001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.juneau.svl;
018
019import static org.apache.juneau.commons.utils.ThrowableUtils.*;
020
021/**
022 * Abstract superclass of all Simple Var Language variables that write their values directly to a writer.
023 *
024 * <p>
025 * Note the difference between this class and {@link SimpleVar} that returns simple string values.
026 * <br>Unlike the {@link SimpleVar} class, the output from this class cannot contain nested variables.
027 * <br>However, this class can be more efficient for variables that produce large amounts of output so that the creation
028 * of large in-memory strings is avoided.
029 *
030 * <p>
031 * Subclasses must implement the following method:
032 * <ul class='javatree'>
033 *    <li class='jm'>{@link #resolveTo(VarResolverSession, java.io.Writer, String)}
034 * </ul>
035 *
036 * <h5 class='section'>See Also:</h5><ul>
037 *    <li class='link'><a class="doclink" href="https://juneau.apache.org/docs/topics/SimpleVariableLanguageBasics">Simple Variable Language Basics</a>
038 * </ul>
039 */
040public abstract class StreamedVar extends Var {
041
042   /**
043    * Constructor.
044    *
045    * @param name The variable name (e.g. <js>"C"</js> for variables of the form <js>"$C{...}"</js>)
046    */
047   public StreamedVar(String name) {
048      super(name, true);
049   }
050
051   @Override /* Overridden from Var */
052   public String resolve(VarResolverSession session, String arg) throws Exception {
053      throw unsupportedOp("Cannot call resolve() on StreamedVar class");
054   }
055}