uk.ac.starlink.gbin

Class ItemReader

java.lang.Object

uk.ac.starlink.gbin.ItemReader

public class ItemReader
extends Object

Object which can read the value of a given table column from the (GaiaRoot) data object representing a table row. ItemReaders are arranged hierarchically, since objects may contain objects, and it is in general the leaf nodes that get turned into columns.

Since:

6 Jun 2017

Author:

Mark Taylor

Field Summary

Fields

Modifier and Type	Field and Description
static ItemReader	ROOT Special instance used as the reader root.

Constructor Summary

Constructors

Constructor and Description
ItemReader(ItemReader parentReader, Method method, String itemName, Representation<?> repr) Constructor.

Method Summary

Modifier and Type	Method and Description
static ItemReader[]	createItemReaders(Class<?> rootClazz, GbinTableProfile profile) Constructs a list of objects that can each read a field from an object.
static String	getColumnName(ItemReader rdr, Map<String,List<ItemReader>> nameMap, boolean forceHier, String separator) Works out what name to use for the table column using data from a given item reader.
Class<?>	getItemContentClass() Returns the class of objects returned by readItem
String	getItemName() Returns the (non-hierarchical) name of the data item represented by this reader.
ItemReader	getParentReader() Returns the parent of this reader.
boolean	isRoot() Determines whether this instance is the tree root.
Object	readItem(Map<ItemReader,Object> itemMap) Reads the value for this reader in the context of a given row object.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

ROOT

public static final ItemReader ROOT

Special instance used as the reader root.

Constructor Detail

ItemReader

public ItemReader(ItemReader parentReader,
                  Method method,
                  String itemName,
                  Representation<?> repr)

Constructor.

Parameters:

parentReader - parent instance

method - the no-arg public instance method whose return value when applied to the parent reader's object gives this column's value

itemName - basic name for this item

repr - value representation

Method Detail

isRoot

public boolean isRoot()

Determines whether this instance is the tree root.

Returns:

true iff this == ROOT

getParentReader

public ItemReader getParentReader()

Returns the parent of this reader.

Returns:

parent, it's null only for ROOT

getItemName

public String getItemName()

Returns the (non-hierarchical) name of the data item represented by this reader.

Returns:

the Xxx for method getXxx() or isXxx()

getItemContentClass

public Class<?> getItemContentClass()

Returns the class of objects returned by readItem

Returns:

item content class

readItem

public Object readItem(Map<ItemReader,Object> itemMap)
                throws IOException

Reads the value for this reader in the context of a given row object. The row object is represented as a map which caches ItemReader->value pairs. The map will be updated by this method, not only by inserting its own value, but also by inserting the values of any missing parent objects as required. Thus each method only needs to be invoked reflectively once per row even for hierarchically nested data items. The only precondition is that the map must contain the entry ROOT->rowObject.

Parameters:

itemMap - reader->value map, may be modified

Returns:

value associated with this reader for the row represented by the submitted map

Throws:

IOException

createItemReaders

public static ItemReader[] createItemReaders(Class<?> rootClazz,
                                             GbinTableProfile profile)

Constructs a list of objects that can each read a field from an object. There is one ItemReader returned for each column in the output table.

Parameters:

rootClazz - class of per-row element

profile - table configuration

getColumnName

public static String getColumnName(ItemReader rdr,
                                   Map<String,List<ItemReader>> nameMap,
                                   boolean forceHier,
                                   String separator)

Works out what name to use for the table column using data from a given item reader.

Parameters:

rdr - item reader supplying data

nameMap - map of all item reader names to a list of the item readers having that name; it can be used to detect name duplication

forceHier - true iff hierarchical names should always be used

separator - separator string for components of a hierarchical column name