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package org.codehaus.plexus.context;
/*
* The MIT License
*
* Copyright (c) 2004, The Codehaus
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of
* this software and associated documentation files (the "Software"), to deal in
* the Software without restriction, including without limitation the rights to
* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
* of the Software, and to permit persons to whom the Software is furnished to do
* so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
import java.io.Serializable;
import java.util.Hashtable;
import java.util.Map;
/**
* Default implementation of Context.
*
* This implementation is a static hierarchial store. It has the normal get()
* and put methods. The hide method will hide a property. When
* a property has been hidden the context will not search in the parent context for the value.
*
* @author Avalon Development Team
* @version $Id: DefaultContext.java 1323 2004-12-20 23:00:59Z jvanzyl $
*/
public class DefaultContext
implements Context
{
/** */
private static Hidden HIDDEN_MAKER = new Hidden();
/** Context data. */
private Map contextData;
/** Parent Context. */
private Context parent;
/** Is the context read only. */
private boolean readOnly;
/**
* Create a Context with specified data and parent.
*
* @param contextData the context data
* @param parent the parent Context (may be null)
*/
public DefaultContext( Map contextData, Context parent )
{
this.parent = parent;
this.contextData = contextData;
}
/**
* Create a empty Context with specified data.
*
* @param contextData the context data
*/
public DefaultContext( Map contextData )
{
this( contextData, null );
}
/**
* Create a Context with specified parent.
*
* @param parent the parent Context (may be null)
*/
public DefaultContext( Context parent )
{
this( new Hashtable(), parent );
}
/**
* Create a empty Context with no parent.
*/
public DefaultContext()
{
this( (Context) null );
}
/**
* Returns true if the map or the parent map contains the key.
*
* @param key The key to search for.
* @return Returns true if the key was found.
*/
public boolean contains( Object key )
{
Object data = contextData.get( key );
if ( null != data )
{
if ( data instanceof Hidden )
{
return false;
}
return true;
}
// If data was null, check the parent
if ( null == parent )
{
return false;
}
return parent.contains( key );
}
/**
* Returns the value of the key. If the key can't be found it will throw a exception.
*
* @param key The key of the value to look up.
* @return Returns
* @throws ContextException If the key doesn't exist.
*/
public Object get( Object key )
throws ContextException
{
Object data = contextData.get( key );
if ( data != null )
{
if ( data instanceof Hidden )
{
// Always fail
throw new ContextException( "Unable to locate " + key );
}
return data;
}
// If data was null, check the parent
if ( parent == null )
{
// There was no parent, and no data
throw new ContextException( "Unable to resolve context key: " + key );
}
return parent.get( key );
}
/**
* Helper method for adding items to Context.
*
* @param key the items key
* @param value the item
* @throws java.lang.IllegalStateException if context is read only
*/
public void put( Object key, Object value )
throws IllegalStateException
{
checkWriteable();
if ( null == value )
{
contextData.remove( key );
}
else
{
contextData.put( key, value );
}
}
/**
* Hides the item in the context.
*
* After remove(key) has been called, a get(key)
* will always fail, even if the parent context
* has such a mapping.
*
* @param key the items key
* @throws java.lang.IllegalStateException if context is read only
*/
public void hide( Object key )
throws IllegalStateException
{
checkWriteable();
contextData.put( key, HIDDEN_MAKER );
}
/**
* Utility method to retrieve context data.
*
* @return the context data
*/
protected Map getContextData()
{
return contextData;
}
/**
* Get parent context if any.
*
* @return the parent Context (may be null)
*/
protected Context getParent()
{
return parent;
}
/**
* Make the context read-only.
* Any attempt to write to the context via put()
* will result in an IllegalStateException.
*/
public void makeReadOnly()
{
readOnly = true;
}
/**
* Utility method to check if context is writeable and if not throw exception.
*
* @throws java.lang.IllegalStateException if context is read only
*/
protected void checkWriteable()
throws IllegalStateException
{
if ( readOnly )
{
throw new IllegalStateException( "Context is read only and can not be modified" );
}
}
/**
* This class is only used as a marker in the map to indicate a hidden value.
*/
private static class Hidden
implements Serializable
{
}
}