JUnit tests can be found here.
/* * 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. */ package org.apache.velocity.tools.view.tools; import org.apache.velocity.context.Context; import org.apache.velocity.tools.generic.NullTool; /** * Tool for working with <code>null</code> in Velocity templates. * It provides a method to set a VTL reference back to <code>null</code>, * automatically using the current context. * Also provides methods to check if a VTL reference is <code>null</code> or not. * <p> * NOTE: <code>set</code> and <code>setNull</code> does not clear attributes in servlet objects. * To remove attributes from <code>request</code>, <code>session</code> and <code>application</code>, * use <code>$request.removeAttribute()</code>, <code>$session.removeAttribute()</code> and * <code>$application.removeAttribute()</code> respectively. * </p> * <p><pre> * Example uses: * #set($foo = "bar") * $foo -> bar * $null.isNull($foo) -> false * $null.isNotNull($foo) -> true * * $null.setNull("foo") * $foo -> $foo (null) * $null.isNull($foo) -> true * $null.isNotNull($foo) -> false * * $null.set($foo, "hoge") * $foo -> hoge * $null.set($foo, $null.null) * $foo -> $foo (null) * * * Toolbox configuration: * <tool> * <key>null</key> * <scope>request</scope> * <class>org.apache.velocity.tools.view.tools.ViewNullTool</class> * </tool> * </pre></p> * * <p>This tool is NOT meant to be used in either application or * session scopes of a servlet environment.</p> * * @author <a href="mailto:shinobu@ieee.org">Shinobu Kawai</a> * @version $Id: $ */ public class ViewNullTool extends NullTool implements ViewTool { /** The Context. */ private Context context = null; /** * Default constructor. */ public ViewNullTool() { } /** * Initializes this instance. * * @param object the current Context */ public void init(Object object) { if (!(object instanceof Context)) { throw new IllegalArgumentException("Tool can only be initialized with a Context"); } this.context = (Context) object; } /** * Sets the given VTL reference back to <code>null</code> using the current context. * @param key the VTL reference to set back to <code>null</code>. */ public void setNull(String key) { this.setNull(this.context, key); } /** * Sets the given VTL reference to the given value using the current context. * If the value is <code>null</code>, * the VTL reference is set to <code>null</code>. * @param key the VTL reference to set. * @param value the value to set the VTL reference to. */ public void set(String key, Object value) { this.set(this.context, key, value); } }