProgressTextPattern
public String getRecordProgressTextPattern()
Retrieve the MessageFormat pattern for the record progress The default is{0} - {1} of {2,choice,0#> |1#}{3}
- Returns:
- the pattern as a string
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setRecordProgressTextPattern
public void setRecordProgressTextPattern(String recordProgressTextPattern)
Set the MessageFormat pattern for the record progress. The default is{0} - {1} of {2,choice,0#> |1#}{3}
The pattern contains four placeholders
- {0} - number of the first record on the page
- {1} - number of the last record on the page
- {2} - 0 if the total number of records is not yet known, 1 otherwise
- {3} - the total number of records
Localized example in German:
Datensätze {0} bis {1} von {2,choice,0#mehr als |1#}{3}
- Parameters:
recordProgressTextPattern
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setMemoryPageLimit
public void setMemoryPageLimit(int memoryPageLimit)
Sets the multiplier that will be used to compute the memory limit when a constructor with no memory page limit is used - the memory limit will be this number multiplied by the page size.- Parameters:
memoryPageLimit
- the maximum number of pages to be in memory at one time.
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getMemoryPageLimit
public int getMemoryPageLimit()
Retrieves the multiplier that will be used to compute the memory limit when a constructor with no memory page limit is used - the memory limit will be this number multiplied by the page size.- Returns:
- memoryPageLimit the maximum number of pages to be in memory at one time.
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getPageProgressText
public String getPageProgressText()
A convenience method that provides text showing progress through the selected rows on a page basis.- Returns:
- progress text in the form of "1 of > 5" where ">" can be
configured using
setMoreIndicator()
.
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getCurrentPageSize
public int getCurrentPageSize() throws TorqueException
Provides a count of the number of rows to be displayed on the current page - for the last page this may be less than the configured page size.- Returns:
- the number of records that are included on the current page of results.
- Throws:
TorqueException
- if invoking thepopulateObjects()
method runs into problems or a sleep is unexpectedly interrupted.
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getFirstRecordNoForPage
public int getFirstRecordNoForPage()
Provide the record number of the first row included on the current page.- Returns:
- The record number of the first row of the current page.
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getLastRecordNoForPage
public int getLastRecordNoForPage() throws TorqueException
Provide the record number of the last row included on the current page.- Returns:
- the record number of the last row of the current page.
- Throws:
TorqueException
- if invoking thepopulateObjects()
method runs into problems or a sleep is unexpectedly interrupted.
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getRecordProgressText
public String getRecordProgressText() throws TorqueException
A convenience method that provides text showing progress through the selected rows on a record basis.- Returns:
- progress text in the form of "26 - 50 of > 250" where ">"
can be configured using
setMoreIndicator()
. - Throws:
TorqueException
- if invoking thepopulateObjects()
method runs into problems or a sleep is unexpectedly interrupted.
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getNextResultsAvailable
public boolean getNextResultsAvailable()
Indicates if further result pages are available.- Returns:
true
when further results are available.
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getPreviousResultsAvailable
public boolean getPreviousResultsAvailable()
Indicates if previous results pages are available.- Returns:
true
when previous results are available.
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hasResultsAvailable
public boolean hasResultsAvailable()
Indicates if any results are available.- Returns:
true
of any results are available.
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invalidateResult
public void invalidateResult() throws TorqueException
Clear the query result so that the query is re-executed when the next page is retrieved. You may want to invoke this method if you are returning to a page after performing an operation on an item in the result set.- Throws:
TorqueException
- if a sleep is interrupted.
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getSearchParam
public String getSearchParam(String name)
Retrieve a search parameter. This acts as a convenient place to store parameters that relate to the LargeSelect to make it easy to get at them in order to re-populate search parameters on a form when the next page of results is retrieved - they in no way effect the operation of LargeSelect.- Parameters:
name
- the search parameter key to retrieve.- Returns:
- the value of the search parameter.
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getSearchParam
public String getSearchParam(String name, String defaultValue)
Retrieve a search parameter. This acts as a convenient place to store parameters that relate to the LargeSelect to make it easy to get at them in order to re-populate search parameters on a form when the next page of results is retrieved - they in no way effect the operation of LargeSelect.- Parameters:
name
- the search parameter key to retrieve.defaultValue
- the default value to return if the key is not found.- Returns:
- the value of the search parameter.
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setSearchParam
public void setSearchParam(String name, String value)
Set a search parameter. If the value isnull
then the key will be removed from the parameters.- Parameters:
name
- the search parameter key to set.value
- the value of the search parameter to store.
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removeSearchParam
public void removeSearchParam(String name)
Remove a value from the search parameters.- Parameters:
name
- the search parameter key to remove.
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