001// Copyright 2005 The Apache Software Foundation 002// 003// Licensed under the Apache License, Version 2.0 (the "License"); 004// you may not use this file except in compliance with the License. 005// You may obtain a copy of the License at 006// 007// http://www.apache.org/licenses/LICENSE-2.0 008// 009// Unless required by applicable law or agreed to in writing, software 010// distributed under the License is distributed on an "AS IS" BASIS, 011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 012// See the License for the specific language governing permissions and 013// limitations under the License. 014 015package org.apache.tapestry.web; 016 017import java.util.List; 018 019/** 020 * Interface for objects that can hold attributes. Attributes are objects that are stored and 021 * retrieved using unique string names. There may be constraints on when attributes can be accessed 022 * (for example, {@link org.apache.tapestry.web.WebSession}attributes should not be 023 * changed once the response is committed). 024 * 025 * @author Howard M. Lewis Ship 026 * @since 4.0 027 */ 028public interface AttributeHolder 029{ 030 /** 031 * Returns a list of all known attributes in ascending alphabetical order. May be empty (but 032 * won't be null). 033 * 034 * @returns Unmodifiable list of string attribute names. 035 */ 036 037 public List getAttributeNames(); 038 039 /** 040 * Returns the named object, or null if no attribute has been stored with the given name. 041 */ 042 043 public Object getAttribute(String name); 044 045 /** 046 * Updates the attribute, replacing (or removing) its value. For certain implementations, the 047 * attribute may need to be serializable (for example, a {@link WebSession} 048 * attribute in a clustered application). 049 * 050 * @param name 051 * the name of the attribute to update 052 * @param attribute 053 * the new value for the attribute, or null to delete the attribute entirely. 054 */ 055 056 public void setAttribute(String name, Object attribute); 057}