001/*
002 * Copyright 2002-2014 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.web.servlet.tags;
018
019import java.io.IOException;
020import javax.servlet.jsp.JspException;
021import javax.servlet.jsp.PageContext;
022
023import org.springframework.context.expression.BeanFactoryResolver;
024import org.springframework.context.expression.EnvironmentAccessor;
025import org.springframework.context.expression.MapAccessor;
026import org.springframework.core.convert.ConversionService;
027import org.springframework.expression.AccessException;
028import org.springframework.expression.EvaluationContext;
029import org.springframework.expression.Expression;
030import org.springframework.expression.ExpressionParser;
031import org.springframework.expression.PropertyAccessor;
032import org.springframework.expression.TypedValue;
033import org.springframework.expression.spel.standard.SpelExpressionParser;
034import org.springframework.expression.spel.support.StandardEvaluationContext;
035import org.springframework.expression.spel.support.StandardTypeConverter;
036import org.springframework.util.ObjectUtils;
037import org.springframework.web.util.JavaScriptUtils;
038import org.springframework.web.util.TagUtils;
039
040/**
041 * JSP tag for evaluating expressions with the Spring Expression Language (SpEL).
042 * Supports the standard JSP evaluation context consisting of implicit variables and scoped attributes.
043 *
044 * @author Keith Donald
045 * @author Juergen Hoeller
046 * @since 3.0.1
047 */
048@SuppressWarnings("serial")
049public class EvalTag extends HtmlEscapingAwareTag {
050
051        /**
052         * {@link javax.servlet.jsp.PageContext} attribute for the
053         * page-level {@link EvaluationContext} instance.
054         */
055        private static final String EVALUATION_CONTEXT_PAGE_ATTRIBUTE =
056                        "org.springframework.web.servlet.tags.EVALUATION_CONTEXT";
057
058
059        private final ExpressionParser expressionParser = new SpelExpressionParser();
060
061        private Expression expression;
062
063        private String var;
064
065        private int scope = PageContext.PAGE_SCOPE;
066
067        private boolean javaScriptEscape = false;
068
069
070        /**
071         * Set the expression to evaluate.
072         */
073        public void setExpression(String expression) {
074                this.expression = this.expressionParser.parseExpression(expression);
075        }
076
077        /**
078         * Set the variable name to expose the evaluation result under.
079         * Defaults to rendering the result to the current JspWriter.
080         */
081        public void setVar(String var) {
082                this.var = var;
083        }
084
085        /**
086         * Set the scope to export the evaluation result to.
087         * This attribute has no meaning unless var is also defined.
088         */
089        public void setScope(String scope) {
090                this.scope = TagUtils.getScope(scope);
091        }
092
093        /**
094         * Set JavaScript escaping for this tag, as boolean value.
095         * Default is "false".
096         */
097        public void setJavaScriptEscape(boolean javaScriptEscape) throws JspException {
098                this.javaScriptEscape = javaScriptEscape;
099        }
100
101
102        @Override
103        public int doStartTagInternal() throws JspException {
104                return EVAL_BODY_INCLUDE;
105        }
106
107        @Override
108        public int doEndTag() throws JspException {
109                EvaluationContext evaluationContext =
110                                (EvaluationContext) this.pageContext.getAttribute(EVALUATION_CONTEXT_PAGE_ATTRIBUTE);
111                if (evaluationContext == null) {
112                        evaluationContext = createEvaluationContext(this.pageContext);
113                        this.pageContext.setAttribute(EVALUATION_CONTEXT_PAGE_ATTRIBUTE, evaluationContext);
114                }
115                if (this.var != null) {
116                        Object result = this.expression.getValue(evaluationContext);
117                        this.pageContext.setAttribute(this.var, result, this.scope);
118                }
119                else {
120                        try {
121                                String result = this.expression.getValue(evaluationContext, String.class);
122                                result = ObjectUtils.getDisplayString(result);
123                                result = htmlEscape(result);
124                                result = (this.javaScriptEscape ? JavaScriptUtils.javaScriptEscape(result) : result);
125                                this.pageContext.getOut().print(result);
126                        }
127                        catch (IOException ex) {
128                                throw new JspException(ex);
129                        }
130                }
131                return EVAL_PAGE;
132        }
133
134        private EvaluationContext createEvaluationContext(PageContext pageContext) {
135                StandardEvaluationContext context = new StandardEvaluationContext();
136                context.addPropertyAccessor(new JspPropertyAccessor(pageContext));
137                context.addPropertyAccessor(new MapAccessor());
138                context.addPropertyAccessor(new EnvironmentAccessor());
139                context.setBeanResolver(new BeanFactoryResolver(getRequestContext().getWebApplicationContext()));
140                ConversionService conversionService = getConversionService(pageContext);
141                if (conversionService != null) {
142                        context.setTypeConverter(new StandardTypeConverter(conversionService));
143                }
144                return context;
145        }
146
147        private ConversionService getConversionService(PageContext pageContext) {
148                return (ConversionService) pageContext.getRequest().getAttribute(ConversionService.class.getName());
149        }
150
151
152        @SuppressWarnings("deprecation")
153        private static class JspPropertyAccessor implements PropertyAccessor {
154
155                private final PageContext pageContext;
156
157                private final javax.servlet.jsp.el.VariableResolver variableResolver;
158
159                public JspPropertyAccessor(PageContext pageContext) {
160                        this.pageContext = pageContext;
161                        this.variableResolver = pageContext.getVariableResolver();
162                }
163
164                @Override
165                public Class<?>[] getSpecificTargetClasses() {
166                        return null;
167                }
168
169                @Override
170                public boolean canRead(EvaluationContext context, Object target, String name) throws AccessException {
171                        return (target == null &&
172                                        (resolveImplicitVariable(name) != null || this.pageContext.findAttribute(name) != null));
173                }
174
175                @Override
176                public TypedValue read(EvaluationContext context, Object target, String name) throws AccessException {
177                        Object implicitVar = resolveImplicitVariable(name);
178                        if (implicitVar != null) {
179                                return new TypedValue(implicitVar);
180                        }
181                        return new TypedValue(this.pageContext.findAttribute(name));
182                }
183
184                @Override
185                public boolean canWrite(EvaluationContext context, Object target, String name) {
186                        return false;
187                }
188
189                @Override
190                public void write(EvaluationContext context, Object target, String name, Object newValue) {
191                        throw new UnsupportedOperationException();
192                }
193
194                private Object resolveImplicitVariable(String name) throws AccessException {
195                        if (this.variableResolver == null) {
196                                return null;
197                        }
198                        try {
199                                return this.variableResolver.resolveVariable(name);
200                        }
201                        catch (Exception ex) {
202                                throw new AccessException(
203                                                "Unexpected exception occurred accessing '" + name + "' as an implicit variable", ex);
204                        }
205                }
206        }
207
208}