NullTool.java
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package com.dili.titan.common.tools;
/*
* Copyright 2003-2004 The Apache Software Foundation.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import org.apache.velocity.context.Context;
/**
* Tool for working with <code>null</code> in Velocity templates.
* It provides a method to set a VTL reference back to <code>null</code>.
* Also provides methods to check if a VTL reference is <code>null</code> or not.
* <p>
* NOTE: These examples assume you have placed an
* instance of the current context within itself as 'ctx'.
* And, of course, the NullTool is assumed to be available as 'null'.
* </p>
* <p><pre>
* Example uses:
* $foo -> bar
* $null.isNull($foo) -> false
* $null.isNotNull($foo) -> true
*
* $null.setNull($ctx, "foo")
* $foo -> $foo (null)
* $null.isNull($foo) -> true
* $null.isNotNull($foo) -> false
*
* $null.set($ctx, $foo, "hoge")
* $foo -> hoge
* $null.set($ctx, $foo, $null.null)
* $foo -> $foo (null)
* </pre></p>
*
* <p>This tool is entirely threadsafe, and has no instance members.
* It may be used in any scope (request, session, or application).
* </p>
*
* @author <a href="mailto:shinobu@ieee.org">Shinobu Kawai</a>
* @version $Id: $
*/
public class NullTool
{
/**
* Default constructor.
*/
public NullTool()
{
}
/**
* Sets the given VTL reference back to <code>null</code>.
* @param context the current Context
* @param key the VTL reference to set back to <code>null</code>.
*/
public void setNull(Context context, String key)
{
if (this.isNull(context))
{
return;
}
context.remove(key);
}
/**
* Sets the given VTL reference to the given value.
* If the value is <code>null</code>,
* the VTL reference is set to <code>null</code>.
* @param context the current Context
* @param key the VTL reference to set.
* @param value the value to set the VTL reference to.
*/
public void set(Context context, String key, Object value)
{
if (this.isNull(context))
{
return;
}
if (this.isNull(value))
{
this.setNull(context, key);
return;
}
context.put(key, value);
}
/**
* Checks if a VTL reference is <code>null</code>.
* @param object the VTL reference to check.
* @return <code>true</code> if the VTL reference is <code>null</code>,
* <code>false</code> if otherwise.
*/
public boolean isNull(Object object)
{
return object == null;
}
/**
* Checks if a VTL reference is not <code>null</code>.
* @param object the VTL reference to check.
* @return <code>true</code> if the VTL reference is not <code>null</code>,
* <code>false</code> if otherwise.
*/
public boolean isNotNull(Object object)
{
return !this.isNull(object);
}
/**
* A convinient method which returns <code>null</code>.
* Actually, this tool will work the same without this method,
* because Velocity treats non-existing methods as null. :)
* @return <code>null</code>
*/
public Object getNull()
{
return null;
}
}