org.xwiki.gwt.user.client
Class BackForwardCache

java.lang.Object
  org.xwiki.gwt.user.client.BackForwardCache

All Implemented Interfaces:

Updatable

public class BackForwardCache
extends Object
implements Updatable

Allows us to preserve the state of the editor against the browser's Back button, the soft page refresh and the browser crash by using the browser's cache mechanism. Modern browsers cache HTML form fields like input and textarea as long as they are generated on the server and not on the client using JavaScript. This class uses the value of such an element to save string properties.

Version:

$Id: fb803524fa4442f7ff594b5dedf1470d9307de92 $

Constructor Summary

BackForwardCache(Element cacheable)
Creates a new cache based on the given HTML element whose value can be cached by the browser.

Method Summary

boolean	canUpdate()
protected Map<String,String>	deserialize(String data) Parses the given string and extracts a map of key-value pairs.
String	get(String key) Retrieves the value of a cached property specified by the given key.
String	get(String key, String defaultValue) Retrieves the value of a cached property specified by the given key, falling back on a default value if the key is not found in the cache.
protected Map<String,String>	getMap()
String	put(String key, String value) Adds a new key in the cache or updates the value of an existing key.
protected String	serialize(Map<String,String> map) Converts the given map of key-value pairs to a string from which it can be recomputed.
void	update() Updates the state of this object.

Methods inherited from class java.lang.Object

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

Constructor Detail

BackForwardCache

public BackForwardCache(Element cacheable)

Creates a new cache based on the given HTML element whose value can be cached by the browser. Examples of such elements are input and textarea.

The browser doesn't cache the HTML elements added dynamically through JavaScript but only the static ones. Moving an element inside the DOM tree prevents the browser from caching its value even if that element was generated on the server.

Parameters:

cacheable - any HTML element whose value can be cached by the browser

Method Detail

get

public String get(String key)

Retrieves the value of a cached property specified by the given key.

Parameters:

key - a key in the cache

Returns:

the value associated with the given key or null if there's no such key in the cache

get

public String get(String key,
                  String defaultValue)

Retrieves the value of a cached property specified by the given key, falling back on a default value if the key is not found in the cache.

Parameters:

key - a key in the cache

defaultValue - the value returned if the specified key is not found in the cache

Returns:

the value associated with the given key or defaultValue if there's no such key in the cache

put

public String put(String key,
                  String value)

Adds a new key in the cache or updates the value of an existing key.

Parameters:

key - a key in the cache

value - the new value for the given key

Returns:

the previous value associated with the given key

getMap

protected Map<String,String> getMap()

Returns:

the Map used to store the cache for quick access

canUpdate

public boolean canUpdate()

Specified by:

canUpdate in interface Updatable

Returns:

true if this object can be updated at this point, false otherwise

update

public void update()

Description copied from interface: Updatable

Updates the state of this object.

Specified by:

update in interface Updatable

deserialize

protected Map<String,String> deserialize(String data)

Parses the given string and extracts a map of key-value pairs.

Parameters:

data - the string to be deserialized

Returns:

the map whose serialization is the given string

See Also:

serialize(Map)

serialize

protected String serialize(Map<String,String> map)

Converts the given map of key-value pairs to a string from which it can be recomputed.

Parameters:

map - the map to be serialized

Returns:

a string representation of the given map

See Also:

deserialize(String)