View Javadoc

    1   /*
    2    * Copyright 2002,2004 The Apache Software Foundation.
    3    *
    4    * Licensed under the Apache License, Version 2.0 (the "License");
    5    * you may not use this file except in compliance with the License.
    6    * You may obtain a copy of the License at
    7    *
    8    *      http://www.apache.org/licenses/LICENSE-2.0
    9    *
    10   * Unless required by applicable law or agreed to in writing, software
    11   * distributed under the License is distributed on an "AS IS" BASIS,
    12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13   * See the License for the specific language governing permissions and
    14   * limitations under the License.
    15   */
    16  package org.apache.commons.jelly.expression;
    17
    18  import java.util.Iterator;
    19
    20  import org.apache.commons.jelly.JellyContext;
    21
    22  /*** <p><code>Expression</code> represents an arbitrary expression using some pluggable
    23    * expression language.</p>
    24    *
    25    * @author <a href="mailto:jstrachan@apache.org">James Strachan</a>
    26    * @version $Revision: 155420 $
    27    */
    28  public interface Expression {
    29
    30      /***
    31       * @return the textual representation of this expression
    32       */
    33      public String getExpressionText();
    34
    35      /***
    36       * Evaluates the expression with the given context
    37       * and returns the result
    38       */
    39      public Object evaluate(JellyContext context);
    40
    41      /***
    42       * Evaluates the expression with the given context
    43       * coercing the result to be a String.
    44       */
    45      public String evaluateAsString(JellyContext context);
    46
    47      /***
    48       * Evaluates the expression with the given context
    49       * coercing the result to be a boolean.
    50       */
    51      public boolean evaluateAsBoolean(JellyContext context);
    52
    53      /***
    54       * Evaluates the expression with the given context
    55       * coercing the result to be an Iterator.
    56       */
    57      public Iterator evaluateAsIterator(JellyContext context);
    58
    59      /***
    60       * This method evaluates the expression until a value (a non-Expression) object
    61       * is returned.
    62       * If the expression returns another expression, then the nested expression is evaluated.
    63       * <p>
    64       * Sometimes when Jelly is used inside Maven the value
    65       * of an expression can actually be another expression.
    66       * For example if a properties file is read, the values of variables
    67       * can actually be expressions themselves.
    68       * <p>
    69       * e.g. ${foo.bar} can lookup "foo.bar" in a Maven context
    70       * which could actually be another expression.
    71       * <p>
    72       * So using this method, nested expressions can be evaluated to the
    73       * actual underlying value object.
    74       */
    75      public Object evaluateRecurse(JellyContext context);
    76  }